Influence Factors of the Evaporation Rate of a Solar Steam Generation System: a Numerical Study

TL;DR

This study uses a numerical model to analyze how factors like porosity, thermal conductivity, air velocity, and humidity affect the evaporation rate in a bi-layer solar steam generation system, providing insights for optimization.

Contribution

It establishes a two-dimensional mathematical model and identifies optimal porosity and influential factors for improved solar steam generation efficiency.

Findings

Optimal second-layer porosity is about 0.45.

Air velocity significantly enhances evaporation rate.

Higher humidity reduces evaporation rate linearly.

Abstract

Many efforts have been dedicated to improve the solar steam generation by using a bi-layer structure. In this paper, a two-dimensional mathematical model describing the water evaporation in a bi-layer structure is firstly established and then the finite element method is used to simulate the effects of different influence factors on the evaporation rate. Results turn out that: besides the high solar energy absorptivity of the first-layer, an optimum porosity of the second-layer porous material should be applied and the optimum porosity is about 0.45 in this work. This optimum porosity is determined by the balance between the positive effect of the lowering effective thermal conductivity of the second layer and the negative effect of the reduced vapor diffusivity in the second layer when the porosity is decreased. The influence of the thermal conductivity of the second-layer porous material is negligible because the effective thermal conductivity of the second layer is determined by the porosity while a larger porosity means more water in the second layer. The ambient air velocity could greatly enhance the evaporation rate, and the evaporation rate will decrease linearly with the increase of the air relative humidity. This study is expected to supply some information for developing a more effective bi-layer solar steam generation system.