1205_Determine of a constant membrane structure parameter in forward osmosis processes...



1. Title & Journal


Determine of a constant membrane structure parameter in forward osmosis processes


2. Background of author


Minkyu Park(a), Ji Jung Lee(a), Sangho Lee(b), Joon Ha Kim(a,c,d)


a School of Environmental Science and Engineering, Gwangju Institute of Science and Technology(GIST), Gwangju 500-712, South Korea

b School of Civil and Environmental Engineering, Kookmin University, Songbuk-gu, Seoul 136-702, South Korea

c Center of Seawater Desalination Plant, GIST, Gwangju 500-712, South Korea

d Sustainable Water Resource Technology Center, GIST, Gwangju 500-712, South Korea


3. Summary

 본 논문은 S value를 중심으로 the finite element method (FEM)을 이용하여 수학적 모델을 개발하고 그 모델을 통하여 일정한 S value를 결정하는 방법을 제안하는 데 목적이 있다.


1)     Modeling procedures

1.1   Membrane orientation and simulation domains


1.2   Feed and draw solution channels

-       follow continuity, steady-state laminar Navier-Stokes, and convection-diffusion equations  

-       The boundary condition  - the parabolic velocity profiles 

-       The amount of permeate water through the active layer is linearly proportional to the osmotic pressure difference 

-       Two main ways to calculate diffusion phenomena : using a diffusion coefficient and a mass transfer coefficient  ?  In this paper, use the Fick’s law with a diffusion coefficient 

-       The impermeable walls ? no slip and no penetration condition / open boundary conditions on both outlet channels


1.3   Support layer region

-       Assume that the velocity in the support layer varies only in the horizontal direction

-       Apply a mass balance solution to the support layer 

-        the effective diffusion coefficient in the support layer


1.4   Determination of diffusion coefficient

-       A equation of average diffusivity from Tan and Ng 

-       This equation is only for dilute solutions and applys narrow range of concentrations of draw solution in FO processes

-       In this paper, compute the diffusivity using the model from Gorden


1.5   Numerical simulations

-       The software which named Comsol was used to simulate the FO performances.


1.6   Sensitivity analysis

-       Implemented the Latin-hypercube one-factor-at-a-time method to define sensitive model parameters

2)     Results and discussion



2.1 Model validation


2.2 The effects of diffusion coefficients


- Compare a model using a constant diffusion coefficient to that using the concentration-variant diffusivity

- Constant diffusivity is accurate to simulate the performance of FO processes (diluted concentrations)

- Insignificant differences in the diffusion coefficients within the support layer

- No need to determine the concentration-variant diffusivity under the simulations


2.3 Determine of membrane structure parameter


- The inconsistency of S values might be attributed to the ideal solution assumption

- S value without assumptions is necessary to obtain

- The equations developed by Tang et al.

- If the porous support layer has a higher resistance against salt transport, the value of the denominator becomes lower; the value of the fraction in the natural log becomes higher

- Since the value of the numerator is always greater than that of denominator, the higher the value of fraction, the more resistant against salt transport the support layer is.

- The ideal solution assumption is the largest factor contributing to the inconsistency of S values

- The ideal solution assumption is needed for the model based on FEM


2.4 Sensitivity analysis: characteristics of FO processes

 - An increase in S value negatively influences FO performance, whereas increase in A results in improvement of water flux

 - The S value is dominant in seawater desalination using osmotically driven membrane processes since ICP becomes severe as the feed concentration increase


3)     Conclusion

- Used the assumption that the ratio of concentrations is approximately identical to the ratio of osmotic pressures

- The model based on FEM can successfully simulate the performance of osmotically driven processes

- Development of a high performance membrane is the most efficient way to maximize FO performance, rather than optimizing operating conditions such as feed and draw solution velocities


4. Originality & Creativity

FO 프로세스에 관한 파라미터 들 중 S value(membrane structure parameter)에 초점을 맞추어진 논문으로, S value FO performance에 미치는 영향과 중요성을 알려준다.


5. Reviewer contact : 심예영 (yyshim@gist.ac.kr)


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