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| United States Patent |
6,102,988
|
|
Tang
, et al.
|
August 15, 2000
|
Moving filter device having filter elements with flow passages and
method of filtering air
Abstract
There is provided an air delivery device and method of moving and filtering
air. The air delivery device comprises a housing having an air inlet and
an air outlet. Between the air inlet and the air outlet is located an air
delivery fan having at least two rotating air moving elements, the
rotating air moving elements intersects the flow of air between the air
inlet and the air outlet and establishes a higher pressure zone at the air
outlet relative to the air inlet. The air delivery fan further comprises
at lest one filter element, having at least one upstream filter face and
at least one downstream filter face, defining at least one primary flow
channel, and rotating along the same axis of rotation as the air moving
elements and preferably forming the air moving elements at least in part.
The upstream filter face moves into a portion of the airflow through the
air delivery fan such that the upstream filter face impacts a portion of
the moving airflow in a flow channel, permitting the air to flow through
the filter element into the airflow of an further flow channel. The filter
elements further define air flow passages or inlets allowing substantially
unimpeded airflow to the primary flow channels and out to the air outlet.
The air filter elements comprise an electret charged filter media.
| Inventors:
|
Tang; Yuan-Ming (New Brighton, MN);
Lira; Ricardo (Woodbury, MN);
Harms; Michael (Woodbury, MN)
|
| Assignee:
|
3M Innovative Properties Company (St. Paul, MN)
|
| Appl. No.:
|
126181 |
| Filed:
|
July 30, 1998 |
| Intern'l Class: |
B01D 033/00; B01D 045/14 |
| Field of Search: |
55/309,400,401,404,467,471,473,524,DIG. 39,498,486
95/277,285,270
|
References Cited
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| 4658707 | Apr., 1987 | Hawkins et al. | 98/2.
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| 5238473 | Aug., 1993 | Femiani | 55/290.
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| 5256476 | Oct., 1993 | Tanaka | 428/241.
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| 5332426 | Jul., 1994 | Tang et al. | 96/153.
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| 5514197 | May., 1996 | Den | 55/405.
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| 5560835 | Oct., 1996 | Williams | 210/783.
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| 5573563 | Nov., 1996 | Odom | 55/301.
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| 5749702 | May., 1998 | Datta et al. | 415/119.
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| Foreign Patent Documents |
| 0 196 337 A1 | Mar., 1985 | EP.
| |
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| |
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| |
| 2219846 | Oct., 1973 | DE | 55/473.
|
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| |
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|
| 2223187 | Apr., 1990 | GB | 55/400.
|
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| |
| WO 97/44624 | Nov., 1997 | WO.
| |
Other References
American National Standard Method for Measuring Performance of Portable
Household Electric Cord-Connected Room Air Cleaners, ANSI/AHAM AC-1-1988,
Association of Home Appliance Manufacturers, 24 pages.
|
Primary Examiner: Simmons; David A.
Assistant Examiner: Hopkins; Robert A.
Attorney, Agent or Firm: Griswold; Gary L., Sprague; Robert W., Bond; William J.
Claims
We claim:
1. An air delivery device comprising a housing having an air inlet and an
air outlet, between the air inlet and the air outlet is located an air
delivery fan having at least two rotating air moving means, the rotating
air moving means intersect the flow of air between the air inlet and the
air outlet and establish a high pressure zone at the air outlet relative
to the air inlet, the air delivery fan further comprising at least one
porous filter element having at least one upstream filter face and at
least one downstream filter face defining at least one primary flow
channel, where the at least one upstream filter face rotates along the
same axis of rotation as the air moving means and where the upstream
filter face moves into a portion of the airflow through the air delivery
fan such that the upstream filter face impacts a portion of the moving
airflow in a flow channel, permitting the air to flow through the filter
element from the upstream filter face to the downstream filter face and
from the downstream filter face into a further portion of the airflow in a
flow channel, the filter elements and/or air moving means further defining
air flow passages allowing unrestricted airflow into and through primary
flow channels to the air outlet, wherein the air filter elements comprise
a filter of electret charged filter media having an average Frazier
Permeability of at least 2000 m.sup.3 /hr/m.sup.2.
2. The air deliver device of claim 1 wherein the at least one filter
element comprises a nonwoven fibrous filter web formed at least in part of
electret charged fibers.
3. The air delivery device of claim 1 wherein the air delivery fan is a
centrifugal fan having an axial air inlet with air delivered radially of
the axis of rotation of the fan wherein the air moving means have an
upstream face that is generally aligned with the axis of rotation and the
air flow passages form at least in part the air inlets and outlets.
4. The air delivery device of claim 1 wherein the air moving means comprise
air moving elements where the air moving elements are parallel with the
filter elements and the axis of rotation.
5. The air delivery device of claim 1 wherein the air flow passages are
formed by a filter element upstream face and an adjacent filter element
downstream face.
6. The air delivery device of claim 5 wherein the air moving elements are
radially inward of the filter elements.
7. The air delivery device of claim 5 wherein the air moving elements are
radially outward of the filter elements.
8. The air delivery device of claim 1 wherein the air moving elements are
radially aligned with the filter elements.
9. The air delivery device of claim 8 wherein the air moving elements
comprise the filter elements.
10. The air delivery device of claim 8 wherein the air moving elements
comprise at least two blade elements extending radially outward from the
axis of rotation.
11. The air delivery device of claim 10 wherein the air moving elements
comprise at least four fan blade elements extending radially outward from
the axis of rotation.
12. The air delivery device of claim 10 wherein the blade elements have
filter elements incorporated across at least a portion of its cross
sectional area.
13. The air delivery device of claim 10 wherein the blade element comprises
a filter element over at least 50 percent of its cross sectional area.
14. The air delivery device of claim 10 wherein the blade element comprises
a filter element over at least 75 percent of its cross sectional area.
15. The air delivery device of claim 10 wherein the blade elements
intersect the axis of rotation of the fan.
16. The air delivery device of claim 1 wherein the air moving elements
comprise at least two blade elements which blade elements are radially
spaced from the axis of rotation forming an annular fan.
17. The air delivery device of claim 10 wherein the blade elements have a
substantially smooth surface across the cross sectional area of the
upstream face.
18. The air delivery device of claim 10 wherein the blade elements have a
structured surface across the cross sectional area of the upstream face.
19. The air delivery device of claim 10 wherein the blade elements extend
linearly in the radial direction.
20. The air delivery device of claim 19 wherein the blade elements extend
nonlinearly or curved in the radial direction.
21. The air delivery device of claim 1 wherein there are two or more filter
elements which are radially displaced from the air moving means and
removably attached thereto.
22. The air delivery device of claim 21 wherein the filter elements form an
annular filter.
23. The air delivery device of claim 5 wherein secondary flow channels are
provided with flow passages allowing unrestricted airflow to the air
outlet.
24. The air delivery device of claim 23 wherein the secondary flow channels
are formed by pleating of the filter media.
25. The air delivery device of claim 23 wherein the secondary flow channels
are in fluid communication with at least one primary flow channel.
26. The air delivery device of claim 25 wherein the secondary flow channels
and primary flow channels in fluid communication are separated by filter
media.
27. The air delivery device of claim 2 wherein the filter media has an
average Frazier Permeability of from 2000 to 8000 m.sup.3 /hr/m.sup.2.
28. The air delivery device of claim 2 wherein the filter media has an
average Frazier Permeability of from 3000 to 6000 m.sup.3 /hr/m.sup.2.
29. The air delivery device of claim 1 wherein the filter media has an
average Frazier Permeability of from 2000 to 8000 m.sup.3 /hr/m.sup.2.
30. The air delivery device of claim 27 wherein the filter media comprises
a nonwoven fibrous web of melt blown microfibers.
31. The air delivery device of claim 27 wherein the filter media comprises
a nonwoven fibrous filter web of split fibrillated charged fibers.
32. The air delivery device of claim 31 wherein the fibrous filter web is
joined to a supporting scrim.
33. The air delivery device of claim 30 wherein the filter web further
includes sorbent particulates or fibers.
34. The air delivery device of claim 27 wherein the filter element further
includes additional functional layers.
35. The air delivery device of claim 34 wherein the additional functional
layers are particle filtration layers.
36. The air delivery device of claim 34 wherein the additional functional
layers are sorptive filtration layers.
37. A method of filtering particles from a moving airstream comprising;
a. providing an air delivery device comprising a housing having an air
inlet and an air outlet, between the air inlet and the air outlet is
located an air delivery fan having at least two rotating air moving means,
the rotating air moving means positioned to intersect the flow of air
between the air inlet and the air outlet and establishing a high pressure
zone at the air outlet relative to the air inlet, the air delivery fan
further comprising at least one filter element having at least one
upstream filter face and at least one downstream filter face defining at
least one primary flow channel wherein the air filter elements comprise a
filter of electret charged filter media having an average Frazier
Permeability of at least 2000 m.sup.3 /hr/m.sup.2 ;
b. rotating the air moving means to establish a moving airflow;
c. rotating the at least one upstream filter face along the same axis of
rotation as the air moving means such that the upstream filter face moves
into a portion of the moving airflow through the air delivery fan;
d. impacting a portion of the moving airflow in a flow channel with the
upstream filter face; and
e. permitting air to flow through the filter element from the upstream
filter face to the downstream filter face and from the downstream filter
face into a further portion of the airflow in a flow channel.
38. The method of claim 37 wherein the filter element upstream and
downstream filter faces define at least one air flow passage allowing
substantially unimpeaded air flow of at least a portion of the moving
airflow through the filter.
39. The method of claim 37 wherein the at least one filter element
comprises a nonwoven fibrous filter web formed at least in part of
electret charged fibers.
40. The method of claim 37 wherein the air enters the air delivery device
by an axial air inlet and the rotating air moving means discharges the
airflow radially of the axis of rotation of the fan wherein the air moving
means have an upstream face that is generally aligned with the axis of
rotation.
41. The method of claim 37 wherein the high pressure zone is at least 5 mm
water higher than the inlet air pressure.
42. The method of claim 41 wherein the air moving elements are radially
aligned with the filter elements.
43. The air method of claim 41 wherein the air moving elements are radially
inward of the filter elements.
44. The method of claim 41 wherein the air moving elements are radially
outward of the filter elements.
45. The method of claim 37 wherein the air moving elements comprise the
filter elements.
46. The method of claim 37 wherein the air moving elements comprise at
least two blade elements extending radially outward from the axis of
rotation.
47. The method of claim 46 wherein the air moving elements comprise at
least four fan blade elements extending radially outward from the axis of
rotation.
48. The method claim 47 wherein the blade elements have filter elements
incorporated across at least a portion of its cross sectional area.
49. The method of claim 48 wherein the blade element comprises a filter
element over at least 50 percent of its cross sectional area.
50. The method of claim 49 wherein the blade element comprises a filter
element over at least 75 percent of its cross sectional area.
51. The method of claim 50 wherein the blade elements intersect the axis of
rotation of the fan.
52. The method of claim 41 wherein the high pressure zone is at least 10 mm
water higher than the inlet pressure.
53. The method of claim 37 wherein the filter media has an average Frazier
Permeability of from 2000 to 8000 cm.sup.3 /hr/m.sup.2.
54. The method of claim 53 wherein the filter media has an average Frazier
Permeability of from 3000 to 6000 cm.sup.3 /hr/m.sup.2.
55. The method of claim 54 wherein the filter media has an average Frazier
Permeability of from 2000 to 8000 cm.sup.3 /hr/m.sup.2.
56. The method of claim 55 wherein the filter media comprises a nonwoven
fibrous web of melt blown microfibers.
