Validity of Performance Factors used in Recent Studies on Heat Transfer Enhancement by Surface Modification or Insert Devices: Constant Heat Flux Case
Keywords:Heat transfer enhancement, validity, performance factor, baffle plate, constant heat flux
Heat transfer enhancement had been widely applied in developing a more compact heat exchanger which can save a lot of energies, materials and costs. Based on our literature review, the performance factors that proposed previously had been widely used in various papers to evaluate the heat transfer enhancement. However, no validation had been conducted before to validate the performance factors. Recently, the performance factors had been studied for the heat transfer enhancement of a circular duct with periodic annular baffle plates which is heated by constant wall temperature, and the result shown that the performance factors are not valid for evaluating the heat transfer. Whereas this study is examined the validity of the performance factors by comparing the heat transfer rate in a fully periodic developed region of a circular duct to a modifies duct with periodic annular baffle plates, which are heated by constant heat flux. The heat transfer rates are obtained numerically. Validity of the performance factors is examined by comparing the average temperature difference between wall temperature and bulk temperature. It was found that the performance factors used in previous papers except for equation (2) defined below are not valid to evaluate the heat transfer enhancement.