Comparative Study on Thermos-Hydraulic Performance of Different Cross Section Shapes of Microchannels with Supercritical CO2 Fluid

Yi Tu,Yu Zeng,Yuanyuan Duan

doi:10.1155/2021/5525235

Abstract

The influence of the cross section shape of microchannels on the thermos-hydraulic performance of the supercritical CO2 fluid is an important issue in the design of industrial compact heat exchangers, but few studies have been conducted about this issue. In this paper, comparative studies of the flow and heat transfer performance of SCO2 fluid in horizontal microchannels with circular, semicircular, rectangle, and trapezoidal cross sections were conducted numerically. The comparison is based on the same hydraulic diameter and length for all channel types and is carried out under the same mass flux, outlet pressure, and wall heat flux. The fluid bulk temperature in this analysis ranges from 285 K to 375 K, which covers the pseudocritical point of SCO2. The results show that the circular channel has the highest average heat convection coefficient, while the trapezoidal channel has the worst convective heat transfer performance under the same hydraulic diameter and boundary conditions. The results also indicate that the effect of cross section shape on the heat convection coefficient is significantly greater than that on the channel pressure drop, and the existence of the corner region in the cross section, especially the acute angle, will weaken the heat transfer performance.

Highlights

High-efficiency and compact printed circuit heat exchangers (PCHEs) use the same technique as for manufacturing printed circuit boards in the electronics industry
It has many favorable characteristics when it is in supercritical state, such as high density, low viscosity, and high thermal conductivity, as shown in Figure 1, which makes supercritical CO2 (SCO2) become the most important candidate working medium in the future compact energy systems [3,4,5]. e application of PCHE has attracted the attention of many design engineers and research laboratories involved in power conversion cycle studies, especially in SCO2 Brayton cycle development [6], and one of the most concerned factors for designers is the flow and heat transfer performance of SCO2 fluid in different types of channels of PCHE
E maximum heat convection coefficient does not occur at the critical point, especially for cooling conditions as Figure 6 shows. is is mainly due to the thermosphysical properties of the fluids near the wall, which are determined by the local wall temperature, Tw, which significantly affect the heat transfer in addition to the bulk fluid thermosphysical properties determined by Tb

Summary

Introduction

High-efficiency and compact printed circuit heat exchangers (PCHEs) use the same technique as for manufacturing printed circuit boards in the electronics industry. E predicted heat convection coefficients were calculated at Qw −12 kW/m2, G 200 kg/m2−s, and P 8 MPa for various bulk temperatures using three sets of meshes, 162981 cells, 396408 cells, and 566979 cells, with the rectangle cross section channel type to check mesh independency.

Results

Conclusion