Modeling and analysis of a printed circuit heat exchanger for supercritical CO2 power cycle applications

Abstract

The supercritical carbon dioxide (S-CO2) based Brayton cycle is a good alternative to conventional power cycles because of high cycle efficiency, compact turbo machinery and compact heat exchangers. In this cycle, the majority of heat transfer (approximately 60–70% of total cycle heat transfer) occurs in the regenerator. For the regenerator, micro-channel heat exchanger is an attractive option because of its high surface-area-to-volume ratio. In this study, the performance of a printed circuit heat exchanger (PCHE) with straight and zigzag channels is evaluated. The study is performed for fully turbulent conditions. The channel diameter and the operating Reynolds number play significant roles in the overall heat transfer and pressure drop of hot and cold channels of S-CO2. For zigzag channels, it is found that a larger bend angle and smaller linear pitch perform better than a smaller bend angle and large linear pitch combination. Correlations for Nusselt number and friction factor are developed using ANSYS Fluent and are subsequently utilized in one dimensional (1D) thermal modeling of the heat exchanger. For the same thermal capacity, the model indicates that the zigzag channel PCHE volume is significantly smaller than that of a straight channel PCHE because of higher heat transfer coefficient. However, the pressure drop incurred in the former design is larger.