scholarly journals Experimental evaluation of two consecutive air-gap membrane distillation modules with heat recovery

2020 ◽  
Vol 20 (5) ◽  
pp. 1678-1691 ◽  
Author(s):  
Mostafa Abd El-Rady Abu-Zeid ◽  
Gamal ElMasry
Keyword(s):  
Water Temperature ◽  
Flow Rate ◽  
Heat Recovery ◽  
Waste Heat ◽  
Water Flow Rate ◽  
Membrane Distillation ◽  
Air Gap ◽  
Feed Water ◽  
System Productivity ◽  
Air Gap Membrane Distillation

Abstract Two rectangular modules with a total interior membrane surface area of 13.53 m2 were consecutively combined to evaluate the use of heat recovery in an air-gap membrane distillation (AGMD) system. Several operating inlet parameters including feed water temperature, mass water flow rate and salinity were investigated. The experimental results revealed that the performance of the system was improved by virtue of efficient heat recovery resulting from combining two AGMD membrane modules in series. Under optimal inlet operating parameters of cooling water temperature of 20 °C, salinity of 0.05% and flow rate of 3 l/min, the system productivity (Pp) increased up to 192.9%, 179.3%, 176.5% and 179.2%, and the thermal efficiency (ηth) by 261.5%, 232.6%, 239.4% and 227.3% at feed water temperatures of 45 °C, 55 °C, 65 °C and 75 °C, respectively. Concurrently, the specific waste heat input (Ew.h.i) decreased by 6.7%, 4.7%, 5.6% and 2.7% due to the efficient heat recovery. The results confirmed that heat recovery is an important factor affecting the AGMD system that could be improved by designing one of the two AGMD modules with polytetrafluoroethylene (PTFE) hollow fibers with a flow length shorter than the other one having a salt rejection rate of 99%.

scholarly journals Experimental analysis of a novel helical air gap membrane distillation system

2021 ◽  
Author(s):  
Vandita T. Shahu ◽  
S. B. Thombre
Keyword(s):  
Flow Rate ◽  
Experimental Analysis ◽  
Membrane Distillation ◽  
Air Gap ◽  
Operating Conditions ◽  
Coolant Temperature ◽  
Feed Water ◽  
Air Gap Membrane Distillation ◽  
Feasible Solutions ◽  
Water Problems

Abstract Membrane distillation presents one of the feasible solutions to fresh water problems. The present study aims to develop an innovative Helical Air Gap Membrane Distillation (HAGMD) system and to analyze its behavior under different operating conditions. In this design the condenser is made up of a cylindrical copper tube with continuous helical fins over it, that increases the total available condensation area by almost 45% and enhances the overall heat transfer throughout the module. The presence of fins in the gap also reduces the total air gap width by almost 64%and therefore improves the flux production. A detailed experimental analysis is carried out for a better understanding of the underlying phenomenon. The effect of feed water temperature, feed flow rate, cold flow rate, coolant temperature and feed salinity on the performance of HAGMD is investigated experimentally. The analysis shows that the finned condenser results in very high flux. The maximum flux obtained from the system was 20 kg/m2 hr with feed of 5gm/liter salinity and a diving force temperature difference of 45 °C.

Performance of Air Gap Membrane Distillation Unit for Water Desalination

2014 ◽  
Author(s):  
Atia E. Khalifa ◽  
Dahiru U. Lawal ◽  
Mohamed A. Antar
Keyword(s):  
Flow Rate ◽  
Membrane Distillation ◽  
Air Gap ◽  
Water Desalination ◽  
Feed Water ◽  
Feed Flow Rate ◽  
Permeate Flux ◽  
Air Gap Membrane Distillation ◽  
Gap Width ◽  
Feed Temperature

Due to water scarcity in the Arabic gulf region, water desalination technologies are considered extremely important. The present work represents a fundamental study on the effect of basic operating and design variables on the flux of an air gap membrane distillation (AGMD) unit for water desalination. The flat sheet, channeled air gap membrane distillation module was designed and manufactured locally. The effect of feed flow rate, feed temperature, coolant water temperature, the air gap width, and the water salinity on the module flux are investigated. Analytical model for heat and mass transfer is used to predict the flux and the model results are compared to the experimental ones. Results showed that the technique has good potential to be used for water desalination. The permeate flux is increased by increasing feed flow rate, feed temperature, decreasing the air gap width, decreasing coolant temperature, and decreasing salinity of feed water. For a given feed flow rate, the width of the air gap and the feed water temperature are found to be the most effective parameters in increasing the distillate flux. Predicting the permeate flux with analytical models for heat and mass transfer showed good agreement with experimental results.

