Simulation based optimizing of fog mesh structures for enhanced fog collection

Sammanfattning: Water scarcity has been an increasing problem in many places around the world. According to the World Resources Institute, in 2019 nearly 2.6 billion people which takes a third of the world's population live in the area with 'high water scarcity', with 1.7 billion people in 17 countries living under 'extreme water scarcity'. Fog collection is thought to be a promising technology as an alternative source of freshwater and has been studied by many researchers. Aerodynamic efficiency happens to be the limiting parameter for fog collection efficiency which has the maximum value of 17% with the harp like fog mesh. In this thesis, aerodynamic behaviour of a multi-layer fog collectors system has been studied with numerical simulation based on two models, the first one is the turbulent SST model in COMSOL Multiphysics while the other one is a LES model with Euler-Lagrangian approach via OpenFOAM. Herein, first, we illustrate the influence of geometry parameter such as mesh characteristics on aerodynamic efficiency of single layer mesh, which is validated with the theoretical prediction of a model developed by Koo et al. in 1973. In the further step, the multi-layer fog mesh system is studied by changing layer distance and number of layers to improve the aerodynamic efficiency. The simulation results show that multi-layer mesh perform better in low shade coefficient and high free stream velocity conditions. The optimal layer distance varies from two to five millimetres with respect to number of layers, as in this range the flow neither bypass the mesh too much due to the tiny distance nor diffuse and lose velocity in the layers’ gap because of the large distance. Maximum increment of aerodynamic efficiency are about 12% between multi-layer and single layer mesh.