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Capacity based performance predictions for positive displacement compressors with low-GWP refrigerants through compressor modeling

Tanveer, Muhammad Mohsin
Regulatory changes aimed at mitigating climate change require compressor manufacturers to replace current refrigerants with those having low Global Warming Potential (GWP). To select suitable refrigerants for different applications, low-GWP refrigerants' performance evaluation in various positive displacement compressors is crucial. A carefully designed simulation model can provide similar outcomes to heuristic evaluation for a significantly reduced cost. A literature review of sub-models for mass flow, valves, and heat transfer is conducted to identify suitable approaches for the current analysis. PDSim is used to evaluate the scroll compressor performance, as it possesses more desirable qualities for performance evaluation study.
A scaling model is developed to design scroll geometry for seven refrigerants within a 1-100 ton range of cooling capacity, based on manufacturing constraints and minimization of leakage. The scaled compressor designs are then simulated using a validated scroll compressor model. The results suggest that an optimum range exists for each refrigerant to achieve good compressor performance, with leakage area being the primary contributor.
The evaluation work is extended to the spool compressor by conducting a parametric study to find the optimum geometric aspect ratio for a spool compressor for five refrigerants and a range of cooling capacities between 1-100 RT. A scaling model is developed to vary the compressor geometry and ports. A spool compressor model which was developed by Bradshaw and Groll (2013), is extended and re-validated and is used to simulate these scaled designs. The results suggest that the volumetric and isentropic efficiencies can be maximized by using an eccentricity ratio of 0.75 and L/D ratios from 1-1.5 for various displacement volumes.
The results of the scroll and spool compressor analysis are presented in a non-dimensional form using the Grabow diagram, which is a useful tool for comparing different fluid machines. This chart provides a comprehensive analysis of various technologies and can aid in selecting the appropriate fluid machine or compressor for a specific application.