Temperature fields calculation in heat exchangers using the finite element method

Abstract

Heat exchanger (HEX) design is an optimization process that seeks to maximize heat transfer between two fluids while minimizing pressure drops. There are several conceptual design methods based on integral equations that only work with specific temperature values at the inlet and outlet of the HEX. However, it is very interesting to obtain approximate temperature distributions in these early stages of analysis to verify that the design criteria are met. To do this, it is necessary to solve systems of differential equations depending on the HEX configuration. Under certain assumptions, these equations have an analytical solution. However, in most cases it is only possible to obtain a numerical approximation. This work presents the solution of these equations for 6 HEX arrangements based on the finite element method. After validating the results in the cases whose analytical solution is known, the proposed method is applied to two realistic cases. Firstly, the effectiveness of a double-pass crossflow heat exchanger is studied. Since the inlet distributions in the second HEX module are not constant, no analytical solution is available. The numerical solution allows to analyze under what conditions the second pass is not effective due to thermal inversion. Secondly, a simplified 2D geometry of a compact intercooler HEX for hydrogen-fueled aero engine is solved. Specifically, an analysis is carried out to locate possible malfunctions due to obstructions of the fluid flows making use only of the metal temperature distributions at the outlets.