浓盐水低压沸腾传热特性的实验研究

在现代社会中,低温多效蒸发是一种有效的海水淡化方法。在低温多效蒸发海水淡化过程中,操作压力和浓缩海水中NaCl浓度是影响传热效率的重要因素。为了系统地研究操作压力和浓度对于盐水沸腾传热特性的影响,在不同的操作压力下,测定了质量分数为0%～25%的NaCl溶液在光滑的不锈钢管外的沸腾传热特性。实验结果表明,在常压下,NaCl的浓度对沸腾传热的影响不大;在低压条件下,随着NaCl浓度的增加,沸腾传热系数增大。纯水和3.5%盐水的传热系数随系统压力的升高而增大;盐水浓度为7%和15%时,沸腾传热系数随系统压力的升高先降低后又升高;NaCl的浓度达到25%时,传热系数随压力的升高而减小。这说明操作压力和浓度二者之间存在着相互制约的关系。

Boiling Heat Transfer of Concentrated Brine at Low Pressure

In the modern society,low temperature multiple-effects evaporation(LTMEE) is one of the most valid methods for desalination.In the LTMEE process,the operation pressure and NaCl concentration are the two of the most important factors affecting the heat transfer efficiency of the system.In the present work,us-ing a smooth horizontal stainless heating tube,the boiling heat transfer experiments of NaCl solutions with concentrations of 0%～25% at different pressures were conducted to systematically investigate the effects of the system pressure and the brine concentration on the boiling heat transfer characteristics.It was found that,at atmospheric pressure,the NaCl concentration affects the boiling heat transfer not obviously,and the effi-ciency of boiling heat transfer increases with the increase of NaCl concentration at the pressure lower than atmosphere.The boiling heat transfer performances of the pure water and 3.5% brine increase with the in-crease of system pressure;however,for the brines with concentrations of 7% and 15%,the boiling heat trans-fer performances decrease at first and then increase with the increase of the system pressure.When the con-centration of the NaCl reaches 25%,the boiling heat transfer performance decrease with the increase of the system pressure.The results show that there is a relationship existing between the system pressure and the brine concentration.