A solar‐driven membrane‐based water desalination/purification system

Lack of fresh water has turned into one of the major challenges of the world in the present century. Desalination of brackish or seawater has been proven to be one of the best solutions to cope with this global challenge. Among all the desalination methods, Membrane Distillation (MD) is well known as a cost effective and profitable technology for treating saline water. However, higher energy consumption compared to other separation techniques has been reported as MD’s main drawback. That is why the application of solar energy to provide the thermal energy requirement of MD modules has been the focal point of research in this field in recent years. Despite many studies and efforts that have been conducted to date, solar driven membrane based systems have still many undiscussed aspects. Integrating solar energy and membrane technology is not yet a straightforward matter and has many opportunities for technical and economic improvements. Utilizing new solar technologies, their combination with thermal driven membrane modules, and trying to improve thermal and overall efficiency of this integration can be the bedrock of novel researches. Furthermore, most of the previous studies and research activities have been focused on desalination systems, while the proposed systems have been either inefficient or energy intensive, and other sources for improving water quality such as wastewater is completely under-researched. That is why, this study proposed a novel integrated solar membrane-based desalination and wastewater treatment system taking advantage of technologies such as heat pipes, vacuum tubes, and direct contact membrane distillation (DCMD) modules. A theoretical study was considered to firstly investigate the performance and feasibility of the proposed system and secondly to obtain the optimum physical and operational characteristics of both solar and desalination systems. The theoretical analysis was performed by using appropriate energy and exergy equations which were solved in Matlab software. Heat and mass transfer equations along with energy and mass balance equations were considered in this study. A new multi-step theoretical approach was proposed and developed to model the DCMD unit, while the thermal resistance network method was applied in the simulation of the solar system including vacuum glasses, heat pipes, and manifold. Based on the optimum data obtained from the mathematical models, an experimental rig was designed, manufactured, and tested under different climatic and operational conditions. The system was controlled using a central control unit including a control unit, a National Instrument Data Acquisition (NI-DAQ) system, and a power unit. An application program interface (API) was programmed in the LabVIEW 2014 software to record the data at 10- second intervals. Climatic data including solar radiation, ambient temperature, and wind velocity were collected from the weather station located at Edith Cowan University, Joondalup Campus which is located 23 km north of Perth business district. The comparison of the theoretical and experimental results revealed the capability of the developed model to accurately predict the performance of the proposed system. In addition, the optimum characteristics of the system, including the optimum solar collector’s surface area, feed and permeate streams mass flow rates and temperatures, were determined. The results revealed that the application of this nanofluid as the solar working fluid along with implementing a variable mass flow rate technique significantly improved the overall efficiency of the solar system. Sodium Dodecyl BenzeneSulfonate (SDBS) at 0.1 wt.% was the optimum concentration of SDBS for 0.05 wt.% Al2O3/DI water nanofluid exhibiting the highest stability and thermal conductivity enhancement. The results also showed the high dependency of the DCMD module to the physical (e.g., length) and operational (e.g., feed and permeate mass flow rates) parameters, while its performance was independent of salinity. The highest freshwater production rates in hot and cold seasons were observed to be 3.81 and 2.1 L/m2h, respectively. Moreover, the maximum gained output ratios of the system were around 0.79 and 0.58 in hot and cold seasons, respectively. The results also indicated that the gained output ratio and overall efficiency of the system improved upon application of a cooling unit in the permeate flow loop of the system, indicating the effectiveness of the proposed configuration. In addition, the freshwater production increased up to 37% when the system was equipped with a cooling unit. However, the economic feasibility of implementing the cooling unit needs further investigations. Moreover, the proposed system effectively removed the contaminating metals from wastewater by showing the removal percentage of 96, 89, 96, 100, 100, and 94% for Fe, Mn, Cu, Na, K, and Ca, respectively

A multipurpose desalination, cooling, and air-conditioning system powered by waste heat recovery from submarine diesel exhaust fumes and cooling water

