scholarly journals Multiscale phase change, heat and mass transfer in direct contact membrane distillation

2020 ◽  
Author(s):  
◽  
Elnaz Norouzi
Keyword(s):  
Temperature Difference ◽  
Direct Contact ◽  
Waste Heat ◽  
Water Flux ◽  
Membrane Distillation ◽  
Operating Conditions ◽  
Feed Water ◽  
Direct Contact Membrane Distillation ◽  
Nacl Concentration ◽  
System Temperature

The global water shortage has become a serious threat for the world and the most promising solution for the water issue is the desalination of seawater or brackish water. In this work, direct contact membrane distillation (DCMD) as one of thermal desalination technologies was numerically and exprimentally analyzed to study its performance. A large DCMD system with multiple membrane modules in a parallel arrangement running on the waste heat from a diesel power generator was numerically analyzed using a thermo-fluid network model to study the technical feasibility of the use of the low-grade engine waste heat and simulate the distillation performance of the DCMD system. Next, a small DCMD experimental apparatus was fabricated to test for the distillation performance for various operating conditions (inlet temperatures, flow rates of feed and permeate streams and NaCl concentration) and design variables (filament spacing of a screen spacer in the flow channels and flow configuration). In the DCMD, two different regimes were observed in the water flux behavior regarding the salinity of feed water. In the first regime, from low NaCl concentration to 90% saturated NaCl concentration, there was a gradual decrease in the water flux due to the suppression of vapor pressure at the feed water which is simulated by a CFD model. In the second regime, at higher 90% saturated NaCl concentration, there was a sharp drop in the water flux due to the deposition of NaCl crystals on the membrane surface which is simulated by an analytical model using the adjusting parameter from the experiment. Finally, a nanoscale DCMD using Carbon Nanotube (CNT) membrane was numerically analyzed using non-equilibrium molecular dynamics (NEMD) simulation for different diameters and lengths of the CNT and operating conditions such as system temperature, temperature difference between the feed (hot) and permeate (cold) reservoirs, and sodium chloride (NaCl) concentration in the feed reservoir. The distillation performance of the DCMD systems is enhanced by increasing system temperature, temperature difference between feed and permeate streams, and decreasing the NaCl concentration. The permeability of the CNT membrane (1.8 x 10-5 liter/m2-s-Pa) was found two orders-of-magnitudes higher than a Polytetrafluoroethylene (PTFE) membrane (1.7 x 10-7 liter/m2-s-Pa ) used in our experimental work.

scholarly journals Simulation of direct contact membrane distillation regeneration of liquid desiccant solutions used in air-conditioning

2020 ◽  
Vol 58 (6) ◽  
pp. 747
Author(s):  
Hung Cong Duong ◽  
Lan Thi Thu Tran
Keyword(s):  
Direct Contact ◽  
Air Conditioning ◽  
Water Flux ◽  
Experimental Tests ◽  
Membrane Distillation ◽  
Operating Conditions ◽  
Membrane Properties ◽  
Experimental Investigations ◽  
Liquid Desiccant ◽  
Direct Contact Membrane Distillation

Membrane distillation (MD) has great potential for the treatment of hyper saline waters, including liquid desiccant solutions used in air-conditioning systems. Previous experimental investigations have demonstrated the technical feasibility of MD for regeneration of liquid desiccant solutions. In this study, a direct contact membrane distillation (DCMD) process of the LiCl liquid desiccant solution was simulated using MATLAB software. The simulation was first validated using data obtained from experimental tests. Then, it was used to elucidate the water temperatures, LiCl concentration, and water flux profiles along the membrane leaf inside the DCMD membrane module. Finally, with the help of the simulation, the effects of membrane properties and process operating conditions on the DCMD process performance were systematically examined. The results obtained from this simulation enrich the knowledge and hence facilitate the realization of MD for the liquid desiccant solution regeneration application.

Experimental and Numerical Study of Water Distillation Performance of Small-Scale Direct Contact Membrane Distillation System

2017 ◽  
Author(s):  
Danielle Park ◽  
Elnaz Norouzi ◽  
Chanwoo Park
Keyword(s):  
Water Temperature ◽  
Direct Contact ◽  
Membrane Distillation ◽  
Small Scale ◽  
Feed Water ◽  
Water Production ◽  
Water Distillation ◽  
Direct Contact Membrane Distillation ◽  
Feed Temperature ◽  
Feed Water Temperature

A small-scale Direct Contact Membrane Distillation (DCMD) system was built to investigate its water distillation performance for varying inlet temperatures and flow rates of feed and permeate streams, and salinity. A counterflow configuration between the feed and permeate streams was used to achieve an efficient heat exchange. A two-dimensional Computational Fluid Dynamics (CFD) model was developed and validated using the experimental results. The numerical results were compared with the experiments and found to be in good agreement. From this study, the most desirable conditions for distilled water production were found to be a higher feed water temperature, lower permeate temperature, higher flow rate and less salinity. The feed water temperature had a greater impact on the water production than the permeate water temperature. The numerical simulation showed that the water mass flux was maximum at the inlet of the feed stream where the feed temperature was the highest and rapidly decreased as the feed temperature decreased.

scholarly journals Highly Saline Water Desalination Using Direct Contact Membrane Distillation (DCMD): Experimental and Simulation Study

Water ◽  
2020 ◽  
Vol 12 (6) ◽  
pp. 1575 ◽  
Author(s):  
Noor A. Mohammad Ameen ◽  
Salah S. Ibrahim ◽  
Qusay F. Alsalhy ◽  
Alberto Figoli
Keyword(s):  
Mass Transfer ◽  
Direct Contact ◽  
Saline Water ◽  
Membrane Distillation ◽  
Operating Conditions ◽  
Water Desalination ◽  
System Of Nonlinear Equations ◽  
Transfer Model ◽  
Transfer Resistance ◽  
Direct Contact Membrane Distillation

