Investigation of Heat Transfer Performance and Enhancement Mechanisms of Supercritical Carbon Dioxide in Pche with Fractal Airfoil Fins

Abstract

A fractal structure with symmetric/asymmetric airfoil ribs is implanted into the smooth channels, which can further enhance the heat transfer performance of the printed circuit heat exchanger (PCHE). In this work, two layers of channels are installed horizontally and the upper channel is dedicated to hot CO2, while the cold CO2 is specified in the lower channel. Two distinct structures of airfoil ribs, i.e., NACA 0021 symmetric airfoil ribs and NACA 4822 asymmetric airfoil ribs, are selected for evaluation. The numerical results show that the heat transfer performance of the channels with the fractal structure of symmetric/asymmetric airfoil ribs is significantly improved compared to the original design. In particular, the channel with asymmetric airfoil ribs exhibits a better heat transfer performance with an improvement factor of 1.05-3.76. The dimensionless friction factor is 0.67-1.31 and it indicates a decrease in pressure drop while improving heat transfer performance. Also, a good heat transfer performance does not depend on a large flow rate between the cold fluid zone and hot fluid zone, but a proper flow matching. In conclusion, the design in this study will improve the heat exchanger efficiency, making it a promising technology for a variety of applications.

Keywords: PCHE, Fractal structure, Symmetric/Asymmetric airfoil rib, Heat transfer efficiency, Vortex structure