Validation of a multi-circuit heat exchanger model for evaluating the effect of refrigerant circuitry on cross-fin conduction in evaporator mode

Abstract

Fin-and-tube heat exchangers can have active circuits directly adjacent to inactive circuits at part load conditions, leading to cross-fin conduction. Cross-fin conduction needs to be accounted for in heat exchanger modelling to accurately predict heat exchanger performance. This study explores how refrigerant circuitry can influence cross-fin conduction in multi-circuit evaporator coils. Our advanced segment-by-segment heat exchanger model is validated against two-phase refrigerant data obtained from our experimental facility. Three, custom designed, multi-circuit fin-and-tube heat exchanger coils with distinct circuities were used for validation purposes, including an interleaved, vertical and block circuited coils, respectively. A total of 162 experiments with several refrigerant and air inlet conditions, at full load (all circuits active) and part load (some circuits active) were carried out. At full load, for all coils, differences in coil capacity between simulated and experimental capacities were no greater than 10%, for part load the differences are larger. For the test coil with interleaved circuitry, operating with 3 of 8 circuits active, the mean average percentage error (MAPE) between experimental and simulated capacity was 2.7% when cross-fin conduction was considered, increasing to 7.7% when it was ignored. Similarly, for test coil with block circuitry, operating with 2 out of 4 circuits active, the MAPE between experimental and simulated capacity was 1.7% when cross-fin conduction was considered, and 3.4% when ignored. Results suggest that the effect of cross-fin conduction on coil capacity is directly proportional to number of inactive circuits, and it is more pronounced on interleaved circuitry compared to block circuitry.