The screw compressors are very often used for the applications where the pressure ratios vary, such as the water chillers, the heat pumps and the vacuum pumps etc. Typically, a screw compressor designed with a fixed volume ratio, that is, a fixed discharge port, is used for these applications. The fixed volume ratio is optimized for a fixed pressure ratio, and if the real pressure ratio is different from the pressure ratio the discharge port is optimized for, the compressor will not operate at the working condition it was optimized for. When this happens, the compressor will operate under so-called over-compression or under-compression conditions, the compressor efficiency shall drop, and the compressor discharge noise level shall increase. This paper presents a screw compressor with a patented flexible discharge port. Such a screw compressor always has its volume ratio or discharge port matched the real pressure ratio. The under-compression or over-compression is eliminated, the compressor discharge noise is always low, and the compressor efficiency is always at its optimum. The screw compressors with the flexible discharge port can be used for the applications with variable pressure ratios. The design techniques of the flexible discharge port are discussed in this paper, and the measurement results of a screw compressor with the flexible discharge port are presented. The potential applications of the flexible discharge port design are also discussed in this paper.
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