Humidification Dehumidification Research Articles

Thermal analysis of humidification–dehumidification desalination system based on evacuated tube solar air heater

Thermal analysis of humidification–dehumidification desalination system based on evacuated tube solar air heater

Carbon Footprint of Seawater Desalination Technologies: A Review

Abstract As an important and effective way of mitigating water shortages, desalination has steadily and rapidly increased its global capacity over the decades. This raises concern about its environmental impacts, especially its carbon footprint (CF). Although the CF of desalination has been extensively studied, the existing literature lacks reviews exclusively for it. To help fill the research gap, this study presents a comprehensive and up-to-date review of the CF of seawater desalination technologies, including the conventional reverse osmosis (RO), multi-stage flash (MSF), multi-effect distillation (MED), electrodialysis (ED), and mechanical vapor compression (MVC), and the emerging membrane distillation (MD) and humidification–dehumidification (HDH). To our knowledge, this is the first review that focuses on the CF of seawater desalination. A general procedure for assessing the CF of a desalination system is discussed. The CF data of 211 scenarios from 34 studies published from 2004 to 2023 are reviewed and analyzed, with special focuses on the CF of different technologies, the roles of different life-cycle phases and material/energy flows, and the mitigation measures. The results highlight the CF advantage of RO and low-carbon heat-driven MSF, MED, and MD, and emphasize the dominant role of the operational energy consumption (the amount, the form, and especially the source of the energy) in the CF of desalination. This review improves the understanding of the CF of seawater desalination technologies and of the ways to reduce it.

New and effective combination of an absorption desalination systems with adsorption and humidification-dehumidification desalination systems utilizing internal heat recovery methods

The fast growth in population and the need for human comfort leads to a significant rise in freshwater shortage and energy usage. This article provides new and effective combinations between absorption (ABDC), adsorption (ADDC), and humidification-dehumidification (HDH) desalination plants. Four new configurations employing different external and internal heat recovery methods between the plants and their components are proposed to enhance the overall system performance, water production, and utilization of the used energy. In all configurations, the solar water heating system is used to power the ABDC. While the ADDC and HDH were powered by the heat recovery from condensation, absorption, or generation processes. Internal heat recovery methods are also applied between the evaporator and condenser in ABDC and ADDC plants to increase energy utilization. The results are evaluated and compared with standalone ABDC results and with previous related studies at different conditions. The production share percentage (%) from each plant for the suggested configurations with regeneration temperatures is also investigated. The maximum water production is achieved by the fourth configuration (3 m3.day−1 with a gain output ratio (GOR) of 1.316 at 120 °C) when the ADDC is worked by the outlet hot water from the ABDC, and internal heat recovery utilized between the condensation and evaporation components of both ABDC and ADDC. The highest GOR is obtained from the second configuration (1.714 at 90 °C). The finding expressed that the proposed configurations have a better performance than traditional ABDC systems. Also, the proposed configurations express another advantage over traditional ABDC, that the configurations have the potential at low-temperature heat sources (55–65 °C) to improve the water productivity to about 455 % and GOR to about 120 %.

Solar-powered adsorption desalination utilizing composite silica gel with a humidification-dehumidification desalination system

This work comes in light of addressing crises of freshwater scarcity, energy demand, and climate change to investigate innovative configurations of hybrid adsorption desalination integrated with a humidification dehumidification system powered by solar energy or waste heat in four operation modes. The investigation includes economic cost analysis and system performance using raw silica gel and silica gel/CaCl2 adsorbents under the weather data of Assiut-Egypt. System performance has been evaluated regarding daily water production, gain output ratio, and cooling effect using TRNSYS and MATLAB software. The combined configuration with heat recovery (the fourth mode) using silica gel/CaCl2 gives a relatively high freshwater production (69 m3/ton.day in June) compared with the basic adsorption desalination system using raw silica gel (7.1 m3/ton.day in June). Silica gel/CaCl2 in the first mode presented the highest cooling effect (555 W/kg) in June compared with silica gel in the primary system (197 W/kg). The third configuration's solar-powered silica gel/CaCl2 system shows a clear superiority of 1.8 in gain output ratio, compared with the basic system with and without heat recovery (0.54 and 0.4, respectively). The third configuration also provided the cheapest freshwater production among all configurations at 2 $/m3 in June.

