• Membrane and Water Treatment
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• 제13권1호
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• pp.51-62
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• 2022

Vacuum-assisted air gap membrane distillation (V-AGMD) has the potential to achieve higher flux and productivity than conventional air gap membrane distillation (AGMD). Nevertheless, there is not much information on technical aspects of V-AGMD operation. Accordingly, this study aims to analyze the effect of membrane deformation on flux in V-AGMD operation. Experiments were carried out using a bench-scale V-AGMD system. Statistical models were applied to understand the flux behaviors. Statistical models based on MLR, GNN, and MLFNN techniques were developed to describe the experimental data. Results showed that the flux increased by up to 4 times with the application of vacuum in V-AGMD compared with conventional AGMD. The flux in both AGMD and V-AGMD is affected by the difference between the air gap pressure and the saturation pressure of water vapor, but their dependences were different. In V-AGMD, the membranes were found to be deformed due to the vacuum pressure because they were not fully supported by the spacer. As a result, the deformation reduced the effective air gap width. Nevertheless, the rejection and LEP were not changed even if the deformation occurred. The flux behaviors in V-AGMD were successfully interpreted by the GNN and MLFNN models. According to the model calculations, the relative impact of the membrane deformation ranges from 10.3% to 16.1%.

• Applied Science and Convergence Technology
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• 제23권5호
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• pp.248-253
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• 2014

Air Gap Membrane Distillation (AGMD) is one of several technologies that can be used to solve problems fresh water availability. AGMD exhibits several advantages, including low conductive heat loss and higher thermal efficiency, due to the presence of an air gap between the membrane and condensation wall. A previous study by Bhardwaj found that the condensation surface properties (materials and contact angle) affected the total collected fresh water in the solar distillation process. However, the process condition differences between solar distillation and AGMD might result in different condensation phenomena. In contrast, N. Miljkovic showed that a hydrophobic surface has higher condensation heat transfer. Moreover, to the best of our knowledge, there is no study that investigates the effect of condensation surface properties in AGMD to overall process performance (i.e. flux and thermal efficiency). Thus, in this study, we treated the AGMD condensation surface to make it hydrophobic or hydrophilic. The condensation surface could be made hydrophilic by immersing and boiling plate in deionized (DI) water, which caused the formation of hydrophilic aluminum hydroxide (AlOOH) nanostructures. Afterwards, the treated plate was coated using hexamethyldisiloxane (HMDSO) through plasma-enhanced chemical vapor deposition (PECVD). The result indicated that condensation surface properties do not affect the permeate flux or thermal efficiency significantly. In general, the permeate flux and thermal efficiency for the treated plates were lower than those of the non-treated plate (pristine). However, at a 1 mm and 3 mm air gap, the treated plate outperformed the non-treated plate (pristine) in terms of permeate flux. Therefore, although surface wettability effect was not significant, it still provided a little influence.

• 멤브레인
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• 제13권3호
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• pp.154-161
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• 2003

본 연구에서는 소수성 PTFE (Polytetrafluoroethylene) 분리막의 산소동위원소 분리특성을 확인하기 위해 물의 온도에 따른 수증기의 막 투과특성을 Air Cap Membrane Distillation (AGMD)과 Vacuum Enhanced Membrane Distillation (VEMD) 방법을 이용하여 각각 측정하였다. 투과된 수증기는 트랩에서 수거하여 투과플럭스 (permeation flux)를 측정하였고$ H_2^{16}O$와 $H_2^{18}O$의 성분비는 다이오드 레이저 흡수분광법을 이용하여 측정하였다. 분리막을 투과한 수증기에서 무거운 산소동위원소의 성분비가 감소함을 확인하였고 분리계수는 실험 조건에 따라 1.004~1.01로 측정되었다. 또한 분리막의 기공에 있는 공기가 산소동위원소의 분리에 미치는 영향을 확인하였고 기공내 공기가 없을 때 동위원소 분리계수가 증가함을 관찰하였다.

