Study On CFD Simulation Of Air Gap Membrane Distillation With Carbon Membrane

Being a kind of membrane separation technology, Membrane distillation (MD) is an effective way to solve the problem of serious shortage of freshwater resources. Membrane distillation has many advantages, such as low energy consumption, simple processes and devices, low requirements for the pretreatment of seawater, and being able to use the solar energy and the industrial waste heat, etc. But at present MD process is still in the stage of experiment, it has received relatively little attention in the desalination industries. The reasons are the lower heat-utilization rate and the smaller permeation flux. Preparation of high-efficiency membrane materials, optimization of the process operation and understanding of the process mechanism are the focuses of the researches at present. In order to determine the distribution of fluid parameters (such as temperature, velocity, concentration) adjacent to the membrane, understand the transfer mechanism of the fluid in the membrane tube, Computational Fluid Dynamics method is introduced to the MD process.Computational Fluid Dynamics (CFD) is a new and independent subject based on the classical fluid dynamics and numerical calculation method. Through the computer numerical calculation and the images display method, numerical solution of the flow field is quantitatively described both in time and space. Being one of CFD commercial software, FLUENT has the most comprehensive feature, the widest availability and is used most widely. With powerful module, professional technical support, high availability, and so on, it has been increasingly concerned about by the vast number of enterprises and scholars.The k-ε turbulence model is proposed to simulate the flow behavior in carbon membrane distillation process for seawater desalination with carbon membrane. Computational Fluid Dynamics (CFD) method is used to study the effects of the feed temperature, flowrate and concentration on the permeate flux. The numerical simulation is validated with the experimental results, and thus is used to simulate the fluid in the membrane tube. By the two-dimensional and three-dimensional heat transfer simulation for the fluid in the membrane tube, the velocity, temperature, pressure and shear stress distribution of the fluid are obtained. By the mass transfer simulation for the fluid in the membrane tube, the concentration polarization factor, the thickness of concentration polarization profile and the mass transfer coefficient in the membrane tube are obtained. Dimensional analysis is used to build a proper correlation for mass transfer coefficient in the MD process. The momentum transfer and heat transfer in the membrane are enhanced by filling the baffle in the membrane channel. The enhanced effect and pressure drop for different baffle height are discussed.