Numerical Studies on Local Heat Transfer Characteristics of Printed Circuit Heat Exchanger for Supercritical CO₂ Power Cycle

The supercritical carbon dioxide (S-CO₂) Brayton cycle is a promising candidate for the power conversion system in VHTR (Very High Temperature Reactor). The compact heat exchanger, PCHE (printed circuit heat exchanger) has become one of the alternatives for the heat exchangers in the S-CO₂ Brayton cycle. In this study, the numerical model of the flow and heat transfer to supercritical CO₂ in a 3D PCHE model units of straight channels with hydraulic diameter of 1.222mm are established using CFD approach. The numerical model is firstly verified by comparison with previous researches. The local heat transfer performances of PCHE are analyzed and discussed based on the numerical results. The local Nusselt numbers along the channel are obtained using the local thermophysical properties of S-CO₂, the local bulk average temperature of S-CO₂ and the local heat flux in each micro unit. The effects of the thermophysical property variations of the S-CO₂ on the flow and heat transfer are discussed. The numerical results are compared with local Nusselt numbers predicted using several previous correlations, such as the Dittus-Boelter correlation, Gnielinski correlation, Baskov correlation and Jackson correlation. The results provide useful information for the design and optimization of PCHE taking the local heat transfer characteristics into account. (author)