Abstract Many efforts have been dedicated to improve the solar steam generation by using a bi-layer structure. In this paper, a two-dimensional mathematical model describing the water evaporation in a bi-layer structure is firstly established and then the finite element method is used to simulate the effects of different influence factors on the evaporation rate. Results turn out that: besides the high solar energy absorptivity of the first-layer, an optimum porosity of the second-layer porous material should be applied and the optimum porosity is about 0.45 in this work. This optimum porosity is determined by the balance between the positive effect of the lowering effective thermal conductivity of the second layer and the negative effect of the reduced vapor diffusivity in the second layer when the porosity is decreased. The influence of the thermal conductivity of the second-layer porous material is negligible because the effective thermal conductivity of the second layer is determined by the porosity while a larger porosity means more water in the second layer. The ambient air velocity could greatly enhance the evaporation rate, and the evaporation rate will decrease linearly with the increase of the air relative humidity. This study is expected to supply some information for developing a more effective bi-layer solar steam generation system.

中文翻译：

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太阳能蒸汽发生系统蒸发率影响因素的数值研究

摘要 许多努力致力于通过使用双层结构来改善太阳能蒸汽的产生。本文首先建立了描述双层结构中水分蒸发的二维数学模型，然后利用有限元方法模拟了不同影响因素对蒸发速率的影响。结果表明：除了第一层具有较高的太阳能吸收率外，还应采用第二层多孔材料的最佳孔隙率，本工作中的最佳孔隙率约为0.45。该最佳孔隙率由降低第二层的有效热导率的积极影响和当孔隙率降低时第二层中蒸汽扩散率降低的消极影响之间的平衡决定。第二层多孔材料的热导率的影响可以忽略不计，因为第二层的有效热导率由孔隙率决定，而较大的孔隙率意味着第二层中的水更多。环境空气流速可以大大提高蒸发率，蒸发率会随着空气相对湿度的增加而线性下降。这项研究有望为开发更有效的双层太阳能蒸汽发电系统提供一些信息。蒸发率会随着空气相对湿度的增加而线性下降。这项研究有望为开发更有效的双层太阳能蒸汽发电系统提供一些信息。蒸发率会随着空气相对湿度的增加而线性下降。这项研究有望为开发更有效的双层太阳能蒸汽发电系统提供一些信息。