57. The method of claim 56 wherein the filter media comprises a nonwoven
fibrous filter web of split fibrillated charged fibers.
58. The method of claim 57 wherein the fibrous filter web is joined to a
supporting scrim.
59. The method of claim 58 wherein the filter web further includes sorbent
particulates or fibers.
60. The method of claim 59 wherein the filter element further includes
additional functional layers.
61. The method of claim 60 wherein the additional functional layers are
particle filtration layers.
62. The method of claim 61 wherein the additional functional layers are
sorptive filtration layers.
Description
BACKGROUND AND FIELD OF INVENTION
The present invention relates to moving filter devices, particularly moving
filters designed to be used in air delivery fans.
Particulate air filters are conventionally formed of porous media. The
particle laden air is passed through the porous media which removes the
particulate based on physical entrapment, impaction, surface attraction,
inertial forces or the like. The porous filter media can be porous films,
open celled foams, woven fabrics, molded particles, or nonwoven fabrics or
webs and the like. The filter media can be flat or formed into a three
dimensional configuration (generally a pleated form). Pass through type
filters will act on the entire airstream passed through the filter media
with an associated pressure drop and filtration efficiency that is
characteristic of the media, its level of particulate loading and the
airstream velocity and pressure. Generally, as the filter media becomes
loaded with particulates the pressure drop increases, however, the
filtration efficiency can increase or decrease depending on the nature of
the media and the particulates being removed.
Generally, most filters when used are static with the particle laden air
driven through the filter. However, filters that move have been proposed,
for example, to keep fresh filter media in the path of the airstream to be
filtered as disclosed in U.S. Pat. No. 5,560,835 (driven slowly by drive
rotor) or U.S. Pat. Nos. 4,038,058 and 3,898,066 (filter media driven by
air impinging on rotor blades). These filters operate like conventional
flow-through static filters and have the associated problem of pressure
drop buildup over time. Flow through type filters have also been
associated with faster moving devices such as rotating disk drives (U.S.
Pat. No. 4,308,041), on an air inlet to a combine vent fan (U.S. Pat. No.
3,392,512), between fan blades on an air inlet fan for a turbine engine
(U.S. Pat. No. 3,402,881), on a fume exhaust fan (U.S. Pat. No.
4,450,756), or in an air inlet to a building ventilation fan (U.S. Pat.
No. 3,126,263). The proposed filters placed on a fan designed to circulate
air (e.g., U.S. Pat. Nos. 3,402,881 and 4,450,756) have the filter media
strategically placed to ensure that all the air passing through the system
is passed through the filter media. In U.S. Pat. No. 3,402,881, the filter
media 100 is woven between fan vanes 98 and sealed to prevent air from
bypassing the filter media. This requires that the filter media be
periodically cleaned. This cleaning is done by a complicated periodic
backflow of air from the engine compressor or like source of high pressure
air in the system. With U.S. Pat. No. 4,450,756, the filter must be
periodically removed and cleaned or replaced. If the filter is not
replaced when loaded, the pressure drop across the filter rises often to
unacceptable levels, cutting off airflow. Although not desirable generally
in certain filter applications this reduction in airflow is unacceptable.
In automotive cabin applications, increases in pressure, due to filter
media particle loading, can drastically reduce airflow which can result in
dangerous window fogging.
In automotive or furnace filter applications, the general approach has been
to place a filter at some location in the airstream (e.g., in the ducts)
to intersect the entire airstream. Commercially the almost universal
approach has been to place filters at various locations between the air
inlet and air outlet in a vehicle or home heating and air conditioning
system. An issue with these filters is they are often difficult to access
unless they are located near the air inlet or outlet(s). However if the
filter is located at or near an air inlet (which generally are easy to
access) only incoming air or recirculated air is filtered, but not both,
unless multiple filters are used at the air inlet(s) for fresh air and the
air inlet(s) for recirculated air. In a novel variant of this general
approach, U.S. Pat. No. 5,683,478 proposes placing a static filter inside
a fan of the blower motor assembly intersecting the airstream immediately
prior to the fan, as both recirculated and fresh air directed through the
fan are filtered.
Generally, filter materials that are used function at very low pressure
drops to ensure that the system, even if the filter is fully loaded with
particulates, does not unacceptably reduce airflow. However, if the filter
media is of the very low pressure drop type it generally is a low
efficiency filter (e.g., an open nonwoven web), has a limited lifetime
(e.g. charged webs with relatively low basis weight) or is very bulky
(e.g., a heavily pleated filter), which is undesirable where there is
limited space such as in an automotive Heating, Ventilation or Air
Conditioning (HVAC) system. Alternatively, it has been proposed that a
certain portion of the airflow bypass the filter to ensure that pressure
drop does not rise unacceptably during the lifetime of the filter. An air
bypass of this type can eliminate the issue of unacceptably reduced
airflow through the HVAC system due to a fully loaded filter but severely
impacts filtration efficiency, particularly when filtering incoming air.
Ideally, to ensure adequate airflow to an automotive cabin, the pressure
drops of a filter in the HVAC system should show little or no pressure
drop over its lifetime, no matter how long it is in use. Similarily, home
heating system filters should not significantly reduce airflow even when
fully particle laden.
SUMMARY OF THE INVENTION
The invention device relates to a novel air filter device for use in a
heating ventilation or air conditioning system or the like where the
filter device shows little or no pressure drop during use. The invention
air filter device comprises a housing having an air delivery fan,
preferably a fan having an axial air inlet and a radial air outlet. An
axially rotating fan and filter unit is located between the air inlet and
air outlet. The fan/filter units, if separate, have a common axis of
rotation, which is generally parallel with the axial air inlet of the
filter housing. The filter unit is comprised of at least one filter
element with a front face and a back face. Adjacent filter element front
and back faces are mutually spaced over at least a portion of their entire
width and/or length such that air can pass unimpeded in an air channel
formed between the adjacent front and back faces. Adjacent filter element
front and back faces are preferably on different filter elements.
Preferably, multiple filter elements are spaced in the radial direction
around the axis of rotation and are parallel with the axis of rotation.
The fan and filter units are also provided with air moving means, which
can be air moving elements and/or air filter elements. The air moving
elements are also preferably spaced in the radial direction around the
axis of rotation and are parallel with the axis of rotation. The optional
air moving means establish the airflow with a general airflow direction at
a given pressure head and volumetric flowrate. With the preferred
centrifugal type fan the air is drawn in axially with the fan and filter
unit axis of rotation and discharged radially outward. The air moving
elements and/or filter elements are spaced from adjacent air moving
elements and/or filter elements to allow the unimpeded passage of air
between the air moving elements and/or filter elements.
BRIEF DESCRIPTION OF THE DRAWINGS
The following drawings illustrate preferred, but not exclusive embodiments
of the invention.
FIG. 1 is a perspective view of a filter according to a first embodiment of
the invention.
FIG. 2 is a perspective view of a filter according to a second embodiment
of the invention.
FIG. 3 is a perspective view of a filter according to a third embodiment of
the invention.
FIG. 3A is a cross-sectional view of the FIG. 3 embodiment.
FIG. 3B is an exploded view of a cross sectional area of FIG. 3A
FIG. 4 is an exploded view of air delivery device in accordance with the
present invention.
FIG. 5 is an exploded view of air delivery device in accordance with the
present invention.
FIG. 6 is a graph of clean air delivery rate (CADR) verses filter media
permeability as described in Example 1.
FIG. 7 is a graph of percentage of air passing through a filter blade
versus filter blade velocity as described in Example 6.
FIG. 8 is a graph of clean air delivery rate (CADR) versus percentage of
air passing through a filter blade verses filter blade velocity as
described in Example 6.
FIG. 9 is a graph of clean air delivery rate (CADR) versus filter media
permeability as described in Example 10.
FIG. 10 is a graph of clean air delivery rate(CADR) versus filter media
permeability as described in Example 11.
DETAILED DESCRIPTION OF THE INVENTION
The invention air delivery device comprises a housing having an air inlet
and an air outlet. The housing generally is continuous between the inlet
and outlet so as not to allow air to enter or leave the device other than
at the inlet and outlet respectively. However, small bypass vents can be
provided so long as the net flow of air to the outlet is not significantly
reduced. Between the air inlet and the air outlet is located an air
delivery fan having at least two rotating air moving means. Air delivery
fan air moving elements are air impermeable and are generally fan blades
that radiate outward from the central axis of rotation or are arranged
around the central axis of rotation (e.g. in an annular array). The
rotating air moving and/or filter elements intersect the flow of air
between the air inlet and the air outlet and establishes a higher pressure
zone at the air outlet and a lower pressure zone at the air inlet. The air
moving or filter elements are positioned in the housing such that there is
a relatively small area available for air to bypass the air moving and/or
filter elements. Air which enters the lower pressure zone formed at the
air inlet is drawn into and through the rotating air moving and/or filter
elements and is forced toward the air outlet under pressure, generally
about 5 mm water or greater, preferably about 10 mm water or greater than
the inlet lower air pressure zone than the air inlet pressure.
The air delivery fan comprises at least one air filter element. The filter
element(s) have an upstream filter face and a downstream filter face where
at least the upstream filter face rotates along the same axis of rotation
as any air moving elements. Like the rotating air moving elements, the
filter elements are preferably situated on the air delivery fan such that
substantially the entire airstream passing through the fan intersects one
or more filter elements prior to being forced to the air outlet by the air
moving elements or the filter elements. The filter elements do this by
being situated in the housing such that the filter elements are generally
coextensive with any air moving means or elements in a given lengthwise
extent. This given lengthwise extent of the air moving means or elements
is generally perpendicular to the direction of the airflow toward the air
outlet or perpendicular to the direction of rotation of the air moving
elements. The air filter elements will extend across the entire
cross-sectional area of the housing which cross-sectional area is
traversed by the air moving means and through which the airflow is passed
toward the air outlet. However, if desired, a given substantial portion of
the given lengthwise extent of an air moving element(s) can be provided
without an air filter element permitting a portion of the airstream to go
unfiltered by bypassing the provided filter element. If multiple air
filter elements are provided at different radial locations of the fan,
each filter element can have different portions provided without filter
media along the same given lengthwise extent.
For each filter element, there is an upstream filter face and a downstream
filter face. The upstream filter face generally faces the direction of
rotation of the fan air moving elements or filter elements with the
downstream filter face facing the direction opposite the direction of
rotation of the air moving or filter elements. As such, the upstream
filter face moves at an angle relative to the airflow in the air delivery
fan such that the upstream filter face impacts the moving airflow,
permitting a portion of the air to flow through the filter element from
the upstream filter face to a downstream filter face and from the
downstream filter face back into a new portion of the airflow. The
upstream filter face acts like an airfoil with higher pressure air on this
face forcing air into and through the filter element to the downstream
filter face which is at a lower air pressure.
Between an adjacent upstream filter face and downstream filter face, along
the filter element in the direction of the given lengthwise extent, there
is a filter element leading edge and a primary trailing edge forming an
upstream filter face. The filter element leading edge is generally
displaced axially outward of the trailing edge and/or is forward of the
trailing edge in the direction of rotation. It is possible that a
secondary trailing edge be displaced axially outward of the leading edge,
for example, where the filter element is in the form of a zigzag filter or
the like, however, the leading edge will be forward of this secondary
trailing edge in the direction of rotation. In any event, the filter
element or elements do not extend continuously in the direction of
rotation of the fan, and as such, air can flow past a given filter element
in the air flow channels provided. The air flow channels are generally
provided between the upstream face of a filter element and an adjacent
downstream filter face, generally an adjacent filter element downstream
face, and are spaced to allow airflow toward the air outlet with minimal
pressure drop (generally by air flow passages such as holes, gaps or the
like, formed in or between the upstream and downstream filter faces).
