Screw compressor acoustic resonance reduction

Abstract

A screw compressor for acoustic resonance reduction and refrigeration systems including the screw compressor are disclosed. The screw compressor has an acoustic barrier integral with the compressor housing for use with a slide valve assembly that includes a piston connected to a slide valve. A shaft connecting the slide valve and the piston passes through an aperture in the barrier with the piston and the slide valve disposed on opposite sides of the barrier. The acoustic barrier protects the piston from discharge pulses of compressed fluid exiting the rotors of the screw compressor, thus attenuating acoustic resonance, reducing compressor noise and premature wear of the slide valve assembly and compressor housing.

1 . A screw compressor comprising: 
 a compressor housing having a passage for the flow of a fluid therethrough from a suction side of the compressor to a discharge side of the compressor, the housing including an integral acoustic barrier;    a pair of intermeshed rotors disposed in the passage, the rotors configured to increase the pressure of the fluid flowing from a suction port on the suction side of the compressor through the passage to a discharge port on the discharge side of the compressor; and    a slide valve assembly movably disposed within the compressor housing to adjust the capacity of the compressor, the slide valve assembly comprising a slide valve connected to a piston by a shaft, wherein the piston and the slide valve are disposed on opposite sides of the acoustic barrier and wherein the acoustic barrier includes an aperture sized to receive the shaft, the acoustic barrier attenuating acoustic resonance and noise in the compressor and wherein the acoustic barrier is positioned a preselected distance from the discharge port.    
   
   
       2 . The screw compressor of  claim 1 , wherein the piston is disposed in a piston cylinder, at least a portion of piston cylinder defined by the compressor housing, the piston cylinder sized to receive the piston and in fluid communication with the suction side and the discharge side of the housing by a conduit assembly.  
   
   
       3 . The screw compressor of  claim 2 , wherein the compressor housing comprises cast iron.  
   
   
       4 . The screw compressor of  claim 2 , wherein the slide valve assembly includes a single piston.  
   
   
       5 . The screw compressor of  claim 2 , wherein the slide valve assembly further includes a biasing means to urge the piston in a first direction and wherein a refrigerant gas introduced into the piston cylinder from the discharge side by the conduit assembly urges the piston in a direction opposed to the first direction.  
   
   
       6 . The screw compressor of  claim 2 , wherein the compressor housing further includes a piston housing portion, wherein the piston housing portion includes at least a portion of the piston cylinder and at least a portion of the conduit assembly.  
   
   
       7 . The screw compressor of  claim 2 , wherein the piston cylinder is sized to receive the piston such that substantially no refrigerant gas leaks across an interface between the compressor housing and the piston.  
   
   
       8 . The screw compressor of  claim 2 , wherein the acoustic barrier comprises a portion of an end wall of the piston cylinder.  
   
   
       9 . The screw compressor of  claim 1 , wherein the slide valve assembly further comprises a spring disposed between the piston and the acoustic barrier, the spring having a bias urging the piston away from the acoustic barrier.  
   
   
       10 . The screw compressor of  claim 1 , wherein the compressor housing comprises an intake housing, a rotor housing, a discharge housing, and a piston housing.  
   
   
       11 . A method for reducing acoustic resonance in a screw compressor comprising the steps of: 
 passing a refrigerant gas through a passage of a compressor housing of a screw compressor from a suction side of the compressor to a discharge side of the compressor through a discharge port, a portion of the passage defined by a pair of intermeshed rotors disposed in the compressor housing passage;    providing an acoustic barrier integral with the compressor housing, the acoustic barrier positioned a preselected distance from the discharge port;    providing a slide valve assembly in the compressor housing, the slide valve assembly comprising a slide valve connected by a shaft to a piston, wherein the shaft passes through an aperture defined by a barrier integral with the compressor housing, the slide valve and the piston on opposite sides of the barrier; and    modifying the flow of the refrigerant gas through the passage by moving the slide valve from a first position with respect to the intermeshed rotors to a second position with respect to the intermeshed rotors.    
   
   
       12 . The method of  claim 11 , wherein the step of passing a refrigerant gas includes passing 134a refrigerant gas.  
   
   
       13 . The method of  claim 11 , wherein the compressor housing for passing a refrigerant gas through the compressor housing comprises a cast material.  
   
   
       14 . The method of  claim 11 , wherein the step of providing a slide valve assembly in the compressor housing comprises: 
 providing a slide valve assembly in the compressor housing such that the piston is movably disposed within a piston cylinder of the compressor housing, the piston cylinder sized to receive the piston, wherein moving the piston results in moving the slide valve, thereby modifying the flow of gas and controlling the capacity of the compressor.    
   
   
       15 . The method of  claim 14 , wherein the moving of the slide valve from a first position to a second position with respect to the intermeshed rotors is accomplished by varying a pressure on one side of the piston with respect to a pressure on an opposing side of the piston.  
   
   
       16 . The method of  claim 14 , wherein a portion of the compressor housing defines at least a portion of an end wall of the piston cylinder.  
   
   
       17 . The method of  claim 16 , wherein the portion of the compressor housing that defines at least a portion of the end wall of the piston cylinder is the acoustic barrier.  
   
   
       18 . The method of  claim 14 , wherein the step of providing a slide valve assembly further comprises: 
 providing a slide valve assembly further comprising a biasing means to urge the piston in a direction opposite the acoustic barrier.    
   
   
       19 . The method of  claim 14 , wherein the moving of the slide valve from a first position to a second position with respect to the intermeshed rotors is accomplished by introducing a high pressure gas into the piston cylinder from the discharge side to increase pressure on one side of the piston, thereby urging the piston in a direction opposite the first direction urged by the biasing means.  
   
   
       20 . A refrigeration system comprising: 
 a condenser;    an evaporator;    an expansion valve; and    a screw compressor comprising a compressor housing having a passage for the flow of a fluid therethrough from a suction side of the compressor to a discharge side of the compressor, the housing including an integral acoustic barrier, a pair of intermeshed rotors disposed in the passage, the rotors configured to increase the pressure of the fluid flowing from a suction port on the suction side of the compressor through the passage to a discharge port on the discharge side of the compressor, and a slide valve assembly movably disposed within the compressor housing to adjust the capacity of the compressor, the slide valve assembly comprising a slide valve connected to a piston by a shaft, wherein the piston and the slide valve are disposed on opposite sides of the acoustic barrier and wherein the acoustic barrier includes an aperture sized to receive the shaft, the acoustic barrier attenuating acoustic resonance and noise in the compressor and wherein the acoustic barrier is positioned a preselected distance from the discharge port,    wherein the condenser, evaporator, expansion valve and screw compressor are serially connected for the passage of a refrigerant therethrough.    
   
   
       21 . The refrigeration system of  claim 20 , wherein the slide valve assembly of the screw compressor comprises a single piston.  
   
   
       22 . The refrigeration system of  claim 20 , wherein the refrigerant comprises 134a refrigerant.