Search Results (27)

Direct contact heat transfer as an efficient heat recovery method. It is used in the fields of waste heat recovery, nuclear engineering, desalination, and metallurgy. This study examined two key issues of the direct contact heat transfer process: difficulty in accurately characterizing the dynamics of the flow field–phase interface; and difficulty in coupling the complex multiphysics fields involved in direct contact heat transfer. This paper systematically reviews the spatio-temporal evolution characteristics and quantitative characterization methods of bubble dynamics in direct contact heat transfer processes, with an in-depth discussion on theoretical modeling approaches and experimental validation strategies for coupled heat and mass transfer mechanisms within multiphase flow systems. An interesting phenomenon was found in this study. Many scholars have focused their research on optimizing the working conditions and structure of direct contact heat transfer in order to improve heat transfer efficiency. The non-equilibrium phenomenon between the two phases of direct contact heat transfer has not been thoroughly studied. The non-equilibrium phase transition model can deepen the understanding of the microscopic mechanism of interfacial energy exchange and phase transition dynamics in direct contact heat transfer by revealing the transient characteristics and non-equilibrium effects of heat and mass transfer at dynamic interfaces. Based on the findings above, three key directions are proposed to guide future research to inform the exploration of direct contact heat transfer mechanisms in future work: 1 dynamic analysis of multi-scale spatio-temporal coupling mechanisms, 2 accurate quantification of unsteady interfacial heat transfer processes, and 3 synergistic integration of intelligent optimization algorithms with experimental datasets. Full article

Sustainable development is linked to the achievement of several different objectives, as outlined by the 17 Sustainable Development Goals (SDGs) defined by the United Nations. Among them are the production of clean water and the combat of climate change, which is strictly linked to the use of fossil fuels as a primary energy source and their related CO₂ emissions. Water and energy are strongly interconnected. For instance, when processing water, energy is needed to pump, treat, heat/cool, and deliver water. Membrane operations for water treatment/desalination contribute to the recovery of purified/fresh water and reducing the environmental impact of waste streams. However, to be sustainable, water recovery must not be energy intensive. In this respect, this contribution aims to illustrate the state of the art and perspectives in desalination by reverse osmosis (RO), discussing the various approaches looking to improve the energy efficiency of this process. In particular, the coupling of RO with other membrane operations, like pressure-retarded osmosis (PRO), reverse electrodialysis (RED), and forward osmosis (FO), as well as the osmotic-assisted reverse osmosis (OARO) system, are reported. Moreover, the possibility of coupling a membrane distillation (MD) unit to an RO one to increase the overall freshwater recovery factor and reduce the brine volumes that are disposed is also discussed. Specific emphasis is placed on the strategies being applied to reduce the MD thermal energy demand, so as to couple the production of the blue gold with the fight against climate change. Full article

This study examines the potential for the smart integration of waste and renewable energy sources to supply industrial heat at temperatures between 150 °C and 250 °C, aiming to decarbonize heat demand in European industry. This work is part of a European project (SUSHEAT) which focuses on developing a novel technology that integrates several innovative components: a Stirling cycle high-temperature heat pump (HTHP), a bio-inspired phase change material (PCM) thermal energy storage (TES) system, and a control and integration twin (CIT) system based on smart decision-making algorithms. The objective is to develop highly efficient industrial heat upgrading systems for industrial applications using renewable energy sources and waste heat recovery. To achieve this, the specific heat requirements of different European industries were analyzed. The findings indicate that industrial sectors such as food and beverages, plastics, desalination, textiles, ceramics, pulp and paper, wood products, canned food, agricultural products, mining, and chemicals, typically require process heat at temperatures below 250 °C under conditions well within the range of the SUSHEAT system. Moreover, two case studies, namely the Pelagia and Mandrekas companies, were conducted to validate the effectiveness of the system. An analysis of the annual European heat demand by sector and temperature demonstrated that the theoretical potential heat demand that could be met by the SUSHEAT system is 134.92 TWh annually. Furthermore, an environmental impact assessment estimated an annual significant reduction of 19.40 million tonnes of CO₂ emissions. These findings underscore the significant potential of the SUSHEAT system to contribute to the decarbonization of European industry by efficiently meeting heat demand and substantially reducing carbon emissions. Full article