Preferably, the adjacent upstream and downstream filter faces forming the
air flow channels are between one filter element and an adjacent filter
element. The air flow passages (e.g., gaps or holes) are provided to allow
substantially unimpeded airflow out of a flow channel and generally
corresponding air flow passages (e.g., holes or gaps) provide
substantially unimpeded airflow into a flow channel between adjacent
upstream and downstream filter faces. However, secondary flow channels can
be formed between upstream and downstream faces of filter elements where
there are only outlet air passages. Generally, these secondary air
channels would be in fluid communication with primary air channels via a
filter element filter, and would be formed by folding or like directional
changes in the filter element creating a flow channel between the
downstream filter face and an opposing portion of the same filter face
acting as a secondary upstream filter face The filter element generally
can extend at least 0.5 cm on average on the upstream face(s) from the
leading edge to the trailing edge, preferably at least 1 cm, however, the
extent of the filter element depends on the size of the air delivery
device and its operation. This distance on the upstream face between the
leading edge and the trailing edge generally defines the amount of
available filter material or media available for filtration of a given
portion of the airstream as this portion of the airstream flows past the
upstream filter face of the filter element. Of course, that fraction of
this airstream portion that passes through the upstream filter face is
available for further filtration as part of a new portion of the airstream
between the downstream filter face and any adjacent upstream filter face.
The filter element generally comprises filter media formed of a fibrous
filter web comprised of electret charged filter fibers. The fibrous filter
is generally a nonwoven fibrous web where at least a portion of the fibers
forming the web are electret charged. However, it is possible for a filter
web to have a variable permeability between the leading and trailing edges
with portions either above or below the preferred ranges. If the filter or
filter web does vary in permeability, preferably the most permeable
material is on that portion of the filter media with the slowest speed of
rotation (e.g., the portion closest to the axis of rotation).
The preferred filter is comprised of a nonwoven fibrous web of charged
electret containing fibers which can be any suitable open nonwoven web of
charged fibers. The filter web could be formed of the split fibrillated
charged fibers as described in U.S. Pat. No. 30,782. These charged fibers
can be formed into a nonwoven web by conventional means and optionally
joined to a supporting scrim such as disclosed in U.S. Pat. No. 5,230,800
forming an outer support layer. The support scrim can be a spunbond web, a
netting, a Claf web, or the like.
Alternatively, the nonwoven fibrous filter web can be a melt blown
microfiber nonwoven web, such as disclosed in U.S. Pat. No. 4,917,942
which can be joined to a support layer during web formation as disclosed
in that patent, or subsequently joined to a support web in any
conventional manner. The melt blown nonwoven web can be charged after it
is formed and before or after joined to a support layer if provided. Also,
it has been proposed to charge the microfibers being collected as a web.
The melt blown nonwoven webs are typically formed by the process taught in
Wente, Van A., "Superfine Thermoplastic Fibers" in Industrial Engineering
Chemistry, Vol. 48, pages 1342 et seq., (1956) or Report No. 4364 of the
Naval Research Laboratories, published May 25, 1954, entitled "Manufacture
of Superfine Organic Fibers" by Wente, Van A., Boone C. D. and Feluharty,
E. L., which fibers are collected in an random fashion, such as on a
perforated screen cylinder or directly onto a support web or in the manner
described in PCT Appln. No. WO 95/05232 (between two corotating drum
collectors rotating at different speeds creating a flat surface and a
undulating surface). The collected material can then subsequently be
consolidated, if needed and charged such as in the manner described in
U.S. Pat. No. 4,215,682. Alternative charging methods for the filter web
layer to form electrets include the methods described in U.S. Pat. Nos.
4,375,718 or 4,592,815 or PCT Appln. No. WO 95/05501.
The fibers of the nonwoven filter web can also be charged by known methods
e.g., by use of corona discharge electrodes, high-intensity electric
fields or by tribo-charging (e.g., as described in U.S. Pat. No.
4,798,850) where fibers of differing dielectric properties are rubbed
together, e.g., during formation of the nonwoven web, creating mutual
charges on the fibers.
The fibers forming the nonwoven fibrous filter web are generally formed of
dielectric polymers capable of being charged to create electret
properties. Generally, polyolefins, polycarbonates, polyamides, polyesters
and the like are suitable, preferred are polypropylenes,
poly(4-methyl-pentenes) or polycarbonates, which polymers are free of
additives that tend to discharge electret properties.
Generally, the filter media web should have an average Frazier Permeability
of about 2000 to about 8000 m.sup.3 /hr/m.sup.2, most preferably 3000 to
6000 m.sup.3 /hr/m.sup.2. The basis weight of the filter web layer or
layers are generally 10 to 200 g/m.sup.2,, preferably 50 to 100 g/m.sup.2.
If higher filtration efficiency is required, two or more filter layers may
be used.
The nonwoven filter web can also include additive particles or fibers which
can be incorporated in known manners such as disclosed in U.S. Pat. No.
3,971,373 or 4,429,001. For example, if odor removal is desired, sorbent
particulates and fibers could be included in the nonwoven electret filter
layer web or in a web joined to this filter layer web.
The air filter element can be in the form of a general planar element such
as a fan blade or a fan blade insert. Nonplanar forms of the filter
element are also possible such as a V-shaped wedge or a structured
sheet-like shape such as an array of adjacent peaks or valleys, or the
like. The air filter element generally is formed by air filter media
(e.g., of a fibrous filter) and support elements. The fibrous filter can
be one or multiple layers of fibrous filter web materials which filter web
may have protective cover layers on one or both faces. The protective
cover layers are generally of a higher Frazier air permeability than the
fibrous filter web generally at least 4000 m.sup.3 /hr/m.sup.2, preferably
at least 5000 m.sup.3 /hr/m.sup.2 or higher, most preferably at least 7000
m.sup.3 /hr/m.sup.2 or higher. The protective cover layers can be spunbond
webs, spunlace webs, calandered nonwovens or otherwise thin strengthen
nonwoven or woven materials. The protective cover layer generally is a
nonextensible material when subject to the forces encountered by the
filter media impacting the airstream.
Other than the filter media further functional layers can be included with
the filter media layer or layers. These further functional layers can be
other particulate filtration layers such as noncharged fibrous webs, foam
filter layers, woven filter layers and the like. Nonparticle filtration
layers useful as additional functional layers would include layers formed
of, or including, particules or fibers capable of sorption or
chemisorption such as adsorbents such as activated carbon particles or
fibers, silica gel, or activated alumina.
The filter media support elements can be located on the ends of individual
filter media elements, the sides of individual filter media elements or in
the plane of the filter media. The support elements can be rigid or
flexible but generally are provided to keep the filter media in place on
the filter elements when the fan is rotated. If the support elements are
located at the ends or sides of the filter media, generally the filter
media is attached to the support elements for example, by mechanical
clips, adhesive attachment, resin potting or the like. If support elements
are located in the plane of the filter media generally at least some of
the support elements are attached to the filter media to prevent the
sidewise movement or slippage of the filter media along the filter
element. Structural support elements on the downstream face of the filter
media need not be intimately attached to the filter media as the
rotational movement of the fan will press the filter media into frictional
engagement with these support elements.
The air delivery device is preferably a centrifugal air delivery fan as
shown in FIG. 1 having an axial air inlet 2 with air delivered radially 7
of the axis of rotation 6 of the fan 1. The air moving elements 4 have an
upstream face 12 that is generally aligned with the axis of rotation and a
downstream face 11. Upstream face 12 faces the direction of rotation 10 of
the fan 1. The upstream face 12 is aligned with the axis of rotation 6
such that when the upstream face intersects the airstream it provides a
substantially radial direction to the airflow.
The radial direction of the airflow out of the fan is best accomplished if
the air moving elements 4, or at least its upstream face 12 is in a plane
that is generally parallel with the axis of rotation 6, however, the air
moving elements 4 can be at a slight incline. For example, the upstream
face 12 can be in a plane which intersects the axis of rotation by about 5
to 10 degrees in either direction and still provide a substantially radial
direction to the airflow 7. If the plane containing the upstream face 12
is at an angle to the axis of rotation 6, this angle is preferably
provided so that any axial airflow component is pushed toward the face of
the fan opposite the air inlet 2 face.
In the embodiment of FIG. 1, the air moving elements 4 extend radially
outward from the axis of rotation. There are eight air moving elements 4,
however, as few as two air moving elements are possible, preferably at
least four. More air moving elements can be used as long as the spacing
between adjacent air moving elements is at least 0.5, preferably at least
1.5 cm. Additional air moving elements at a spacing of less than 0.5 cm
generally provide little added benefit. In the embodiment of FIG. 1, the
air moving elements 4 also comprise the filter elements where the filter
media 3 is retained by support elements 9. The filter media 3 is retained
by two substantially identical support element frames 9 which support
element frames 9 can be engaged with each other and the filter media by
mechanical engagement, adhesives, or the like.
The filter elements extend in the direction perpendicular to the airflow 7
by a lengthwise extent 5. This lengthwise extent 5 extends from the air
inlet edge 13 of the fan to the opposite edge 14. When the fan is placed
in a housing, the housing sidewalls will preferably be closely adjacent
both the air inlet edge 13, except in a central region corresponding to
the air inlet 2, and the opposite edge 14. As such the filter element
extends across the entire lengthwise extent 5 of the cross sectional area
in the housing that is traversed by the air moving elements, through which
passes the many portions of the airflow 7. If a substantial portion (e.g.,
more than 75 percent) of the lengthwise extent 5 were not provided with
filter media (e.g., if all the top panels 16 were blocked off),
substantial portions of the radial airflow would bypass, or move through,
the fan and not intersect filter media 3 and be unfiltered. Relatively
thin support elements 9 at the edges 14 and 13 (e.g., less than 1.3 cm) do
not result in this effect due to the turbulent nature of the airflow. The
filter element shown in FIG. 1 extends across the entire width 18 of the
air moving element 4 from a leading edge 15 to a trailing edge 19.
However, the filter element could extend over only a portion of the width
18 and still function to intersect substantially the entire airflow
although with less filtration efficiency.
FIG. 2 illustrates a second embodiment of a centrifugal fan 20 in
accordance with the invention. In this embodiment, the air moving elements
24 are again filter elements formed of filter media 23 and support
elements (29, 30 and 31). The filter media is attached to the support
elements 29 such as by use of adhesive. The support elements 29 are in the
plane of the filter media 23 and are on the downstream face 11 of the
filter media. The filter media 23 of the filter elements extend across the
entire lengthwise extent 25 of the air moving element 24 such that the
entire airflow is ensured of contacting the filter element filter media 23
when the fan is rotated in the direction of rotation 10. The upper support
plate 30 is provided with an air inlet opening 2. The bottom support plate
31 can be solid as no air is discharged axially out from this face of the
fan. The support elements 29 are retained between the support plates 30
and 31.
The planar upstream face of the air moving element/filter element 24 is
aligned with and parallel with the axis of rotation providing a
substantially entirely radial airflow 7. The upstream face 12 in the FIG.
2 embodiment however, does not extend linearly in the radial direction as
in the embodiment of FIG. 1 rather is curved in the radial direction from
leading edge 15 to trailing edge 19. The air moving element and/or filter
element can curve in either direction. In the FIG. 2 embodiment, the
upstream face curves in the radial direction such that the conave face is
the downstream face 11 and the convex face is the upstream face 12.
