Modelling of a Transient VCRS and Virtual Optimal Charge Determination for Automobiles

Experimental research on the Vapor Compression Refrigeration System (VCRS) used in automobiles and other air conditioning systems is abundant in literature but it comes with inherent problems like the cost of the setup, time consumption, and tediousness of the process. Therefore, the objective of this study is to develop the fully-fledged transient or dynamic model of R134a based VCRS and further utilize it to virtually determine the optimal refrigerant charge quantity. The Simulink model developed in this work is an integration of physics-based mathematical models for each component (compressor, heat exchangers, and expansion valve), working together in a cycle where the compressor dictates the transient process. A sample simulation has been performed by taking 5 bar as the initial pressure of suction and discharge tanks and the steady state results (Discharge pressure, suction pressure, refrigerant mass flow rate, superheat and subcool temperatures) obtained. The results are found to closely follow the similar trends as the experimental results, hence validating the correctness of the Simulink model. Further, Using the proposed transient model, simulations have been performed for different initial state conditions and steady state plots (discharge pressure V/s charge, cooling capacity V/s charge, COP V/s charge, Subcool and Superheat V/s charge ) have been constructed. Analysis of these plots shows that the values of cooling capacity and COP attain maxima simultaneously corresponding to 650 grams of charge. Hence, using maximum COP method for optimal charge determination, the optimal charge quantity has been calculated to be around 650 grams. In the end, this work hopes to provide researchers a transient model that can be used as a cost-effective substitute of the experimental process.