scholarly journals A Comparison Study of Brine Desalination using Direct Contact and Air Gap Membrane Distillation

2019 ◽  
Vol 25 (11) ◽  
pp. 47-54
Author(s):  
Ahmed Shamil Khalaf ◽  
Asrar Abdullah Hassan
Keyword(s):  
Flow Rate ◽  
Direct Contact ◽  
Polyvinylidene Fluoride ◽  
Membrane Distillation ◽  
Air Gap ◽  
Feed Flow Rate ◽  
Permeate Flux ◽  
Air Gap Membrane Distillation ◽  
Flat Sheet ◽  
Feed Temperature

Membrane distillation (MD) is a hopeful desalination technique for brine (salty) water. In this research, Direct Contact Membrane Distillation (DCMD) and  Air Gap Membrane Distillation (AGMD) will be used. The sample used is from Shat Al –Arab water (TDS=2430 mg/l). A polyvinylidene fluoride (PVDF) flat sheet membrane was used as a flat sheet form with a plate and frame cell. Several parameters were studied, such as; operation time, feed temperature, permeate temperature, feed flow rate. The results showed that with time, the flux decreases because of the accumulated fouling and scaling on the membrane surface. Feed temperature and feed flow rate had a positive effect on the permeate flux, while permeate temperature had a reverse effect on permeate flux. It is noticeable that the flux in DCMD is greater than AGMD, at the same conditions. The flux in DCMD is 10.95LMH, and that in AGMD is 7.14 LMH.  In AGMD, the air gap layer made a high resistance. Here the temperature transport reduces in the permeate side of AGMD due to the air gap resistance. The heat needed for AGMD is lower than DCMD, this leads to low permeate flux because the temperature difference between the two sides is very small, so the driving force (vapor pressure) is low.                                                                                               

scholarly journals Analysis and optimization of a new cylindrical air gap membrane distillation system

2019 ◽  
Vol 20 (1) ◽  
pp. 361-371 ◽  
Author(s):  
Vandita T. Shahu ◽  
S. B. Thombre
Keyword(s):  
Flow Rate ◽  
Membrane Separation ◽  
Negative Impact ◽  
Membrane Distillation ◽  
Air Gap ◽  
Cylindrical Shape ◽  
Hydrophobic Membrane ◽  
Tube Heat Exchanger ◽  
Whole Process ◽  
Air Gap Membrane Distillation

Abstract Membrane distillation is a rate-governed non-isothermal membrane separation technique that utilizes trans-membrane temperature difference for evaporating water and thereby separating it from brackish feed for reproducing fresh water. A novel design of a cylindrical air gap membrane distillation module is presented. The module is fabricated in a way similar to a shell and tube heat exchanger. A PTFE hydrophobic membrane is used and is formed in a cylindrical shape. Design of experiments (DOE) is used to design the experiments statistically and to identify the significant operating parameters. Experiments were performed according to the Taguchi design approach using an L16 orthogonal array. Optimization of the whole process is performed by response surface methodology. It is shown that the feed temperature and feed flow rate have a positive effect, whereas the salinity has a negative impact on flux. The maximum value of flux achieved with this system is 3.6 kg/m2 hr. A high value of flux of 2.6 kg/m2 hr was achieved under optimum conditions at a temperature of 45 °C and a flow rate of 1.5 lpm with a salinity of 5 g/litre.

scholarly journals A novel internal heat recycling concept for reducing energy consumption and increasing flux through three-stage air-gap–water-gap membrane distillation system

2020 ◽  
Vol 20 (7) ◽  
pp. 2858-2874
Author(s):  
Mostafa Abd El-Rady Abu-Zeid ◽  
Xiaolong Lu ◽  
Shaozhe Zhang
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Energy Consumption ◽  
Heat And Mass Transfer ◽  
Waste Heat ◽  
Internal Heat ◽  
High Energy ◽  
Membrane Distillation ◽  
Air Gap ◽  
Air Gap Membrane Distillation