FIGS. 3, 3A and 3B illustrate a third embodiment of filter elements used in
an air delivery fan of the invention. The filter elements 44 are formed
from a zig-zag pleated filter media 43 supported by an upper annular
support disk 45 and a lower annular support disk 46. The filter media 43
is preferably also supported by rigid support elements or by support bands
47 intersecting the tips or ends of the filter media on one or both outer
annular surfaces. The filter media outer pleat tips are removed to create
flow passages 48. Upstream face 58 and downstream face 59 of the pleated
filter media create primary flow channel 55. The filter elements 44 as
such are V or U-shaped with flow through primary air channels 55 formed
between the upstream face 58, formed by the leading edge 51 and trailing
edge 54 of an adjacent filter element 44, and the downstream face 59 of an
adjacent filter element 44, which downstream face 59 is formed between
trailing edge 54 and trailing edge 52. This primary air channel 55 also
forms an air passage. The air passages in this embodiment can be any
appropriate size or shape but are generally at least 0.02 cm.sup.2,
preferably at least 0.06 cm.sup.2 on average in its minimum cross
sectional area. The cross sectional area of all the air flow passages for
this embodiment (taken at their minimum cross sectional area for air flow
passages that extend along an air channel) generally comprise from 5 to 25
percent, preferably 10 to 20 percent, of the total cross sectional area of
the filter elements and any flow passages between adjacent filter
elements.
A secondary air channel 56 is formed between a downstream face 68 formed
between leading edge 51 and trailing edge 54 and a secondary upstream face
69, formed between trailing edge 54 and secondary trailing edge 52. This
secondary air channel has an air outlet 57 but no air inlet. As such air
entering air channel 56 from the downstream filter face can form a
secondary airflow and exit out an air flow passage formed by the air
outlet gap 57 and rejoin the primary airflow 7.
Annular filter 40 of FIGS. 3 and 3A can be attached to a fan 60 with
separate air moving elements 61 in a housing as shown in FIG. 4. The air
moving elements 61 are fan blades. The spacing between the leading and
trailing edges (51 and 52) of adjacent filter elements creates airflow
channels 55 that ensure that air can freely move into the air filter
elements and outward as a radial airflow 7 even when the filter media 43
forming the filter elements 44 is fully loaded with particulates.
Alternatively, the filter media could be provided with holes to form flow
channels between upstream and downstream filter element faces to ensure
continuous airflow even when the media is fully loaded.
FIG. 4 illustrates the filter of FIG. 3 used in a housing 62 having an air
inlet 63 and an air outlet 64. The air moving elements 61 are spaced
radially from the axis of rotation and form fan blades provided in an
annular array on a radial blower wheel 60. The air inlet is provided on a
cover 66 that fits onto the main housing 62. The radial airflow from the
blower wheel is directed through the filter 40 where it intersects the
upstream faces of the filter elements 44. The filter and its filter
elements are shown radially outward of the air moving elements in FIG. 4,
however, the filter and its filter elements could be located radially
inward of the air moving elements of the fan by being located inside the
blower wheel.
FIG. 5 illustrates a further embodiment of the invention where a filter 80
as shown in FIG. 3 is attached to a blower wheel 84 in a housing 85 of a
centrifugal air delivery fan such as would be used in the HVAC system of a
vehicle. The air inlet 82 is centrally located in the housing with the
radial outlet 90 extending off the side designed to deliver air at a
pressure head. The filter 80 engages the blower 82 by a friction fitting.
When the air moving means are formed by the filter elements as shown in
FIGS. 1 and 2, preferably all the air moving means are formed in whole or
in part by the filter elements to ensure filtration of the entire airflow.
However, one or more air moving means can be formed other than as filter
elements with a resulting decrease in filtration efficiency due to bypass
of the airflow without intersecting any filter elements. Where air moving
elements or a fan blade form a portion of the air moving means, preferably
the air moving elements are at least 25 percent of the cross sectional
area of air moving means, preferably at least 75 percent of the cross
sectional area.
Although not preferred, the air delivery device can also be provided by a
axial fan in which case the air moving elements and/or filter element
intersect the axis of rotation of the fan. In this case, a substantial
portion of the airflow is given an axial flow direction and the air outlet
is located on the axial face of the air delivery fan opposite the air
inlet face. The filter element (s) are preferably provided along the
entire widthwise extent 18 of the air moving means to prevent any air
bypass without filtration.
In operation the filter elements rotate in the direction of rotation
intersecting the airstream and also imparting axial and/or radial movement
to the airstream. At least 95 percent of the airstream is filtered by at
least partially passing through the air filter element filter media. The
filter elements are spaced relative to one another or otherwise provide
air flow channels that permit the passage of air along or past the filter
elements. Preferably these air flow channels have outlets located at the
outermost edge of the filter element where the airstream moves away from
the filter elements with flow channels being defined by adjacent upstream
and downstream faces of the filter element(s).
The air flow passages in or through the air flow channels allow for the
substantially unimpeded passage of air through the filter even when the
filter elements are substantially loaded with particles. This allows the
filter elements to operate without creating significant pressure drops
over their useful life with nominal reductions in airflow through the
filter device. The reduction in airflow of the filtration device over the
useful life of the filter elements is generally less than 15 percent,
preferably less than 10 percent, and most preferably less than 5 percent.
The filter elements operate at decreasing efficiency as they become
particle loaded due to the decrease in permeability and loading of the
electret charged filter media.
Overall, the filter media operates best when in the preferred Frazier air
permeability range, both initially and when fully or partially loaded with
particles. Generally, at least 5 percent of the airflow should flow
through the filter media in operation, preferably from 10 to 75 percent,
and most preferably 10-50 percent. Higher percent airflow through the
filter media is less desirable as there is reduced efficiency of the media
due to the decreased basis weight needed to obtain this increase in
airflow through the media. As premeability and the percent air passing
through the media decreases with an uncharged filter media, the filtration
performance generally stays the same or decreases. However, with the
invention charged filter media, there is a significant increase in
performance until the permeability decreases to less than 2000 m.sup.3
/hr/m.sup.2. The inter-relationship between charged media and permeability
is not fully understood, but it is clear that with a charged filtration
media there is a significant increase in filtration performance with a
moving filter device in accordance with the invention particularly in the
preferred permeability ranges.
EXAMPLES
Test Procedures
Clean Air Delivery Rate
Clean air delivery rate provides a measure of the air cleaner performance
by using an ANSI standard procedure entitled "Method for Measuring
Performance of Portable Household Electric Cord-Connected Room Air
Cleaners", ANSI/AHAM AC-1-1988, dated Dec. 15, 1988. This method was
modified, as described below in the Time to Cleanup (Particulate
Challenge) test, to accommodate and test a variety of filter systems and
constructions. Clean Air Delivery Rate (CADR) is defined by the equation
CADR=V(k.sub.e -k.sub.n)
Where V is the volume of the test chamber, k.sub.e (1/t.sub.min) is the
measured decay rate of the particle count in the test chamber resulting
from the operation of the air cleaning device being tested per the
standard requirements, and k.sub.e (1/t.sub.min) is the natural decay rate
of particle count in the test chamber in the absence of an air cleaning
device.
Frazier Permeability
Frazier permeability, a measure of the permeability of a fabric or web to
air, was determined according to Federal Test Standard 191A, Method 5450
dated Jul. 20, 1978.
Blower Pressure
Pressure developed by the mini-turbo fan assembly was defined as the
difference between the dynamic pressure created between the leading and
trailing faces of each blade component while rotation at a specified speed
(i.e. the differential of the dynamic pressure across the filter media).
This pressure was determined by using Bernoulli's equation of static
pressure as described in "Fluid Mechanics" by V. L. Streeter & E. B.
Wylie, McGraw-Hill Book Co., pp. 101, 1979. The pressure developed by the
centrifugal blower unit configuration is defined as the differential in
air fluid pressure between the inlet of the blower assembly (i.e. the
inlet of the scroll unit of the blower unit) and the dynamic pressure at
the scroll outlet. The pressure drop of the moving filter in the
centrifugal blower unit was determined by using Bernoulli's equation of
static pressure mentioned above.
Time to Cleanup (Particulate Challenge)
This test was designed to characterize the rate at which a filter
configuration reduced the particle count of a known volume of air in a
re-circulation mode. The test chamber consisted of a "Plexiglas" box
having a one cubic meter (m.sup.3) volume. The front sidewall of the test
chamber was equipped with a door to allow placement of instrumentation,
sensors, power supplies, etc. into the chamber. Each of the two adjacent
sidewalls were each equipped with a 10 cm (4 inch) port which served as
inlet and/or outlet ports to introduce or evacuate particles from the
chamber. One of three smaller 3.8 cm (1.5 inches) diameter ports located
on the back sidewall of the chamber was used to probe the particle level
in the test chamber. The two other ports were fitted with 0.0254 m (1
inch) diameter 3M Breather Filters, Part No. N900 (available from 3M, St.
Paul, Minn.) which exhibited 99.99% efficient capture of
particles.ltoreq.0.3 .mu.m in size. The thus protected ports functioned as
breathers to maintain a balanced atmospheric pressure between the test
chamber and ambient surroundings. The interior of the test chamber was
also equipped with power outlets that were controlled from outside the
chamber. The particle challenge level was adjusted to a constant,
controlled level prior to the start of each test by means of a portable
room cleaner (available from Holmes Products Corp., Milford, Mass.). A
recirculation fan (available from Duracraft Corp., Whitinsville, Mass.)
was used to maintain a uniform mixing of the particulate challenge before
the test started. This fan was set at maximum speed during re-circulation
and turned off once particle testing started. The particle count analyzer
(a "Portable Plus" HIAC/ROYCO particle counter, available from Pacific
Scientific, Silver Spring, Md.) was connected to the test chamber by means
of a 6.35 mm OD (1/4 inch) tube which was 1.22 m (4 foot) in length. All
openings into the test chamber were carefully sealed with gaskets or
sealants to minimize particle leakage during testing.
All testing was conducted using background particles from the environment
with an additional paper smoke load to bring the initial particle level to
about 1.41.times.10.sup.8 particles/m.sup.3 (4.times.10.sup.6 particles
per cubic feet). The smoke generator consisted of a stick made of bond
paper that was ignited and introduced in the test chamber for a few
seconds. The resulting particle concentration was typically above the
desired value and the room cleaner would be used to reduce the count to a
constant baseline of 1.41.times.10.sup.8 particles/m.sup.3
(4.times.10.sup.6 particles/ft.sup.3) for all tests. Once the desired
particle concentration level was attained, the moving filter apparatus was
turned on and the particle concentration of the chamber was sampled every
30 seconds at a rate of 5.66 liters/min (0.2 ft.sup.3 /min) to generate
the particle decay curve over a period of ten minutes. After each test the
chamber was purged of particles. In addition to logging the particle decay
curves, the voltage, amperage consumption and rpm's of each filter
configuration was recorded using a Fluke instrument, model 87, Everett,
Wash. The filtration performance characterization of each moving filter
was made following the ANSI/AHAM AC-11-1988 standard. Variations to the
standard were the test chamber dimensions, re-circulation fan size, no
humidity control, use of a manual smoke generator (paper smoke), frequency
of data taking and length of the test (10 minutes).
Web Thickness
Web thickness was measured using an electronic digital caliper, Model 721B,
available from Starrett, Athol, Mass.
Airflow Through Filter Media
Airflow through the various media used as filter material was calculated
according to the formula:
Flow (m.sup.3 /hr)=(Q.sub.M /Q.sub.S).times.100
where
Q.sub.M =Calculated flow through the media using the equation
PERM.times.filter area;
where PERM is defined below.
