Investigation of the thermodynamic process of the refrigerator compressor based on the m-θ diagram

The variation of refrigerant mass in the cylinder of refrigerator compressor has a great influence on the compressor's thermodynamic process. In this paper, the m-θ diagram, which represents the variation of refrigerant mass in compressor cylinder (m) and the crank angle (θ), is proposed to investigate the thermodynamic process of the refrigerator compressor. Comparing with the traditional pressure-Volume (p-V) indicator diagram, the refrigerant's backflow trigged by the delayed closure of valve can be clearly expressed in the m-θ diagram together with the mass flow rate. A typical m-θ diagram was obtained by experimental and theoretical investigations. To improve the thermodynamic model of the compressor, a 3D fluid-structure interaction (FSI) FEA model has been introduced to find out the effective flow area of the valves. Based on the m-θ diagram, the effect of rotating speed on the backflow through the valve, which depends on the movement of the valve, has been investigated. Specific to the compressor used in this study, the maximum backflow through the suction valve and discharge valve occur at 3500 r·min⁻¹ and 5500 r·min⁻¹, respectively.