Optimization of Elliptical U-Tube Heat Exchanger (EUTHE) for Spray Cooling Based on the Taguchi and CFD Method

The elliptical U-tube heat exchanger (EUTHE) is widely used in various cooling systems of nuclear engineering for its simple geometrical structure and small space cost. In this paper, a two-phase flow field model of an EUTHE is constructed to analyze the flow characteristics in the elbow zone under different structures with the influence mechanism of droplet motion and liquid film distribution. The Taguchi method is used to investigate the influence of heat transfer performance by structural parameters, and the fitted model is analyzed by regression analysis as well as ANOVA to ensure the accuracy of the prediction results.

The results show that thick tubes have a wider liquid film distribution because they are more difficult to trap droplets, achieving high heat transfer capacity while reducing separation efficiency and pressure drop. In addition, the heat transfer capacity and the pressure drop are mostly improved by the increase of the U-tube cross-section long axis length (L₂) at the expense of reduced separation efficiency. The optimal cases for each target were obtained by analyzing the influence mechanism of each structural factor, for example, the largest heating tube section (L₁) and the U-tube cross-section long axis length (L₂), to determine which will lead to the highest heat transfer capacity, which mainly is due to the fact that an increase in these factors leads to the increment of contact area between the fluid and the wall. This work provides a guideline for the design of EUTHE and brings greater benefits to the development of nuclear engineering.