Experimental investigation on pinch points and maximum temperature differences in a horizontal tube-in-tube evaporator using zeotropic refrigerants

An experimental investigation is conducted on the occurrence and location of either a pinch point (PP) or maximum temperature difference (MTD) between a zeotropic refrigerant mixture and a heat transfer fluid (HTF) in a tube-in-tube evaporator. The zeotropic refrigerant used in the PP investigation is a R290/R600 mixture with a 0.15/0.85 mass fraction; the refrigerant used in the MTD investigation is a R245fa/R152a mixture with a 0.6/0.4 mass fraction. The inlet HTF temperature and the HTF and refrigerant flow rate were chosen as variable parameters at several sets of different working conditions to observe their effects on the location of a PP or MTD. The collected experimental data was then analyzed to determine the position of the PP or MTD. The position of the PP or MTD from the experiments did not show good agreement compared to predictions using existing available theoretical methods. The disagreement between theoretical and experimental results can be attributed in part to the nonlinear temperature change of the HTF along the evaporator which is not accounted for with existing theoretical methods.