Thermodynamic analysis and examining the effects of parameters in BSR-HDH system using response surface methodology

1) BackgroundIn this study, biogas steam reforming (BSR) coupled with a humidification dehumidification unit (HDH) was proposed and the novel thermodynamic analysis interaction effects on energy efficiency and exergy efficiency via the design of experiments was used. 2) MethodsComprehensive thermodynamic modelling has been performed using EES software. Thus, by utilizing the thermodynamic analysis of the combined system by EES software and transferring the experiments based on the central composite design for the input parameters (the inlet temperature of the dehumidifier, humidifier and dehumidifier circulated mass flow rate and the desalination heater inlet temperature) extracted by the design expert software, the results obtained from the EES provides responses that shows the impact of the interaction of the input parameters. In RSM model, the central composite design (CCD) is employed in the experimental design. 3) Significant FindingsFrom the thermodynamic outlet results, the energy efficiency, exergy efficiency, hydrogen mass flow rate and freshwater mass flow rate of the system are obtained 82.39% and 72.65%, 0.1071 kg/s and 0.211 kg/s, respectively. R2 values in energy and exergy efficiency responses were calculated 99.99% and 99.97%, respectively that shows the model has a good accuracy. The optimum points for parameters of the inlet temperature of dehumidifier (T14), humidifier and dehumidifier circulated mass flow rate (m19) and the desalination heater inlet temperature (T10) and also responses of energy efficiency and exergy efficiency are obtained 310 K, 8 kg/s, 450 K, 0.9051% and 0.7313%, respectively. Also, the variables of the inlet temperature of dehumidifier and humidifier and dehumidifier circulated mass flow rate (m19) have more interaction with each other based on their slope changes in the upper and lower ranges.

Multi-stage humidification–dehumidification system integrated with a crystallizer for zero liquid discharge of desalination brine

Desalination plants discharge a massive volume of brine every day, which negatively affects the ecosystem, particularly the subsurface ecology and marine life. To mitigate the brines' detrimental effects on the environment and facilitate the recovery of salt crystals and freshwater, the Zero Liquid Discharge (ZLD) approach was proposed. This study proposes four different configurations of multistage humidification dehumidification systems integrated with a crystallizer, exploring their energy and economic implications. Key findings from the study include the higher Gained Output Ratio (GOR) in series configurations due to lower temperature differences, resulting in lower heater energy consumption. The crystallizer significantly enhances water productivity, but it is a major consumer of both electricity (85%) and thermal energy (50.45–57.7%) in the system. Increasing the heat source temperature reduces the Specific Electrical Energy Consumption (SEEC) and the specific area while slightly increasing the Specific Thermal Energy Consumption (STEC). Elevated cooling water temperature raises SEEC and specific area but has negligible effects on STEC. Higher feed water flow rates increase SEEC but lower both STEC and specific area. Feed salinity elevation decreases productivity, SEEC, STEC, and specific area. The crystallizer constitutes 15.43–26.44% of the total capital cost, with series configurations incurring higher costs. Unit freshwater production costs, considering salt selling, range from 1.733 to 4.821 $.m−3. In a waste heat scenario, parallel configurations become profitable, where freshwater can be distributed at zero cost, while the produced salt crystals can be sold at an even lower price of $58.09 per tonne and $57.04 per tonne, respectively.

Energy, exergy, economic, exergo and enviro-economic analysis of solar powered humidification dehumidification desalination system: An experimental investigation

A solar-powered humidification dehumidification (SPHDH) desalination system presents an economically viable thermal desalination approach for satisfying the requirement of freshwater. The traditional solar air heater and saline water as the cooling fluid in the condenser, impose restrictions on the SPHDH system’s performance and lifespan. The present study involves a solar air heater, humidifier (packed bed type), and heat exchanger coupled with a direct evaporative cooler to develop a SPHDH desalination system. The collector employed in this study consists of double-end open evacuated tubes, while the cooling medium utilized is ambient air. Moreover, in the context of a humidifier, two distinct packing materials, specifically cellulose and aspen pads are employed in order to examine the impact of the packing material on the system. The performance evaluation is conducted through the energy, exergy, GOR, effectiveness, economic, exergo, and enviro-economic assessments. The findings indicate that the cellulose pad exhibits superior performance when compared to the aspen pad. This is due to lower air flow resistance and a greater contact surface area. The system’s highest mean energy and exergy efficiency is obtained with cellulose pads, i.e., 31.2 % and 5.10 %, respectively. Moreover, the cellulose pads have shown to achieve a maximum production of 3.12 kg/m2/day at a cost of 0.038 $/kg. The exergo-economic values based on energy and exergy are 14.76 kWh/$ and 2.56 kWh/$, respectively.