Q.sub.S =Flow delivered by the system due to the media, and is calculated
as the difference Q.sub.C -Q.sub.F, where
Q.sub.F, the airflow due to the frame of the fan blades, was determined by
operating the mini turbo fan (described below) at the indicated speed
(rpms determined by a stroboscope, (model 1000, available from Ametek
Inc., Largo, Fla.) recording the voltage and current draw corresponding to
the rotational speed for subsequent calculations, determining the air
velocity (an average of three data points) at the fan outlet using a hand
held anomometer, (Model "Velocicalc Plus", available from TSI Inc., St.
Paul, Minn.), and calculating the flow rate Q.sub.F by multiplying the air
velocity times the cross-sectional area of the outlet.
Q.sub.C, the combined airflow due to the filter media and frame, was
determined using a procedure identical to that used to determine Q.sub.F
except that the bare turbo blade frames were replaced with frames fitted
with filter media.
PERM, the permeability of the filter media on a moving turbo blade, was
calculated using the equation:
PERM=(Frazier permeability.times.P.sub.A)/ P.sub.B
where
Frazier permeability for the filter media was determined as described
above;
P.sub.A, the pressure exerted on the filter media of a moving turbo blade,
was calculated using the formula:
P.sub.A =F.sub.M /Filter area
where F.sub.M, the force exerted on the media, defined as T.sub.M /(2/3)R,
where T.sub.M is the torque exerted on the media and R is the radius of
the mini turbo impeller. This calculation was based on the assumptions
that the velocity profile on the media was triangular, zero at the axis
and maximum at the blade tip, that the net force acted at 2/3 of the
impeller radius, and that torque T.sub.M could be calculated as the
difference between the torque with filter media on the turbo blades and
torque with only the turbo blade frames as calculated from the
torque/current relationships for the electric motor used in the blower.
P.sub.B, the pressure on the face of the moving filter media in the blower,
was determined by placing a sample of the filter media from the turbo fan
blade in a TSI Model 8110 Automated Filter Tester apparatus (available
from TSI Inc.), adjusting the flow rate through the media to that
calculated for an individual turbo blade (1/8 of the total flow rate), and
obtaining a value for P.sub.B as a standard machine output.
Test Configurations
Mini Turbo Fan
The mini turbo fan consisted of a centrifugal flat blade filter
configuration. The DC fan motor, a 9 cm Disc motor, (Part No. 090SF10,
available from Hansen Corporation, Princeton, Ind.), was secured to a
mounting panel which allowed the motor to be positioned outside the scroll
unit with only the motor shaft extending into the scroll unit to allow
mounting of the fan blades. A scroll housing, designed using standard fan
& blower design principles using a 10 degree diffuser angle, was
constructed from art poster board (1.2 mm thickness, Cat. No. 666,
available from Crescent Cardboard Co., Wheeling Ill.) which was glued
together using a hot melt adhesive. The scroll unit was 6.35 cm in height,
the inlet was 14.3 cm in diameter, the rectangular outlet was
10.8.times.5.7 cm in cross-section, and the air expansion ratio of the
scroll was 1:8. The shaft of the motor was equipped with an 1.9 cm
aluminum hub having eight uniformly spaced dovetail slots which received
the rectangular frame units of the individual fan blades. The frames,
which were 5.1 cm.times.5.7 cm (2 in..times.2.25 in.) in dimension with a
central, longitudinal support element, were machined from PVC plastic. The
assembled circular cross-section of the unit was approximately 14 cm in
diameter. Power was supplied to the motor by a variable voltage power
source, which allowed the speed of the fan to be controlled and power
consumption of the motor to be monitored.
Add-on Filter Configuration
A centrifugal blower assembly having a blower wheel 15.25 cm outside
diameter, 13.0 cm inside diameter and blade height of 4.3 cm with 38
forward curved blades was used for this test configuration. The blower
assembly was driven by a DC motor, which was connected to variable voltage
power source allowing the speed of the fan to be controlled and power
consumption of the motor to be monitored. The scroll was designed using
standard fan & blower design principles. The diffuser angle of the scroll
was 8 degrees. Filter elements used in conjunction with this test
configuration were sized to fit exterior to the fan blades on the blower
wheel.
Automotive HVAC Configuration
A dash assembly, including the air circulation ducting components, was
removed from a Ford Taurus and used in this test configuration. An access
panel was cut into the blower housing to allow various filter element
configurations to be inserted into the blower wheel of the unit. Power was
supplied to the motor by a variable voltage power source, which allowed
the speed of the fan to be controlled and power consumption of the motor
to be monitored. A 15 cm diameter, 130 cm long duct was connected to the
inlet side of the HVAC system. A hot wire anemometer (Model "Velocicalc
Plus") was mounted at the end of the duct to measure the airflow rate. A
manometer was used to measure the pressure developed across the blower
wheel with the full HVAC system in place. A second, identical, HVAC system
was then modified by removing the coils, ducting, and cutting the exit
side of unit to a size which would fit into the cubic meter box. A solid,
sliding baffle plate was placed on the exit of the modified system to
enable the system flow and pressure to be adjusted to duplicate the flow
and pressure parameters of the system prior to what it had been before
several components were removed. This modified unit was then used for all
particulate and gas testing. The original full HVAC system was used for
all further flow, and power measurements.
Particulate Filter Media
GSB30
A charged fibrillated film filtration media having a basis weight of 30
g/m.sup.2 (available from 3M Co., St. Paul, Minn. under the designation
"FITRETE" Air Filter Media Type GSB30).
GSB50
A charged fibrillated film filtration media having a basis weight of 50
g/m.sup.2 (available from 3M Co. under the designation "FITRETE" Air
Filter Media Type GSB50).
GSB70
A charged fibrillated film filtration media having a basis weight of 70
g/m.sup.2 (available from 3M Co. under the designation "FITRETE" Air
Filter Media Type GSB70).
GSB150
A charged fibrillated film filtration media having a basis weight of 150
g/m.sup.2 (available from 3M Co. under the designation "FITRETE" Air
Filter Media Type GSB150).
Meltblown
A charged blown microfiber web having fiber diameters in the range of 0.3
.mu.m to 5 .mu.m and basis weight of 70 g/m.sup.2. The web prepared
substantially as described in Report No. 4364 of the Naval Research
Laboratories, published May 25, 1954, entitled "Manufacture of Super Fine
Organic Fibers" by Van Wente et. al. and charged substantially as
described in U.S. Pat. No. 4,749,348 (Klaase et. al.)
Fiber Glass
A commercially available 70 g/m.sup.2 fiber glass paper with 95% ASHRE
efficiency, available from Bernard Dumas S. A., Creysse, France, under the
designation B-346W.
Paper
A white, 100% cellulosic paper available from Georgia Pacific Papers,
Atlanta, Ga., under the designation Spectrum-Mimeo, 75 g/m.sup.2.
Filter Assembly
Mini Turbo Fan Blades
The filter media was cut into rectangular pieces 5.1 cm.times.5.7 cm (2
in..times.2.25 in.) in size, a thin bead of hot melt adhesive (Jet Melt,
Product No. 3748-Q, available from 3M) was applied to the perimeter and
central support member of the fan blade frame, a piece of the filter media
was placed on the hot adhesive and slight hand pressure was applied. The
adhesive was allowed to cool before any testing.
Pleated Filter Cartridges
A rectangular piece of the filter media (sized to provide the desired
length of pleated filter media (dependant on the diameter of the blower
wheel, pleat depth and pleat density) was formed into pleats using a
"Rabofsky" pleater, (available from Rabofsky GmbH, Berlin, Germany). The
pleated strip was mounted on a jig to hold the pleat tips at the desired
spacing and two pieces of adhesive thread ("String King", available from
H.B. Fuller Co., St. Paul Minn.) were attached across the pleat tips to
secure their spacing. The spaced, stabilized pleat pack was then wrapped
around the blower wheel (or inserted into the blower wheel) and pleats
were trimmed to produce a precise fit. The pleat pack was then removed
from the blower wheel, the two ends of the pleat pack were brought
together to form a continuous loop and two pieces of adhesive thread about
used to span across the inner pleat tips, securing the pleat pack into a
cylindrical shape. Two annular poster board rings having the same diameter
as the pleated cylinder were attached to the top and bottom of the filter
structure using a hot melt adhesive to maintain the cylindrical shape of
the filter. The outer diameter tips of the pleated filter constructions
were optionally left intact or slit, to provide a by-pass configuration,
prior to testing.
Example 1
The filtration performance of several filter media as a function of the
permeabilty of the media was studied using Time to Cleanup (Particulate
Challenge) test described above. A mini turbo fan was fitted with each of
the indicated filter media and placed in the test apparatus, a known
particulate L challenge introduced into the box, and the fan operated at
2900 rpm. Particle count data for these studies are reported in TABLE 1.
TABLE 1
__________________________________________________________________________
Particle count vs. Time
(Particle Count .times. 10.sup.5)
Time
(min)
Baseline
GSB30
GSB50
GSB70
GSB150
Melt Blown
Fiber Glass
Paper
__________________________________________________________________________
0 3.08 3.10
3.11
3.11
3.12 3.11 3.07 3.08
0.5
3.05 3.00
2.97
2.93
2.83 3.00 2.97 3.01
1.0
3.02 2.86
2.74
2.69
2.27 2.78 2.84 2.94
1.5
2.98 2.68
2.49
2.21
1.65 2.52 2.70 2.87
2.0
2.95 2.48
2.21
1.79
1.10 2.22 2.56 2.79
2.5
2.91 2.27
1.92
1.38
0.700
1.89 2.41 2.71
3.0
2.89 2.05
1.64
1.05
0.441
1.58 2.25 2.64
3.5
2.85 1.83
1.38
0.772
0.277
1.29 2.09 2.57
4.0
2.82 1.62
1.14
0.561
0.173
1.03 1.95 2.49
4.5
2.78 1.43
0.949
0.405
0.112
0.819 1.79 2.40
5.0
2.75 1.25
0.775
0.296
0.071
0.636 1.63 2.32
5.5
2.71 1.10
0.632
0.213
0.050
0.495 1.50 2.24
6.0
2.68 0.937
0.515
0.156
0.038
0.386 1.36 2.15
6.5
2.65 0.815
0.419
0.117
0.030
0.301 1.24 2.08
7.0
2.62 0.701
0.348
0.085
0.025
0.233 1.12 2.00
7.5
2.58 0.592
0.287
0.063
0.022
0.183 1.01 1.91
8.0
2.55 0.511
0.235
0.049
0.018
0.143 0.901 1.84
8.5
2.51 0.447
0.196
0.038
0.016
0.112 0.807 1.75
9.0
2.48 0.383
0.163
0.030
0.016
0.091 0.727 1.68
9.5
2.45 0.330
0.136
0.023
0.014
0.074 0.651 1.60
10.0
2.40 0.290
0.119
0.020
0.013
0.061 0.586 1.54
__________________________________________________________________________
Examination of the data in TABLE 1 shows that when operating at comparable
conditions in a "moving filter" configuration, more porous filtration
materials (i.e. GSB30, GSB50, GSB70, GSB150, and meltblown) are more
effective in removing particles than less permeable materials (i.e. fiber
glass, & paper).
The Clean Air Delivery Rate (CADR) calculated on the data shown in TABLE 1
for the various filtration media are shown in TABLE 2 and graphically
presented in FIG. 6, where the CADR is compared to the permeability of the
filtration media.
