Exergetic Relationship Between the Thermal Properties of Direct Contact Membrane Distillation

2020 ◽  
Vol 142 (3) ◽  
Author(s):  
D. Perdue ◽  
L. Chen ◽  
L. Schaefer
Keyword(s):  
Thermal Properties ◽  
Direct Contact ◽  
Chemical Potential ◽  
Direct Simulation Monte Carlo ◽  
Monte Carlo Analysis ◽  
Membrane Distillation ◽  
Flow Speed ◽  
Hydrophobic Membrane ◽  
Direct Contact Membrane Distillation ◽  
Temperature Polarization

Abstract Direct contact membrane distillation (DCMD) is a process that has shown promise within the field of desalination due to its less energy intensive methods and widespread applications. DCMD is a thermally driven microfiltration separation process that operates on the principle of vapor–liquid equilibrium conditions where heat and mass transfer occur simultaneously. Fundamentally, DCMD is based on a porous hydrophobic membrane separating the hot solution (feed) from the cold solution (permeate) where desalinated water condenses. The membrane interfacial temperatures determine the vapor pressure difference across the membrane. In this work, a direct simulation Monte Carlo analysis is employed to investigate how the exergy of the system relates to some key thermal properties, namely, the temperature polarization coefficient (TPC) and the thermal efficiency (TE), as other parameters are changed, such as feed temperature, flow speed, and membrane porosity. Through molecular simulation, phase equilibrium is reached by calculating the chemical potential at the membrane interface and the entropy of the system is found. Since exergy is a function of entropy, enthalpy, and temperature, the amount of useful work is calculated. Finally, exergy is compared to the TPC and TE as the flowrate and porosity are varied. We demonstrate that with these exergy calculations, the information about the thermal relationship between microscopic and macroscopic parameters will improve future experimental work.

scholarly journals Performance modelling of direct contact membrane distillation using a hydrophobic/hydrophilic dual-layer membrane

2021 ◽  
Author(s):  
Inci Boztepe ◽  
Stephen Gray ◽  
Jianhua Zhang ◽  
Jun-De Li
Keyword(s):  
Mass Transfer ◽  
Thermal Efficiency ◽  
Direct Contact ◽  
Single Layer ◽  
Membrane Distillation ◽  
Experimental Results ◽  
Conductive Heat ◽  
Hydrophobic Membrane ◽  
Direct Contact Membrane Distillation ◽  
Layer Membrane

Abstract HFP-co-PVDF/N6 hydrophobic/hydrophilic dual-layer membrane was used to study desalination with direct contact membrane distillation (DCMD). A one-dimensional (1-D) model was proposed to predict the flux and thermal efficiency. Heat and mass transfer equations were solved numerically for the combined hydrophilic and hydrophobic layers. The membrane characteristics of the hydrophobic layer were considered for the calculation of the mass transfer coefficients, while the hydrophilic layer was ignored since it was assumed to be filled with water. However, the hydrophilic layer was taken into account during the calculations of conductive heat transfer. Therefore, the equations are different, compared to single-layer hydrophobic membranes. It was found that with the same hydrophobic membrane characteristics, the single-layer membranes performed with better flux and thermal efficiency than the dual-layer membranes. Furthermore, the improvement of flux and thermal efficiency by an addition of the hydrophilic layer has not been observed experimentally, and it is suggested that the improved performance for dual-layer membranes reported previously is due to improved permeability by using thinner and more porous hydrophobic layers that can be mechanically reinforced by the hydrophilic layer. The validation of the model was conducted by comparing the experimental results for single- and dual-layer membranes with the modelling results. The predicted flux and thermal efficiency by the modelling were within 10% error to the experimental results.

