Experimental Investigation of Controlling Piston Offset in Oil-Free Linear Compressors for J-T Throttling Refrigerator

Abstract

The linear compressor provides the indispensable pressure ratio and mass flow for the Joule-Thomson (J-T) throttling refrigerator. The piston of the single-piston linear compressor will be offset from its initial position at a high-pressure ratio, which may result in reduced compressor performance. Three methods of controlling the offset are compared in the paper, which is adopting the symmetrical dual-piston structure, increasing the initial clearance volume, and applying direct current (DC) voltage, respectively. The linear compressor was tested with nitrogen, and the performance of the linear compressor with different adjustment methods was evaluated. The experimental results reveal that the symmetrical dual-piston structure can considerably improve the piston offset and ensure the remarkable performance of the compressor. The method of applying DC voltage can also achieve good performance, but it increases the copper loss of the motor and the complexity of the operation. The research furnishes an effective quantitative analysis for mitigating piston offset and supplies the direction for optimizing compressor performance.