A study on a new maritime lifesaving multiple-effect solar still

所提出的海上救生太阳能蒸馏器的结构与向下加热的多效扩散式太阳能蒸馏器几乎相同，由透明的覆盖膜和许多水平平行的隔板组成，隔板之间有狭窄的气隙，隔板与盐水浸泡的灯芯接触。第一个隔板或最上面的隔板吸收太阳能，使第一个隔板下面的灯芯中的海水蒸发。水蒸气通过隔板之间的潮湿空气层扩散，并在第二个隔板上凝结，在那里凝结的潜热被回收，用于从第二个隔板的灯芯进一步蒸发。这样的蒸发和冷凝过程在所有分区重复，以大大增加馏出物的总产量。我们从理论上考察了该蒸馏器的性能，发现在太阳辐射为22 MJ/m^2d的晴天，该蒸馏器估计可产生约15 kg/m^2d的淡水，并且该淡水产量足够大，超过了SOLAS规定的最低标准。在室内和室外进行了单效无覆盖膜的实验，结果表明：(1)用天然胶贴合盐浸灯芯的隔断比用天然胶贴合氨基甲酸乙酯膜的隔断生产效率高28%。(2)当蒸发面与冷凝面之间的扩散间隙为5 mm时，生产效率比扩散间隙为7 mm时提高83%。(3)盐沉积面积约占总蒸发面积的4%。(4)晴天时，单效无保护膜产生的淡水量约为2.8 kg/m^2d，满足SOLAS规定的最低要求。

The proposed maritime lifesaving solar still has almost same structure with a downward-heating multiple-effect diffusion-type solar still, and consists of a transparent cover film and a number of horizontal parallel partitions in contact with saline-soaked wicks with narrow air gaps between partitions. The first partition, or uppermost partition, absorbs solar energy to cause evaporation from seawater in the wick on underside of the first partition. The water vapor diffuses through a humid air layer between partitions and condenses on the second partition where latent heat of condensation is recovered to be used further evaporation from the wick of the second partition. Such evaporation and condensation process repeats on all partitions to greatly increase overall production of distillate.We theoretically investigated the performance of the proposed still, and found that the proposed still is estimated to produce about 15 kg/m^2d of fresh water on a sunny day of 22 MJ/m^2d of solar radiation, and such amount of fresh water production is large enough, exceeding the minimum standard set by SOLAS.We also performed indoor-and outdoor-experiments using a single effect still without cover film, which may be easily applied for practical use, and the results of the experiments are summarized as follows: (1) Productivity is 28 % larger with using the partition, on which saline-soaked wick is attached, as natural gum than urethane film. (2) Productivity is 83 % larger for the still of diffusion gap between evaporation and condensation surfaces is 5 mm than that of 7 mm. (3) Salt deposition area is about 4 % of total evaporation area. (4) Single effect still without cover film produced about 2.8 kg/m^2d at a sunny day, and this amount of fresh water meets the minimum requirements set by SOLAS.