Design optimization of an heat exchanger using Gaussian process

Abstract

The objective of this work is to optimize the internal shape of a single-started helically ribbed heat exchanger. Large Eddy Simulation (LES) is used to simulate the turbulent flow in a wall-resolved periodic channel configuration, heated via a uniform heat flux at the wall. In order to enhance the heat exchange with the flow, the inner surface of the channel features rounded rib. This however increases the pressure loss, and an optimum shape of the rib is to be found. The rib pitch and height as well as rib discontinuities are the geometrical parameters to optimize, allowing a wide variety of inner wall roughness. To limit the number of LES, the optimization procedure is based on a surrogate model constructed from Gaussian Process Regression and adaptive resampling with the Efficient Global Optimization (EGO) method [1]. The optimization consists in the maximization of the cost function proposed by Webb and Eckert [2], which aims at maximizing the heat transfer efficiency for similar pumping power. Results show that a rib induced swirling motion in the near wall region significantly decreases the heat transfer efficiency, leading to an optimum roughness shape featuring large and multiple discontinuities. Moreover, the efficiency of helically dimpled tubes is also found sensitive to the shape of the transitions between the discontinuous parts of the rib. Smoother transitions lead to lower pressure loss but also to lower heat transfer due to smaller recirculation zones.