Screw compressor with a shunt-enhanced compression and pulsation trap (secapt)

Abstract

A shunt-enhanced compression and pulsation trap (SECAPT) for a screw compressor assists internal compression (IC), reduces gas pulsation and NVH, and improves off-design efficiency, without using a slide valve and/or a serial pulsation dampener. The SECAPT includes an inner casing (e.g., an integral part of the compressor chamber) and an outer casing (e.g., surrounding part of the inner casing near the compressor discharge port) forming at least one diffusing chamber with a nozzle and a feedback region that provides a feedback flow loop between the compressor chamber and the compressor discharge port. The SECAPT automatically compensates cavity pressure to meet different outlet pressures (hence eliminating under-compression and/or over-compression when the discharge port opens), partially recovers potential energy associated with the under-compression (UC), and traps and attenuates gas pulsations and noise before the discharge port opens.

What is claimed is: 
     
         1 . A screw compressor, comprising:
 a compression chamber and a pair of meshing multi-helical-lobe rotors housed within the compression chamber, wherein the compression chamber has a flow suction port and a flow discharge port, wherein the rotors rotate to cooperatively form a series of moving cavities within the compression chamber for trapping and compressing fluid and propelling the trapped fluid from the suction port to the discharge port; and   a shunt-enhanced compression and pulsation trap (SECAPT) apparatus including a diffusing chamber having a first flow nozzle providing fluid communication between the moving cavities inside the compression chamber and the diffusing chamber and having a feedback region providing fluid communication between the diffusing chamber and the discharge port, wherein the SECAPT defines a first stage of a feedback flow loop,   wherein in operation the SECAPT achieves high gas pulsation and NVH reduction and improved compressor off-design efficiency without using a serial pulsation dampener or a slide valve.   
     
     
         2 . The screw compressor as claimed in  claim 1 , wherein the first flow nozzle is positioned at a distance at least one lobe span away, or is totally sealed or isolated, from the suction port, but is positioned before the discharge port. 
     
     
         3 . The screw compressor as claimed in  claim 2 , further comprising a second flow nozzle that is positioned at a distance at least one lobe span away, or totally sealed or isolated, from the first flow nozzle, but is positioned before the discharge port, and defining a second stage of the feedback flow loop. 
     
     
         4 . The screw compressor as claimed in  claim 1 , further comprising a third flow nozzle that is positioned at a distance at least one lobe span away, or totally sealed or isolated, from the second flow nozzle, but is positioned before the discharge port, and defining a third stage of the feedback flow loop. 
     
     
         5 . The screw compressor as claimed in  claim 1 , wherein the first flow nozzle has a circular cross-sectional shape with a converging or a converging-diverging cross-sectional area transitioning along an axis of the nozzle. 
     
     
         6 . The screw compressor as claimed in  claim 1 , wherein the first flow nozzle has a rectangular cross-sectional shape with a converging cross-sectional area transitioning along an axis of the nozzle. 
     
     
         7 . The screw compressor as claimed in  claim 5 , wherein the converging cross-sectional area has a continuous transition from a circular cross-sectional shape at a throat of the nozzle to a generally rectangular slot shape at the compression chamber, with a longer side of the rectangular slot shaped nozzle at the compression chamber oriented generally along a longer side of the moving cavity. 
     
     
         8 . The screw compressor as claimed in  claim 5 , wherein the converging-diverging cross-sectional area has a continuous transition from a circular cross-sectional shape at a throat of the nozzle to a generally rectangular slot shape at the compression chamber, with a longer side of the rectangular slot shaped nozzle at the compression chamber oriented generally along a longer side of the moving cavity. 
     
     
         9 . The screw compressor as claimed in  claim 1 , wherein the first flow nozzle is positioned a distance away from the rotor axis and aimed in generally the same direction as an angular rotation of one of the rotors. 
     
     
         10 . The screw compressor as claimed in  claim 1 , wherein the pair of meshing multi-helical-lobe rotors includes a male rotor and a female rotor, and wherein two of the first flow nozzles are provided with one first flow nozzle positioned at the male rotor and with the other first flow nozzle positioned at the female rotor, and wherein the two nozzles are open simultaneously to moving male and female cavities in the compression chamber. 
     
     
         11 . A screw compressor, comprising:
 a compression chamber and a pair of meshing multi-helical-lobe rotors housed within the compression chamber, wherein the compression chamber as a flow suction port and a flow discharge port, wherein the rotors rotate to cooperatively form a series of moving compression cavities within the compression chamber for trapping and compressing fluid and propelling the trapped fluid from the suction port to the discharge port; and   a shunt-enhanced compression and pulsation trap (SECAPT) apparatus including a diffusing chamber having a first flow nozzle providing fluid communication between the moving cavities inside the compression chamber and the diffusing chamber and the diffusing chamber and having an access port providing fluid communication between the diffusing chamber and ambient atmosphere, wherein the SECAPT defines a first stage of a feedback flow loop,   wherein in operation the SECAPT achieves deep vacuum with high gas pulsation and NVH reduction and improved compressor off-design efficiency without using a slide valve.   
     
     
         12 . The screw compressor as claimed in  claim 11 , wherein the first flow nozzle is positioned at a distance at least one lobe span away, or is totally sealed or isolated, from the suction port, but is positioned before the discharge port. 
     
     
         13 . The screw compressor as claimed in  claim 11 , further comprising a second flow nozzle that is positioned at a distance at least one male lobe span away, or totally sealed or isolated, from the first flow nozzle, but is positioned before the discharge port, and defining a second stage of the feedback flow loop. 
     
     
         14 . The screw compressor as claimed in  claim 11 , further comprising a third flow nozzle that is positioned at a distance at least one male lobe span away, or totally sealed or isolated, from the second flow nozzle, but is positioned before the discharge port, and defining a third stage of the feedback flow loop. 
     
     
         15 . The screw compressor as claimed in  claim 12 , wherein the first flow nozzle has a circular cross-sectional shape with a converging or a converging-diverging cross-sectional area transitioning along an axis of the nozzle. 
     
     
         16 . The screw compressor as claimed in  claim 12 , wherein the first flow nozzle has a rectangular cross-sectional shape with a converging cross-sectional area transitioning along an axis of the nozzle. 
     
     
         17 . The screw compressor as claimed in  claim 15 , wherein the converging cross-sectional area has a continuous transition from a circular cross-sectional shape at a throat of the nozzle to a generally rectangular slot shape at the compression chamber, with a longer side of the rectangular slot shaped nozzle at the compression chamber oriented generally along a longer side of the moving cavity. 
     
     
         18 . The screw compressor as claimed in  claim 15 , wherein the converging-diverging cross-sectional area has a continuous transition from a circular cross-sectional shape at a throat of the nozzle to a generally rectangular slot shape at the compression chamber, with a longer side of the rectangular slot shaped nozzle at the compression chamber oriented generally along a longer side of the moving cavity. 
     
     
         19 . The screw compressor as claimed in  claim 11 , wherein the first flow nozzle is positioned a distance away from the rotor axis and aimed in generally the same direction as an angular rotation of one of the rotors. 
     
     
         20 . The screw compressor as claimed in  claim 11 , wherein the pair of meshing multi-helical-lobe rotors includes a male rotor and a female rotor, and wherein two of the first flow nozzles are provided with one first flow nozzle positioned at the male rotor and with the other first flow nozzle positioned at the female rotor, and wherein the two nozzles are open simultaneously to moving male and female cavities in the compression chamber.