热力学超临界流体换热计算与分析

超临界流体技术是新兴的化工技术之一 ,换热是其工程应用研究的重要方向。该文以水作为超临界流体的代表 ,以逆流操作的套管式换热器为对象建立简化的物理模型 ,再通过微元热量平衡分析 ,建立数学模型 ,并用数值方法求解。文中研究了 2 5MPa、 30MPa和 35MPa ,及 2 5— 6 0 0℃范围内冷热流体的温度、总传热系数和热流密度沿管长的变化 ,结果显示了在近临界区由于物性变化剧烈 ,使占整个管长的 1/ 3— 1/ 2的区段换热效率变低的独特规律。压力升高有利于换热的进行 ,并讨论了管径的影响。

Heat Transfer Calculation and Analysis for Thermodynamic Supercritical Fluids

Supercritical fluid process is one of newly-developed chemical technologies. Heat transfer is very important in its industrial application. Water is chosen as the supercritical fluid. A simplified physical model is established based on countercurrent double-pipe heat exchanger, and a mathematical model is also made via the analysis of infinitesimal heat balance, which is then solved using the numerical method. The research is given to the changes of cold and thermal fluids temperature, overall heat-transfer coefficient and heat flux density along the pipes at 25MPa, 30MPa and 35MPa, 25-600℃. The result shows that the efficiency of sector heat exchange occupying l /3-l /2 of the whole pipe is getting lower due to severe changes of physical characteristics at near-critical region. Higher pressure is favorable to heat exchange. The influence of pipe diameter is also discussed.