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.

scholarly journals A non-invasive optical method for mapping temperature polarization in direct contact membrane distillation

2017 ◽  
Vol 536 ◽  
pp. 156-166 ◽  
Author(s):  
S. Santoro ◽  
I.M. Vidorreta ◽  
V. Sebastian ◽  
A. Moro ◽  
I.M. Coelhoso ◽  
...  
Keyword(s):  
Optical Method ◽  
Direct Contact ◽  
Membrane Distillation ◽  
Non Invasive ◽  
Direct Contact Membrane Distillation ◽  
Temperature Polarization

scholarly journals Desalting of RO Waste and Drainage Water by Direct Contact Membrane Distillation

2018 ◽  
Vol 24 (9) ◽  
pp. 41
Author(s):  
Asrar Abdullah Hassan ◽  
Ahmed Khalid Mohammed Reda
Keyword(s):  
Fresh Water ◽  
Direct Contact ◽  
Membrane Surface ◽  
Membrane Distillation ◽  
Drainage Water ◽  
Operating Conditions ◽  
Hydrophobic Membrane ◽  
Membrane Area ◽  
Direct Contact Membrane Distillation ◽  
Two Samples

Direct contact membrane distillation is an effective method for production of fresh water from saline water. In this study two samples were used as feed solutions; the first one was RO waste from Al-Hilla Coca-Cola Factory (TDS= 2382 mg/l) and the other was Haji Ali drainage water (TDS= 4127 mg/l). Polytetrafluoroethylene (PTFE) hydrophobic membrane supported with polypropylene (PP) was used as flat sheet form with plate and frame cell. Results proved that membrane distillation is an effective technique to produce fresh water with high quality from brine with low salinity content. With membrane area of 8x8 cm2, the volume of treated water decreased from 34.97 ml at first half hour to 33.02 ml after 180 min of an experiment for first feed type and from 36.92 ml to 33.84 ml for the second feed type due to the fouling accumulated on the membrane surface. The temperature on both sides of the membrane surface and TDS of permeate was measured every 30 min of experiment time, also some tests were made on feed and permeate ions. Time of experiment was 180 min with the same operating conditions.   

scholarly journals Bispacer Multi-Stage Direct Contact Membrane Distillation System: Analytical and Experimental Study

Processes ◽  
2021 ◽  
Vol 9 (8) ◽  
pp. 1297
Author(s):  
Morteza Aliabadi ◽  
Hassan Ghorashi ◽  
Shamim Shokri Motlagh ◽  
Seyedeh Fatemeh Nabavi ◽  
Seyed Arash Pakzad ◽  
...  
Keyword(s):  
Direct Contact ◽  
Mechanical Stability ◽  
Membrane Distillation ◽  
Operating Conditions ◽  
Permeate Flux ◽  
Direct Contact Membrane Distillation ◽  
Multi Stage ◽  
Temperature Polarization ◽  
Output Ratio ◽  
Polarization Coefficient

A multi-staged direct contact membrane distillation (MDCMD) system is designed considering a novel bispacer configuration in the present study. The proposed bispacer DCMD, which has not been addressed in the literature to best of our knowledge, is considered with two purposes, including increasing mechanical stability and turbulence. As increasing turbulence leads to increasing Nusselt number, the bispacer MDCMD provides higher permeate flux. An analytical approach is considered using energy and mass balance correlation. The effect of bispacer and feed operating conditions, including feed temperature, feed flow rate, feed salinity, and the number of stages on permeate flux and salt rejection of the developed MDCMD, are examined both analytically and experimentally. The performance and sustainability of the developed system were investigated by analyzing the parameters, including thermal efficiency (η), gained output ratio (GOR), and temperature polarization coefficient (TPC).

Effect of Hydrophobicity Degree on PVDF Hollow Fiber Membranes for Textile Wastewater Treatment Using Direct Contact Membrane Distillation

2013 ◽  
Vol 65 (4) ◽  
Author(s):  
N. M. Mokhtar ◽  
W. J. Lau ◽  
P. S. Goh
Keyword(s):  
Contact Angle ◽  
Hollow Fiber ◽  
Direct Contact ◽  
Polyvinylidene Fluoride ◽  
Textile Wastewater ◽  
Membrane Distillation ◽  
Hollow Fiber Membranes ◽  
Hydrophobic Membrane ◽  
Direct Contact Membrane Distillation ◽  
Fiber Membranes

The objectives of this study are to study the effect of hydrophobicity degree of  polyvinylidene fluoride (PVDF) hollow fiber membranes blended with different types of additives i.e. ethylene glycol (EG) and polyvinylpyrrolidone (PVP) on textile wastewater application. The degree of hydrophobicity of each membrane was analyzed using contact angle goniometer. The membrane morphology and gas permeability were characterized prior to filtration experiment. Both membranes were tested using direct contact membrane distillation (DCMD) system and their performances were evaluated with respect to water flux and dye removal. This study revealed that the membrane with higher contact angle has greater stability in terms of flux and dye rejection compared to the membrane with low hydrophobic property. This is mainly due to the low surface energy obtained by the highly hydrophobic membrane that prevented the liquids from both sides to penetrate through membrane pores.