Different approaches have been suggested for the waste heat recovery of high-temperature exhausted gas of a solid oxide fuel cell (SOFC). In such systems, mostly gas turbine (GT) and organic Rankine cycle (ORC) are added as bottoming systems to the SOFC (Configuration 1). However, the SOFC-GT-ORC has a considerable amount of waste energy which can be recovered. In the present research, the waste energy of ORC in the heat rejection stage and the residual exhausted gas of the system were recovered by a thermoelectric generator (TEG) and a hot water unit, respectively. Then, the extra produced power in the TEG was directed to a proton exchange membrane electrolyzer and a reverse osmosis desalination unit (RODU) for hydrogen and potable water outputs. The performance of SOFC-GT, Configuration 1, and Configuration 2 was compared through a 4E (energy, exergy, exergy-economic, and environmental) analysis. In the best performance point, the exergy efficiency and unit cost of product (UCOP) of SOFC-GT were obtained as 69.41% and USD 26.53/GJ. The exergy efficiency increased by 2.56% and 2.86%, and the UCOP rose by 0.45% and 12.25% in Configurations 1 and 2. So, the overall performance of Configuration 1 was acceptable and Configuration 2 led to the highest exergy efficiency, while its economic performance was not competitive because of the high investment cost of RODU. Full article

This study presents a novel approach that will address escalating demands for water and cooling in regions vulnerable to climate change through the proposal of an optimal integrated cooling–freshwater cogeneration system powered by renewable energy sources. Comprising three subsystems (integrated multi-effect evaporation distillation, absorption heat pump, and vapor compression refrigeration (MAV); renewable energy unit incorporating solar panels, wind turbines, batteries, and hydrogen facilities (RHP/BH); and combined heat and power (CHP)), the system aims to produce both cooling and freshwater. By recovering cooling from combined desalination and refrigeration subsystems to chill the air taken into the gas turbine compressor, the system maximizes efficiency. Through the recovery of waste heat and employing an integrated thermo-environ-economic framework, a novel objective function, termed modified total annual cost (MTAC), is introduced for optimization. Using a genetic algorithm, parametric iterative optimization minimizes the MTAC. The results reveal that under optimum conditions, the MAV, RHP/BH, and CHP subsystems account for 67%, 58%, and 100% of total annual, exergy destruction, and environmental costs, respectively. Notably, the system exhibits lower sensitivity to fuel prices than renewable energy sources, suggesting a need for future research that will incorporate dynamic product prices and greater fuel consumption to produce enhanced operational robustness. Full article

Membrane distillation (MD) is an attractive separation process that can work with heat sources with low temperature differences and is less sensitive to concentration polarization and membrane fouling than other pressure-driven membrane separation processes, thus allowing it to use low-grade thermal energy, which is helpful to decrease the consumption of energy, treat concentrated solutions, and improve water recovery rate. This paper provides a review of the integration of MD with waste heat and renewable energy, such as solar radiation, salt-gradient solar ponds, and geothermal energy, for desalination. In addition, MD hybrids with pressure-retarded osmosis (PRO), multi-effect distillation (MED), reverse osmosis (RO), crystallization, forward osmosis (FO), and bioreactors to dispose of concentrated solutions are also comprehensively summarized. A critical analysis of the hybrid MD systems will be helpful for the research and development of MD technology and will promote its application. Eventually, a possible research direction for MD is suggested. Full article

This study presents a novel cooling-power-desalination combined cycle for recovering shipboard diesel exhaust heat, integrating a freezing desalination sub-cycle to regulate the ship’s cooling-load fluctuations. The combined cycle employs ammonia–water as the working fluid and efficiently utilizes excess cooling capacity to pretreat reverse osmosis desalination. By adjusting the mass flow rate of the working fluid in both the air conditioning refrigeration cycle and the freezing desalination sub-cycle, the combined cycle can dynamically meet the cooling-load demand under different working conditions and navigation areas. To analyze the cycle’s performance, a mathematical model is established for energy and exergy analysis, and key parameters including net output work, comprehensive efficiency, and heat exchanger area are optimized using the MOPSO algorithm. The results indicate that the system achieves optimal performance when the generator temperature reaches 249.95 °C, the sea water temperature is 22.29 °C, and 42% ammonia–water is used as the working fluid. Additionally, an economic analysis of frozen seawater desalination as RO seawater desalination pretreatment reveals a substantial cost reduction of 22.69%, showcasing the advantageous features of this proposed cycle. The research in this paper is helpful for waste energy recovery and sustainable development. Full article

