Accuracy of one-dimensional design procedures for finned-tube heat exchangers

In design procedures for finned-tube heat exchangers a common simplification is assuming that the temperature distribution is one-dimensional. In this way, the heat exchanger can be schematized as a thermal circuit with three thermal resistances in series: internal convection to the tube, conduction through the tube wall, and external convection through the fin assembly. The aim of this work is to quantitatively evaluate the accuracy of one-dimensional schematizations in the context of finned-tube heat exchangers utilized in air-conditioning applications. To this purpose, first three-dimensional benchmark results are obtained employing an in-house FEM code. Afterwards, a simplified two-dimensional model is proposed and validated through a comparison with the three-dimensional results. Finally, the simplified two-dimensional model and the commercial software COMSOL Multiphysics are used to conduct a parametric study aimed at assessing the accuracy of one-dimensional schematizations. The main conclusion is that the accuracy of one-dimensional design procedures is quite acceptable for practical purposes, since it leads to errors in the estimation of heat flow rates that are always less than 2%.