Volume 50

Optimizing Supercritical Heat Exchangers: A Study on Entrance Effect and Multi-Stage Heating Approach Zhenghui Hou, Chaofan Yang, Haijun Wang

Abstract

Supercritical heat exchangers encounter a variety of non-uniform heat flux during operation, which significantly influence the flow and heat transfer processes. Numerical simulation is employed to investigate the process of supercritical water entering and leaving the heated section, which are divided into three stages: Thermal Establishment Stage, Axially Asymptotic Developed Stage, and Thermal Removal Stage. During Thermal Establishment Stage, influenced by entrance effect, the affected range in this study extends up to 150 z/d. This stage is characterized by a heat transfer coefficient higher than that of the stable state with the same bulk enthalpy. Following sufficient heating, supercritical water reaches the Axially Asymptotic Developed Stage, where the flow and heat transfer processes become independent of inlet parameters. After heating, the top wall temperature drops rapidly, primarily due to the convective heat transfer of the supercritical fluid inside the tube. The Multi-Stage Heating Approach proposed on the basis of this study can effectively relieve the heat transfer deterioration and significantly enhances the overall heat transfer performance of the heat exchanger near the pseudo-critical temperature. Results indicate that, compared to conditions without entrance effect, the overall heat transfer coefficient can increase by up to 28.15%, 58.01%, and 92.24% for one-stage, two-stage, and three-stage heating, respectively.

Keywords Supercritical water heat exchangers, advanced energy technologies, the entrance effect, horizontal tubes, multi-stage Heating Approach