The path for water molecules transported across a membrane in real porous membranes has been considered to be a constant factor in the membrane distillation (MD) process (i.e., constant tortuosity); as such, its effect on membrane performance at various operating conditions has been ignored by researchers. Therefore, a simultaneous heat and mass transfer model throughout the direct contact membrane distillation (DCMD) module was developed in this study by taking into account the hypothetical path across the membrane as a variable factor within the operating conditions because it exhibits the changes to the mass transfer resistance across the membrane under the DCMD run. The DCMD process was described by the developed model using a system of nonlinear equations and solved numerically by MATLAB software. The performance of the poly-tetra-fluoroethylene (PTFE) membrane was examined to treat 200 g/L NaCl saline at various operating conditions. The simulation results in the present work showed that the hypothetical proposed path across the membrane has a variable value and was affected by changing the feed temperature and feed concentration. The results estimated by the developed model showed an excellent conformity with the experimental results. The salt rejection remained high (greater than 99.9%) in all cases. The temperature polarization coefficient for the DCMD ranged between 0.88 and 0.967, and the gain output ratio (GOR) was 0.893. The maximum thermal efficiency of the system was 84.5%.

scholarly journals Influence of Hydraulic Pressure on Performance Deterioration of Direct Contact Membrane Distillation (DCMD) Process

Membranes ◽  
2019 ◽  
Vol 9 (3) ◽  
pp. 37 ◽  
Author(s):  
Seung-Min Park ◽  
Sangho Lee
Keyword(s):  
Mass Transfer ◽  
Direct Contact ◽  
Membrane Distillation ◽  
Operating Conditions ◽  
Hydraulic Pressure ◽  
Transfer Coefficients ◽  
Hydrophobic Membrane ◽  
Mass Transfer Coefficients ◽  
Efficient Operation ◽  
Direct Contact Membrane Distillation

Direct contact membrane distillation (DCMD) is a membrane distillation (MD) configuration where feed and distillate directly contact with a hydrophobic membrane. Depending on its operating conditions, the hydraulic pressures of the feed and distillate may be different, leading to adverse effects on the performance of the DCMD process. Nevertheless, little information is available on how hydraulic pressure affects the efficiency of DCMD. Accordingly, this paper investigates the effect of external hydraulic pressure on the process efficiency of DCMD. Gas permeabilities of MD membranes were measured to analyze the effect of membrane compaction by external pressure. Mass transfer coefficients were calculated using experimental data to quantitatively explain the pressure effect. Experiments were also carried out using a laboratory-scale DCMD set-up. After applying the pressure, the cross-sections and surfaces of the membranes were examined using a scanning electron microscope (SEM). Results showed that the membrane structural parameters such as porosity and thickness were changed under relatively high pressure conditions (>30 kPa), leading to reduction in flux. The mass transfer coefficients were also significantly influenced by the hydraulic pressure. Moreover, local wetting of the membranes were observed even below the liquid entry pressure (LEP), which decreased the rejection of salts. These results suggest that the control of hydraulic pressure is important for efficient operation of DCMD process.

One-step nanotopography construction by polyaniline polymerization for a superhydrophobic nanofibrous membrane towards direct contact membrane distillation

2019 ◽  
Vol 6 (8) ◽  
pp. 2553-2564 ◽  
Author(s):  
Lingling Zhong ◽  
Zhigao Zhu ◽  
Yu Han ◽  
Qiao Wang ◽  
Dongmei Liu ◽  
...  
Keyword(s):  
Direct Contact ◽  
Water Flux ◽  
High Water ◽  
Membrane Distillation ◽  
Nanofibrous Membrane ◽  
Direct Contact Membrane Distillation ◽  
One Step ◽  
Nanofibrous Membranes

In situ polymerization of aniline is used to prepare superhydrophobic PVDF nanofibrous membranes for direct contact membrane distillation with high water flux and long wetting times.

scholarly journals HYDROPHOBIZATION OF PET TRACK-ETCHED MEMBRANES FOR DIRECT CONTACT MEMBRANE DISTILLATION OF LIQUID RADIOACTIVE WASTES

2020 ◽  
Vol 17 (2) ◽  
pp. 45-54
Author(s):  
A.B. Yeszhanov ◽  
Keyword(s):  
Direct Contact ◽  
Gamma Ray ◽  
Water Flux ◽  
Atomic Emission ◽  
Membrane Distillation ◽  
Radioactive Wastes ◽  
Low Level ◽  
Direct Contact Membrane Distillation ◽  
Hydrophobic Membranes ◽  
Entry Pressure

This article provides the results of liquid low-level radioactive wastes treatment by direct contact membrane distillation using polyethylene terephthalate hydrophobic track-etched membranes. The hydrophobization of track-etched membranes was carried out by UV-induced graft polymerization of triethoxyvinylsilane with styrene and coating with fluorine-containing silanes. Hydrophobic membranes were investigated by scanning electron microscope, Fourier-transform infrared spectroscopy, contact anglemeasurements, and liquid entry pressure analysis. Prepared membranes were tested in treatment of liquid low-level radioactive wastes by membrane distillation. The influence of pore sizes on water flux and rejection degree was studied. Rejection degree was evaluated by conductometry and atomic emission method. Decontamination factors evaluated by gamma-ray spectroscopy for 60Co, 137Cs, and 241Am are 85.4, 1900 and 5.4 for membranes modified with polystyrene and triethoxyvinylsilanewith pore diameters of 142 nm; 85.0, 1462 and 4 for membranes modified with perfluorododecyltrichlorosilanewith pore diameters of 150 nm respectively.

Sign in / Sign up

Export Citation Format

Share Document