Variable Volume-Ratio and Capacity Control in Twin-Screw Compressors

This paper presents different means for variable built-in volume ratio and capacity control for the twin-screw refrigeration compressor. Sophisticated methods for such controls are mostly needed on refrigeration compressors but are of course applicable to any twin-screw compressor. Two different types of variable built-in volume ratio are presented: Vi slide valve and Vi lift valve. For capacity control, emphasis is placed on suction-port control and variable speed. The different means presented for suction port control are: capacity slide valve regulating discharge port capacity slide valve which does not regulate the discharge port capacity slot valve capacity lift valve Each capacity control arrangement is studied in conjunction with fixed and variable built-in volume ratio.