Abstract

Understanding and predictions of the local thermal-hydraulic performance of supercritical CO₂ in channels of printed circuit heat exchanger geometries are of great importance to the design and optimization of the pre-cooler and recuperators in supercritical CO₂ cycle. The local flow and heat transfer of supercritical CO₂ in horizontal semicircular zigzag channel during cooling near the critical or pseudo-critical point have been numerically investigated in this paper. The effects of thermophysical property variations, mass flux, and the channel geometrical parameters on the flow and heat transfer are discussed. It is found that the extrude angle in the zigzag channel impedes the bulk flow and generates secondary flow, which induces asymmetric flow and temperature distribution, and enhances fluid mixing and mitigates the temperature stratification. A dimensionless secondary flow velocity is adopted to evaluate the influence of secondary flow on the heat transfer, which is more enhanced for cases with relatively large mass flux and in channels with relatively large inclined angle and small pitch length, however, the pressure drop increases meanwhile. Finally, pitch-averaged local flow and heat transfer correlations have been developed based on the numerical results and mechanism analysis accounting for the thermophysical property variations and the channel geometrical parameters.

摘要

了解和预测印刷电路换热器几何结构通道中超临界 CO ₂的局部热工水力性能对于超临界 CO ₂循环中的预冷器和换热器的设计和优化具有重要意义。超临界CO ₂的局部流动和传热本文对临界或准临界点附近冷却过程中水平半圆形锯齿形通道中的温度进行了数值研究。讨论了热物理性质变化、质量通量和通道几何参数对流动和传热的影响。研究发现，锯齿形通道中的挤压角阻碍了整体流动并产生了二次流动，从而导致了不对称的流动和温度分布，增强了流体混合并减轻了温度分层。采用无量纲二次流速度评价二次流对传热的影响，对于质量流量较大的情况和倾斜角较大和节距较小的通道，这种影响更大，但同时压降增加. 最后，