Fundamental Limits of the Dew-Harvesting Technology
Minghao Dong, Zheng Zhang, Yu Shi, Xiaodong Zhao, Shanhui Fan, Zhen Chen
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 (m˙′′) 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.