Note: Descriptions are shown in the official language in which they were submitted.
1042368
AIR CLEANER ASSEMBLY
This invention relates to air cleaners of the flow-
through type, for use in cleaning gas streams for the removal
of suspended particles, especially dust, therefrom. More
particularly, it relates to air cleaners of the flow-through
type for use with air purifying and air conditioning apparatus.
Commercial flow-through air cleaners for use with
air conditioning and circulating apparatus as currently avail-
able have somewhat contradictory technical requirements to
fulfil. They must be coarse enough to allow air streams to
pass through without unduly increasing the power requirements
of the unit. At the same time, they must be fine enough or
otherwise able to provide efficient filtering of gas streams.
~ - One type of flow-through air cleaner available commer-
:,
cially consists of two thin layers of a close woven mesh of a
synthetic organic resin material, namely polypr~pylene, and
is known as PERMA~RON*. This material is inefficlent in its
air cleaning abilities, although it is readily cleanable and
is relatively air permeable. However, when subjected to fast
~ air flows, the mesh tends to bow outwardly to an excessive
extent. Other types of such cleaners have a fibrous media,
e.g. of glass fiber or of packed paper, treated with a mineral
oil. Whilst such oil treated cleaners are relatively effi-
cient during their initial period of use, they operate by
25~ having the suspended dust and dirt particles adhere to the oil
- with which the cleaner has been treated. After a certain
a unt of dust and dirt has been removed by adhesion to or
oil
absorption by the oil, the dust laden/becomes detached from
the filter medium, with the result that dust laden oil is
released into the air stream. Whilstin large scale,
*trade mark
104Z368
sophisticated air conditioning and circulating apparatus,
electrostatic precipitators are sometimes employed for air
cleaning purposes, they are generally too expensive for gen-
eral application.
The present invention provides a novel alr cleaner
of the flow-through type for use with air conditioning and
air circulating systems, which is of improved efficiency for
removing dust and dirt particles suspended in the air passing
therethrough.
Thus according to the present invention, there is
provided an air cleaner assembly of the flow-through type,
and comprising:
a central element comprising at least one sheet of
.
rubbery synthetic foam material;
first and second series of rods of thermoplastic
material capable of holding a positive electrostatic charge,
the first and second series of rods sandwiching the central
element~therebetween, and contacting the respective outer
surface of the centraI element.
20~ first and second air permeable outer sheet elements
of~interwoven fibers of synthetic organic resin aapable of
; holding a~negative electrostatic charge, said sheet elements
- being disposed outwardly of the respective first and second
series of rods.
ZS In the preferred embodiment, the central element
comprises two sheets of rubbery synthetic open cell foam
material disposed mutually parallel and adjacent to one
another, with the first and second series of rods contacting
outer surfaces of respective ones of the two sheets of foam
material. The series of rods are conveniently arranged
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mutally parallel to one another and extend from side to side
across the surfaces of the sheets of foam material. The
sheets of foam material may have their inner surfaces in con-
tact with one another, or may be closely spaced from one an-
other.
The central element preferably comprises sheets of
an open cell foam material which develops andholds a positive
electrostatic charge on flow of air therethrough. A particu-
larly suitable such material is open cell foam polyurethane.
10~ ~ ~Such a material is available commercially. It has the appear-
ance of a fibrous network, i8 very readily compressible, and
hao a low resistance to air flow.
The rods ~which term i8 to be understood to include
hollow tubular items and solid bar items) are preferably made
l5 ~ of~a~synthetic th~e~rmoplastic resin material which develops
and~holds a positive charge~on flow of air therethrough. A
suitable such material is~acrylic resin. For appearance sake
the~rods~are~preferably made of a clear, transparent resin.
In~oddition~to contribut~ing to~the air cleoning efficiency,
20~ ~they~nhance the s~tructurol rigidity of the assembly of the
nvention. ~
The air permeable~sheet:elements are preferably of
interwo~en fibers~of~polypropylène, in one or more layers.
`y`~ Such-fibers develop and hold a negative electrostatic charge
25;~ on flow~of oir therethrough. Commercially available sheets
of PE~MATRO~ ore especially~suitable.
e air cleaner a8~emb1y according to the invention
may conveniently be constructed as a unitary, self-supporting
structure, for ease of,handling and installation in an air
~ 30 conditioning or air circulating system. For this purpose,
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the ends of the series of thermoplastic rods may be received
in side frame elements. The edges of ~he outer fibrous sheet
elements may also be received in a frame work. These outer
fibrous sheet elements and thermoplastic rods and their side
frame elements are conveniently of the same shape and surface
area, so that the assembly can be received in and held togeth-
er by means of an outer frame work, so as to form a unitary
self-supporting structure.
