Fundamental Limits of the Dew-Harvesting Technology

TL;DR

This paper establishes the fundamental performance limits of dew-harvesting technology, demonstrating how spectral atmospheric transmittance and selective emitters can significantly enhance water collection in arid conditions.

Contribution

It introduces the theoretical upper bounds of dew-harvesting efficiency considering atmospheric transmittance and proposes a multilayer selective emitter design to operate effectively in dry environments.

Findings

Maximum dew flux of 13 g/m²/hr at 20°C and 40% humidity with an ideal emitter.

Blackbody emitters are insufficient for arid conditions, but selective emitters can overcome this limitation.

Spectral transmittance and emitter design critically influence dew-harvesting performance.

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 a 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 the spectral directional atmospheric transmittance in a wide range of parameters such as the ambient temperature, the relative humidity, and the convection coefficient. 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 gram per square metre per hour even at ambient temperature of 20 degrees Celsius with relative humidity of 40%, whereas the black emitter cannot operate. We provide a numerical design of such a selective emitter, consisting of six layers, optimized for dew-harvesting purposes.