超临界状态下流体状态介于液态和气态之间,其扩散性更接近气体,密度依然为液体量级,这种特殊的性质导致超临界压力下流体流动换热特性与亚临界压力下有很大不同.本文以超临界压力条件下水、二氧化碳和碳氢燃料为研究对象,综合分析了超临界流体在管内的换热规律,系统总结了浮升力、热流密度、质量流速、压力、进口温度、流道形状等因素对流动换热特性的影响.其中,浮升力、热流密度和质量流速影响作用较大,在较高热流密度条件下,浮升力会导致传热恶化发生;在较低热流密度下,流体临界点附近会发生传热强化;质量流速增加能够使管内换热效果显著增强.传热强化和传热恶化现象的发生与临界点附近流体物性的剧烈变化密切相关.

The fluid state in supercritical conditions is between liquid and gas. Its diffusivity is close to gas while the density level is equal to liquid. Such special characteristics lead to a different pattern in heat transfer under supercritical pressure conditions compared to subcritical pressure situations. According to the heat transfer properties of water, carbon dioxide as well as carbon and hydrogen fuels under supercritical conditions, this paper gives an analysis on supercritical fluid heat transfer characteristics, and summaries the influences of the physical factors (buoyancy, heat flow density, mass flow, pressure and inlet temperature) on fluid heat transfer properties, in which the buoyancy, heat flow density and mass flow are dominant factors. This paper also makes a comprehensive analysis of supercritical fluid heat transfer patterns inside the tube. The enhancement and deterioration of heat transfer is closely concerned with the changes of supercritical fluid physical properties.