Analysis of the influence of the heat transfer model on the effectiveness of the heat exchanger on the example of cross flow device

One of the methods of analyzing a heat exchanger consists in determining the heat transfer rates and outlet temperatures of the fluids for known mass flows, inlet temperatures, and exchanger type and size. This requires calculating the exchanger performance for known transfer surface area but unknown outlet temperatures. The concept of the heat transfer effectiveness (HTE) can be applied to determine the heat transfer rate of the specified heat exchanger without knowing the outlet temperatures of the fluids. This article presents the results of calculations of the HTE parameter for a cross-flow heat exchanger with staggered tube banks. The analysis takes into account six different models of convection heat transfer over the tube banks. In this scenario, the impact of the applied convection model on the value of HTE for the considered heat exchanger was examined. For the considered calculation cases, the value of the HTE parameter is in the range from 0.3 to 0.48 and it decreases with the increase of the flow rate of both air and the flue gases. It has been shown that the results of all four models are very similar, while the other two models bring about either an increase or a decrease of the values of the parameter investigated. It was found that for the analyzed heat exchanger a simplified criterion for the convection heat transfer over tube banks can be used to determine the effectiveness of the heat transfer with the Reynolds number being the only parameter.