Flash evaporation processes are widely adopted in the desalination, food processing, waste heat recovery and other industries for heat extraction or product separation. In this paper, a pressure-driven phase transition model is developed by improving the Lee model and combined with the VOF (Volume of Fluid) method to numerically simulate the flash evaporation process. In this modified Lee phase transition model, the driving force for the rates of the local phase transition is calculated using the local temperature and static pressure magnitude. Numerical simulations are carried out in a water-circulating flash chamber and compared with the experimental results to obtain the values of the time relaxation parameters. And the non-equilibrium fraction of the outlet water can be effectively obtained under different conditions of flow rate, inlet temperature and initial liquid level height. The time relaxation factor takes values from 0.195 to 0.43 (P_out,v = 19.9 kPa) and from 0.31 to 0.92 (P_out,v = 31.2 kPa) with increasing superheat. In addition, the model can effectively represent the evolution of the unstable flow flash evaporation from the initial rapid boiling state to dynamic equilibrium. Full article

With rising electricity demand and environmental concerns, renewable energy is increasingly important. Geothermal power plants offer an opportunity to utilize natural energy sources advantageously. These systems can be coupled with other power cycles, like gas Brayton cycles, to maximize their potential output. Biogas is considered a viable replacement for fossil fuels such as natural gas to further mitigate pollutant gas emissions. In this paper, a biogas-fueled gas turbine coupled with a double-expansion geothermal cycle is proposed that uses, for heat recovery, combustion product gases to run a Kalina cycle. After heating the geothermal fluid twice for double expansion, the product hot gases also heat water in a domestic water heater. Also, three thermoelectric generators are utilized to increase the overall output. Using the geothermal cycle’s waste heat, a humidifier–dehumidifier desalination unit is considered for freshwater production. Green energy, freshwater, and heat are the system’s products, all of which are useful. The proposed system is examined from a thermodynamic perspective using EES V.10.561 (Engineering Equation Solver) software. For the considered input parameters, energy and exergy efficiencies of 36% and 44% are achieved. Full article

Water scarcity is a pressing global issue driving the need for efficient and sustainable water reuse and desalination technologies. In the last two decades, humidification–dehumidification (HDH) has emerged as a promising method for small-scale and decentralized systems. This paper presents a comprehensive review of recent scientific literature highlighting key advancements, challenges, and potential future directions of HDH research. Because the HDH process suffers from low heat and mass transfer, as well as thermodynamic limitations due to the mild operating conditions, this work indicates three main strategies for HDH enhancement: (1) Advanced Heat and Mass Transfer Techniques, (2) Integration with Other Technologies, and (3) Optimization of System Operative Conditions. Particularly for advanced HDH systems, the reference GOR values exceed 3, and certain studies have demonstrated the potential to achieve even higher values, approaching 10. In terms of recovery ratio, there appear to be no significant process constraints, as recycling the brine prepared in innovative schemes can surpass values of 50%. Considering electricity costs, the reference range falls between 1 and 3 kWh m^–3. Notably, multi-stage processes and system couplings can lead to increased pressure drops and, consequently, higher electricity costs. Although consistent data are lacking, a baseline SEC reference value is approximately 360 kJ kg^–1, corresponding to 100 kWh m^–3. For comparable SEC data, it is advisable to incorporate both thermal and electric inputs, using a reference power plant efficiency of 0.4 in converting thermal duty to electrical power. When considering the utilization of low-temperature solar and waste heat, the proposed exergy-based comparison of the process is vital; this perspective reveals that a low-carbon HDH desalination domain, with II-law efficiencies surpassing 0.10, can be achieved. Full article

Cold energy recovery in LNG-powered vessels can not only improve the utilization efficiency of energy, but also benefit environmental protection. This paper put forward a new cascade scheme for utilizing flue gas waste heat and LNG cold energy comprehensively. The scheme was integrated by a dual organic Rankine circulation system (ORC), a high- and low-temperature cold storage system (TCS), an air conditioning system (ACS) and a seawater desalination system (SDS). The working medium of the dual ORC system was firstly determined by considering exergy efficiency and economic index simultaneously. On this basis, the adaptive weighted particle swarm optimization algorithm was employed to enhance thermodynamic performance of the scheme with the net output power as the optimization objective. The maximum net power and annual net interest rate can reach 725.78 kW and $115,300, respectively. Furthermore, the economic benefit of the scheme was analyzed by referring to the running track and the operation condition of the target ship. The results showed that the proposed scheme is a potential large-scale cryogenic technology and can bring considerable economic benefits to ship navigation. Full article

