壁面结构参数对液膜厚度分布及其波动特性的影响

Effect of Wall Structure Parameters on Liquid Film Thickness Distribution and Its Fluctuation Characteristics

受热应力分布不均的影响,降液管壁面会产生变形,其对湍流降膜的影响十分显著。利用超声波多普勒测速仪和高速摄像机研究了高雷诺数下(Rel≈1.72×104)波纹板结构参数(振幅和波长)对液膜厚度分布及其波动特性的影响。研究结果表明:波纹板上的平均液膜厚度随轴向距离的增加呈“波动减小”的趋势。波谷至波峰处的“加速”作用促进了液膜波动的增强,而波峰至波谷处的“减速”作用则使液膜波动减弱。波纹板波长的减小会导致共振效应的产生。液膜波动的加剧促进了液膜瞬时厚度概率密度函数趋于正态分布,并导致液膜因Plateau–Rayleigh不稳定性而产生拉丝破裂。修正后的平均液膜厚度预测模型可以很好地估算不同波纹壁面下的平均液膜厚度,相对误差在±15%以内。

Influenced by the uneven distribution of thermal stress,the downcomer’s wall can be deformed,and its effect on the turbulent falling film is very significant.The effect of corrugated plate structural parameters(amplitude and wavelength)on the distribution of liquid film thickness and its fluctuation characteristics are investigated at a high Reynolds number(Rel≈1.72×104)by ultrasonic doppler velocimetry and a high-speed camera.The results show that the mean thickness of the liquid film on the corrugated plate tends to"fluctuation and decrease"with the increase of the axial distance.The"acceleration"effect from the trough to the crest enhances the fluctuation of liquid film,while the"deceleration"effect from the crest to the trough weakens the fluctuation of liquid film.The decrease of the wavelength leads to the resonance effect.The intensification of the liquid film fluctuation promotes the normal distribution of the probability density function of the instantaneous liquid film thickness,and leads to the wire drawing rupture of the liquid film due to Plateau-Rayleigh instability.The modified mean liquid film thickness prediction model can well estimate the mean liquid film thickness under different corrugated walls with a relative error within±15%.