水膜闪蒸真空制冰的换热特性

Heat transfer characteristics of water film flash evaporation in vacuum ice making

引言当一定温度的液体突然暴露在低于其饱和压力的环境下时,液体由最初的平衡状态变成过热状态,液体中的过热量已经不能以显热的方式来包含能量,不能继续存在于液体中,会迅速转换为蒸发潜热,形成汽泡,同时液体温度迅速下降,这个过程被称为液体的闪蒸。由于闪蒸现象伴随着大量的水蒸气生成和剧烈的温度下降,在现代工业中。

A water film flash evaporation vacuum ice-making system is developed.The experiment was carried out to investigate the influence of flash evaporation pressure,thickness and initial temperature of water film on the flash evaporation process.The thickness of the water film was 15,35,55 and 75 mm.Initial temperature of water film ranged from 2℃ to 10℃,and flash evaporation pressure varied from 100 Pa to 600 Pa.The characteristics of the flash evaporation process were recorded using a CCD camera of the visualization system.The experimental results show that under the operating conditions,lower flash evaporation pressure leads to faster change of water film temperature at constant initial temperature of water film.Higher initial temperature of water film makes the water film temperature varies more quickly at constant pressure.As water film thickness increases,the decrease rate of water film temperature reduces.Based on the experimental results,a correlation for water film temperature with flash evaporation pressure,thickness and initial temperature of water film is presented with the maximum error of 24.19%.