内螺纹管流动沸腾气泡行为及换热特性研究

为探究内螺纹管流动沸腾过程中的气泡行为及其对换热的影响机理,采用VOF模型(Volume of Fluid Model)及相变模型对工质在小尺寸水平内螺纹管中的流动沸腾过程进行二维非稳态数值模拟。获得了不同质量流速下工质在管道内的气相分布以及管壁不同位置处的温度、换热系数。分析了内螺纹管流动沸腾过程中的气泡行为特点以及不同气泡行为对换热性能的影响。研究表明:在内螺纹管中随着质量流速的增加,管内含气率降低,平均换热系数增大。管壁面上气泡的滑移、长大行为会削弱对流换热,而近壁面气泡的聚并行为会增强对流换热。

Research on bubble behavior and heat transfer characteristics of flow boiling in rifled tubes

In order to investigate the bubble behavior and how it influences heat transfer in the flow boiling process of the rifled tube, the two-dimensional unsteady numerical simulation of the flow boiling process of the working medium in the small-size horizontal rifled tube was carried out by the VOF model and the phase-change model. The gas phase distribution of working medium in the tube at different mass velocities, temperature and heat transfer coefficient at different locations of tube was obtained. The features of bubble behavior in the flow boiling process inside the rifled tube and the influences of different bubble behaviors on the heat-exchange performance were analyzed. The study shows that, with the increase of mass velocity inside the rifled tube, the gas fraction inside the tube decreases and the average heat transfer coefficient increases. The heat convection is weakened because of the sliding and growing of the bubbles on the surface of the tube wall, while it is enhanced by the bubble coalescence.