Dynamic modeling and analysis of a direct contact membrane distillation system with heat recovery

Membrane Distillation (MD) system has been widely used for desalination for past decades to produce potable water for human cinsumption. However, current MD systems are fully dependent on electrical power supply for operation. In this work, a Parabolic Solar Thermal Collector (PSTC) integrated with Direct Contact Membrane Distillation (DCMD) system was designed to study the influence of a PSTC towards membrane performance. The objective of this w is to analyze the performance of the hybrid PSTC system with DCMD system in purifying seawater. PSTC was used as a support system to pre-heat seawater until the it reaches a certain temperature. In this project, as the temperature of seawater in the pre-heated tank reaches 45 °C, a 12 V submersible water pump will be automatically switched on and channel the seawater in the pre-heated tank into the feed tank of the DCMD system. In terms of energy consumption, less amount of energy is required to channel the seawater sample into the feed tank. In regards of system performance analysis, the hybrid system was compared to a DCMD system which utilises an electrical heater. It was noticed that only a marginal reduction in terms of permeate flux (7.1% difference) and salt rejection (0.8% difference) was observed when using the PSTC system. As a conclusion, the utilization of solar technology via a PSTC can potentially bring a lot of benefits in the desalination industry and in the future of employing MD system in the industry.

Performance investigation of a solar-assisted direct contact membrane distillation system

Innovative solar-assisted direct contact membrane distillation system: Dynamic modeling and performance analysis

Performance and cost comparison of different concentrated solar power plants integrated with direct-contact membrane distillation system

Compared with traditional membrane distillation system, the heat pump two-effect direct contact membrane distillation system has an advantage of low energy consumption. However, affected by many kinds of parameters, such as materials, components and operation conditions as well as the complex coupling between these parameters, it is difficult to achieve the optimal operation conditions and high gained output ratio (GOR) by optimizing the parameters. Therefore, analyses of mathematical modeling and optimal operation conditions of heat pump two-effect direct contact membrane distillation system were carried out in this paper. According to the operating principle and physical characteristics of key components, such as membrane distillation system, heat pump system, intermediate heat exchanger and auxiliary cooler, the mathematical model of heat pump two-effect direct contact membrane distillation system was established, the process of system performance simulation was designed and system performance simulation software was compiled to analyze the effect of ten parameters on GOR and total water production(Wtot). The optimal operation conditions analysis method of heat pump two-effect direct contact membrane distillation system was proposed. Through the developed simulation software of the heat pump membrane distillation system, using the proposed optimal operation conditions analysis method, When Wtot was 10.0kg/h and heat pump compressor power was 688W, the GOR of the optimized system could reach 9.43

Performance analysis of a thermal-driven tubular direct contact membrane distillation system

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.

Behavior and removal of microplastics during desalination in a lab-scale direct contact membrane distillation system

Enhanced performance of a direct contact membrane distillation (DCMD) system with a Ti/MgF2 solar absorber under actual weather environments

The oil palm industries generate large amounts of effluent that can cause pollution and, as a result, pose serious threats to the environment. Recently, membrane distillation (MD) has been identified as a potential candidate for treatment of palm oil mill effluents (POME). This is because the release of POME at high temperature may reduce the need to preheat the effluent prior to operation. The objective of this article is to manufacture a bench-scale MD system and assess the performance of the system in POME treatment. This project started with the design of a process and instrumentation diagram (P&ID) and continued with the fabrication part. Subsequently, the performance of the direct contact membrane distillation (DCMD) system was tested using POME as a feed solution. Three different feed temperatures (55 °C, 65 °C and 75 °C) were analyzed during the testing. The results obtained show that the permeate flux increased with the increase of feed temperature with the highest flux is 10.76 kg/m2.hr. More than 85% of pollutants including ammonia nitrogen, color, chemical oxygen demand (COD) and turbidity were rejected. This shows that the system is capable of treating POME and producing high quality permeate water.