Preferably, the side frame elements in which the
thermoplastic rods are received are of thermoplastic synthetic
resinous material which is different from the material from
which the rods are made. It is preferred to make the side
frame elements from a thermoplastic material which develops
no significant electrostatic cha~ge on co~tact with air flows.
A suitable s wh material is thermoplastic polycarbonate resin.
; It has been found that the provision of aforementioned
~; thermoplastic rods capable of holding a positive electrostatic
charge arranged with the foam and interwoven fiber sheet
elements as described, leads to remarkable and unexpected
~,
improvements in air cleaning efficiency of the unit. When
air was passed through an air cleaning structure comprising
two sheets of open cell polyurethane foam material arranged
mutually parallel to an adjacent to one another, overlaid on
:
each side by a sheet of interwoven fibers of polypropylene
(PERMATRON), at a velocity of 1200 ft. per minute, the air
cleaner assembly rem~ved 60-65% of the fine dust particles
suspended in the air. However, when the air cleaner assem-
bly was modified to include first and second series of mut-
ually parallel acrylic rods, disposed between the central
element and PERMATRON layers, and in contact with the outer
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surfaces of the central element, in accordance with the
present invention, about 98% of the suspended fine dust par-
ticles were removed, from a similar sample of air at the same
flow rate.
This dramatic improvement in air cleaning efficiency
is believea aue to electrostatic effects. Thus the preferred
air cleaner assembly according to the present invention has,
in the order in which they contact an air stream flowing there-
through, a polypropylene layer which develops a negative elec-
trostatic charge in use, acrylic rods which develop a positive
electrostatic charge in use, first and second foam polyurethane
layers which develop a positive electrostatic charge in use,
acrylic rods which develop a positive electrostatic charge
in use, and finally another polypropylene layer which develops
.
a negative electrostatic charge in use.
lS~; In addition to the improved air cleaning efficiency
of the assembly of the present invention, it is also found
that air which has passed through the assembly has an in-
creased concentration of negative ions. The negative ion
concentration in a closed area in which an assembly according
20;~ to the invention is used with the air circulating apparatus
leads~to an overall negative charge in the atmosphere of
the ~ closed area. A high concentration of negative ions in
. ~ :
the atmosphere is understood to be generally beneficial to
the health and welfare of persons exposed thereto.
- 25 The acrylic rods, which develop a positive electro-
static charge to contribute to the air cleaning efficien~y
and which are rigid to contribute structual rigidity to
the assembly, can be of any suitable cross-sectional shape,
such as circular, they may have diameters of from about 1/8
30 to 1/2 inch, dictated largely by the requirement for struc-
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tural rigidity. The spacing of adjacent acrylic rods of one
series does not appear to be critical, provided that they are
close enough to confer the necessary structural rigidity to
the assembly, and far enough apart not to increase unduly the
S power requirement for air flow through the assembly. Rods of
one series are suitably spaced from one another a distance
from about 1/2 to 1- V2 inches, preferably about 1 inch. m e
overall thickness of the air filter assembly according to the
present invention is suitably from about 3/4 to about 2 inches,
10 ; with a separation of the first series of rods from the second
series of rods being about 1/2 to 1 inch.
A specific embodiment of the invention is illustrated
in the accompanying drawings, in which:
FIGURE l is a perspective view, partly cut away, of
l5 ~ an air cleaner a-sembly according to the present invention;
FIGURE 2 is a cross sectional view along the line 2-2
` of Fig. l; ~
FIGUKE 3 is a cross sectional view along~the line
3-3 of~Fig. 1.
20~ In tne-~drawings, like reference numerals indicate
like~parts.
e air cleaner assembly according to the invention
has a centra} element 10 comprising a first sheeb 11 and a
second sheet 12 of open cell foam polyurethane material.
2~5 In appearance, the material is an open cell foam rubber of
; Yery coarse nature, in which the rubber is in "fibrous~ form,
of the nature of a three dimen8ional honeycomb. The sheets
lI, 12 are disposed mutually parallel to one another, with
inner surfaces in contact.