scholarly journals Enhancing the Permeate Flux of Direct Contact Membrane Distillation Modules with Inserting 3D Printing Turbulence Promoters

Membranes ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 266
Author(s):  
Hsuan Chang ◽  
Chii-Dong Ho ◽  
Yih-Hang Chen ◽  
Luke Chen ◽  
Tze-Hao Hsu ◽  
...  
Keyword(s):  
3D Printing ◽  
Direct Contact ◽  
Polarization Effect ◽  
Membrane Distillation ◽  
Flow Channel ◽  
Permeate Flux ◽  
Geometric Shapes ◽  
Flux Enhancement ◽  
Direct Contact Membrane Distillation ◽  
Temperature Polarization

Two geometric shape turbulence promoters (circular and square of same areas) of different array patterns using three-dimensional (3D) printing technology were designed for direct contact membrane distillation (DCMD) modules in the present study. The DCMD device was performed at middle temperature operation (about 45 °C to 60 °C) of hot inlet saline water associated with a constant temperature of inlet cold stream. Attempts to reduce the disadvantageous temperature polarization effect were made inserting the 3D turbulence promoters to promote both the mass and heat transfer characteristics in improving pure water productivity. The additive manufacturing 3D turbulence promoters acting as eddy promoters could not only strengthen the membrane stability by preventing vibration but also enhance the permeate flux with lessening temperature polarization effect. Therefore, the 3D turbulence promoters were individually inserted into the flow channel of the DCMD device to create vortices in the flow stream and increase turbulent intensity. The modeling equations for predicting the permeate flux in DCMD modules by inserting the manufacturing 3D turbulence promoter were investigated theoretically and experimentally. The effects of the operating conditions under various geometric shapes and array patterns of turbulence promoters on the permeate flux with hot inlet saline temperatures and flow rates as parameters were studied. The distributions of the fluid velocities were examined using computational fluid dynamics (CFD). Experimental study has demonstrated a great potential to significantly accomplish permeate flux enhancement in such new design of the DCMD system. The permeate flux enhancement for the DCMD module by inserting 3D turbulence promoters in the flow channel could provide a maximum relative increment of up to 61.7% as compared to that in the empty channel device. The temperature polarization coefficient (τtemp) was found in this study for various geometric shapes and flow patterns. A larger τtemp value (the less thermal resistance) was achieved in the countercurrent-flow operation than that in the concurrent-flow operation. An optimal design of the module with inserting turbulence promoters was also delineated when considering both permeate flux enhancement and energy utilization effectiveness.

Experimental Investigation of Heat Transfer Correlation for Direct Contact Membrane Distillation

2019 ◽  
Vol 142 (1) ◽  
Author(s):  
Quoc Linh Ve ◽  
Kawtar Rahaoui ◽  
Mohammed Bawahab ◽  
Hosam Faqeha ◽  
Abhijit Date ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Experimental Investigation ◽  
Direct Contact ◽  
Membrane Distillation ◽  
Copper Plate ◽  
Heat Transfer Correlation ◽  
Hydrophobic Membrane ◽  
Flow Channels ◽  
Direct Contact Membrane Distillation ◽  
Turbulent Flow Regime

Abstract This paper presents an experimental investigation of heat transfer in direct contact membrane distillation (DCMD) flow channels with and without the spacer. In this experiment, the usual hydrophobic membrane of DCMD is replaced by a copper plate to eliminate mass transfer. The study shows the most appropriate heat transfer correlations for empty channel cases with different channel heights and flow rates. For the case with the spacer in the flow channels, two spacer materials are investigated: nonwoven plastic and woven stainless steel. The paper presents the most appropriate heat transfer correlation for both these spacer materials. Further, the paper presents finding with two more spacer materials, woven fiberglass and aluminum spacer. It is found that the most appropriate heat transfer correlation for these materials is in the turbulent flow regime although the experimentally estimated Reynolds number suggests laminar flow is presented.

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