As the need for freshwater is continuously growing, seawater desalination technologies are increasingly used to meet these demands. The high solutes’ rejection factor and the low energy consumption of Membrane Distillation (MD) technologies make them high potential desalination techniques. However, they suffer from membrane fouling which deteriorates the system’s performance and causes high maintenance costs. This paper presents a novel approach based on a learning observer for detecting and localizing fouling in Direct Contact Membrane Distillation (DCMD) systems which allows to significantly decrease the maintenance costs. This approach has the advantage of being flexible and computationally inexpensive. Before the architecture and the design steps of the proposed observer are presented, the DCMD module layout in the fault free scheme and in presence of fouling is explained. To illustrate the effectiveness of the proposed fouling monitoring approach, several tests were simulated and two scenarios were considered: homogeneous and non-homogeneous fouling evolution along the membrane. The various simulations demonstrated very encouraging results in both fouling estimation and localization.

Solar energy assisted direct contact membrane distillation (DCMD) process for seawater desalination

Solar-powered membrane distillation (SP-MD) technology has proven to be an ideal solution for providing fresh water in remote and off-grid locations. In this study, a novel solar energy-driven direct contact membrane distillation (DCMD) cycle is proposed in which a nanofluid-based volumetric absorption solar collector (VASC) is used to drive the DCMD process. The present work focuses on the use of volumetric collector instead of commercially available surface absorption-based solar collector in case of two-loop indirect SP-MD systems, which are installed to control the scaling and corrosion issues in solar collectors. The thermodynamic performance of this two-loop indirect solar-powered DCMD (SP-DCMD) system has been evaluated with the help of a mathematical model prepared in matlab. For modeling the DCMD unit, the ɛ-number of transfer unit (NTU) method used for designing heat exchangers has been employed. The performance of the overall system is evaluated by gained output ratio (GOR), thermal efficiency (η) of the membrane distillation, and water flux (Jw), and effects of various operating parameters related to both DCMD and VASC systems have been understood on the overall system performance. Finally, it has been shown that VASC-driven DCMD system has been approximately 4–15% higher gained output ratio compared to surface absorption-based solar collector (SASC)-driven DCMD system under similar operating conditions.

Understanding the energy efficiency of direct contact membrane distillation (DCMD) is important for the widespread application and practical implementation of the process. This study analyzed the available energy, known as exergy, in a DCMD system using computational fluid dynamics (CFD). A CFD model was developed to investigate the hydrodynamic and thermal conditions in a DCMD module. After the CFD model was verified, it was used to calculate the temperature polarization coefficient (TPC) and exergy destruction magnitudes under various operating conditions. The results revealed that slight decreases and increases in the TPC occurred with distance from the inlet in the module. The TPC was found to increase as the feed temperature was reduced and the feed and permeate flow rates were increased. The exergy destruction phenomenon was more significant under higher feed temperatures and higher flux conditions. Although the most significant exergy destruction in the permeate occurred near the feed inlet, the effect became less influential closer to the feed outlet. An analysis of exergy flows revealed that the efficiency loss in the permeate side corresponded to 32.9–45.3% of total exergy destruction.

In this study, two composite nanofibrous membranes of Polyvinylidenefluoride (PVDF) and [poly(vinylidenefluorideco-hexafluoropropylene)] (PVDF-co-HFP) prepared by the electrospinning process were employed in a direct contact membrane distillation (DCMD) system. We changed the pump flow rate and temperature difference to examine their effects on permeate flux and salt rejection. The SEM observations, porosity analyzer technique, and contact angle measurement indicated the nanobrous membrane with an average fiber diameter of 170 nm and maximum pore diameter distribution of 0.3 µm is the best membrane for the DCMD system. However, the ability of the hydrophobic membrane affects the filtration efficiency of the DCMD system. The contact angle of the PVDF-HFP electrospun membrane (128°) shows better hydrophobic than the PVDF electrospun membrane (125 °). From the experiment of 12 hours, the salt rejection of PVDFHFP (99.9901 %) was better than that of PVDF composite membrane (99.9888 %) and was almost the same as that of the PTFE commercial membrane (99.9951 %). In addition, the permeate flux of the PVDF-HFP composite membrane is 4.28 kg/ m2hr higher than the PTFE commercial membrane.