ESEL Paper Review_20140408
By Hong Guo
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1, Title and Author
Title: Mathematical model of flat sheet membrane modules for FO process: Plate-and ?frame module and spiral-wound module
Journal: Journal of Membrane Science
B.Gua,*, D.Y.Kima, J.H.Kimb, D.R. Yanga,*
a Department of Chemical and biological Engineering, Korea University, Seoul 136-713,Republic of Korea
b Department of Environmental Science and Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju 500-712, Republic of Korea
2. Summary of Paper
? In this study, modelling and simulations for a plate-and frame and a modified spiral-wound module are carried out for the FO process.
? The mathematical models consist of mass balance, a permeate flux model, and concentration polarization equations
? Plate-and-frame module
? Only one dominant flow direction is considered, and the flow velocity and the concentration are calculated
? In regions A and C, higher water fluxes take place, because the channel is not shared by two membranes, unlike the rest of the region; consequently, it appears to have twice the channel height compared to the other region. Also, lower flow velocities in regions A and C are observed because the water permeates to the outside envelope by only one membrane, unlike in region B. As a result of the lower flow velocity with the low salt permeability, the concentrations are higher than those in the region B. Unlike outside the envelope, the flow velocity and the concentration are continuous, since there are no distinguished region inside.
? Modified spiral-wound module
? For all cases, the water flux increases as the flow rate of the solutions and the concentration of the draw solution increase. In a comparison between AL-DS and
AL-FW modes, the permeate flux tends to be smaller in AL-FW mode. It is thoughts that the ICP phenomenon plays a more significant role than ECP in AL-FW mode in which the draw solution of the higher concentration is in contact with the porous support layer. In other words, the concentration gradient is steeper than in AL-DS mode since more salts are inhibited from freely diffusing into the porous support lyer.
? Compare the performance according to the feed flow location, the water flux is lower when the porous support layers are on the inside of the envelope. This is caused by the differenct distances that the solutions travel inside and out side the envelope. Since the effect length that the solution flows inside the envelope is longer due to the curved path, the concentration change by ICP is much more remarkable.
? For the consideration of ECP effects, it is regarded that ECP does not differ much by fixing the flow rate for both solution. Thus, for the modified spiral-wound module to obtain higher performance, the configuration of the membranes and the solutions is critical ;
? In order to achieve the targeted performance, the optimal conditions of the design parameters can be found using the model developed in this work, such as the specifications of the membrane geometry, initial conditions of the solutions, and so on.
? Comparisons of the plate-and ?frame and the modified spiral-wound module
? The same order of magnitude in water flux for the both modules in obtained in the operating condition range studied.
? In the investigated range of the flow rate, the modified spiral-wound module can generally obtain high water flux. However, the order of the magnitude in the flux is the same along the whole range. Since the plate-and-frame module is simulated with one sheet of membrane, the packing density is lower than the modified spiral-wound module with a pair of membranes.
? The plate-and-frame has the higher water flux in some cases in the low flow rate range. Moreover, for each module, the performance in respect to the water flux is highly dependent on the membrane orientation, the solution locations, and the membrane geometry. Thus, it is necessary to research the selection of a suitable module design and operating conditions for FO desalination process with respect to the priority of concerns.
This research would be fully studied and applied to the future FO membrane structure studies
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