TABLE 2
______________________________________
CADR vs. Media Permeability
Frazier Permeability.sup.1
CADR.sup.2
Filtration Material
m.sup.3 /h/m.sup.2
ft..sup.3 /h/ft.sup.2
m.sup.3 /h
ft..sup.3 /min
______________________________________
GSB30 10,122 553.5 13.8 8.1
GSB50 7,888 431.3 20.0 11.8
GSB70 5,969 326.4 32.5 19.1
GSB150 3,261 178.3 45.7 26.9
Meltblown 2,011 110 24.6 14.5
Fiber Glass 554 30.3 10.0 5.9
Paper 6.4 0.35 2.7 1.6
______________________________________
.sup.1 Determined as described in the Frazier Permeability test procedure
above.
.sup.2 Calculated as described in the "Method for Measuring Performance o
Portable Household Electric CordConnected Room Air Cleaners," ANSI/AHAM
AC1-1988.
The inter-relationship of media permeability (Frazier Permeability) and
CADR is readily apparent from an examination of the data in TABLE 2
suggests that the two parameters can be balanced against each other
depending on the requirements of the application.
Example 2
The filtration performance of a filter media as a function of changing
permeability of the media was studied using the Time to Cleanup
(Particulate Challenge) test. GSB70 media, GSB70/posterboard laminate
(prepared by laminating the poster board to the GSB70 media with a bead of
hot melt adhesive along the edge of the poster board), and a cellulosic
paper filter media (described above) were used as filter media in this
study. The mini turbo fan was sequentially fitted with each of the
materials mentioned above, the mini turbo fan placed in the test
apparatus, a known particulate challenge introduced into the box and the
fan operated at 2900 rpm. Particle count data for these studies are
reported in TABLE 3.
TABLE 3
______________________________________
Particle Removal vs. Blade Porosity
(Particle Count .times. 10.sup.5)
GSB70/Poster
Time (minutes)
Baseline GSB70 Board Laminate
Paper
______________________________________
0 3.08 3.11 3.11 3.08
0.5 3.05 2.93 3.00 3.01
1.0 3.02 2.60 2.85 2.94
1.5 2.98 2.21 2.69 2.87
2.0 2.95 1.79 2.51 2.79
2.5 2.91 1.38 2.31 2.71
3.0 2.89 1.05 2.10 2.64
3.5 2.85 0.772 1.90 2.57
4.0 2.82 0.560 1.69 2.49
4.5 2.78 0.405 1.49 2.40
5.0 2.75 0.296 1.30 2.32
5.5 2.71 0.213 1.14 2.24
6.0 2.68 0.156 0.973 2.15
6.5 2.65 0.117 0.845 2.08
7.0 2.62 0.085 0.721 2.00
7.5 2.58 0.063 0.620 1.91
8.0 2.55 0.049 0.539 1.84
8.5 2.51 0.038 0.454 1.75
9.0 2.48 0.030 0.388 1.68
9.5 2.45 0.023 0.333 1.60
10 2.40 0.020 0.288 1.54
CADR 32.3 8.1 1.6
______________________________________
Examination of the data shown in TABLE 3 clearly shows that superior
particle removal rates are realized when more airflows through the filter
media (unbacked vs. backed GSB70). The calculated CADRs for the GSB70,
GSB70/paper laminate and paper filter configurations based on the data of
TABLE 3 of 32.5 m.sup.3 /h (19.1 ft..sup.3 /h), 8.1 m.sup.3 /h (13.7
ft..sup.3 /h), and 1.6 m.sup.3 /h (2.8 ft..sup.3 /h), respectively, for
the three media configurations further substantiates the importance of
airflow through the filter media to achieve good filtration performance.
Example 3
Filtration performance of two identical pleated filter constructions in
"moving" and "static" configurations were studied using the Time to
Cleanup (Particulate Challenge) test described above. In this study the
mini-turbo fan was replaced with the Add-on Filter test unit (described
above) wherein the filter elements in both configurations were placed
outside the blower wheel.
The filter elements were assembled as described above using GSB70 media
approximately 2.55 m (8.4 feet) by 4.13 cm (1.62 inches), which was
converted into a pleated filter cartridge with an OD of 19 cm (7.5 in.),
an ID of 15.75 cm (6.2 in.) and a height of 4.13 cm (1.62 in.), and having
85 pleats at a 6 mm spacing. Subsequent to assembly into the cartridge,
the pleat tips were slit.
The "moving" filter cartridge was mounted directly onto the blower wheel.
The "static" filter was positioned just off the surface of the blower
wheel by mounting it to the stationary scroll housing such that it did not
contact the blower wheel in operation. In both tests, the Add-on Filter
test unit was operated at 13 volts and the particle count of the test
chamber monitored. Particle count data for the two test configurations are
summarized in TABLE 4.
TABLE 4
______________________________________
"Moving" vs. "Static"
Filtration Performance
(% Cleanup)
Time
(Minutes) Baseline "Moving" "Static"
______________________________________
0 3.08 0.00 0.00
0.5 3.05 11.7 9.0
1.0 3.02 33.1 21.5
1.5 2.98 54.5 37.0
2.0 2.95 72.5 51.1
2.5 2.91 84.4 64.7
3.0 2.89 91.1 74.9
3.5 2.85 94.8 82.5
4.0 2.82 97.1 88.0
4.5 2.8 98.3 91.8
5.0 2.75 98.9 94.5
5.5 2.71 99.3 96.2
6.0 2.68 99.5 97.4
6.5 2.65 99.7 98.1
7.0 2.62 99.8 98.7
7.5 2.58 99.8 99.0
8.0 2.55 99.8 99.3
8.5 2.51 99.8 99.5
9.0 2.48 99.9 99.6
9.5 2.45 99.9 99.7
10.0 2.40 99.9 99.7
CADR (m.sup.3 /h) 36.6 25.5
______________________________________
While both the "moving" and "static" filter configurations eventually
reached similar particle concentrations in the test apparatus, it is
apparent from an examination of the data in TABLE 3 that the "moving"
filter configuration was able to reduce the particle count more rapidly
than the "static" filter configuration. This performance difference is
also reflected in the calculated CADR for the "moving" filter
configuration and the "static" filter configuration (36.6 m.sup.3 /h vs.
25.6 m.sup.3 /h).
Example 4
The mini turbo fan apparatus was used to study the effect of charge on the
filtration media of a "moving" filter configuration.
Filtration performance of GSB70 media and GSB70 media which had been
discharged by washing the media in isopropyl alcohol were used as the
filter media for this study. The mini turbo fan was sequentially fitted
with the two filter media, the mini turbo fan placed in the Time to
Cleanup (Particulate Challenge) apparatus, a known particulate challenge
introduced into the box, and the fan operated at 2800 rpm. Particle count
data for these studies are reported in TABLE 5.
TABLE 5
______________________________________
Effect of Charge on Filtration Performance
(Particle Count .times. 10.sup.5)
Time Charged Uncharged
(Minutes) Baseline GSB70 GSB70
______________________________________
0 3.08 3.11 3.08
0.5 3.05 2.93 3.00
1.0 3.02 2.69 2.89
1.5 2.98 2.21 2.76
2.0 2.95 1.79 2.62
2.5 2.91 1.38 2.48
3.0 2.89 1.05 2.33
3.5 2.85 0.772 2.17
4.0 2.82 0.561 2.00
4.5 2.8 0.405 1.86
5.0 2.75 0.296 1.69
5.5 2.71 0.213 1.56
6.0 2.68 0.156 1.42
6.5 2.65 0.117 1.29
7.0 2.62 0.085 1.17
7.5 2.58 0.063 1.06
8.0 2.55 0.049 0.962
8.5 2.51 0.038 0.867
9.0 2.48 0.030 0.787
9.5 2.45 0.023 0.706
10.0 2.40 0.020 0.629
CADR (m.sup.3 /h) 32.5 8.5
______________________________________
The calculated CADRs for the charged GSB70 and uncharged GSB70 filter media
based on the data in TABLE 5 of 32.5 m.sup.3 /h and 8.5 m.sup.3 /h
respectively for the two media, the data in TABLE 5 clearly demonstrate
that charged media provides superior filtration performance to uncharged
media in moving filter configurations.
Example 5
Filtration performance as a function of the speed of the moving filter was
studied using the mini turbo filter apparatus.
A mini turbo fan having GSB70 filtration media on its blades (prepared as
described above) was placed in the Time to Cleanup (Particulate Challenge)
apparatus, a known particulate challenge introduced into the box, and the
fan operated at the speed indicated in TABLE 6. (The fan blades were
replaced with new blades having new filtration media for each test speed.)
Particle count data for these studies are reported in TABLE 6.
TABLE 6
______________________________________
Filtration Performace vs. Filter Speed
(Particle Count .times. 10.sup.5)
Time Filter Speed (rpm)
(min.)
2900 2500 2100 1700 1300 900 500
______________________________________
0 3.10 3.12 3.10 3.10 3.12 3.08 3.11
0.5 2.88 2.98 2.96 3.00 3.04 3.05 3.07
1.0 2.48 2.74 2.75 2.84 2.92 2.96 3.02
1.5 2.00 2.43 2.52 2.65 2.80 2.87 2.97
2.0 1.54 2.10 2.23 2.45 2.65 2.78 2.93
2.5 1.12 1.75 1.96 2.23 2.50 2.68 2.87
3.0 0.804 1.42 1.68 1.99 2.34 2.58 2.82
3.5 0.567 1.13 1.42 1.77 2.16 2.47 2.76
4.0 0.396 0.880 1.20 1.55 1.99 2.37 2.70
4.5 0.281 0.680 0.986 1.36 1.81 2.27 2.64
5.0 0.204 0.530 0.818 1.16 1.65 2.15 2.57
______________________________________
TABLE 7
______________________________________
Calculated Clean Air Delivery Rate vs.
Fan Blade Speed
Velocity Velocity CADR CADR
Rpm (m/sec) (Ft./min) (m.sup.3 /h)
(ft..sup.3 /min.)
______________________________________
2900 21.2 4176 33.3 19.6
2500 18.3 3600 20.4 12
2100 15.4 3024 15.6 9.2
1700 12.4 2448 11.6 6.8
1300 9.5 1872 7.8 2.9
900 6.6 1296 4.9 2.9
500 3.7 720 3.1 1.8
______________________________________
It is apparent from an examination of the data in TABLE 6 and the
calculated CADR shown in TABLE 7 that the filtration performance of the
GSB70 media showed a decided improvement as the speed of the mini turbo
fan was increased. It is recognized that this data is unique to the test
configuration described in a recirculation mode, and, as such, no absolute
speed/filtration performance values can be defined which will apply to all
filtration applications. However, the data does show a definite
inter-relationship between the filter speed and filtration performance,
which needs to be optimized for each combination of filter media and
apparatus configuration.
Example 6
The mini turbo fan was used as a model to calculate the percentage of air
passing through various filtration media as a function of the rotational
speed of the filter media. An average velocity, taken at 2/3 of the
diameter of the mini turbo fan blade assembly, and the Frazier
permeability were used to calculate the airflow through the various media,
the results of which are reported in TABLE 8 and graphically presented in
FIG. 7.