Abstract The low flux and high energy consumption problems of the conventional three-stage air-gap membrane distillation (AG-AG-AG)MD system caused by the low temperature difference between hot and cold feed at both sides of the membrane and high boundary layer thickness were solved successfully by replacing one of the three stages of air gaps by a water gap. The novel three-stage air-gap–water-gap membrane distillation (AG-AG-WG)MD system reduced energy consumption and increased flux due to efficient internal heat recycling by virtue of a water-gap module. Heat and mass transfer in novel and conventional three-stage systems were analyzed theoretically. Under a feed temperature of 45 °C, flow rate of 20 l/h, cooling temperature of 20 °C, and concentration of 340 ppm, the (AG-AG-WG)MD promoted flux by 17.59% and 211.69%, and gained output ratio (GOR) by 60.57% and 204.33% compared with two-stage (AG-WG)MD and one-stage AGMD, respectively. This work demonstrated the important role of a water gap in changing the heat and mass transfer where convection heat transfer across the water gap is faster by 24.17 times than conduction heat transfer through the air gap. The increase in flux and GOR economized the heating energy and decreased waste heat input into the system. Additionally, the number of MD stages could increase the achieving of a high flux with operation stability.

scholarly journals Performances of air gap and water gap MD desalination modules

2018 ◽  
Vol 13 (1) ◽  
pp. 200-209 ◽  
Author(s):  
Atia E. Khalifa
Keyword(s):  
Specific Energy Consumption ◽  
Membrane Distillation ◽  
Air Gap ◽  
Dominant Factor ◽  
Feed Water ◽  
Permeate Flux ◽  
Hydrophobic Membrane ◽  
Air Gap Membrane Distillation ◽  
Gap Width ◽  
Feed Temperature

Abstract Membrane distillation (MD) is a promising thermally-driven membrane separation technology for water desalination. In MD, water vapor is being separated from the hot feed water solution using a micro-porous hydrophobic membrane, due to the difference in vapor pressures across the membrane. In the present work, experiments are conducted to compare the performance of water gap membrane distillation (WGMD) and air gap membrane distillation (AGMD) modules under the main operating and design conditions including the feed and coolant temperatures, membrane material and pore sizes, and the gap width. Results showed that the WGMD module produced higher fluxes as compared to the AGMD module, for all test conditions. The feed temperature is the dominant factor affecting the system flux. The permeate flux increases with reducing the gap width for both water and air gap modules. However, WGMD module was found to be less sensitive to the change in the gap width compared to the AGMD module. The PTFE membrane produced higher permeate flux as compared to the PVDF membrane. Bigger mean pore diameter enhanced the permeate flux, however, this enhancement is marginal at high feed temperatures. With increasing the feed temperature, the GOR values increase and the specific energy consumption decreases.

scholarly journals ANALISIS EKSPERIMEN LAJU ALIRAN VOLUME AIR TERHADAP TEMPERATUR AIR PANAS PADA HEAT RECOVERY SISTEM AC JENIS WATER CHILLER

2011 ◽  
Vol 1 (2) ◽  
Author(s):  
I Made Rasta
Keyword(s):  
Water Temperature ◽  
Water Flow ◽  
Flow Rate ◽  
Heat Recovery ◽  
Tap Water ◽  
Water Flow Rate ◽  
Maximum Heat ◽  
Heating Water ◽  
Compressor Work ◽  
Heat Released

Refrigerant in refrigeration machines will absorb heat from a room space and released the heat to the environment. The heat balancing in the system is heat released from condenser equal with heat absorbed from room space added by the heat equivalent from compressor work. Based on this heat cycle, the writer try to conduct research on using this heat rejection from condenser to heating tap water, focusing on water flow rate increased from 0.5 liter/min to 2.5 liter/min. From experiment and analysis result obtained that the maximum heat water temperature which can be reached is 47.5°C in 0.5 liter/min, with the equipment specifications are 2 HP- split air conditioning and the tank volume is 75 liters. The additional result is heating water temperature is fallen when the water flow rate is increased.

scholarly journals Solar Desalination by Humidification-Dehumidification of Air

2018 ◽  
Vol 149 ◽  
pp. 02092 ◽  
Author(s):  
J. Moumouh ◽  
M. Tahiri ◽  
L. Balli
Keyword(s):  
Water Temperature ◽  
Flow Rate ◽  
Energy Use ◽  
Mechanical Energy ◽  
Water Flow Rate ◽  
Operating Conditions ◽  
Water Desalination ◽  
Arid Zones ◽  
Transfer Coefficients ◽  
System Productivity

