US 5,317,930 A · Constant flowrate controller for an aerosol sampler using a filter

Abstract

A constant flow rate controller apparatus for an aerosol sampler using a filter includes an enclosed channel for channeling a stream of air, a filter positioned in the channel to capture and retain particles while allowing the stream of air to flow therethrough, an air or vacuum pump to pull the air through the filter, and a flow controller that maintains a constant volumetric flow rate of air through the sampler and filter, regardless of how much particulate matter is deposited on the filter or how much pressure drop across the filter changes due to particulate loading. The filter can be a substantially non-fibrous, porous, this film membrane medium, for which the flow controller of this invention is particularly beneficial, or it can be a more conventional fibrous medium. The flow controller can include a critical or choked flow orifice with a variable effective flow area, which effective flow area can be varied in response to changes in pressure drop across the filter to maintain constant volumetric flow rate. An expandable and contractible bellows with an appropriate spring constant can be used to both sense changes in air pressure drop across the filter or changes in stagnation pressure downstream of the filter and to actuate a variation in the effective flow area of the orifice in response to such changes in air pressure to maintain constant volumetric flow rate of the air. The air or vacuum pump has to have enough capacity to maintain critical or choked flow conditions in the orifice.

Claims46

Dependent claims

Aerosol sampler apparatus for collecting liquid or solid matter that is borne in air, comprising:

air channeling means for channeling a said stream of flowing air through said sampler apparatus;
filter means positioned in said air channeling means for intercepting and retaining said matter that is borne in said stream of air while allowing said stream of air to pass therethrough;
flow controller means positioned in said air channeling means downstream of said filter means for maintaining said stream of air flowing at a constant volumetric flow rate, said flow controller means including a critical flow orifice having a variable flow area positioned in said air channeling means, and flow area adjusting means for adjusting the flow area through said critical flow orifice in response to changes in resistance to the flow of air through said filter means to keep the volumetric flow rate of the air flowing through said air channeling means constant;
and
air pump means in said air channeling means for causing said stream of air to flow through said critical flow orifice at sonic velocity to maintain sonic shock wave choked flow condition in said critical flow orifice.

2 more elements

A method of maintaining constant volumetric flow rate of air through an aerosol sampler that has an air channel for conducting a stream of air collected from ambient air at ambient pressure P.sub.0 through a filter to capture aerosol particulate matter from the stream of air, comprising the steps of:

positioning a partition with an orifice having a variable cross-sectional or flow area therethrough across said air channel downstream from said filter;
pulling air through said air channel at a sufficient capacity to cause a pressure drop through said orifice such that a back pressure P.sub.B is created downstream of said orifice and maintaining said back pressure P.sub.B low enough such that the ratio of the back pressure P.sub.B to the stagnation pressure P.sub.1 downstream of said filter and upstream of said orifice does not exceed 0.53, (P.sub.B /P.sub.1 .ltoreq.0.53), to create and maintain critical or choked flow condition in said orifice;
and
increasing the effective cross-sectional or flow area of said orifice in response to increases in the amount of pressure drop across the filter medium.

1 more element

Aerosol sampler apparatus, comprising:

air channeling means for channeling a stream of flowing air through said sampler apparatus;
filter means positioned in said air channeling means for intercepting and retaining particle that are borne in said stream of flowing air while allowing said stream of flowing air to pass therethrough;
flow controller means positioned in said air channeling means downstream of said filter means for maintaining said stream of air flowing at a constant volumetric flow rate, said flow controller means including a partition positioned across said air channeling means with an orifice in the configuration of an elongated slot having substantially parallel lateral sides extending through said partition, a slide positioned adjacent and partially occluding said orifice, said slide being moveable along an axis parallel to said parallel lateral sides of said orifice;
and
air pump means in said air channeling means for causing said stream of air to flow through said orifice at sonic velocity.

2 more elements

Aerosol sampler apparatus, comprising:

air channeling means for channeling a stream of flowing air through said sampler apparatus;
filter means positioned in said air channeling means for capturing and retaining particles from the air stream flowing therethrough;
flow controller means positioned in said air channeling means for maintaining said stream of air flowing at a constant volumetric flow rate through said filter means, said flow controller means including a partition positioned across said air channeling means with an orifice extending through said partition, a gate slidably positioned adjacent and partially occluding said orifice, a bellows that has an axially expandable and contractible wall connected to said gate and enclosing an interior bellows chamber, said wall being expandable and contractible in response to changes in pressure in said interior bellows chamber, and said interior bellows chamber being connected in common pressure relation to said air channeling means between said filter means and said orifice such that decreases in pressure between said filter means and said orifice cause movement of said gate to occlude less of said orifice and increases in pressure between said filter means and said orifice cause movement of said gate to occlude more of said orifice;
and
air pump means in said air channeling means for causing said stream of air to flow through said orifice at sonic velocity.

2 more elements

Aerosol sampler apparatus, comprising:

air channeling means for channeling a stream of flowing air through said sampler apparatus;
filter means positioned in said air channeling means for capturing particles from the air stream flowing through the air channeling means and filter means;
a partition positioned in said air channeling means downstream from said filter means with an orifice extending through said partition;
closure means adjacent said orifice for adjustably occluding portions of said orifice to vary the effective cross-sectional area of said orifice;
actuator means connected to said closure means and responsive to pressure between said filter means and said orifice for moving said closure means to decrease occlusion of said orifice when pressure between said filter means and said orifice decreases;
and
air pump means in said air channeling means for causing said stream of air to flow through said orifice at sonic velocity.

4 more elements

Dependencies are inferred from the claim text.

Constant flowrate controller for an aerosol sampler using a filter

Life of this patent

Constant flowrate controller for an aerosol sampler using a filter

Life of this patent

Abstract

Claims46