Effect of Pump Performance Curves and Geometric Characteristics of Offset Fins on Heat Exchanger Design Optimization

Abstract

This study analyzes several design cases to identify the optimum geometric structure of the offset fin, determined by two design factors: the number of fins in the flow direction and the number of fins in the vertical direction. Increasing the number of fins in the vertical direction has relatively minor effects on the heat transfer rate and surface area. In contrast, adding more fins in the flow direction results in enhancement of thermal performance. Correlations for the Colburn j factor and the Fanning f factor, incorporating Nfin,v and Nfin,f, are established. The resistance curve of each case is yield based on the f factor correlation, and the heat transfer rate at the actual coolant flow rate is obtained the j factor correlation. A difference in the pressure drop resulted in a different coolant flow rate despite using the same circulation pump, showing a difference of 1.67 times between the minimum and maximum values. Although a different coolant circulates in each case, there was no reversal in the heat transfer rate compared to the situation in which a constant amount flows. The impact of the pump’s performance curve on the heat transfer rate becomes relatively pronounced with an increased pressure drop. When Nfin,f was 30, the ratio of maximum to minimum heat transfer rate was 8.73% with a constant coolant flow rate, but this ratio increased to 13.08% when considering the actual coolant flow rate facilitated by a pump.