Thermo-environmental multi- investigation and ANN-based optimization of a novel heat integration criteria system integrated with a marine engine generating liquefied hydrogen

Marine transportation is a significant contributor to overall energy consumption among transportation sectors and is responsible for producing a considerable amount of greenhouse gases. A potential solution for alternative applications involves implementing combined heat integration, thereby enabling the production of additional utilities and mitigating emissions. The current work introduces an innovative heat integration process for a marine engine, focusing on implementing an optimal thermal matching technique to minimize overall irreversibility in producing liquefied hydrogen and coolant. The process incorporates an organic flash-bi-evaporator cooling cycle, a humidification dehumidification desalination, a polymer electrolyte membrane water electrolysis process, and a Claude cycle. The generated freshwater is delivered to the electrolyzer to produce gaseous hydrogen. This product and the cooling for freezing are utilized in the Claude cycle for hydrogen liquefaction. The study utilizes an advanced thermo-environmental multi-criteria investigation and optimization, considering sensitivity analysis and optimization based on artificial intelligence method. The optimization process incorporates the training and testing of artificial neural networks, NSGA-II method, and TOPSIS decision-making. The primary objective functions include exergetic efficiency and carbon dioxide emission. The findings demonstrate that the specified objectives are computed to be 0.121 and 2.67 kg/MWh, correspondingly. Besides, this condition exhibits a liquefied hydrogen flow rate of 6.44 L/h and a cooling output of 43.61 kW, showing an energy efficiency of 0.1145. Also, the total exergy destruction rate associated with the arranged structure is 124.5 kW. Furthermore, the optimum state reveals an exergoenvironmental index of 0.840 and an exergetic stability factor of 0.869.

Energetic performance of a solar driven absorption refrigeration system integrated with humidification dehumidification desalination system

Integrating cooling and desalination systems with a single heat source is a shortcut technique to meet the shortage of fresh water and energy as well as enhancing the efficiency of energy utilization. In this paper, the energetic performance of a double effect vapor absorption refrigeration system integrated with humidification-dehumidification desalination system has been optimized·H2O–LiCl achieves higher system primary energy ratio and needs lower heat source temperature by 5 °C and 11 °C at evaporation temperature of 10 °C and 4 °C, respectively as compared with H2O–LiBr. Therefore, a parametric study has been performed to get the optimum operating conditions for the integrated system using H2O–LiCl as working pair by varying generation, condensation, and evaporation temperatures. The optimum system conditions are generation, condensation, and evaporation temperatures of 103 °C, 103 °C and 7 °C, respectively. The corresponding system COP, GOR and EUF are 1.471, 2.391 and 3.863, respectively. Finally, the transient performance of the proposed integrated system assisted by solar energy has been evaluated for Marsa-Matrouh city in Egypt. The proposed integrated system could save 71.2 % of the input energy without solar assistance and 88.5 % with solar assistance as compared with separated systems.

Performance analysis of heat pump polygeneration system

A heat pump polygeneration system is a promising technology to meet daily needs such as drinking water, power, space cooling or heating, and hot water generation. This work is focused on integrating the solar heat pump and two-stage humidification–de-humidification with a minimum space requirement. In this integrated cycle, the desired outputs i.e. condenser heat and evaporator heat are used for maximizing hot water and desalinated water production with minimal thermal pollution. For warm or hot air generation, an air reheater device is used after the heat pump. By using the switching operation, the air reheater is used accordingly as per climatic conditions. So in this integrated cycle, a coconut coir-packed humidifier is used for the humidification process, and a water-cooled heat exchanger and heat pump evaporator are used for the dehumidification process to meet the desired outputs from the system. The MATLAB simulation tool is used to simulate the thermodynamic model of the integrated cycle, and it is focused on studying the effect of mass flow rate, atmospheric temperature, relative humidity, evaporator temperature, and hot/cold water temperature, on outputs, as well as the energy conversion factor of the plant and cycle. At 25°C ambient air temperature, the energy conversion factor of the plant and cycle are 0.866 and 2.2, respectively. Similarly, at 75% humid air and 35°C surrounding air temperature, the gained output ratio and coefficient of performance are 4.03 and 1.964, respectively. And also, the plant and cycle energy conversion factors are 0.903 and 2.4.

Design of a solar air heater for a direct-contact packed-bed humidification–dehumidification desalination system

The performance of solar desalination systems based on a humidification–dehumidification (HDH) approach is significantly enhanced by preheating the air entering the evaporator. To estimate this potential benefit, we present an analysis of integrating a novel solar air heater (SAH) with an HDH system. The combination of both units leads to intriguing applications, such as incorporating these systems into buildings. A model of the solar thermal system is developed, and its predictions are validated with experimental data. The SAH model is combined with a previously validated model of an HDH. This allows us to estimate the performance of a combined SAH/HDH system under different environmental conditions and to evaluate the annual water treatment capacity at various sites around the world. Simulations suggest that a system with a 3.5 m2 solar collector in arid regions (Middle-East, north of Africa, south-west of the USA, East of South America), has the potential to treat 30 tons of water and reduce the CO2 emission by 150 kg annually.

