Abstract:

The phenomenon of heat transfer deterioration occurs during the heat transfer process of supercritical carbon dioxide (SCO₂) flow, and there is still significant controversy in the field about the mechanism. Based on the four different types of heat transfer deterioration mechanisms proposed, numerical simulation research is conducted to analyze the flow and heat transfer process of a vertical upward tube with an inner diameter of 5 mm under different operating conditions, and to explore the heat transfer deterioration mechanism from a microscopic perspective. The research results indicate that the heat transfer deterioration of SCO₂ is mainly caused by the buoyancy effect caused by density changes. When the influence of gravity is ignored, the heat transfer deterioration disappears. The buoyancy effect reduces the generation of turbulent kinetic energy (laminarization) by changing the turbulent flow structure of the internal flow field, and the weakening of turbulent thermal diffusion reduces the heat transfer efficiency, leading to the deterioration of heat transfer. The research results have certain guiding significance for the theoretical research and prediction correlation of heat transfer deterioration in supercritical carbon dioxide_.

Key words: supercritical carbon dioxide, numerical simulation, heat transfer deterioration, buoyancy, heat transfer

摘要：

超临界二氧化碳（SCO₂）流动传热过程中会发生传热恶化现象，领域内对该现象产生的机理仍存在较大争议。针对现有提出的四类不同的传热恶化机理，通过数值模拟研究，分析在不同工况下内径为5 mm的垂直上升管流动传热过程，从微观层面探究传热恶化机理。研究结果表明，四类机理观点中浮升力效应能更好地解释传热恶化现象，其他三类均具有一定的局限性。SCO₂传热恶化现象主要由密度变化引起的浮升力效应导致，当前工况下忽略重力影响时，传热恶化消失。浮升力效应通过改变内部流场的湍流结构，降低了湍动能的产生（层流化），湍流热扩散作用削弱使得传热效率下降，导致了传热恶化现象。研究结果对于SCO₂传热恶化的理论研究和预测关联式具有一定的指导意义。

关键词: 超临界二氧化碳, 数值模拟, 传热恶化, 浮升力, 传热