Multifunctional Screw Compressor Rotors

For many years the authors have been investigating the use of twin screw machines to fulfil both the expansion and compression. One of potential advantages of screw machines over other types of positive displacement machine is their ability to perform both the compression and expansion functions simultaneously, using only one pair of rotors. A further feature is the use of the rotors which seal on both contacting surfaces so that the same profile may be used both for the expander and the compressor sections. By using the same profile for both, the compressor and expander rotors can be machined or ground in a single cutting operation and then separated by machining a parting slot in them on completion of the lobe formation. Moreover, in such a case, by proper location of the machine ports, pressure loads and thereby, mechanical friction losses will be less than if the two functions are performed in separate machines. Fields of application of such machines are replacement of the throttle valve in refrigeration and air conditioning plants, high-pressure application, fuel cells, multistage compression or expansion and, really, any other application where simultaneous compression and expansion are required. One example of such unusual, but convenient application is the compressor capacity control by partial expanding of compressed gas.