Thermal expansion in liquid-injected screw compressors

Abstract

In screw compressors gaps between rotors and casing have to be small, in the range of 30 to 300 μm. These gaps are influenced by thermal expansion when the screw compressor is in operation. The amount of thermal expansion is about the same size as the gaps, even in oil-injected screw compressors. Especially when starting a cold compressor, there are temperature differences. These temperature differences were measured in a 22 kW oil-injected screw compressor for industrial compressed air as an easily manageable example. Measuring the temperatures in the rotor teeth was done with Pt1000-sensors and transmission with Wireless-LAN. The results showed lower temperature differences than expected. The influence of the oil-injection-temperature is dominant. In bigger screw compressors the temperature differences tend to be larger because of dimensional reasons: A simple numerical model for the temperature differences in a screw compressor with fluid injection allows an extrapolation for larger rotors.