Mixed temperature gradient evaporator for solar steam generation
Haoran Li, Xiaoyi Liu, Xiaojuan Niu, Boyu Li, Wenpeng Hong, Yan Li
Abstract
Solar-driven interfacial water evaporation enables us to build flexible, extensible, and decentralized evaporators with zero carbon dioxide emission. The theoretical limit of evaporation rate is not tolerable for users with large-capacity water requirements. Here, we report how a wicking solar absorber with a columnar structure can generate a counterintuitive evaporation enhancement mechanism: both positive- and negative-temperature gradients, which we term mixed temperature gradient, are generated in the wicking material. This allows a ∼3.8 times equivalent evaporation rate compared with the theoretical limit. We demonstrate that the mixed temperature gradient is a new thermal equilibrium achieved by the combined effect of solar heating and evaporative cooling. Importantly, the sidewall height should be consistent with the capillary height dominated by imbibition and diffusion. Specifically, designing a solar absorber with a balanced water supply and demand allows a higher evaporation rate in both light and darkness.