::
In contact with the respective outer surfaces 13, 14
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in generally parallel relationship to one another. The
spacing between adjacent rods of the first series 15 and of
the second series 16 is about 1 inch. At each end the
rods are received in respective side frame members 17, 18
of polycarbonate, which also enclose the vertical edges of
the sheets 11, 12. The series of rods 15 and 16 are in
respective vertral alignment. The side frame members 17,18
and the rods 15, 16 are secured together by suitable means
! as shown.
Outwardly of the series of rods 15, 16 are provided
respective outer sheets 19, 20 of interwoven fibers of poly-
propylene, namely PERMATRON. The polypropylene sheets 19, 20
have respective peripheral frameworks 21, 22. m e polypro-
pylene sheets 19, 20 and associated peripheral frameworks 21,
22 are of a size and rectangular shape substantially corres-
ponding to that defined by the series of rods 15, 16 and their
asssociated side frame members 17, 18 so that, on assembly,
the peripheral frameworks 21, 22 of the polypropylene sheets
19, 20 abut against the edges of the side frame members 17,
18, leaving a space between the rods 15, 16, and the respec-
tive~polypropylene sheets 19, 20. The assembly is completed
by an outer-most framework 23, of generally channel section,
;fitting around the outer edges of the peripheral frameworks
, ~
21, 22 of the polypropylene sheets.
As illustrated, the members of the first series of
; rods 15 are in staggered relation~hip to those of the second
series 16. This construction as illustrated has been found
to provide efficient alr purifying, of streams of air pass-
ing through from one polypropylene sheet to the other, the
- 30 suspended particles being primarily collected and deposited
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in the vicinity of the acrylic rods 15, 16. The air cleaner
assembly of the invention, however, does not offer excessive
resistance to air flow therethrough, so that the power re-
quriements for a unit with which it is used are not signi-
ficantly increased.
The assembly according to the invention can be used
for extended periods of time for efficient air cleaning. It
will not yield up collected dust particles to outgoing air
- streams unless it becomes effectively clogged with dust or
dirt. m e assembly is readily removed from its associated
power unit, and cleaned with water, on an infrequent periodic
basis, without disassembly, by merely hosing it with a water
; stream. The parts used are simple and cheap to obtain and
construct. Individual parts can be replaced and renewed if
necessary or desired, without damage to the basic structural
elements of the filter assembly. The device can be made in
standard sizes as required. It is useful with household and
industrial forced air heating furnaces, air conditioners and
air circulation apparatus in general.
20~ ; The~efficiency of an air cleaner assembly according
to the~invention~and as;illustrated was tested in comparison
with other commerically available air cleaners of the flow-
through type. To conduct the tests, an unpurified air stream
was passed through the air cleaner assembly at a standard
velocity, and the air sampled before and after passing through
; the air cleaner assembly, by mean~ of an air pollution moni-
toring apparatus containing an ultimate filter. Such a test
: :
apparatus is well ~nown, and is used to determine air pollu-
tion index. It essentially consists of a box containing a
fan, which blows air at the rate of 30 cu. ft. per second
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through the ultimate filter, for a standard period of time.
The ultimate filter is weighed before and after the test, and
the pollution index is computed from the difference in weight.
For the purposes of the present tests, the above
apparatus was used to sample air before and after passage
through air cleaner assemblies. The air before passage
through the air cleaner assembly was found to have an air
pollution index of about 35. A comparison of the weight
increase of the ultimate filters from the air pollution moni-
toring apparatus when used to test the air before and after
its passage through the air cleaner assembly of the invention
showed that 98~ of the particles suspended in the air had
been removed. The test was repeated with a flow-through air
cleaner currently on the market known as Airmat Oiled Media
(4-ply paper impregnated with oil). This device in similar
test conditions re ved 78% of the suspended particles.
Visual observance of the ultimate filters from the apparatus
used to test air after passage through the assembly of the
~ present invention and the Airmat device gave striking evidence;~ 20 of the improved efficiency of the assembly of the invention,
even when the incident air stream prior to flowing through
the devices had a pollution index as low as 7. The resis-
;~ tance to air flow of the assembly of the present invention
(a standard test involving measurements of pressure drop
. . .
across a flow barrier) was measured and found to be 0.06 wg,
highly acceptable figure; In a similar test, the Airmat
filter gave a resistance of 0.2 wg. In addition, there
is the disadvantage with oil impregnated media that, even-
tually, the oil will be released and discharged into the
air stream.
g