The role of cooling and air-conditioning systems in submarines is assessed as indispensable, and a reliable water supply is essential for both crew and equipment. At the same time, the large amounts of high-temperature exhaust fumes discharged from submarine engines provide an excellent opportunity to recover and apply this waste energy in required applications. This paper introduces a novel multipurpose desalination, cooling, and air-conditioning system to recover waste heat from both the exhaust fumes and the cooling water of submarine engines. The whole system is mathematically modelled and analysed based on the actual thermo-physical parameters of the engine\u27s exhaust fumes. The analysis indicates that at cooling water flow rate of 0.25 kg/s and diesel exhaust mass ratio (X) of 0.25, the mass flux through the membrane in the desalination unit reaches 8.3 kg/m2h. Whereas for the same cooling water flow rate, the mass flux increases by 2 kg/m2h as X increases from 0.25 to 0.3. The results also show that a 160 kW cooling power is only achievable when X varies between 0.8 and 0.95 and the refrigerant mass flow rate is in the range of 0.27 kg/s to 0.34 kg/s

Integration of heat pipe solar water heating systems with different residential households: An energy, environmental, and economic evaluation

This study presents a detailed methodology for evaluating the energy, environmental, and economic contributions of heat pipe solar water heating (HPSWH) systems in various households. The hot water consumption patterns of Perth residents in Australia in one, two, and four-occupant houses are extracted in hourly basis throughout a year. The annual performance of the system is evaluated based on parameters such as saved energy, solar fraction, avoided CO2 emission, saved money, and payback period. Moreover, an experimental rig is designed, manufactured, and tested. The results show that the contribution of the solar system in meeting the hot water demand is around 99% in summer, while this contribution drops to 36–51% in winter. Almost 387–1146.8 kg of CO2 emissions can be avoided annually in Perth if HPSWH systems are integrated with the conventional heating systems. In addition, it is shown that the HPSWH system has its most economic justification in households with higher number of occupants. Moreover, the payback period is much lower for houses with conventional electric water heating systems compared to houses with LPG systems

Small scale desalination technologies: A comprehensive review

In recent decades, problems related to fresh water has become a very important issue for humans. Small-scale desalination (SSD) systems, besides large-scale desalination (LSD) systems, fulfil an important role in meeting freshwater demand by eliminating the cost of transmission and have the advantage of treating water on-site. In this study, for the first time, a comprehensive review of previous studies has been carried out on SSD systems (less than 25 m3/d water production). These systems are powered using renewable, non-renewable or hybrid sources of energy, incorporating different treatment technologies such as: reverse osmosis (RO); electro dialysis (ED); capacitive deionization (CDI); membrane desalination (MD); humidification–dehumidification processes (HDH); multi-effect desalination (MED); and hybrid technologies, including a combination of RO-UF, RO-ED and RO-MED. The advantages and drawbacks of the systems that operate using fossil fuels and renewable energy (RE) systems have been studied, considering membrane, evaporation and salinity features. Among these, solar-based desalination systems are the most popular. Accordingly, numerous studies on RO, ED, MD, HDH and MED technologies for solar-SSD systems have been compared in terms of their freshwater productivity, energy consumption and cost of produced water. Attention has also been paid to SSD systems powered via wind, geothermal, tidal and hybrid energies. It has been determined that the RO system holds the largest market share in both non-renewable (25 %) and renewable energy (40 %) systems. In addition, a comparison of low-cost SSD and LSD systems shows that SSD systems are economically competitive with LSD systems. The outlook for the future shows that the use of SSD systems powered using non-renewable energy is likely to decrease, except in areas where energy costs are very low. In addition, the use of solar-SSD systems is likely to increase, where systems that operate solely on wind or geothermal energy will be replaced by hybrid renewable energy systems

The use of variable coil pitch of helical tube on the hydro-thermal performance improvement