The importance of supplying potable water can hardly be overstressed. In many arid zones, coastal or inlands, seawater or brackish water desalination may be the only solution to the shortage of fresh water. The process based on humidification-dehumidification of air (HDH) principle mimic the natural water cycle. HDH technique has been subjected to many studies in recent years due to the low temperature, renewable energy use, simplicity, low cost installation and operation. An experimental test set-up has been fabricated and assembled. The prototype equipped with appropriate measuring and controlling devices. Detailed experiments have been carried out at various operating conditions. The heat and mass transfer coefficients have been obtained experimentally. The results of the investigation have shown that the system productivity increases with the increase in the mass flow rate of water through the unit. Water temperature at condenser exit increases linearly with water temperature at humidifier inlet and it decreases as water flow rate increases. HDH desalination systems realised on also work at atmospheric pressure; hence they do not need mechanical energy except for circulation pumps and fans. These kinds of systems are suitable for developing countries. The system is modular, it is possible to increase productivity with additional solar collectors and additional HDH cycles.

Development and Testing of a Lab-Scale Air-Gap Membrane Distillation Unit for Water Desalination

2018 ◽  
Author(s):  
Reza Baghaei Lakeh ◽  
Keaton Cornell ◽  
Benny Ly ◽  
Aaron Chan ◽  
Sepideh Jankhah
Keyword(s):  
Elevated Temperatures ◽  
Membrane Distillation ◽  
Air Gap ◽  
Water Desalination ◽  
Coolant Temperature ◽  
Feed Water ◽  
Permeate Flux ◽  
Flow Rates ◽  
Air Gap Membrane Distillation ◽  
Membrane Porosity

As the population grows, one issue that is continually being addressed is the lack of clean water resources. In order to explore viable solutions, rapid experimentation and research has been underway to alleviate the water crisis. With the addition of new emerging technology, the development, improvement, and understanding of various techniques used to treat non-potable water has expanded. One subcategory of water filtration in particular that has seen rapid growth is Membrane Distillation (MD). MD is a filtration process that utilizes thermal energy to desalinate and decontaminate water. Compared to current industry leading techniques such as reverse osmosis, MD does not require such large operating pressures, leading to less power consumption. MD is accomplished primarily by flowing contaminated feed water at elevated temperatures across semi-permeable membranes. The membranes used are made to allow water vapors to penetrate through and separate from the contaminated liquid portion. By maintaining a temperature difference across the membrane, a pressure gradient is created, which drives the vapor of feed water through the pores in the membrane. Once the vapor passes through the membrane, it condenses through various methods and is collected. Air Gap Membrane Distillation (AGMD) has shown significant ability to desalinate water effectively in small scales. The air gap between the membrane and condensation plate minimizes heat loss through conduction, making AGMD a more attractive option for upscaling. In this project a laboratory-scale test cell was developed to test AGMD using different membranes, and operational parameters. In order to test such parameters, a unique design with baffled channels to induce turbulence was designed and manufactured. Feed water and coolant temperature differences, flow rates, membrane porosity, and air gap thickness are among the parameters that has been studied in this research. Temperatures of the hot feed were varied from 40°C to 80°C while the cold feed temperature was kept at a near constant temperature of 0°C. Flow rates of feed water and coolant water range from 1 to 3 L/Min. It was observed that the permeate flux is an increasing function of feed water temperature and membrane porosity. The air gap thickness plays a major role in permeate flux and energy consumption of the system.

Experimentation and Mathematical Model Reseach on Air Gap Membrane Distillation

2012 ◽  
Vol 581-582 ◽  
pp. 89-93
Author(s):  
Ying Guan ◽  
Hong Jiang Cui
Keyword(s):  
Mathematical Model ◽  
Mass Transfer ◽  
Flow Rate ◽  
Membrane Distillation ◽  
Air Gap ◽  
Working Fluid ◽  
Fluid Temperature ◽  
Air Gap Membrane Distillation ◽  
Set Up ◽  
The Mathematical Model

Air gap membrane distillation (AGMD) experiments were done to reseach flux of membrane distillation at different working fluid temperature and mass flow rate. The driving power of distillation experiments is solar power. The experimental flux of membrane distillation reached 49kg/m2•h. The mathematical model of AGMD’ heat and mass transfer was set up. The biggest relative error is less than 9% between results of experiment and mathematical model calculation. The mathematical model can be used to forecast the distillation flux and the thermal efficiency.

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