Thermodynamic analysis of diaphragm compressor in hydrogen refuelling stations by using fluid-structure interaction method

Abstract

Low efficiency is a significant challenge for diaphragm compressors used in hydrogen refuelling stations. To investigate the thermodynamic performance of diaphragm compressors, a mathematical model using the fluid–structure interaction (FSI) method was proposed. Thermodynamic equations of the gas and oil, valve plate movement, and large diaphragm deformation were combined in the model. The deformation of the diaphragm is assumed to be quasi-static free, and fluid leakage and heat transfer are disregarded in this model. Experiments using a 90 MPa diaphragm compressor were conducted to validate the model simulation results. The performance of the diaphragm compressor was studied using three types of pressure–volume diagrams (overall, gas, and oil pressure–volume diagrams) obtained via simulations. The results showed that suction volume loss owing to the expansion of the hydraulic oil and clearance gas was more than 40 % of the stroke volume, reducing the volumetric efficiency to less than 60 %. The effects of the oil overflow pressure on the diaphragm compressor performance were also analysed. According to the simulation results, the volumetric efficiency and isentropic indicated efficiency of the compressor were largest when the oil overflow pressure was adjusted to 1.1 times the discharge pressure. The performance of the diaphragm compressor was predicted with different suction pressures. Volumetric efficiency and isentropic indicated efficiency decreased considerably with suction pressure; when the suction pressure of the compressor was reduced to 8 MPa, the volumetric and isentropic indicated efficiencies were less than 15 % and less than 55 %, respectively.