TABLE 8
______________________________________
Percent Air Passing Through Filter Media
vs. Filter Speed
V.sub.ave
Speed (m/ Melt Fiber
(rpm) sec) GSB30 GSB50 GSB70 GSB150 blown Glass
______________________________________
500 2.2 19.2 21.1 15.6 5.6 2.7 0.3
900 4.0 24.1 18.3 14.1 4.2 2.8 0.2
1300 5.8 32.7 17.7 10.9 6.7 2.5 0.4
1700 7.5 37.8 21.6 15.0 8.0 4.0 0.5
2100 9.3 47.6 30.0 19.2 12.3 5.0 0.8
2500 10.6 62.6 42.7 28.8 14.2 5.8 1.0
2900 12.9 73.5 45.5 31.6 17.9 6.9 1.0
______________________________________
The CADR for the various media was subsequently calculated for 2900 rpm,
the results of which are shown in TABLE 9 and are graphically presented in
FIG. 8.
TABLE 9
______________________________________
Percent Air Passing Through Filter Media
vs. Clean Air Delivery Rate (CADR)
% Air Passing Through
CADR
Media Media (m.sup.3 /h)
______________________________________
GSB30 73.5 13.8
GSB50 45.5 20
GSB70 31.6 32.5
GSB150 17.9 45.7
Meltblown 6.9 24.6
Fiber Glass 1.0 10
Paper 0 2.7
______________________________________
The data in TABLES 8 and 9 and FIGS. 7 and 8 provide a good picture of the
inter-relationship of filtration performance and air passing through the
filter media as influenced by the velocity or speed at which the filter
media is moving. This data suggests that filter performance can be
optimized for a given application by selection of filtration media and its
associated permeability and the velocity at which the filtration media is
moved in the particulate containing atmosphere.
Example 7-9
The particle loading performance and subsequent impact on the air delivery
of moving filters according to the present invention was examined in the
following examples.
An air inlet duct 15 cm in diameter by 46 cm long was vertically mounted
above the Add-on Filter apparatus described above, with air entering the
duct at the top and exiting at the bottom, into the center of the blower
wheel. The inlet duct was positioned inside the hood of a TSI model 8370
"Accubalance" flow measuring hood (available from TSI Inc., St. Paul,
Minn. 55164). The 60 cm by 60 cm bottom of the flow measuring hood was
blanked off with a sheet of cardboard, with the 15 cm duct projecting
through the cardboard blank. In this manner, any air entering the flow
measuring hood exited through the 15 cm duct and moving filter unit.
The test dust used for this study was PTI fine (ISO 12103-1, A2), available
from Powder Technology Incorporated, Burnsville Minn. 55337, which was
dispersed with an ASHRAE 52.1 dust feeder, as described in ASHRAE
publication #52.1-92, pages 6-8. (Dust feeders are available from Air
Filter Testing Laboratories, Inc., Crestwood, Ky.) The dust feed rate was
chosen to produce a dust concentration at the moving filter air inlet of
about 75 milligrams per cubic meter. Dispersed dust from the dust feeder
was conveyed by compressed air through a 2 cm ID "Tygon" tube to the
throat of the 15 cm duct. Filters were challenged with 15-20 grams of fine
test dust, which represents a significantly greater dust challenge than an
average automobile HVAC system will encounter over the course of one year
of normal operation.
The fan was operated at 13 volts to rotate the wheel at about 2400 rpm or
at 6.5 volts to rotate the wheel at about 1350 rpm (as indicated in the
following tables).
Cartridge filter units were assembled using "FITRETE" GSB70 media as
described above to produce a filter cartridge having an inside diameter of
15.2 cm, an outside diameter of 19.4 cm, and a height of 4.2 cm with 81
pleats at a 6 mm spacing. The outer diameter tips of the pleated filter
constructions used in Examples 7 and 8 were slit, while they were left
intact (not slit) in the filter used in Example 9.
Example 7
A slit tip pleated filter constructed as described above was weighed, the
blower wheel and the filter unit (with the clean filter) operated at 13
volts (8 amps) which produced an airflow rate of 4.09 cubic meters per
minute (146 cubic feet per minute).
PTI fine test dust was fed to the blower in increments of 2 grams, after
which the voltage and amp draw were recorded and the filter removed from
the blower wheel and weighed. After weighing, the filter was reinstalled
on the blower wheel, the filter unit returned to operation at the original
voltage, and the unit exposed to the next increment of test dust. In this
way the gravimetric particle collection was measured for comparison
against blower performance, the results of which are reported in TABLE 10.
TABLE 10
______________________________________
Particle Loading Airflow Correlations
Filter Particle Airflow
Cumulative
Weight Gain
Removal Rate
Dust Fed (gms)
(gms) Efficiency (%)
(m.sup.3 /min)
Volts
Amps
______________________________________
0 -- -- 4.09 13 8.0
2 0.77 38.5 3.92 13 8.0
4 0.71 35.5 3.86 13 7.8
6 0.70 35.0 3.86 13 7.7
8 0.75 37.5 3.92 13 7.8
10 0.65 32.5 3.89 13 7.6
12 0.75 37.5 3.92 13 7.6
14 0.63 31.5 3.92 13 7.6
16 0.55 27.5 3.89 13 7.6
18 0.67 33.5 3.89 13 7.6
20 /0.55 27.5 3.89 13 7.7
______________________________________
Examination of the data in TABLE 10 shows that the filter unit exhibited an
average particle removal efficiency of 33.7% (corresponding to 6.73 gms
dust collected) with a minimal reduction (4.9%) in airflow rate through
the unit.
Example 8
A filter loading/performance study was conducted as described in Example 7
except that the filter unit (with the clean filter) was operated at 6.5
volts (2.7 amps) which produced an airflow rate of 2.1 cubic meters per
minute (74 cubic feet per minute). The gravimetric loading/filter
performance data are reported in TABLE 11.
TABLE 11
______________________________________
Particle Loading Airflow Correlations
Filter Particle Airflow
Cumulative
Weight Gain
Removal Rate
Dust Fed (gms)
(gms) Efficiency (%)
(m.sup.3 /min)
Volts
Amps
______________________________________
0 -- -- 2.1 6.5 2.7
2 0.97 48.5 2.0 6.5 2.6
4 1.12 56.0 2.0 6.5 2.6
6 0.96 48.0 2.0 6.5 2.6
8 0.83 41.5 2.0 6.5 2.6
10 0.74 37.0 2.0 6.5 2.6
12 0.77 38.5 2.0 6.5 2.6
14 1.03 51.5 2.0 6.5 2.5
16 0.57 28.5 1.9 6.5 2.5
18 0.94 47.0 1.9 6.5 2.5
20 0.66 33.0 1.9 6.5 2.5
______________________________________
Examination of the data in TABLE 11 shows that the filter unit exhibited an
average particle removal efficiency of 42.95% (corresponding to 8.59 gms
dust collected) with a nominal reduction (9.5%) in airflow rate through
the unit.
Example 9
A filter loading/performance study was conducted as described in Example 7
except that the tips of the pleated filter were not slit. The filter unit
(with the clean filter) was operated at 13 volts (7.5 amps) and produced
an airflow rate of 3.98 cubic meters per minute (142 cubic feet per
minute). PTI fine test dust was fed to the blower in increments of 1 gram
until a total of 5 grams had been fed, after which the dust was fed in 2
gram increments. The gravimetric loading/filter performance data are
reported in TABLE 12.
TABLE 12
______________________________________
Particle Loading Airflow Correlations
Filter Particle Airflow
Cumulative
Weight Gain
Removal Rate
Dust Fed (gms)
(gms) Efficiency (%)
(m.sup.3 /min)
Volts
Amps
______________________________________
0 -- -- 3.98 13 7.5
1 0.81 8l.0 3.86 13 7.5
2 0.67 67.0 3.78 13 7.5
3 0.65 65.0 3.70 13 7.6
4 0.59 59.0 3.70 13 7.5
5 0.78 78.0 3.70 13 7.5
7 1.25 62.5 3.67 13 7.5
9 1.29 64.5 3.53 13 7.6
11 1.31 65.5 3.53 13 7.5
13 1.17 58.5 3.36 13 7.6
15 1.22 61.0 3.25 13 7.6
______________________________________
Examination of the data in TABLE 12 shows that while the filter cartridge
having intact tips (i.e. unslit) exhibited a particle capture efficiency
of 64.9% (corresponding to 9.74 gms dust collected), the higher efficiency
was realized at the expense of a significant reduction (18%) in airflow
rate through the unit.
The data in TABLES 10 and 11 also demonstrate that the gravimetric
efficiency of moving filters is higher at lower rotational speeds than at
higher rotational speeds, and that over the course of exposure to 20 gms
of test dirt, filters having slit pleats are non-plugging while offering
useful particle removal performance.
Example 10
The filtration performance of several filter media as a function of the
permeability of the media was studied using the Automotive HVAC
Configuration -second configuration (described above) in the Time to
Cleanup (Particulate Challenge) test (also described above). The blower
wheel of the automobile HVAC unit was fitted with a pleated filter
cartridge having an OD of 12.38 cm, an ID of 10.48 cm, and a height of 5.4
cm, prepared as described above, with 56 pleats at a pleat spacing of 6
mm, each pleat being 10 mm in height and made from the indicated filter
media (described above). All of the pleated cartridges used in this
example had intact pleat tips (i.e. the pleat tips were not slit). The
blower unit was placed in the test apparatus, a known particulate
challenge introduced into the box, and the unit operated at 2600 rpm (9
volts). Particle count data for these studies are reported in TABLE 13.
TABLE 13
______________________________________
Pleat Tips Intact
Particle count vs. Time
(Particle Count .times. 10.sup.5)
Time Melt Fiber
(min) Baseline GSB30 GSB50 GSB70 Blown Glass
Paper
______________________________________
0 3.08 3.11 3.11 3.10 3.08 3.11 3.09
0.5 3.05 2.78 2.55 2.22 2.73 2.92 3.00
1.0 3.02 2.18 1.62 1.03 2.22 2.64 2.91
1.5 2.98 1.55 0.868 0.389 1.64 2.30 2.83
2.0 2.95 1.03 0.436 0.150 1.13 1.94 2.73
2.5 2.91 0.665 0.214 0.064 0.758 1.60 2.63
3.0 2.89 0.421 0.114 0.035 0.483 1.29 2.53
3.5 2.85 0.275 0.067 0.026 0.314 1.02 2.44
4.0 2.82 0.187 0.043 0.023 0.204 0.802
2.34
4.5 2.78 0.130 0.034 0.022 0.136 0.623
2.23
5.0 2.75 0.097 0.029 0.021 0.093 0.490
2.13
5.5 2.71 0.078 0.027 0.021 0.067 0.388
2.02
6.0 2.68 0.062 0.026 0.021 0.053 0.303
1.92
6.5 2.65 0.055 0.027 0.021 0.044 0.245
1.82
7.0 2.62 0.049 0.026 0.022 0.040 0.200
1.72
7.5 2.58 0.047 0.026 0.022 0.036 0.163
1.63
8.0 2.55 0.044 0.025 0.023 0.034 0.142
1.53
8.5 2.51 0.042 0.026 0.022 0.032 0.121
1.46
9.0 2.48 0.040 0.027 0.023 0.031 0.106
1.36
9.5 2.45 0.043 0.026 0.022 0.031 0.094
1.27
10.0 2.40 0.042 0.026 0.022 0.030 0.086
1.21
______________________________________
Examination of the data in TABLE 13 shows that when operating at comparable
conditions in a "moving filter" configuration, more porous filtration
materials (i.e. GSB30, GSB50, GSB70, and meltblown) are more effective in
removing particles than less permeable materials (i.e. fiber glass, and
paper).
The Clean Air Delivery Rate (CADR) calculated on the data shown in TABLE 13
for the various filtration media are shown in TABLE 14 and graphically
presented in FIG. 9, where the CADR is compared to the permeability of the
filtration media.
