闪急沸腾条件下的乙醇气泡生长数值模拟

Numerical Simulation of Bubble Growth in Ethanol Under Flash Boiling Condition

采用能量方程和动量方程耦合求解的方法,开展了闪急沸腾条件下的乙醇气泡生长数值模拟研究.通过与过热水和三氟三氯乙烷气泡生长的实验数据对比,验证了数值模拟方法的准确性.在此基础上,通过改变环境压力和过热度,研究了不同初始状态下乙醇气泡半径、生长速度、生长加速度、不同的力、热边界层温差和厚度等参数随时间的变化规律.结果表明,乙醇气泡生长过程中表现出的生长特性是抑制生长的表面张力、黏性力、流动阻力和促进生长的气泡内外压差及热反馈效应相互竞争的结果.雅各比数Ja对不同阶段的气泡生长特性有较大影响,随雅各比数增大,乙醇气泡生长过渡阶段由热传递控制逐渐转变为惯性力控制;环境压力一定时,雅各比数越大,乙醇气泡在表面张力控制阶段的生长延迟时间越短,最大加速度越大,在热传递控制阶段的生长速度也越快.

A method for solving bubble growth equation by coupling energy equation and momentum equation was adopted to investigate the bubble growth process in ethanol under flash boiling condition. The accuracy of numerical model was verified by comparing the predictions with the experimental data of bubble growth in superheated water and trichlorotrifluoroethane. By investigating the effect of ambient pressure and degree of superheat on bubble radius, speed, acceleration, various forces, temperature difference and thickness of thermal boundary layer, the evolution of bubble in ethanol was revealed. The results show that different bubble growth characteristics of ethanol are due to the competition between surface tension, viscous force, and fluid dynamic resistance, which inhibit the growth of bubble and pressure difference, thermal feedback effects, which promote the growth of bubble. Jacob number （Ja）has great influence on bubble growth characteristics in different stages. In the transition stage, the etha- nol bubble growth gradually transforms from the heat transfer dominated regime to the inertial force dominated regime with increased Jacob number. At constant pressure, the bubble growth delay decreases and the maximum acceleration increases with the increase of Jacob number in surface tension dominated regime, and bubble growth velocity in- creases with increased Jacob number in heat transfer dominated regime.