超临界CO2水平细微管内层流流动与换热的数值模拟

对超临界CO2在水平细微管内层流流动与换热进行了数值模拟.给出了冷却和加热条件下,细微管(d＜1.0 mm)内有代表性的速度、温度剖面,以及Nusselt数随流体温度的变化.研究表明超临界CO2在水平细微管内层流流动时,由于流体热物性随温度剧烈变化,浮升力的影响非常显著,加强了管内换热;且由于流体强变物性特点,只要流体和壁面存在温差,速度及无量纲温度分布就不断变化,充分发展流不可能达到.研究结果对超临界CO2高效紧凑式换热器的设计与优化有重要的意义.

Numerical solution of mixed convective heat transfer of supercritical carbon dioxide in horizontal mini tubes

Investigation of laminar flow and convective heat transfer of supercritical carbon dioxide in horizontal miniature tubes was carried out numerically. The flow patterns and isotherms in typical cross sections with tube diameters less than 1.0 mm under both cooling and heating conditions with and/or without gravity were presented. The variations of Nusselt numbers with bulk temperature were also obtained. The results indicate that the buoyancy effects are significant for all cases considered due to the sharply varied physical properties of the fluid. The velocities and nondimensional temperatures keep changing and fully developed flows can never be reached unless the fluid and tube wall are under thermal equilibrium condition. The results of this work are of significance for the design of high efficiency compact heat exchangers of supercritical carbon dioxide.