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