Study Of The Effect Of Spacers On Separation Process In Flat Sheet Membrane Module

Pervaporation is a new membrane process which has been used in manyseparation fields, such as environmental remediation, ground water purification andrecovering flavor compounds during food production. The driving force for thepervaporation separation is partial vapor pressure difference between the two sides ofthe membrane. One of the problems for pervaporation application is concentrationpolarization, which will reduce the flux of the membrane. In order to reduceconcentration polarization and improve mass transfer, spacers filled membranemodules are introduced. The spacers in membrane modules may reduce concentrationpolarization by disturbing the concentration boundary layer. Computational fluiddynamics (CFD) has been widely used to simulate the fluid flow and mass transfer inmembrane modules for a long time which can describe the distribution of velocity,pressure drop, shear stress and concentration effectively.CFD software FLUENT14.0and meshing software Gambit2.4.6were used inthis simulation.2D and3D simulation were conducted for the membrane channelsfilled with parallel arranged spacers. The spacers are arranged in two types. Thesimulation for empty channel shows the velocity boundary layer and the concentrationboundary layer exit in the channel. The velocity boundary layer and the concentrationboundary layer can influence mass transfer efficiently. The simulation of channelswith spacers shows that wall shear stress fluctuates for the presence of spacer which isbenefit to mass transfer. However, the pressure drop which is related to energy loss isalso improved. With the changing of spacer’s size and inlet velocity, the shear stressand pressure drop also change. A comparison of channels with the two typearrangement spacers was conducted, the simulation result reveals that when thespacers are arranged in the middle of the channel, the shear stress and pressure dropare bigger. In order to improve mass transfer, a new shape of spacer was proposed.From the result, the new spacer filled channels have higher shear stress comparedwith the original spacer filled channels. The3D results are compared with those from2D simulations. The data matches very well.A3D simulation of1-layer and2-layer net type spacers was also conducted. TheCFD results were analyzed in terms of wall shear stress and pressure drop. The resultsshow that wall shear stress and pressure fluctuate for the presence of spacer. The filament orientation makes a great influence on wall shear stress and pressure drop.The angle between the filaments affects the shear stress and pressure drop significantlyfor both1-layer and2-layer net-type spacers filled channels. The simulation alsoreports that1-layer spacer shows higher shear stress than2-layer spacer. However, thehigh pressure drop may limit the application of1-layer spacer.