Using a Porous Medium Model to Simulate the Air Flow Through Fog Water Collectors

Abstract

Harvesting water from coastal fog is a promising alternative for regions of water scarcity. The fog water collector (FWC) is a mesh screen usually installed perpendicular to the main wind direction, intercepting the air flow and extracting some of the water droplets contained in it. In order to maximise the water output, many FWC have to be located in an optimised manner. For optimising the layout, computational simulations that consume significant computational resources are necessary. The aim of the present study is to develop a computationally cheap methodology of simulating flow through FWCs. For this, a porous medium model was validated in order to adequately represent the aerodynamics of FWC at open flow conditions. Computational simulations of airflow were carried out through a mesh screen and through a porous medium at confined flow. The pressure drop coefficients of both simulations at confined flow were compared to experimental data, yielding differences of 2,8% for the mesh screen simulation and 7,2% for the porous medium simulation. The results were then extrapolated to air flow through a mesh screen at open flow conditions. It was shown that outside the wake the difference between full simulations and the porous medium approach does not exceed 5%, while the mass flow rate error within the wake is close to 9%. This indicates that the model of porous medium is a valid methodology to simulate the flow through a FWC for both, confined and open flow conditions at a significantly smaller computational cost.