Experimental study on the performance of single screw expanders by gap adjustment

•The experiment for three single screw expander prototypes at different gaps was carried out.•Maximum shaft efficiency is about 60%.•Minimum gas consumption rate is about 65 kg/kWh.•Maximum volumetric efficiency is about 66%.•Leaked gas still has part of working capability.

Improving thermodynamic efficiency of prime movers is the key issue for efficient utilization of low-temperature heat resources. Single screw expander may be a good candidate because of its many good characteristics. Precisions in manufacture and assembly are very important factors to the performance of single screw expanders. In this paper, the shaft efficiency, volumetric efficiency and gas consumption rate of the single screw expander prototypes were tested and discussed. We have manufactured three prototypes with different gaps to investigate their performance. The first prototype (A) has the largest gap, and the second one (B) has the smallest gap, the third prototype (C) has the medium gap configuration. Experimental result of the prototypes was obtained. From the experimental data of prototype A, the power output was about 5 kW, the gas consumption rate was above 105 kg/kWh and the volumetric efficiency was below 20%, the shaft efficiency was only 34%. From experimental data of prototype B, the mass flow rate was significantly decreased. The power output was only 1.4 kW and the volumetric efficiency was slightly lower than prototype A. The gas consumption rate was much more than that of prototype A. From the experimental data of prototype C, the power output was about 4.5 kW, but the mass flow rate was sharply decreased. The gas consumption rate was about 65 kg/kWh, the maximum volumetric efficiency was about 66%, and the shaft efficiency was about 60%. The experimental results indicated that prototype C of single screw expanders had the best overall performance, which may be further improved by optimizing its configuration.