不同加热条件下工质苯核态沸腾模拟研究

Simulation of Nucleate Boiling of Benzene under Different Heating Conditions

利用Volume of Fluid(VOF)方法结合Lee相变模型对单气泡沸腾过程进行了模拟。通过控制加热面的尺寸,在压力为1.9 MPa、接触角为30°条件下对有机工质苯单个气泡的沸腾进行计算。分析了单个气泡的生长过程、速度场随时间变化的规律以及过热度对气泡直径及脱离频率的影响。模拟结果表明:通过观察单个气泡的速度场,发现在气泡长大过程中内部会形成环流。随着气泡脱离壁面,气泡底部的液体会形成涡流,涡流在气泡上升过程中会增大。对比不同过热度下的气泡脱离直径,发现过热度对气泡的脱离直径无影响,测得气泡直径均约为2.35mm,过热度越大气泡生长脱离所需的时间越短,脱离频率越大,能有效的增强换热。

Using the Volume of Fluid(VOF) method in combination with the Lee phase transition model to simulate the boiling process of single bubble. By controlling the size of the heating surface, the boiling of single bubble of organic working substance benzene was calculated at a pressure of 1.9 MPa and a contact angle of 30°. The growth process of single bubble, the variation of velocity field with time and the influence of superheat degree on bubble diameter and detachment frequency is analyzed. The simulation results show that a circulation would form inside the bubble during its growth. As the bubble leaves the wall, the liquid at the bottom of the bubble forms vortices, which increase as the bubble rises. The bubble detachment diameter(the initial size of the bubble completely leaving the heating surface) under different superheat degree conditions was compared. It was found that the superheat degree had no effect on the bubble detachment diameter, and the measured bubble diameter was about 2.35 mm. The larger the superheat degree, the shorter the time needed for the bubble to grow and the greater the detachment frequency, which could effectively enhance the heat transfer.