Mechanisms and Scale-up Potential of 3D Solar Interfacial-Evaporators

TL;DR

This paper models 3D solar interfacial evaporators, revealing how their design and environmental factors influence their ability to surpass the solar-thermal limit, and discusses their scalability and limitations.

Contribution

It provides a physics-based model explaining the transition from 2D to 3D evaporation and analyzes the scalability of large-scale 3D evaporator arrays.

Findings

3D evaporators can exceed the solar-thermal limit by environmental heat absorption.

Scalability of 3D evaporators is limited in closed environments.

Design choices in previous works may hinder performance.

Abstract

Evaporation rates from porous evaporators under sunlight have been reported to exceed the solar-thermal limit, determined by relating the incoming solar energy to the latent and sensible heat of water, for applications in desalination and brine pond drying. Although flat two-dimensional (2D) evaporators exceeding the solar limit implies a non-thermal process, tall three-dimensional (3D) solar evaporators can exceed it by absorbing additional environmental heat into its cold sidewalls. Through modeling, we explain the physics and identify the critical heights in which a fin transitions from 2D to 3D evaporation and exceeds the solar-thermal limit. Our analyses illustrate that environmental heat absorption in 3D evaporators is determined by the ambient relative humidity and the airflow velocity. The model is then coarse-grained into a large-scale fin array device on the meters scale to analyze their scalability. We identify that these devices are unlikely to scale favorably in closed environment settings such as solar stills. Our modeling clearly illustrates the benefits and limitations of 3D evaporating arrays and pinpoints design choices in previous works that hinder the device's overall performance. This work illustrates the importance in distinguishing 2D from 3D evaporation for mechanisms underlying interfacial evaporation exceeding the solar-thermal limit.