Search Results (50)

This paper reviews recent advancements in integrated thermoelectric power generation and water desalination technologies, driven by the increasing global demand for electricity and freshwater. The growing population and reliance on fossil fuels for electricity generation pose challenges related to environmental pollution and resource depletion, necessitating the exploration of alternative energy sources and desalination techniques. While thermoelectric generators are capable of converting low-temperature thermal energy into electricity and desalination processes that can utilize low-temperature thermal energy, their effective integration remains largely unexplored. Currently available hybrid power and water systems, such as those combining conventional heat engine cycles (e.g., the Rankine and Kalina cycles) with reverse osmosis, multi-effect distillation, and humidification–dehumidification, are limited in effectively utilizing low-grade thermal energy for simultaneous power generation and desalination, while solid-state heat-to-work conversion technology, such as thermoelectric generators, have low heat-to-work conversion efficiency. This paper identifies a key research gap in the limited effective integration of thermoelectric generators and desalination, despite their complementary characteristics. The study highlights the potential of hybrid systems, which leverage low-grade thermal energy for simultaneous power generation and desalination. The review also explores emerging material innovations in high figure of merit thermoelectric materials and advanced MD membranes, which could significantly enhance system performance. Furthermore, hybrid power–desalination systems incorporating thermoelectric generators with concentrated photovoltaic cells, solar thermal collectors, geothermal energy, and organic Rankine cycles (ORCs) are examined to highlight their potential for sustainable energy and water production. The findings underscore the importance of optimizing material properties, system configurations, and operating conditions to maximize efficiency and output while reducing economic and environmental costs. Full article

The experiment of loess crack development under dry–wet cycle conditions is of great significance for the study of groundwater preferential flow channels and the prevention and control of infrastructure engineering disasters in loess areas. The loess samples in Chencang District of Baoji City, Shaanxi Province, were taken as the samples in the test. The multiple humidification and dehumidification tests were used to simulate multiple rainfall evaporation, and the moisture content changes in the loess samples during the dry–wet cycle were calculated. With the help of digital image technology, the fracture parameters of the loess samples were extracted, and the variation law of crack parameters was analyzed by combining fractal dimension, Bayesian factor, and Pearson correlation coefficient. The findings indicate that variations in soil moisture content and the number of dry and wet cycles contribute to fluctuations in soil evaporation rates, resulting in varying degrees of soil cracking development. The increase in the number of dry and wet cycles leads to evident soil shrinkage, an accelerated water evaporation process, pronounced surface deterioration, and a higher degree of crack development. The rate of crack propagation varies at different locations, with a higher rate observed in the horizontal plane compared to the vertical plane. The influence of temperature and humidity varies due to the different dimensions of cracks (horizontal and vertical). Horizontal crack development is primarily influenced by temperature, while vertical crack development is primarily influenced by humidity. Temperature and humidity inhibit each other. When one factor is dominant, the other indirectly affects crack development by influencing the dominant factor. The research findings can serve as a valuable reference for effectively mitigating and minimizing the impact of crack development-induced disasters. Full article

This study aims to assess the stability of silica gel/polymer composites designed for open-cycle air dehumidification, humidification, and heat storage by employing a comprehensive set of characterization methods. To evaluate their resistance to various environmental factors, the materials were subjected to a series of aging treatments: (i) repeated adsorption/desorption cycles under representative operational conditions; (ii) post-drying at 30 °C, 40 °C, and 60 °C; (iii) immersion in water for 30 days; (iv) exposure to a salt–fog environment for 30 days; and (v) accelerated aging by alternation between wet and dry cycles. Prolonged exposure to liquid water significantly reduced the material’s stability, resulting in an 83% reduction in tensile strength after 30 days of immersion. However, discontinuous exposure to liquid water at low drying temperatures did not critically affect the material’s mechanical properties during wet/dry cycles. Furthermore, post-drying (performed at 22 °C and 50% RH) allows the recovery of mechanical performance, with a tensile strength reached comparable to those of the unaged composites. Similarly, adsorption/desorption cycles in water vapor did not trigger degradation in the material, with its water vapor adsorption capacity remaining comparable to the unaged material after 100 cycles. The results confirm the reliability of these composite materials as to their potential uses in open-cycle dehumidification, humidification, and heat-storage applications. Full article

