Gas separation: processes – Electric or electrostatic field – Including baffling – deflection – or restriction of gas flow
Reexamination Certificate
2003-01-16
2004-09-14
Chiesa, Richard L. (Department: 1724)
Gas separation: processes
Electric or electrostatic field
Including baffling, deflection, or restriction of gas flow
C095S079000, C096S066000, C096S077000, C096S097000
Reexamination Certificate
active
06790259
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to methods and devices for cleaning a gaseous fluid of particles present in said fluid, particularly where the fluid is ionized and then filtered.
2. Prior Art
Swedish patent no. A-9604817-8 discloses a device using an active electret filter. An electric field is directed towards the precipitator unit that consists of medium being electrically non-conductive and whose molecules are easily polarized or oriented by an electric field directed towards the precipitator unit. An electric field is created inside the fiber material comprising the precipitator unit. The particles that pass into the filter medium, being first charged by the ionization unit, are attracted by the filter fibers regardless of the charge polarity of any particular fiber and particle, as each fiber and each particle has spaced-apart positive and negative charges thereon.
U.S. Pat. No. 6,364,935, issued Apr. 2, 2002, to the present inventor, discloses and claims an advanced HEPA filter using polypropylene filter media to attract and capture ionized particles from a gaseous stream, as of household or office air. The arrangement normally provides superior filtering performance, but where the incoming fluid stream is very clean it sometimes happens, as the present inventor has discovered, that ions not bound to particles will impinge on the filter media and themselves charge the media fibers, reducing filter performance by the ions' repelling, rather than attracting, charged particles in the fluid stream.
Coppom U.S. Pat. No. 5,593,476 shows in
FIG. 1
a pre-charging grid
32
and an insulated-wire electrode grid
34
upstream of a polypropylene or other filter
36
, and a grounded carbon electrode grid
42
downstream of the filter
36
. Power source
48
is attached between the grids
32
and
42
.
FIG. 2
shows a system in which both upstream grids are charged negatively and the downstream grid is charged positively, thus polarizing the filter media, subject to migration of charges back to the grids. Examples of filter efficiency are shown both with and without ionization.
Gibbs U.S. Pat. No. 5,807,425 shows a charged grid
3
located between two filter mats
1
and
2
, which may be of polypropylene. Non-conductive screens
8
and
9
outside the filter mats simply hold the mats in place. Charging of the grid
3
polarizes the filter media, for attracting and holding particles in the media due to their natural polarities—no ionization is imparted to them upstream of the filter media.
Dudley U.S. Pat. No. 5,906,677 shows a passive, electrostatic “supercharging” screen
10
located downstream of a filter
14
. The screen comprises a thin, fine mesh layer
32
of polypropylene that is supported by metal mesh material
36
on either side. The screen
10
is said to remove fine particles not removed by the conventional filter
14
. No ionization is provided.
SUMMARY OF THE INVENTION
A flat, open grid or mesh of conductive material is positioned on the upstream side of a pleated polypropylene filter medium, as a first element in a replaceable filter box or cartridge used in an ionizing air cleaner. The grid is not insulated from contact with passing air or the filter medium. The grid is grounded to the charging system in a drain form of the invention, or alternatively it is not so grounded, in a shield form. The effect of either form is to avoid polarization of the filter medium by ions in the air stream that are not attached to particles to be removed from the air stream. A 20-30% increase in filter efficiency is seen when the grid is added onto a filter box or cartridge in this arrangement.
REFERENCES:
patent: 3999964 (1976-12-01), Carr
patent: 5330559 (1994-07-01), Cheney et al.
patent: 5403383 (1995-04-01), Jaisinghani
patent: 5407469 (1995-04-01), Sun
patent: 5474600 (1995-12-01), Volodina et al.
patent: 5484472 (1996-01-01), Weinberg
patent: 5518531 (1996-05-01), Joannu
patent: 5573577 (1996-11-01), Joannou
patent: 5593476 (1997-01-01), Coppom
patent: 5807425 (1998-09-01), Gibbs
patent: 5906677 (1999-05-01), Dudley
patent: 6251171 (2001-06-01), Marra et al.
patent: 6364935 (2002-04-01), Wennerstrom
patent: 54-11571 (1979-01-01), None
Rittri Bengt
Wennerstrom Johan
Blueair AB
Chapman and Cutler LLP
Chiesa Richard L.
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