Experimental and numerical investigation of suction muffler outlet pipe geometry effect on volumetric efficiency and COP

This study investigates how the design of the muffler outlet pipe and the compressor speed affect the volumetric efficiency and COP using both experimental and numerical methods. Three distinct muffler outlet pipe designs, characterized by varying lengths and diameters, are tested across four different compressor speeds using R600a refrigerant. Experimental measurements include displacement data of the suction valve obtained via strain gauges, while pressure fluctuations in the suction plenum and cylinder volume are recorded using pressure transducers. Additionally, a magnetic encoder is employed to monitor crank angle and cylinder volume. A numerical model is developed using the GT-SUITE™ platform and subsequently validated against the experimental results. After successful validation, the numerical model is used to investigate the impacts of compressor speed and muffler geometry in more depth. The investigation encompasses the analysis of pressure drop, compressor speed, and valve timing in relation to mass flow rate and valve displacement curves. A general linear model is constructed to quantify the contribution of each parameter and the R-sq (adjusted) is 75 %. The model indicates that compressor speed accounts for 75 % of the variation in volumetric efficiency whereas the pipe diameter is the second-largest contributor, accounting for nearly 22 % and the effects of the pipe length is 3 %.