The use of helical tubes in heat transfer appliances is desirable due to their better heat transfer characteristics, but the higher pressure drop decreases the overall performance. The variation of pitch design of a helical tube is proposed to alleviate this situation so that the pitch number does not remain constant in the total tube length. A total of six variable pitch numbers with three different diameters are proposed and investigated on the thermal and fluid characteristics. To better understand the helical tube efficiency, PEC (performance evaluation criteria) is selected as a performance indicator in the present work and simulations are performed in a laminar regime (100 ≤ Re ≤ 1600) at a constant heat flux boundary condition using computational fluid dynamics. The numerical results show that variable radial pitch has higher effects on the overall performance than variable axial pitch, and it can intensify the helical tube performance by up to 10%. The results also indicate that increasing the tube diameter leads to heat transfer and friction factor increment while increasing the Reynolds number deteriorates the overall performance

Performance enhancement of photovoltaic-thermal modules using a new environmentally friendly paraffin wax and red wine-rGO/H2O nanofluid

Photovoltaic/thermal systems are one of the most efficient types of solar collectors because they absorb solar radiation and generate electricity and heat simultaneously. For the first time, this paper presents an investigation into the impact of red wine-rGO/H2O nanofluid and paraffin wax on the thermohydraulic properties of a photovoltaic/thermal system. The study focuses on three innovative nonlinear arrangements of the serpentine tubes. The effects of these materials and configurations are analyzed through numerical simulations. To improve the performance, environmentally friendly materials, including red wine-rGO/H2O nanofluid and paraffin wax, have been used. Various performative parameters such as electrical and thermal efficiency of the photovoltaic/thermal system, exergy, and nanofluid concentration were investigated. The results demonstrated a significant enhancement in the system’s performance when using innovative serpentine tubes instead of simple tubes for the fluid flow path. The use of paraffin C18 increases electrical efficiency, while the use of paraffin C22 improves thermal efficiency. Moreover, the incorporation of phase change materials along with the utilization of innovative geometries in the serpentine tube led to a notable improvement in the outlet temperature of the fluid, increasing it by 2.43 K. Simultaneously, it substantially reduced the temperature of the photovoltaic cells, lowering it by 21.55 K. In addition, the new model demonstrated significant improvements in both thermal and electrical efficiency compared to the simple model. Specifically, the maximum thermal efficiency improvement reached 69.2%, while the maximum electrical efficiency improvement reached 11.7%

Performance enhancement of a solar-driven DCMD system using an air-cooled condenser and oil: Experimental and machine learning investigations

Solar-driven direct contact membrane distillation systems (DCMD) are disadvantaged by low freshwater productivity and low gain-output-ratio (GOR). Consequently, this study aims to achieve two primary objectives: i) improving the solar DCMD performance, and ii) harnessing machine learning models for precise and straightforward modeling of the solar DCMD system. To achieve these goals, a novel solar DCMD system powered with oil-filled heat pipe evacuated tube collectors (HP-ETCs) and equipped with an air-cooled condenser was used for the first time. The system was evaluated under eight different scenarios covering both its energy and economic performances. The performance prediction of three different machine learning models including ANN, SVR and RF was assessed for the proposed system. The results showed that integrating an air-cooled condenser and oil-filled HP-ETCs into the solar DCMD system significantly improved the performance and reduced freshwater cost, resulting in: a 35.39–37 % increase in freshwater productivity; a 30.64–31.57 % enhancement in GOR; a 35–38 % rise in daily efficiency; and a 20 % decrease in freshwater cost. The results demonstrate that ANN and SVR have excellent performance for modeling the solar-driven DCMD system, achieving MAPEtest values of approximately 1 % and 4 % for predicting permeate flux and GOR, respectively

Evaluation of mechanical vapor recompression and easy multi-effect desalination systems in different climate conditions-sensitivity and 7E analysis