• Membrane and Water Treatment
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• 제8권6호
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• pp.529-541
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• 2017

A multi-effect air gap membrane distillation (ME-AGMD) module for pesticide wastewater treatment is studied with internal heat recovery, sensible heat of brine recovery, number of stages and the use of fresh feed as cooling water in a single module is implemented in this study. A flat sheet polytetrafluroethylene (PTFE) membrane was used in the 4-stage ME-AGMD module. The maximum value of permeate flux could reach $38.62L/m^2h$ at feed -coolant water temperature difference about $52^{\circ}C$. The performance parameter of the module like, specific energy consumption and gain output ratio (GOR) was investigated for the module with and without heat recovery. Also, the module performance was characterized with respect to the separation efficiency of several important water quality parameters. The removal efficiency of the module was found to be >98.8% irrespective water quality parameters. During the experiment the membrane fouling was caused due to the deposition of the salt/crystal on the membrane surface. The membrane fouling was controlled by membrane module washing cycle 9 h and also by acidification of the feed water (pH=4) using 0.1M HCl solution.

• 상하수도학회지
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• 제30권4호
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• pp.441-447
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• 2016

Development of shale gas has drawn increasing attention since it is one of promising alternative energy resources. However, contamination of groundwater and surface water during the extraction of shale gas is becoming a serious environmental issues, which brings the needs to treat wastewater generated from hydraulic fracking. In this study, the feasibility of membrane distillation (MD) for the treatment of shale gas wastewater was investigated using a laboratory scale experimental setup. Flat-sheet MD membranes were used to treat produced water from a shale gas well in the United States. Different configurations such as direct contact MD (DCMD) and air gap MD (AGMD) were compared in terms of flux and fouling propensity. The foulants on the surface of the membranes were examined. The results suggest that MD can treat the shale gas produced water containing more than 200,000 mg/L of total dissolved solids, which is impossible by other technologies such as reverse osmosis (RO) and forward osmosis (FO). In this study, we investigated the possibility of processing and characterization of shale gas produce wastewater using membrane distillation. Laboratory scale membrane distillation experimental device was developed. It was compared the flat-sheet direct contact membrane distillation and flat-sheet air gap membrane distillation. AGMD flux in lower than the flux of DCMD, it was expected that the contamination caused by organic matters.

• Membrane and Water Treatment
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• 제2권3호
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• pp.159-173
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• 2011

The air gap membrane distillation (AGMD) process was applied for water desalination. The main objective of the present work was to study the heat and mass transfer mechanism of the process. The experiments were performed on a flat sheet module using aqueous NaCl solutions as a feed. The membrane employed was hydrophobic PTFE of pore size 0.22 ${\mu}m$. A mathematical model is proposed to evaluate the membrane mass transfer coefficient, thermal boundary layers' heat transfer coefficients, membrane / liquid interface temperatures and the temperature polarization coefficients. The mass transfer model was validated by the experimentally and fitted well with the combined Knudsen and molecular diffusion mechanism. The mass transfer coefficient increased with an increase in feed bulk temperature. The experimental parameters such as, feed temperature, 313 to 333 K, feed velocity, 0.8 to 1.8 m/s (turbulent flow region) were analyzed. The permeation fluxes increased with feed temperature and velocity. The effect of feed bulk temperature on the boundary layers' heat transfer coefficients was shown and fairly discussed. The temperature polarization coefficient increased with feed velocity and decreased with temperature. The values obtained were 0.56 to 0.82, indicating the effective heat transfer of the system. The fouling was observed during the 90 h experimental run in the application of natural ground water and seawater. The time dependent fouling resistance can be added in the total transport resistance.

• Membrane and Water Treatment
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• 제6권6호
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• pp.451-476
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• 2015

Membrane distillation (MD), which can utilize low-grade thermal energy, has been extensively studied for desalination. By incorporating solar thermal energy, the solar membrane distillation desalination system (SMDDS) is a potential technology for resolving the energy and water resource problems. Small-scale SMDDS (s-SMDDS) is an attractive and viable option for the production of fresh water for small communities in remote arid areas. The minimum-cost design and operation of s-SMDDS are determined by a systematic method, which involves a pseudo steady state approach for equipment sizing and the dynamic optimization using overall system mathematical models. The s-SMDDS employing three MD configurations, including the air gap (AGMD), direct contact (DCMD) and vacuum (VMD) types, are optimized. The membrane area of each system is $11.5m^2$. The AGMD system operated for 500 kg/day water production rate gives the lowest unit cost of $5.92/m^3$. The performance ratio and recovery ratio are 0.85 and 4.07%, respectively. For the commercial membrane employed in this study, the increase of membrane mass transfer coefficient up to two times is beneficial for cost reduction and the reduction of membrane heat transfer coefficient only affects the cost of the DCMD system.