TABLE 14
______________________________________
Pleat Tips Intact
CADR vs. Media Permeability
Filtration Frazier Permeability.sup.1
CADR.sup.2
Material m.sup.3 /h/m.sup.2
ft..sup.3 /h/ft.sup.2
m.sup.3 /h
ft..sup.3 /min
______________________________________
GSB30 10,122 553.5 39.2 23.1
GSB50 7,888 431.3 62.9 37.0
GSB70 5,969 326.4 83.1 48.9
Meltblown 2,011 110 41.5 24.4
Fiber Glass
554 30.3 22.9 13.5
Paper 6.4 0.35 4.2 2.5
______________________________________
.sup.1 Determined as described in the Frazier Permeability test procedure
above.
.sup.2 Calculated as described in the "Method for Measuring Performance o
Portable Household Electric CordConnected Room Air Cleaners," ANSI/AHAM
AC1-1988.
The inter-relationship of media permeability (Frazier Permeability) and
CADR in a pleated filter cartridge configuration operating in the
automotive HVAC unit is readily apparent from an examination of the data
in TABLE 14 or FIG. 9 and paralleled the inter-relationship demonstrated
with the mini-turbo fan configuration.
Example 11
Example 10 was repeated using a pleated filter cartridge having slit tips
to increase the permeability of the filter media. Particle count data for
these studies are reported in TABLE 15.
TABLE 15
______________________________________
Slit Pleat Tips
Particle count vs. Time
(Particle Count .times. 10.sup.5)
Time Melt Fiber
(min)
Baseline GSB30 GSB50 GSB70 blown Glass
Paper
______________________________________
0 3.08 3.11 3.08 3.08 3.09 3.07 3.07
0.5 3.05 2.83 2.62 2.52 2.83 2.87 2.98
1.0 3.02 2.35 1.89 1.57 2.34 2.26 2.87
1.5 2.98 1.83 1.20 0.817 1.79 2.26 2.76
2.0 2.95 1.36 0.733 0.398 1.28 1.90 2.64
2.5 2.91 0.960 0.444 0.194 0.866 1.55 2.50
3.0 2.89 0.676 0.282 0.111 0.571 1.25 2.36
3.5 2.85 0.472 0.191 0.070 0.371 0.976
2.23
4.0 2.82 0.340 0.135 0.049 0.244 0.769
2.10
4.5 2.78 0.252 0.096 0.040 0.160 0.594
1.96
5.0 2.75 0.189 0.075 0.037 0.107 0.467
1.81
5.5 2.71 0.153 0.061 0.033 0.073 0.367
1.69
6.0 2.68 0.126 0.055 0.034 0.052 0.300
1.56
6.5 2.65 0.104 0.047 0.039 0.039 0.248
1.43
7.0 2.62 0.091 0.047 0.037 0.031 0.208
1.32
7.5 2.58 0.077 0.041 0.033 0.026 0.181
1.21
8.0 2.55 0.075 0.039 0.030 0.023 0.160
1.10
8.5 2.51 0.067 0.036 0.030 0.021 0.136
1.01
9.0 2.48 0.058 0.036 0.027 0.021 0.120
0.921
9.5 2.45 0.058 0.036 0.026 0.023 0.110
0.841
10.0 2.40 0.058 0.034 0.030 0.021 0.099
0.764
______________________________________
Examination of the data in TABLE 15 shows that when operating at comparable
conditions in a "moving filter" configuration, more porous (i.e. slit
pleat tip filter configurations) are capable of reducing particulate
challenges to levels approximating those produced by filter cartridges
having intact pleat tips, but that the clean-up occurs at a slower rate.
The Clean Air Delivery Rate (CADR) calculated on the data shown in TABLE 15
for the various filtration media are shown in TABLE 16 and graphically
presented in FIG. 10, where the CADR is compared to the permeability of
the filtration media.
TABLE 16
______________________________________
Slit Pleat Tips
CADR vs. Media Permeability
Fazier Permeability.sup.1
CADR.sup.2
Filtration Material
m.sup.3 /h/m.sup.2
ft..sup.3 /h/ft.sup.2
m.sup.3 /h
ft..sup.3 /min
______________________________________
GSB30 10,122 553.5 30.6 18.0
GSB50 7,888 431.3 47.7 28.1
GSB70 5,969 326.4 67.8 39.9
Meltblown 2,011 110 40.9 24.1
Fiber Glass 554 30.3 23.4 13.8
Paper 6.4 0.35 7.1 4.2
______________________________________
.sup.1 Determined as described in the Frazier Permeability test procedure
above.
.sup.2 Calculated as described in the "Method for Measuring Performance o
Portable Household Electric CordConnected Room Air Cleaners," ANSI/AHAM
AC1-1988.
The inter-relationship of media permeability (Frazier Permeability) and
CADR in a pleated filter cartridge configuration operating in the
automotive HVAC unit is readily apparent from an examination of the data
in TABLE 16 or FIG. 5 and exhibited a pattern similar to the pleated
filter cartridge having intact pleat tips. Increasing the overall
permeability of the filter media by slitting the pleat tips reduces the
CADR for filter cartridges based on more permeable filtration media
(GSB30, GSB50, & GSB70) while it maintains or increases the CADR for
filter cartridges based on less permeable filtration media (meltblown,
fiber glass and paper).
Example 12
Filtration performance of GSB30, GSB50, GSB70, meltblown filtration media
was compared in moving/charged, moving/uncharged, and static/uncharged
configurations using the Time to Cleanup (Particulate Challenge) test and
the automotive HVAC test configuration. The blower wheel of the HVAC unit
was fitted with a clean pleated filter made of the indicated media, which
was prepared as described above, for each test run. The filter cartridges
had 50 pleats, a 6 mm pleat spacing, a pleat height of 10 mm, and 11.43 cm
OD.times.9.53 cm ID.times.5.08 cm height with a poster board rings added
to the top and bottom of the cartridge for added strength. Each filter
cartridge was also fitted with a 3.81 cm diameter paper cone inside the
filter loop to avoid air bypass in the blower wheel. Moving filters were
attached directly to the blower wheel by means of poster board tabs and
the static filters were mounted to a supporting ring made of poster board
attached to the back side of the housing unit of the blower assembly,
which provided a clearance of 0.635 cm between the filter and the blower
wheel sides and 0.95 cm clearance between the filter and the base of the
blower wheel. The static filters were also fitted with a paper cone to
avoid air by pass in the blower wheel. All filter configurations were
subject to the same particle challenge, the HVAC unit was operated at 9
volts (2800 rpm) and the particle count in the test apparatus was
monitored at 30 second intervals for a period of 10 minutes. Particle
count data for the GSB30 filters is reported in TABLE 17, particle count
data for the GSB50 filters is reported in TABLE 18, particle count data
for the GSB70 filters is reported in TABLE 19, and particle count data for
the meltblown filters is reported in TABLE 20.
TABLE 17
______________________________________
Filtration Performance of GSB30 Media
(% Cleanup)
GSB30 GSB30 GSB30
Time Charged/ Uncharged/
Uncharged/
(minutes) Moving Moving Static
______________________________________
0 0 0 0
0.5 12.8 7.15 5.4
1.0 35.1 19.95 14.6
1.5 56.6 34.3 24.9
2.0 73.6 48.6 35.8
2.5 84.6 61.2 46.4
3.0 91.1 71.5 55.8
3.5 94.7 79.4 64.8
4.0 96.9 85.1 72.0
4.5 98.0 89.4 77.9
5.0 98.7 92.3 82.5
5.5 99.0 94.3 86.2
6.0 99.2 95.9 89.0
6.5 99.4 96.9 91.1
7.0 99.5 97.5 92.7
7.5 99.5 98.0 93.8
8.0 99.6 98.4 94.6
8.5 99.5 98.6 95.5
9.0 99.5 98.8 96.1
9.5 99.6 98.9 96.7
10.0 99.6 99.1 97.0
CADR (m.sup.3 /h)
53.3 33.0 22.9
______________________________________
TABLE 18
______________________________________
Filtration Performance of GSB50 Media
(% Cleanup)
GSB50 GSB50 GSB50
Time Charged/ Uncharged/
Uncharged/
(minutes) Moving Moving Static
______________________________________
0 0 0 0
0.5 19.5 6.4 4.9
1.0 51.8 18.6 13.8
1.5 76.5 32.2 24.4
2.0 88.7 46.5 35.8
2.5 94.7 58.7 46.7
3.0 97.2 69.5 56.9
3.5 98.4 77.5 66.0
4.0 98.0 83.7 73.2
4.5 99.2 88.1 79.2
5.0 99.3 91.3 83.8
5.5 99.3 93.7 87.5
6.0 99.3 95.3 90.3
6.5 99.4 96.5 92.5
7.0 99.4 97.2 94.1
7.5 99.4 97.6 95.4
8.0 99.4 98.0 96.5
8.5 99.4 98.3 97.2
9.0 99.4 98.5 978.7
9.5 99.4 98.7 98.1
10.0 99.4 98.7 98.4
CADR (m.sup.3 /h)
70.8 31.5 26
______________________________________
TABLE 19
______________________________________
Filtration Performance of GSB70 Media
(% Cleanup)
GSB70 GSB70 GSB70
Time Charged/ Uncharged/
Uncharged/
(minutes) Moving Moving Static
______________________________________
0 0 0 0
0.5 23.2 5.3 3.9
1.0 60.2 12.0 8.7
1.5 83.8 19.8 14.4
2.0 93.7 28.2 20.0
2.5 97.4 36.9 25.9
3.0 98.9 45.1 32.2
3.5 99.4 52.6 38.2
4.0 99.6 60.2 44.7
4.5 99.7 66.5 50.2
5.0 99.8 71.4 55.4
5.5 99.7 76.0 60.4
6.0 99.8 80.1 65.0
6.5 99.8 83.2 68.9
7.0 99.8 86.2 72.8
7.5 99.8 88.5 76.0
8.0 99.8 90.5 79.1
8.5 99.8 91.9 81.4
9.0 99.8 93.1 84.0
9.5 99.7 94.2 86.1
10.0 99.7 95.0 87.6
CADR (m.sup.3 /h)
87.7 17.9 11.7
______________________________________
TABLE 20
______________________________________
Filtration Performace of Meltblown Media
(% Cleanup)
Meltblown Meltblown Meltblown
Time Charged/ Uncharged/
Uncharged/
(minutes) Moving Moving Static
______________________________________
0 0 0 0
0.5 16.6 6.5 6.2
1.0 42.4 15.4 14.2
1.5 65.5 26.3 24.0
2.0 81.1 37.4 34.2
2.5 90.2 48.5 44.6
3.0 94.5 58.9 53.8
3.5 97.0 67.7 62.8
4.0 98.1 75.2 70.0
4.5 98.8 81.1 76.0
5.0 99.2 85.5 81.1
5.5 99.3 89.0 85.2
6.0 99.5 91.6 88.2
6.5 99.5 93.6 90.6
7.0 99.5 95.0 92.3
7.5 99.5 96.0 93.8
8.0 99.6 96.9 94.9
8.5 99.6 97.5 95.8
9.0 99.6 98.0 96.4
9.5 99.6 98.4 96.9
10.0 99.5 98.6 97.3
CADR (m.sup.3 /h)
62.3 27.0 22.7
______________________________________
Examination of the data in TABLES 17-20 clearly demonstrates that all four
media studied can remove a particulate challenge more rapidly in a moving
configuration than in a static configuration and that this performance
advantage is realized whether the media is charged or uncharged. Optimum
particle removal performance for all four media was realized when the
media was charged.
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