Aerosol Collection Apparatus and Methods

Abstract

The lifetime of aerosol monitoring, concentration and collection equipment is extended by acoustic cleaning of accreted particle deposits from internal surfaces where fouling occurs by application of acoustic energy to the particle accretion surface, optionally in combination with a liquid wash or sampling volume. In one application, acoustic cleaning or sampling of particle deposits for analysis is triggered by a signal indicating changes in gas flow associated with particle loading. In another application, electro-acoustic transducers may be used to prevent particle buildup without interruption of particle monitoring.

1 . An aerosol monitoring, concentration, or collection apparatus, which comprises
 a) an internal channel for conveying aerosol particles in a gas stream flow therethrough, said internal channel having an inlet, an outlet, and a particle accretion surface therein;   b) a pressure source for driving the gas stream flow from said inlet to said outlet; and   c) an electro-acoustic transducer operatively coupled to said particle accretion surface, said electro-acoustic transducer having a power supply and control circuitry for applying pulses of acoustic energy to said particle accretion surface, said pulses having an on/off pulse duration, repetition rate, duty cycle, amplitude or frequency.   
     
     
         2 . The apparatus of  claim 1 , wherein said pulses are actuated intermittently during uninterrupted operation of said pressure source. 
     
     
         3 . The apparatus of  claim 1 , wherein said particle accretion surface is an inside surface of a particle collector. 
     
     
         4 . The apparatus of  claim 1 , wherein said particle accretion surface is an inside surface of an air-to-air particle concentrator. 
     
     
         5 . The apparatus of  claim 1 , wherein said electro-acoustic transducer is operatively coupled to said particle accretion surface through a solid body enclosing said internal channel, and said electro-acoustic transducer is a piezoelectric, magnetostrictive, or capacitive electro-acoustic transducer, and optionally wherein said solid body includes an acoustic waveguide for directing said acoustic energy to said inside surface. 
     
     
         6 . The apparatus of  claim 1 , wherein
 a) said on/off pulse duration, repetition rate, duty cycle, amplitude or frequency is adjusted in response to a change in said gas stream flow, wherein said change in flow is associated with fouling of said particle accretion surface, and wherein said change in flow is measured by a sensor operatively connected to said control circuitry, or   b) said on/off pulse duration, repetition rate, duty cycle, amplitude or frequency is adjusted in response to accretion of particles on said particle accretion surface, wherein said accretion of particles is measured by a sensor operatively connected to said control circuitry.   
     
     
         7 . The apparatus of  claim 6 , wherein said sensor is selected from a backpressure sensor, a gas flow sensor, an optical sensor, or an electrometric sensor. 
     
     
         8 . The aerosol collection or monitoring apparatus of  claim 1 , further comprising:
 a) a sensor operatively disposed to monitor said internal channel for accretion of particles on said particle accretion surface, and for emitting a signal indicative thereof;   b) a pneumatic control system controlled by said control circuitry for interrupting said gas stream flow through said internal channel in response to said signal; and   c) a liquid hydraulic system controlled by said control circuitry, wherein said liquid hydraulic system is configured for injecting a discrete liquid volume onto said particle accretion surface and insonating said wetted particle accretion surface in response to said signal.   
     
     
         9 . The apparatus of  claim 8 , further comprising means for removing or sampling particle deposits suspended or dissolved by said acoustic pulses in said insonated liquid volume. 
     
     
         10 . The apparatus of  claim 1 , wherein said liquid hydraulic system comprises a liquid reservoir, a pump functionality, and an injection duct fluidly connecting said liquid reservoir to said particle accretion surface. 
     
     
         11 . The apparatus of  claim 8 , wherein said liquid is aqueous, and optionally further comprises a surface-active agent, an oxidizer, a chaotrope, a microbubble suspension or a microbubble precursor agent. 
     
     
         12 . The apparatus of  claim 8 , wherein said liquid comprises a non-aqueous solvent or a co-solvent, and optionally further comprises a surface active agent or a chaotrope. 
     
     
         13 . The apparatus of  claim 12 , wherein said solvent or co-solvent is dimethylsulfoxide, N,N-dimethylformamide, N-methyl-pyrrolidinone, 2-pyrrolidone, acetone, diethylene glycol monoethyl ether, acetonitrile, acetone, methylethylketone, methyl tert-butyl ether (MBTE), tetrahydrofuran, propylene carbonate, ethyl acetate, chloroform, butyrolactone, or methanol, said optional chaotrope is urea, thiourea, sodium perchlorate, guanidine HCl, or guanidinium isothiocyanate. 
     
     
         14 . The apparatus of  claim 8 , wherein said liquid hydraulic system further comprises a hydraulic sampling subsystem for sampling said particle deposits suspended or dissolved by said acoustic pulses in said discrete liquid volume, wherein said hydraulic sampling subsystem is configured with pump functionality and ducting for withdrawing a liquid sample of said discrete liquid volume, and for fluidly conveying said liquid sample for downstream collection or analysis. 
     
     
         15 . The apparatus of  claim 14 , wherein said signal is further indicative of a targeted constituent in said accreted particles, and triggers actuation of said hydraulic sampling subsystem. 
     
     
         16 . The apparatus of  claim 8 , wherein said control circuitry is configured for operating in a dry cleaning mode, a wet cleaning mode, and a wet sampling mode, wherein said dry cleaning mode involves actuation of said electro-acoustic transducer without liquid injection, said wet cleaning mode involves actuation of said electro-acoustic transducer with liquid injection, and said wet sampling mode involves actuation of said electro-acoustic transducer with liquid injection and liquid sample withdrawal. 
     
     
         17 . The apparatus of  claim 16 , wherein said dry cleaning mode is actuated at regular intervals prophylactically; said wet cleaning mode is actuated in response to a signal detecting persistent accreted particles; and said wet sampling mode is performed in response to a signal indicative of a targeted constituent in said accreted particles. 
     
     
         18 . A method for cleaning a particle accretion surface in an internal channel of an aerosol monitoring, concentration, or collection apparatus, which comprises:
 a) in dry cleaning mode, at regular intervals insonating said particle accretion surface without liquid injection while flowing a gas stream through said internal channel and continuously over said particle accretion surface;   b) in wet cleaning mode, in response to a change in a first signal, insonating said particle accretion surface after stopping said gas flow and injecting a liquid;   c) in wet sampling mode, in response to a second signal, insonating said particle accretion surface after stopping said gas flow and injecting a liquid thereon, then withdrawing a liquid sample of said insonated liquid volume; and   d) monitoring said first and second signals and repeating steps b and c in response to changes in said first and second signals.   
     
     
         19 . The method of  claim 18 , further comprising a step for sonically interrogating said flowing gas stream to sense a change in a flow rate, a flow velocity, or a backpressure, and outputting a sonometric signal indicative thereof. 
     
     
         20 . The method of  claim 19 , comprising modulating said sonometric signal by insonating said particle accretion surface according to a feedback control loop.