The combination of global climate change and the urban heat island effect has given rise to a deterioration in the livability of residential districts within cities, posing challenges to enhancing the health quality of urban environments. Meanwhile, the intensification of daytime changes in temperature and humidity in residential districts has rendered the sensory representation of the urban heat island effect more pronounced. This study selects the residential districts in Fuzhou City as the research case area, which have witnessed a discernible warming trend in recent years, and acquires temperature and humidity parameter data at three time periods (early morning, noon, and evening) to represent the daytime temperature and humidity change phase. Through aerial photography and field research, three types of spatial morphological indicators (buildings I, vegetation II, and the combination of buildings and vegetation II) of residential districts are quantified to represent the three-dimensional spatial form of the case study area. The analysis results show the following: ➀ Residential districts experience two phases of daytime changes in temperature and humidity: a warming and drying phase (WDP) in the morning and a cooling and humidifying phase (CHP) in the afternoon. The characteristics of changes in temperature and humidity show a spatial correlation with each other. ➁ The impact of urban three-dimensional morphology on changes in temperature and humidity in WDP is minor, whereas, in CHP, it is influenced by Class II and Class III indicators. The two types of urban morphology exert a synergistic regulatory effect on changes in temperature and humidity. ➂ Vegetation has a significant regulatory effect on temperature and humidity variations in residential areas through changes in its three-dimensional form. Enlarging the area of individual trees while reducing their canopy volume can restrain the warming and dehumidification of residential districts and promote cooling and humidification. In contrast to only planting trees, a vegetation configuration combining trees, shrubs, and grass can bring a more obvious cooling effect to residential districts. The research results can provide a reference for urban planners in the planning and design of residential areas as well as the optimization and improvement of urban living environments. Full article

One of the technical solutions to improve indoor thermal comfort and reduce energy consumption in buildings is the use of demand-controlled ventilation (DCV) systems. The choice of the control method becomes more important when the walls in the room are finished with moisture-buffering materials. This study explores the impact of four DCV system control scenarios (control of temperature, relative humidity, and carbon dioxide concentration for two different supply airflows to the room) combined with various indoor moisture-buffering materials (gypsum board and cement–lime plaster) on the variability of indoor air quality parameters, thermal comfort, and energy. The analysis was performed by computer simulation using WUFI Plus v.3.1.0.3 software for whole-building hydrothermal analysis. Control-based systems that maintain appropriate relative humidity levels were found to be the most favourable for localised comfort and were more effective in terms of energy consumption for heating and cooling without humidification and dehumidification. This research also revealed that the moisture-buffering effect of finishing materials can passively contribute to enhancing indoor air quality, regardless of the room’s purpose. However, higher energy consumption for heating was observed for better moisture-buffering materials. Full article

The air humidification-dehumidification (HDH) technique for water desalination can be useful in many water production applications. Researchers from all around the world have examined various implementations of this technology to improve it. The present research investigates the effect of three dehumidifier coolants on the system. These coolants include water, helium, and hydrogen. The impact of these coolants on the parameters of the humidification-dehumidification desalination system will be discussed. The investigation’s parameters are tested at various mass ratios, air flow rates, and air outlet heaters. The results show that when hydrogen is employed as a dehumidifier coolant, the gained output ratio (GOR) achieves its peak of 6.37 in the considered mass ratio range of 2.1 to 3. On the other hand, when hydrogen is utilized as a dehumidifier coolant, the system produces the maximum entropy, with the dehumidifier contributing the most. When the mass ratio changes from 2 to 3, the average entropy generation for the system using hydrogen in the dehumidifier increases by 3.8 and 2.9 times, respectively, compared to the average entropy generation for the system using water and helium. However, when hydrogen is used as a dehumidifier coolant, safety concerns must be addressed, as well as the size and cost of heat exchangers in comparison to water. Full article

The paper presents a wind–photovoltaic-thermal hybrid-driven two-stage humidification and dehumidification desalination system for remote island regions lacking access to electricity and freshwater resources. By conducting an analysis of the wind and solar energy resources at the experimental site, a suitable wind power station and photovoltaic power station are constructed. The performance of the wind–solar complementary power generation system is then evaluated based on factors such as output power, seawater desalination load power, battery compensation output, system energy consumption, and water production costs. A variable step gradient disturbance method based on the power–duty ratio is proposed for tracking the maximum power point (MPPT) of wind power generation. The output power of the photovoltaic power generation system is optimized, employing a fuzzy logic control (FLC) method to track the MPPT of photovoltaic power generation. This approach effectively addresses the issues of slow speed and low accuracy encountered by traditional MPPT algorithms in tracking the maximum power point (MPP) of both photovoltaic and wind power generations. In order to ensure that the desalination system can operate stably under different weather conditions, eight working modes are designed, and a programmable logic controller (PLC) is used to control the system, which provides a guarantee for stable water production. Experimental results demonstrate that the system exhibits stable performance, achieving a maximum water output of 80.63 Kg/h and daily water yield is 751.32 Kg, the cost of desalination equipment is 1.4892 USD/t. Full article