• Membrane and Water Treatment
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• 제13권5호
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• pp.235-243
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• 2022

The paper presents the effect of operating temperatures and flow rates on the distillate flux that can be obtained from a hydrophobic membrane having the characteristics: pore size of 0.15 ㎛; thickness of 130 ㎛; and 85% porosity. That membrane in the present investigation could be the direct contact (DCMD) or the air-gap membrane distillation (AGMD). To model numerically the membrane distillation processes, the two-dimensional computational fluid dynamic (CFD) is used for the DCMD and AGMD cases here. In this work, DCMD and AGMD models have been validated with the experimental data using different flows (Parallel and Counter-current flows) in non-steady-state situations. A good agreement is obtained between the present results and those of the experimental data in the literature. The new approach in the present numerical modeling has allowed examining effects of the nature of materials (Polyvinylidene fluoride (PVDF) polymers, copolymers, and blends) used on thermal properties. Moreover, the effect of the area surface of the membrane (0.021 to 3.15 ㎡) is investigated to explore both the laminar and the turbulent flow regimes. The obtained results found that copolymer P(VDF-TrFE) (80/20) is more effective than the other materials of membrane distillation (MD). The mass flux and thermal efficiency reach 193.5 (g/㎡s), and 83.29 % using turbulent flow and an effective area of 3.1 ㎡, respectively. The increase of feed inlet temperatures and its flow rate, with the reduction of cold temperatures and its flow rate are very effective for increasing distillate water flow in MD applications.

• Membrane and Water Treatment
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• 제9권4호
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• pp.221-231
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• 2018

A new procedure to produce poly(vinylidene fluoride)/boron nitride hybrid membrane is presented for application in membrane distillation (MD) process. The influence of hexagonal boron nitride (h-BN) incorporation on the performance of the polymeric membranes is studied through the present investigation. For this aim, h-BN nanopowders were successfully synthesized using the simple chemical vapor deposition (CVD) route and subsequent solvent treatments. The resulting h-BN nanosheets were blended with poly(vinylidene fluoride) (PVDF) solution. Then, the prepared composite solution was subjected to phase inversion process to obtain PVDF/h-BN hybrid membranes. Various examinations such as scanning electron microscopy (SEM), wettability, permeation flux, mechanical strength and liquid entry pressure (LEP) measurements are performed to evaluate the prepared membrane. Moreover, Air gap membrane distillation (AGMD) experiments were carried out to investigate the salt rejection performance and the durability of membranes. The results show that our hybrid PVDF/h-BN membrane presents higher water permeation flux (${\sim}18kg/m^2h$) compared to pristine PVDF membrane. In addition, the experimental data confirms that the prepared nanocomposite membrane is hydrophobic (water contact angle: ${\sim}103^{\circ}$), has a porous skin layer (>85%), as well competitive fouling resistance and operational durability. Furthermore, the total salt rejection efficiency was obtained for PVDF/h-BN membrane. The results prove that the novel PVDF/h-BN membrane can be easily synthesized and applied in MD process for salt rejection purposes.

• 대한기계학회논문집B
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• 제39권3호
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• pp.279-284
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• 2015

전 세계적으로 셰일가스와 같은 비전통 석유자원이 널리 개발되고 있다. 이에 따라 셰일가스 채굴과정에서 발생하는 폐수의 적절한 처리가 중요해지고 있다. 그러나, 폐수 내의 오일 및 유기 물질, 유해성 화학물질, 무기 이온과 같은 물질이 고농도로 함유하고 있기 때문에 기존 처리 방법으로 많은 어려움을 격고 있다. 본 연구에서는 셰일가스 폐수에 대한 새로운 처리방법으로 정삼투 공정 및 막증발법에서의 가능성을 연구하였다. 실험실 규모의 정삼투 및 막증발법 장치를 제작하여 실험을 실시하였다. 그 결과, 합성 폐수를 처리하는데, 정삼투 공정에서 적용 가능하다고 판단되었다. 유도용액으로 5M의 염화나트륨수용액을 사용하였고, 낮은 범위의 폐수(66,000mg/L TDS)에서 약 $6L/m^2-hr$의 플럭스를 나타냈다. 그럼에도 불구하고, 높은 범위의 폐수(261,000mg/L TDS)에서 막증발법으로 처리하는 것이 더 효과적이었다.