Water scarcity is a global issue recognized by the United Nations under Goal 6 of its Sustainable Development Goals (SDGs), which is to ‘Ensure availability and sustainable management of water and sanitation for all’. This challenging goal requires innovations, especially in areas with freshwater scarcity. Coupling this with the expected significant growth in population, especially in developing countries, presents major challenges to obtaining the appropriate levels of water provision needed. The development of seawater desalination technologies offers hope to alleviate freshwater shortages whilst supporting SDG 6. This research addresses the development of small-scale technology utilizing solar energy for providing clean drinking water in rural, hot, arid, and remote communities. To alleviate water scarcity in rural and isolated areas, a micro solar still (MSS) system that supports a multistage distillation process can be utilized, which evaporates and condenses the saline feed water into pure drinking water with highly efficient solar heat collectors. The focus of this study was to assess the performance of two prototypes, with minor improvements to the wicking structure. Such a system has the advantage of recycling wasted latent heat in the process to increase productivity. Two prototypes were tested to assess the performance of the solar still construction material and yield, and to test the water quality and quantity under the climatic conditions of Kuwait. The operation and efficiency of the prototypes were observed across four characteristics: solar irradiance, ambient temperatures, feed water and water production. The performances of the two prototypes were comparable to the results of previously published work on MSS prototypes that utilize wicking. The recovery rates of the two prototypes were 22 and 25%, respectively. The maximum production of potable water achieved from the two prototypes was 900 and 1160 g, respectively, using a feed of 4 and 3.7 kgs. The quality of the produced water met the WHO’s standards for drinking water. Full article

In this study, theoretical models for specific energy consumption (SEC) were established for water recovery in different integrated processes, such as RO-PRO, RO-MD and RO-MD-PRO. Our models can evaluate SEC under different water recovery conditions and for various proportions of supplied waste heat. Simulation results showed that SEC in RO increases with the water recovery rate when the rate is greater than 30%. For the RO-PRO process, the SEC also increases with the water recovery rate when the rate is higher than 38%, but an opposite trend can be observed at lower water recovery rates. If sufficient waste heat is available as the heat source for MD, the integration of MD with the RO or RO-PRO process can significantly reduce SEC. If the total water recovery rate is 50% and MD accounts for 10% of the recovery when sufficient waste heat is available, the SEC values of RO, RO-PRO, RO-MD and RO-MD-PRO are found to be 2.28, 1.47, 1.75 and 0.67 kWh/m³, respectively. These critical analyses provide a road map for the future development of process integration for desalination. Full article

Water serves as an indispensable part of human life and production. On account of the overexploitation of traditional water sources, the demand for wastewater recycling is expanding rapidly. As a promising water treatment process, membrane distillation (MD) has been utilized in various wastewater treatments, such as desalination brine, textile wastewater, radioactive wastewater, and oily wastewater. This review summarized the investigation work applying MD in wastewater treatment, and the performance was comprehensively introduced. Moreover, the obstructions of industrialization, such as membrane fouling, membrane wetting, and high energy consumption, were discussed with the practical investigation. To cope with these problems, various strategies have been adopted to enhance MD performance, including coupling membrane processes and developing membranes with specific surface characteristics. In addition, the significance of nutrient recovery and waste heat utilization was indicated. Full article

A hybrid capacitive deionization and humidification-dehumidification (CDI–HDH) desalination system is theoretically investigated for the desalination of brackish water. The CDI system works with two basic operations: adsorption and regeneration. During adsorption, water is desalted, and during the regeneration process the ions from electrodes are detached and flow out as wastewater, which is higher in salt concentration. This wastewater still contains water but cannot be treated again via the CDI unit because CDI cannot treat higher-salinity waters. The discarding of wastewater from CDI is not a good option, since every drop of water is precious. Therefore, CDI wastewater is treated using waste heat in a process that is less sensitive to high salt concentrations, such as humidification-dehumidification (HDH) desalination. Therefore, in this study, CDI wastewater was treated using the HDH system. Using the combined system (CDI–HDH), this study theoretically investigated brackish water of various salt concentrations and flow rates at the CDI inlet. A maximum distillate of 1079 L/day was achieved from the combined system and the highest recovery rate achieved was 24.90% from the HDH unit. Additionally, two renewable energy sources with novel ideas are recommended to power the CDI–HDH system. Full article