The pressing demand for clean water worldwide has increased attention to developing innovative desalination processes. In this work, the second law of thermodynamics is used to examine and assess two coupled desalination systems: a separation-based reverse osmosis (RO) system and a thermal desalination-based humidification–dehumidification (HDH) system. The HDH unit configuration used here is based on the working principle of the heat pump, where the process is open-air, open-water, and air-heated. The RO system is equipped with a pressure exchanger (PX) and has been examined under various operating circumstances, such as different feed water pressures, salinities, and flow rates. To improve the system’s sustainability, a solar photovoltaic system (PV) was integrated. An exergy model was used to precisely evaluate the system components and the hybrid systems by employing a proper exergy efficiency definition. The evaluation of the second law of thermodynamics for the RO–HDH–PX and RO–HDH–PX–PV systems indicated maximum efficiencies of 23% and 23.25%, respectively. A cost analysis was also performed on the hybrid RO–HDH–PX–PV desalination system using two approaches: the first included a battery storage system, whereas, in the second, the battery was not considered. When a battery storage system is included, the cost per cubic meter varies from USD 3.22 to USD 5.10. In contrast, it varies from USD 3.96 to USD 7.12 without a battery storage system. Full article

The humidifier plays a key role in a humidification–dehumidification (HDH) desalination system; it directly affects both the freshwater production efficiency and energy consumption ratio of the system. In this study, for a humidifier in an HDH system, a heat–mass coupled differential equation model of spray water and air on the surface of the packing material was established, and the effects of parameters such as the spray water temperature (t_w), mass flow rate of spray water (m_w), air temperature (t_a), and air mass flow rate (m_a) on the humidification performance of humidifiers composed of eight different types of packing materials were investigated. The results show the following: (1) Under the same inlet spray water and air conditions, the humidification performance of different packing materials from good to bad is as follows: cellulose paper, polypropylene, hackettes, saddles, snowflakes, wooden slats, polyvinyl chloride, gunny bag cloth. (2) Increasing the t_w can significantly improve the humidification performance. To achieve higher humidification energy efficiency, it is recommended to increase the t_w to above 80 °C. (3) With the increase in the m_w, although the humidification efficiency (ε_hum) decreases slightly, the humidification rate (m_hum) increases, and the specific humidification energy ratio (η_hum) decreases accordingly. To maintain a high m_hum and a low η_hum, it is advisable to control the m_w at not less than 0.5 kg/s. (4) Increasing the humidifier inlet t_a can improve the m_hum, ε_hum, and η_hum, although not as effectively as increasing t_w. (5) Increasing the m_a can improve m_hum and ε_hum. However, it simultaneously increases the η_hum. The results of this study can provide theoretical guidance for the selection of efficient packing materials and the optimization of humidifier operating conditions in HDH desalination systems. 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

This paper presents a numerical study of a closed-cycle evaporation system for the desalination of seawater. The system couples the condensing end of a heat pump with a humidifier, where the air is dehumidified in the heat pump evaporator. First, the mechanism of action of the closed-cycle evaporation system was analyzed from the perspective of heat transfer, and the control equations for the heat and mass transfer of the system were investigated. In addition, a mathematical model of the system was developed and validated. The influence of several important parameters of the air and seawater entering the system on the system’s performance under the design conditions was investigated numerically. The parametric analysis showed that the effect of the seawater mass flow rate on the system’s productivity was not significant. As the air mass flow rate increases, the freshwater production rate increases and then decreases. The output ratio (GOR) of the system was estimated and found to be competitive with other reported HDH systems. Full article

Solar desalination systems are a promising solution to the water scarcity problem since the majority of the earth’s water resources are salty. With the increasing focus on desalination research, many innovative methods are being developed to extract salts from saline water. Energy consumption is a significant concern in desalination, and renewable energy, particularly solar energy, is considered a viable alternative to fossil fuel energy. In this review, we will focus on direct and indirect solar desalination methods, specifically traditional direct solar desalination methods such as solar still and humidification dehumidification (HDH) desalination systems. We will also briefly discuss a recent advancement in the desalination method known as the fogging process, which is a development of the HDH desalination system. Full article

