水雾/蒸汽相变冲击冷却的数值模拟

利用ANSYS-CFX软件对T.Wang等人实验研究的水雾/蒸汽相变冲击冷却系统进行了数值模拟.并与蒸汽单相冲击冷却数值计算结果进行比较,数值研究水雾对冷却的强化作用.相变计算过程中,蒸汽作为连续相,直径为5 μm的水滴作为离散相;水滴在接近高温壁面过程中吸收汽化潜热,发生相变,变为水蒸气,以此达到强化冷却的作用.数值分析结果与实验数据比较接近,壁面加热热流为3 000 W/m2,加入4%浓度水滴的结果表明,由于水雾的作用在滞止点附近热传导系数比蒸汽单项冷却提高130%左右,在远离滞止点区域冷却效果减弱,在距离滞止区6倍喷射宽度时,冷却效果减少到可以忽略的水平;水滴的汽化吸收的热量对于冷却作用的贡献比较大.

Numerically simulating mist/steam impingement cooling with phase change

Numerical simulations were carried out on T. Wang's phase change mist/steam impingement cooling system and the results compared with those from cooling with steam impingement alone. The analysis focused on enhancements to cooling caused by liquid water mist in the steam. The Navier-Stokes (N-S) solver used was ANSYS-CFX. When simulating phase change, steam was regarded as a continuous fluid. Drops of mist were about 5 μm in a dispersed phase. When drops approached the high-temperature boundary, drops vaporized as they absorbed latent heat and turned into steam (H_2O). This mechanism enhanced heat transfer. Our numerical results were similar to those found in physical tests. Injection of 4% mist at the high-temperature boundary, with 3000 W/m~2 of heat flux, showed the mist increased the heat transfer coefficient at the stagnation point 130% more than single phase steam impingement. The cooling effect weakened as distance increased from the stagnation point and was negligible at a distance 6 times the jet width. Heat absorbed by drops of vapor contributes significantly to cooling.