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 500712, South Korea
b School of Civil and Environmental Engineering, Kookmin University, Songbukgu, Seoul 136702, South Korea
c Center of Seawater Desalination Plant, GIST, Gwangju 500712, South Korea
d Sustainable Water Resource Technology Center, GIST, Gwangju 500712, 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, steadystate laminar NavierStokes, and convectiondiffusion 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

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 Latinhypercube onefactoratatime 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 concentrationvariant 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 concentrationvariant 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 value가 FO performance에 미치는 영향과 중요성을 알려준다.
5. Reviewer contact : 심예영 (yyshim@gist.ac.kr)