ABSTRACT Dew-harvesting technology radiatively cools a condenser below the dewpoint to achieve condensation of the water vapor from the atmosphere. Due to its passive nature, this technology has attracted broad interest, in particular in the context of the worldwide drinking-water scarcity. However, the fundamental limit of its performance has not yet been clarified. Moreover, the existing applications have been limited to humid areas. Here, we point out the upper bound of the performance of this technology by carefully considering various parameters such as the ambient temperature (Tambient), the relative humidity (RH), and the convection coefficient (h). Moreover, we highlight the potential of a condenser consisting of a selective emitter, which is capable of condensing water vapor under significantly more arid conditions as compared with the use of a blackbody emitter. For example, a near-ideal emitter could achieve a dew-harvesting mass flux () of 13 gm−2hr−1 even at Tambient = 20°C with RH = 40%, under which condition the blackbody emitter cannot harvest any dew. We provide a numerical design of such a selective emitter, consisting of six layers, optimized for dew-harvesting purposes.

中文翻译：

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露水收集技术的基本限制

摘要 露水收集技术以辐射方式将冷凝器冷却到露点以下，以实现大气中水蒸气的冷凝。由于其被动性质，这项技术引起了广泛的兴趣，特别是在全球饮用水短缺的背景下。然而，其性能的根本限制尚未阐明。此外，现有的应用仅限于潮湿地区。在这里，我们通过仔细考虑环境温度 (Tambient)、相对湿度 (RH) 和对流系数 (h) 等各种参数来指出该技术的性能上限。此外，我们强调了由选择性发射器组成的电容器的潜力，与使用黑体发射器相比，它能够在更加干旱的条件下冷凝水蒸气。例如，即使在 Tambient = 20°C 和 RH = 40% 的情况下，近乎理想的发射器也可以实现 13 gm-2hr-1 的露水收集质量通量 ()，在这种情况下，黑体发射器无法收集任何露水。我们提供了这种选择性发射器的数值设计，由六层组成，针对露水收集目的进行了优化。