Computational Fluid Dynamics Study of Wire Mesh Demister of Multi Stage Flashing Chamber

  • Ashraf Hasania

Student thesis: Master's Thesis

Abstract

Potable water shortage problem is getting more serious as time passes. The drastic increase of world population, the increase in pollution of water resources and the limitation of the amounts of fresh water have led the human to look into alternative solutions to reduce the severity of the problem. Nowadays, desalination is one of the major sources of drinking water, especially in the Middle East and Gulf Co-operation Counsel (GCC) Countries. Multi-stage flashing (MSF) desalination, one of the major thermal desalination processes, is commonly used in Gulf Region. Generated vapor in MSF evaporator is entrained by the gas phase momentum toward the condenser where the product water is collected. Mist carryover droplets with vapor raise the salinity of the collected water which is unfavorable. In order to solve this issue, wire mesh mist eliminators (demisters) are widely used for the two phase separation. Wire mesh mist eliminators are placed in the vapor flow path in order to isolate water droplets from the vapor mainly by inertia. There are two main concerns usually associated with the use of wire mesh demisters: the pressure drop across the demister and the mist separation efficiency of the mesh pad. In the present research, a computational fluid dynamics (CFD) program was developed to study the pressure drop and the mist separation efficiency across the demister. The demister was simulated as porous media to predict the pressure drop and the Eularian multiphase modeling was used to predict the mist separation efficiency of the mesh. The CFD results obtained showed good agreement with the results obtained from the experimental equations found in literature. Simulating the demister as porous media gave results of -12% to 9% difference from the experimental results. Modeling the separation efficiency of the demister wires using Eularian model showed that the model is valid for droplets diameter of more than 50 μm as the separation efficiency of smaller particles diameters is zero.
Date of Award2011
Original languageAmerican English
SupervisorHassan Fath (Supervisor)

Keywords

  • Fluid Dynamics
  • Environmental Engineering.

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