Seawater desalination is a promising solution to global water shortage. Commercially available desalination technologies typically require large installations which can be impractical for developing regions without well-developed infrastructure. Passive solar desalination promises a viable solution, but can suffer from low efficiencies. Recent advances in the thermal design of small-scale solar desalination systems have demonstrated the potential for high-efficiency solar desalination in portable systems. In particular, the concept of a thermally-localized multistage solar still (TMSS) – which combines localized heating of a capillary flow with condensation heat recycling – has been experimentally demonstrated very recently and achieved over 100% solar-thermal cumulative efficiency. However, a fundamental understanding of the heat and mass transfer, efficiency limits and optimization strategies are missing in the literature. This work presents a modeling framework that evaluates the thermal and vapor transport in a model TMSS system with varying device configuration and predicts its solar desalination efficiency. We demonstrate that an ultrahigh solar-thermal cumulative efficiency, many times higher than that of conventional solar stills, can be achieved by optimizing the number of stages and device geometry. Specifically, our modeling shows that the efficiency of the capillary fed TMSS is limited by the dissipation of thermal energy to the environment during condensation and significant gains in efficiency can be achieved by minimizing this loss. This work provides insights into physical processes critical for thermally-localized portable solar distillation which could lead to high-performance desalination or water purification technologies.

海水淡化是解决全球缺水的有希望的解决方案。市售的淡化技术通常需要大型安装，这对于没有发达基础设施的发展中地区来说是不切实际的。被动式太阳能淡化有望提供可行的解决方案，但效率低下。小型太阳能脱盐系统的热设计方面的最新进展表明了便携式系统中高效太阳能脱盐的潜力。特别是，最近通过实验证明了热局部多级太阳能蒸馏器（TMSS）的概念，该概念结合了毛细管流的局部加热和冷凝热循环，并实现了超过100％的太阳热累积效率。然而，文献中缺少对传热和传质，效率极限和优化策略的基本了解。这项工作提出了一个建模框架，该模型可以评估具有不同设备配置的TMSS模型系统中的热和蒸汽传输，并预测其太阳能脱盐效率。我们证明，通过优化级数和设备几何形状，可以实现超高的太阳热累积效率，这是传统太阳能蒸馏器的许多倍。具体而言，我们的模型表明，在冷凝过程中，毛细管供料的TMSS的效率受到热能向环境的耗散的限制，并且可以通过最大程度地减少这种损失来实现效率的显着提高。