In this paper, the relative humidity sensor properties of graphene oxide (GO) and graphene oxide/multiwalled nanotubes (GO/MWNTs) composites have been investigated. Composite sensors were fabricated by direct laser scribing and characterized using UV-vis-NIR, Raman, Fourier transform infrared, and X-ray photoemission spectroscopies, electron scanning microscopy coupled with energy-dispersive X-ray analysis, and impedance spectroscopy (IS). These methods confirm the composite homogeneity and laser reduction of GO/MWNT with dominant GO characteristics, while ISresults analysis reveals the circuit model for rGO-GO-rGO structure and the effect of MWNT on the sensor properties. Although direct laser scribing of GO-based humidity sensor shows an outstanding response (|ΔZ|/|Z| up to 638,800%), a lack of stability and repeatability has been observed. GO/MWNT-based humidity sensors are more conductive than GO sensors and relatively less sensitive (|ΔZ|/|Z| = 163,000%). However, they are more stable in harsh humid conditions, repeatable, and reproducible even after several years of shelf-life. In addition, they have fast response/recovery times of 10.7 s and 9.3 s and an ultra-fast response time of 61 ms when abrupt humidification/dehumidification is applied by respiration. All carbon-based sensors’ overall properties confirm the advantage of introducing the GO/MWNT hybrid and laser direct writing to produce stable structures and sensors. Full article

The present study aims to evaluate the performance of evaporation-assisted humidification–dehumidification (E-HDH) desalination, specifically direct evaporative (DE-HDH), indirect evaporative (IE-HDH), and Maisotsenko evaporative (ME-HDH) systems. To achieve this, a thermodynamic modeling approach is utilized, which incorporates the wet bulb effectiveness method, psychrometric relationships of humid air, and equations that govern heat and mass balance. The key performance indicators of the studied E-HDH desalination systems are estimated concerning operating parameters. The results show that the ME-HDH system is capable of producing a comparatively higher water production rate (WPR) ranging between 0.01 and 7.92 g/s as compared to the DE-HDH and IE-HDH systems. The sensible cooling flux was observed to be high at a dry-bulb temperature (T_db) of 50 °C and relative humidity (RH) < 0.2, having a value of 5.26 kW for the DE-HDH system, followed by the ME-HDH system (3.23 kW) and the IE-HDH system (3.11 kW) due to relatively high mass flow rates. The latent heat flux was observed to be relatively high in the case of the ME-HDH system. Minimum specific energy consumption was observed from the ME-HDH system, and consequently, a maximum gain output ratio (3.32) was realized. In addition, the study realized that an increment in air velocity and wet bulb effectiveness significantly improves the WPR. In accordance with the climatic conditions of the studied Saudi Arabia cities, it has been realized that Al-Hofuf and Riyadh produce relatively high WPRs with minimum energy consumption. In the case of Al-Hofuf, the average WPR was recorded as 185.51 kg/day, followed by Riyadh (180.33 kg/day). The energy required was estimated to be 0.042 kWh/kg and 0.034 kWh/kg for both cities, accordingly. Full article

In this paper, the cooling and freshwater generation performance of a novel hybrid configuration of a solid desiccant-based M-cycle cooling system (SDM) combined with a humidification–dehumidification (HDH) desalination unit is analysed and compared in three operational modes: ventilation, recirculation, and half recirculation. The HDH unit in this system recycles the moist waste air sourced from the M-cycle cooler and rotary desiccant wheel of the SDM system to enhance water production. A mathematical model was established and solved using TRNSYS and EES software. The results of this study indicate that the recirculation mode exhibited superior cooling performance compared to the other two modes, producing up to 7.91 kW of cooling load and maintaining a supply air temperature below 20.85 °C and humidity of 12.72 g/kg under various ambient conditions. All the operational modes showed similar water production rates of around 52.74 kg/h, 52.43 kg/h, and 52.14 kg/h for the recirculation, half-recirculation and ventilation modes, respectively, across a range of operating temperatures. The recirculation mode also exhibited a higher COP compared to the other modes, as the environmental temperature and relative humidity were above 35 °C and 50%. However, it should be noted that the implementation of the recirculation mode resulted in a higher water consumption rate, with a maximum value of 5.52 kg/h when the inlet air reached 45 °C, which partially offset the benefits of this mode. Full article