Abstract:

Relatively low productivity is a common problem for conventional tubular solar stills when running at atmospheric pressure. An improved tubular solar still is proposed to enhance the productivity, which can operate under conditions of vacuum pressure and feeding water continuously. An experimental prototype is tested under both constant heating temperature and constant heating power conditions. Its productivity and systematic temperature under vacuum condition is obtained, proving that it has better performance than a common distillation method running at atmospheric pressure. At operating pressure 40 kPa and fixed heat power of 200 W, the temperature difference between distilling water and condensation shell decreases 40%, and the daily accumulated freshwater yield increases 22.5%, with a value of 1.9 kg. An modified correlation to calculate the mass transfer inside the cavity under vacuum condition is obtained against the experimental data in steady state, based on that a model is built to predict the freshwater yield of the tubular solar still under vacuum condition. The model has deviations for present prototype of about 2.1% for daily accumulated productivity, and 4% for maximum freshwater yield rate.

Key words: solar energy, distillation, heat transfer, mass transfer, vacuum, negative pressure

摘要：

针对目前管式太阳能蒸馏装置在常压运行时产水率较低的问题，提出了一种可在真空负压条件下连续补水运行的管式蒸馏方法，并在定温及定功率加热条件下，测试了实验样机负压运行时的温度及产水率变化，证明了所提出的负压条件下运行的管式蒸馏方法优于常压运行的一般蒸馏方法。在P_T=40 kPa、Q_h=200 W定功率加热实验中，空腔传热温差比常压运行时降低约40%；装置全天累计产水量为1.9 kg，比常压运行时产水量增加22.5%。基于稳态实验数据得到了负压修正的空腔传质计算关系式，在此基础上构建了管式蒸馏装置在负压条件运行时的产水率预测模型，其对实验样机全天累计产水预测误差和最大产水率误差分别为2.1%和4%。

关键词: 太阳能, 蒸馏, 传热, 传质, 真空, 负压