Evaporative desalination systems, such as Multi-Effect Desalination (MED) and Mechanical Vapor Recompression (MVR), play important roles in addressing this challenge. Although large-scale desalination systems possess limitations in catering to the water demands of remote regions and islands and entail the cost of water transportation to residential areas, it is imperative to concentrate on studying the feasibility of employing centralized evaporative water production systems. Firstly, in this study, the initial focus is on conducting energy and exergy analyses of MVR and Easy MED systems, with a goal of enhancing knowledge about the energy consumption, exergy destruction and exergetic efficiency of these systems. Secondly, an economic analysis is undertaken to assess the feasibility of deploying these systems in various global regions. The analysis takes into account different geographical and techno-economic conditions, such as sea water temperature, interest rates, and electricity costs. This investigation also aims to explore variations in Annual Operative Cost (AOC), Total Annual Cost (TAC) and the cost of fresh water across these diverse regions. Thirdly, a sensitivity analysis is performed for the economic assessment of MVR and Easy MED systems. Lastly, exergoeconomic, environmental, enviroeconomic and exergoenvironmental analyses are conducted for both of these systems. The results show that the exergy efficiency of the Easy MED system surpasses that of the MVR, whereby the exergy destruction for Easy MED and MVR are recorded to be 5460 W and 6360 W respectiveyl. In addition to this, the MVR system demonstrated a higher TAC across all cities. The freshwater production cost of the Easy MED system was less expensive than of the MVR system. Perth was the most cost-effective city, with freshwater costs of 6.8 /m3 and 11.91 /m3 for MVR and Easy MED systems, respectively. Further to this, sensitivity analysis revealed that both systems are sensitive to fluctuations in electricity costs and seawater temperatures. The MVR system incurred higher fuel, product, and exergy destruction costs. However, the MVR system also exhibited greater environmental friendliness due to its lower emission of pollution gases

Performance improvement of thermal-driven membrane-based solar desalination systems using nanofluid in the feed stream

Different techniques have been proposed so far to improve the performance of thermal-driven membrane modules applied in solar desalination systems. These techniques have increased the freshwater productivity of the system but at the cost of its increased overall specific energy requirement. Due to this major drawback, the main objective of this study is to implement nanofluid in the feed stream of a heat pipe solar membrane-based desalination system, which not only aims to improve the freshwater productivity of the system, but also has the capability of decreasing its specific energy requirement. Synthetic seawater (with the salinity of 3.5%) was generated by dissolving appropriate amount of Sodium Chloride (NaCl) salt in normal tap water and used as the base fluid. Then, Aluminium oxide (Al2O3) nanoparticles were applied to fabricate the nanofluid. The performance of the system in terms of freshwater productivity, quality of treated water, specific thermal and electrical energy consumptions, gained output ratio, and overall efficiency was experimentally studied and compared under hot and cold climatic conditions of Perth in Australia. The results indicated that the application of nanofluid increased the freshwater productivity in hot and cold seasons by 18% and 22%, respectively. It also decreased the specific thermal energy consumption as this parameter was 17.5% and 14% lower in hot and cold seasons compared to the system without nanofluid. Moreover, using nanofluid improved the gained output ratio of the system by 9% and 18% under hot and cold climatic conditions, respectively. The overall efficiency of the system was also proved to be enhanced upon the application of nanofluid where the results showed 17.4% and 18% increase in hot and cold seasons, respectively

Experimental investigation of varying design parameters on the production rate and temperature polarisation of a DCMD system

Much of the research in the analysis of Temperature polarisation (TP) and the productivity of a membrane distillation (MD) system tends to concentrate on operational conditions. However, substantial enhancements in permeate flux can be realised through the incorporation of fundamental design modifications. This research showed that TP can be successfully mitigated almost to a level of non-existence, by manipulating the module orientation and flow channel height of an in-house designed direct contact membrane distillation (DCMD) system. Notably, at higher flow channel heights, changing the module orientation from the default horizontal position with the feed side on top (FST) to a sideway orientation led to a remarkable 90% increase in the permeate flux of the DCMD module. Permeate side on top (PST) and sideways orientations performed significantly better than FST for larger channel heights, while at low channel heights, the improvement was slight. Temperature measurements proved that thermal convective currents and secondary flows played a vital role in assisting or opposing TP and cannot be disregarded when investigating the hydrodynamics of a DCMD system. The impact of flow directions was insignificant with different channel heights, while the proximity of the flow inlets played a pivotal role in shaping the temperature profiles along the membrane