Pressure-based airflow sensing in particle impactor systems

Patent metadata

Field	Value
Publication number	US-9810558-B2
Application number	US-201514656170-A
Country	US
Kind code	B2
Filing date	Mar 12, 2015
Priority date	Mar 14, 2014
Publication date	Nov 7, 2017
Grant date	Nov 7, 2017

Abstract

Provided are systems and methods for accurate sensing of particle concentrations in fluids by employing a particle impactor system that allows for collection, growth and analysis of biological particles. The disclosed systems and methods make use of a pressure based flow sensor which permits the particle impactor system systems to accurately and reliably provide measurements of biological particle concentrations in the ambient environment. By incorporation of pressure sensors and pressure measurements into the flow measurement techniques, embodiments provide for the ability to use a particle impactor system to accurately measure environmental biological particle concentrations at a variety of atmospheric pressure conditions, such as at high altitude or with minimal perturbation from atmospheric weather conditions, without requiring recalibration or other adjustment of the sensors and control systems.

First claim

We claim:

1. A method of controlling a volumetric flow rate of a fluid flow through a particle impactor system, the method comprising the steps of:
pulling said fluid through a plurality of intake apertures of a sampling head of said particle impactor system, wherein said fluid contains a plurality of particles;
pulling said fluid past an impact surface positioned in fluid communication with each of said plurality of intake apertures, causing a change in direction of said fluid, whereby at least a portion of the particles are directed onto said impact surface for collection;
determining a flow rate of said fluid;
determining ambient pressure;
determining said volumetric flow rate as a function of said flow rate of said fluid and said ambient pressure; and
controlling the fluid flow in said particle impactor system using said volumetric flow rate.

2. The method of claim 1 , wherein said ambient pressure is atmospheric pressure.

3. The method of claim 1 , wherein said particle impactor system comprises:
said sampling head having said plurality of intake apertures; and
an impactor base supporting said impact surface, wherein said impactor base comprises a fluid outlet;
wherein said sampling head and said impactor base together form a fluid tight seal such that said fluid can only flow into or out of said particle impactor system through said plurality of intake apertures and said fluid outlet.

4. The method of claim 3 , wherein said impactor base is in fluid communication with one or more pressure sensors positioned to measure one or more of a pressure of said fluid within said particle impactor system, a differential pressure of said fluid within said particle impactor system and said ambient pressure.

5. The method of claim 3 , wherein said particle impactor system further comprises a restriction along a flow path of said fluid flow within said particle impactor system.

6. The method of claim 5 , wherein said particle impactor system further comprises a first pressure sensor comprising a differential pressure sensor positioned to measure a differential pressure across said restriction.

7. The method of claim 6 , wherein said differential pressure sensor measures a ratio or a difference of a first pressure upstream of said restriction and a second pressure downstream of said restriction.

8. The method of claim 6 , wherein said differential pressure sensor comprises a differential pressure sensor that directly measures the ratio or difference between a pressure upstream of said restriction and a pressure downstream of said restriction.

9. The method of claim 6 , wherein said differential pressure sensor comprises a first absolute pressure sensor positioned to measure a pressure upstream of said restriction and a second absolute pressure sensor positioned to measure a pressure downstream of said restriction.

10. The method of claim 6 , wherein said particle impactor system further comprises a second pressure sensor for measuring said ambient pressure inside or outside said system.

11. The method of claim 10 , wherein said particle impactor system further comprises a third pressure sensor, wherein said second pressure sensor measures an ambient pressure outside of said system and said third pressure sensor measures a pressure inside said system.

12. The method of claim 3 , wherein said particle impactor system further comprises a mass flow sensor for determining said flow rate of said fluid, wherein said mass flow sensor is positioned in fluid communication with said plurality of intake apertures, said fluid outlet or both said plurality of intake apertures and said fluid outlet.

13. The method of claim 1 , wherein said step of determining said ambient pressure comprises determining an absolute pressure outside said particle impactor system, determining an absolute pressure within said particle impactor system, or determining both an absolute pressure outside said particle impactor system an absolute pressure within said particle impactor system.

14. The method of claim 1 , wherein the method uses only two pressure sensors.

15. The method of claim 1 , wherein said step of determining said volumetric flow rate comprises determining said volumetric flow rate as Q in the following relationship (FX1):
Q=k ·[(2· P DPS )/ P APSE ] 1/2   (FX1);

(FX1) where k is an empirically determined constant, PDPS is a differential pressure within the system and PAPSE is said ambient pressure.

16. The method of claim 15 , wherein said differential pressure (PDPS) is across a restriction within said particle impactor system.

17. The method of claim 1 , wherein said step of determining said volumetric flow rate comprises determining said volumetric flow rate as Q in the following relationship (FX2):
Q=k ·[( P APSO ·P DPS )] 1/2 /P APSE   (FX2);

where k is an empirically determined constant, PAPSO is an absolute pressure within said particle impactor, PDPS is a differential pressure within the system and PAPSE is said ambient pressure.

18. The method of claim 1 , wherein said step of determining said volumetric flow rate comprises utilizing the following relationship (FX3) in evaluation of Q:
Q=k ·[(2Δ P )/ρ] 1/2   (FX3);

where k is an empirically determined constant; where ΔP is a differential pressure across a restriction in said particle impactor system and p is a density of said fluid.

19. The method of claim 1 , wherein said step of determining said flow rate of said fluid comprises determining a mass flow rate of said fluid.

20. The method of claim 1 , further comprising a step of:
increasing an absolute pressure within the particle impactor system if the volumetric flow rate is determined to be larger than a specified value; or
reducing an absolute pressure within the particle impactor system if the volumetric flow rate is determined to be smaller than a specified value.

21. The method of claim 1 , wherein said fluid flow is generated by one or more flow generating devices selected from the group consisting of a fan, a blower, a pump and any combination of these.

22. The method of claim 21 , further comprising a step of:
reducing a speed of one or more of said flow generating devices if said volumetric flow rate is determined to be larger than a first specified value; or
increasing a speed of one or more of said flow generating devices if said volumetric flow rate is determined to be smaller than a second specified value.

23. The method of claim 1 , wherein said fluid comprises air or one or more process gases.

24. The method of claim 1 , wherein the impact surface comprises a receiving surface of a growth medium.

25. A method of measuring a volumetric flow rate of a fluid flow through a particle impactor system, the method comprising the steps of:
pulling said fluid through a plurality of intake apertures of a sampling head of said particle impactor system, wherein said fluid contains a plurality of particles;
pulling said fluid past an impact surface positioned in fluid communication with each of said plurality of intake apertures, causing a change in direction of said fluid, whereby at least a portion of the particles are directed onto said impact surface for collection;
determining a flow rate of said fluid;
determining ambient pressure; and
determining said volumetric flow rate as a function of said flow rate of said fluid and said ambient pressure.

26.

Assignees

• Particle Measuring Syst
• Particle Measuring Syst

Inventors

• Bates Thomas
• Ketcham Cliff
• Hartigan Paul B
• Adkins Ronald W

Classifications

• G01F1/42

  Orifices or nozzles · CPC title

• G01F1/74

  Devices for measuring flow of a fluid or flow of a fluent solid material in suspension in another fluid · CPC title

• G01F1/36

  the pressure or differential pressure being created by the use of flow constriction · CPC title

• G01F1/76

  Devices for measuring mass flow of a fluid or a fluent solid material · CPC title

• G01F1/34 Primary

  by measuring pressure or differential pressure · CPC title