空气冷凝影响下的超临界氢传热特性

Heat Transfer Characteristics of Supercritical Hydrogen Affected by Air Condensation

摘要:

采用数值模拟方法，利用Fluent软件和用户自定义函数（UDF）对内外流体及管壁的耦合二维传热过程建模并仿真。以理论计算得到的出口温度和传热系数结果作为参考，通过计算流体力学仿真计算方法，探究在管外存在空气液化现象的场景下，超临界氢在不同入口状态及不同外界空气域时的传热特性。结果显示，在空气液化现象为主导的液氢温度段（50~70 K），外界空气温度对整体传热效果的影响可忽略不计，即使空气流速达到8 m·s^-1时，对总换热系数的提升也仅为20%；采用强制对流提高空气流速，改变环境温度和入口端流量，都不能显著提升该温度段的总传热系数，该温度段的总传热系数主要受蒸汽液化传热系数的影响，即低温流体温度的影响占主导。

Abstract:

A numerical simulation method with ANSYS Fluent software and user-defined function （UDF） was employed to model and simulate the coupled two-dimensional heat transfer process involving internal/external fluids and the pipe wall. Taking theoretically calculated outlet temperatures and heat transfer coefficients as benchmarks， through the computational fluid dynamics （CFD） investigation， the heat transfer characteristics of supercritical hydrogen in different inlet states and surrounding air domains were explored under the condition of external air liquefaction. It is shown that within the liquid hydrogen temperature range dominated by the air liquefaction （50 to 70 K），the temperature of the external air has a negligible impact on the overall heat transfer effectiveness. Even when the air velocity reaches 8 m·s^-1， the enhancement in the overall heat transfer coefficient is only approximately 20%. Neither forcing convection to increase air velocity， altering the ambient temperature， nor modifying the inlet mass flow rate can significantly improve the overall heat transfer coefficient within the temperature range. Instead， the coefficient is predominantly governed by the heat transfer coefficient associated with air liquefaction， meaning that the temperature of the cryogenic fluid is the dominant influencing factor.