含不凝气体的蒸汽凝结换热数值研究

Numerical Study of Condensation Heat Transfer of Steam with Non-condensable Gas

为研究水下半闭式循环动力系统中高压换热器的性能,建立适用于高压下含大比例不凝气体的蒸汽凝结过程的数值模型,并考虑重力对水平套管式换热器的燃气流道进行多工况仿真计算与试验验证。研究结果表明:由于重力的存在,管道顶部和底部的液膜厚度不均匀,同时管内气相工质会产生二次旋流,两种作用将导致管内换热的不均匀特性;管径的减小将使管内工质流速增加,增大雷诺数的同时也使底部液膜变薄,有助于增强换热;流速增加削弱了重力的影响,使管道顶部和底部换热强度的差距变小;在所设工况下,即使考虑总换热面积的缩减,减小管径仍有助于总换热功率的提升;试验与仿真的管内温度最大误差为19.5%。所得成果可为水下半闭式循环动力系统高压换热器的设计提供参考。

In order to study the performance of a high-pressure heat exchanger in an underwater semi-closed cycle power system,we establish a numerical model to analyze the condensation process of steam containing a significant proportion of non-condensable gas under high pressure.The model is verified through a specific experiment,and we conduct simulations of the gas flow channel in the heat exchanger under different working conditions,taking gravity into consideration.The results show that due to the gravity,the liquid film thicknesses at the top and bottom of the pipe are not uniform,resulting in swirling flow within the gas phase.These two effects lead to uneven heat transfer characteristics in the pipe.Additionally,the flow velocity increases with the decreasing pipe diameter,causing a rise in the Reynolds number and a thinning of the bottom liquid film.This contributes to heat transfer.The increased flow velocity also reduces the effect of gravity,reducing the disparity in heat transfer intensity between the top and bottom sections of the pipe.Under the working conditions in this paper,even with a reduced total heat transfer area,reducing the pipe diameter remains conducive to the improvement of the total heat transfer power.The maximum temperature error between the experimental and simulated results is 19.5%.The conclusions contribute to the design of high-pressure heat exchangers in underwater semi-closed cycle power systems.