Real-time control of exhaust flow

Abstract

A flow control system for controlling exhaust flow can measure effluent escaping from the exhaust hood at a given flow rate. An interferometric detector can measure fluctuations in fluid properties external to and/or in the vicinity of the exhaust hood. The flow control system may vary a flow rate of the exhaust hood and/or control exhaust hood structures responsive to the measurements to contain the effluent while minimizing the exhaust of air from the occupied space.

1 . A method of controlling exhaust flow of an exhaust hood, the exhaust hood having a recess therein, the method comprising:
 interfering a sample light beam with a reference light beam, the sample light beam passing through a first region of gaseous fluid, said first region being external to recess of the exhaust hood and in the vicinity of an edge of the exhaust hood; and   controlling a rate of the exhaust flow of the exhaust hood responsively to a result of the interfering.   
     
     
         2 . The method of  claim 1 , wherein said controlling includes increasing a rate of the exhaust flow when the interfering indicates that exhaust gases from the recess are present in said first region. 
     
     
         3 . The method of  claim 1 , wherein the sample continuously changes over time and the controlling includes continuously controlling the exhaust flow rate in response to changes in the result of the interfering. 
     
     
         4 . The method of  claim 1 , wherein the interfering includes transmitting light across an open gap, which permits said sample of gaseous fluid to move through the gap by convection, so as to generate said sample light beam. 
     
     
         5 . The method of  claim 4 , wherein said open gap is located at an edge of the exhaust hood external to said recess. 
     
     
         6 . The method of  claim 4 , wherein the controlling includes filtering the result of the interfering so as to eliminate fluctuations below a predetermined frequency. 
     
     
         7 . A method for controlling exhaust flow of an exhaust hood, the exhaust hood having a recess therein, the method comprising:
 positioning a sample path of an interferometer adjacent to an edge of the exhaust hood and outside the exhaust hood recess such that effluent escaping from the exhaust hood recess passes through at least a portion of the sample path of the interferometer;   positioning a reference path of an interferometer protected from effluent;   interfering a sample light beam, which passes through said sample path, with a reference light beam, which passes through said reference path; and   controlling a flow rate of the exhaust flow of the exhaust hood responsively to a result of the interfering.   
     
     
         8 . The method of  claim 7 , wherein said controlling includes increasing the flow rate when the interfering indicates that effluent from the recess is present in said sample path. 
     
     
         9 . The method of  claim 7 , wherein the controlling includes continuously controlling the exhaust flow rate in response to changes in the result of the interfering. 
     
     
         10 . The method of  claim 7 , wherein the interfering includes transmitting light along said sample path so as to generate said sample light beam, the sample path including an open gap that permits said effluent escaping from the exhaust hood recess to move through the gap by convection. 
     
     
         11 . The method of  claim 10 , wherein the controlling includes filtering the result of the interfering so as to eliminate fluctuations below a predetermined frequency. 
     
     
         12 . A method for controlling exhaust flow of an exhaust hood, the exhaust hood having a recess therein, the method comprising:
 combining a sample light beam, which has been transmitted along a sample path, with a reference light beam so as to generate an interference light beam;   detecting the interference light beam; and   controlling a rate of the exhaust flow of the exhaust hood in response to the detecting,   wherein the sample path is located external to the exhaust hood recess such that effluent escaping from the exhaust hood recess passes through at least a portion of the sample path, and   the detected interference light beam is indicative of a presence of the effluent escaping from the exhaust hood recess in the at least a portion of the sample path.   
     
     
         13 . The method of  claim 12 , wherein the sample path is proximal to a perimeter edge of the exhaust hood. 
     
     
         14 . The method of  claim 12 , wherein the controlling includes increasing the exhaust flow rate until the detected interference beam indicates that no effluent is in said at least a portion of the sample path. 
     
     
         15 . The method of  claim 12 , wherein the combining a sample light beam includes transmitting a light beam along said sample path so as to generate said sample light beam, the sample path including an open gap external to the exhaust hood recess that permits said effluent escaping from the exhaust hood recess to move through the gap by convection. 
     
     
         16 . The method of  claim 12 , wherein the detecting includes generating an effluent signal based on the detected interference light beam. 
     
     
         17 . The method of  claim 16 , wherein the detecting includes passing the effluent signal through a filter so as to eliminate fluctuations below a predetermined frequency. 
     
     
         18 . The method of  claim 16 , wherein the detecting includes passing the effluent signal through an integrator so as to minimize transient effects. 
     
     
         19 . The method of  claim 16 , wherein the detecting includes passing the effluent signal through a slicer so as to remove components below a threshold level.