Optimum Design of Micro Bare-Tube Heat Exchanger

Abstract

Micro bare-tube heat exchangers can accomplish high performance and compactness with their simple structure. In general, decreasing characteristic length leads to higher heat transfer area density at the expense of larger pressure drop. The trade-off has been so far optimized by trial and error. In the present study, simulated annealing (SA) is employed to optimize various design parameters of heat exchangers, which composes a multiple-variable highly nonlinear system. Although the heat transfer coefficient and the pressure drop on the air-side make major contribution to the total heat resistence and pumping power, empirical correlations of flow around tube bank can not predict them accurately in the low Reynolds number range, which is characteristic of compact heat exchangers. Hence, we make a series of numerical simulation for heat transfer and pressure drop of flow in the tube bank at various tube spacings and Reynolds numbers, and correlation functions are developed using an artificial neural network. Finally, optimum design is made for three types of micro bare-tube heat exchangers, i. e., heater core and radiator for automobiles, electronic equipement cooling system, and recuperator for micro gas turbine.