A discretization method for the characterization of a plate heat exchanger working as evaporator during transient conditions

Abstract

In this work, a method for the characterization of a plate heat exchanger working as evaporator is presented. It is based on a one-dimensional discretization of the exchanger, which solves the heat transfer balance equations by means of an iterative methodology based on a heat transfer area converging method. The inputs of the method are the flow rates of the fluids, the inlet enthalpy of the refrigerant, the superheating, and the inlet temperature and pressure of the secondary fluid. Once the inlet pressure of the refrigerant is assumed, pressure drop is calculated in each cell and then enthalpy. The consideration of the proper heat transfer coefficient (HTC) correlations allows the calculation of the heat transfer area, which is after compared to the actual one. The method has been validated by means of a database of 366 experimental data obtained for eight plate heat exchangers working as evaporators by using six different refrigerants, namely R134a, R1234yf, R513A, R744, R290, and R507A. As the method requires suitable correlations for the calculation of the HTC and pressure drop, several correlations for the HTC and Δp found in the literature are studied and the results obtained by using them are presented in terms of the maximum absolute relative deviation (MARD). The results corresponding to the correlation which yields the best results are graphically represented. Finally, the method is used to predict the evaporator performance operating in transient conditions. The results obtained show an excellent agreement with the experimental results collected during the transient operation of a transcritical CO2 water heater coupled to a storage tank.