A parametric analysis of a solar humidification/dehumidification desalination system using a bio-inspired cascade humidifier

ABSTRACT Water scarcity is a significant challenge for a growing world’s population, particularly in remote locations where solar energy is plentiful. Of the existing solutions, the Humidification-Dehumidification (HDH) desalination technique can work effectively with low-grade energy sources, such as solar. However, HDH desalination systems often have a low yield, leading to a focus on ever-more complex humidification systems. This work aims to examine the performance of a novel bioinspired humidifier as a low-cost and effective solution to increase the yield of small-scale HDH desalination systems. To this end, an HDH desalination system using a cascade humidifier was conceptually developed and parametrically modelled. It was shown that the evaporation rate in the humidifier could be increased by increasing both the air and water flow rates. It was also found that an evaporation rate of 0.91 × 10−3 kg/s could be achieved for an evaporation area of 0.36 m2. Considering the entire desalination system, it was noted that increasing the water flow rate reduced the water temperature entering the humidifier and thus reduced production. Conversely, increasing the airflow rate enhanced the production rate. More importantly, it was shown that under appropriate conditions this novel desalination system can have a production of 10.2 litre/day/m2.

RETRACTED: Enhancing desalination efficiency using waste heat from household air conditioning: A heat pipe-assisted HDH system performance analysis

This study presents an experimental exploration of a desalination system that produces freshwater from saltwater using a novel heat pipe-assisted humidification-dehumidification (HDH) process. The system utilizes waste heat recovered from residential air conditioners that use vapour compression refrigeration systems. The study focuses on the mass and heat transfer within the system's components, with performance evaluations conducted at three different air conditioning temperatures (19 °C, 20 °C, and 21 °C). The experiments highlight the freshwater production of the R32 heat pipe over the R134a and R600a heat pipes. The study estimates the system's cost-effectiveness at $0.0085/L, emphasizing its economic viability. Preheating resulted in significant improvements in freshwater yield, ranging from 43.33 % to 51.5 %, at temperatures of 21 °C and 20 °C, respectively. The Gain Output Ratio (GOR) doubled from 0.75 to 1.52, indicating a more energy-efficient process with significant improvements in the effectiveness of humidification and dehumidification. The pH levels improved from 8.32 to 7.07, representing a 15 % reduction and falling within the WHO-recommended range of 6.5–8.5. Electrical Conductivity (EC) shows a notable reduction from 62,720 to 826.1 micromhos/cm, representing a 98.68 % reduction, and well below the permissible limit of 1500 micromhos/cm. Total Dissolved Solids (TDS) also experienced a drop from 31,777 to 413.1 ppm, representing a 98.7 % reduction, and falls under the WHO guideline of <600 ppm for drinking water. The experiments prove that the use of waste heat from household air conditioners for sustainable freshwater production through the HDH desalination method, with the added efficiency benefits of heat pipe.

Design methodology based on multi-objective optimization with evolutionary algorithms for humidification-dehumidification desalination systems using updated approaches

This paper develops a methodology for multi-objective optimization using Non-Dominated Sorting Genetic Algorithm II (NSGA-II). The methodology aims to address the problem of the close relation between variables based on a mathematical model that simulates design variants of humidification-dehumidification (HDH) desalination systems, where the variation of one parameter can affect another. The approach consists of an exhaustive study of the state of the art to incorporate as many results as possible, including variable and parameter constraints established by previous research. Energy efficiency and potable water production are optimized with respect to the total area of the system's active components and the ratio of seawater converted to potable water. The calculations generate 20 Pareto optimal solutions, with an average pure water production of 14.01 l/h, and an average of the total and solar heating areas of 22.43 m2 and 8.52 m2, respectively, including many other parameters with similar values compared to other publications. The methodology is flexible, updatable, and generates high efficiency values, confirmed by the comparison of equivalent parameters and the pinch analysis, also with respect to previous results. The sensitivity analysis performed, presents different trends in the relation between variables in this scenario contributing to feedback on the behavior of hyperparameters of the algorithm, indicating a very wide potential of solutions. For the water temperature entering the dehumidifier, the range between 30 and 37 °C is determined as the optimum range, however, this is not the only result from the trend analysis of these 20 solutions, compared with other references. This methodology is a contribution to the overall objective of improving the HDH technology design process; optimal solutions are obtained for systems of the configuration chosen to apply it, but it can be adapted to others.

The impact of a balanced humidification-dehumidification desalination system driven by a vapor-compression heat-pump system

This study adopts a numerical thermo-economic investigation of a novel desalination system. In this system, a vapor compression (VC) heat pump is used to drive a balanced humidification-dehumidification (HDH) desalination unit with multiple extractions. The mathematical model of the proposed VC-HDH system is validated experimentally. The system is examined for water production under a condenser temperature of 45 °C, evaporator temperature of −5°C, feed saline water temperature of 30 °C, feed saline water flow rate of 1 kg/s, and an energy effectiveness value of 0.85 for the HDH unit’s components. The results show that without air extraction, the system can produce 6.62 kg/h of desalinated water for 0.011 $/l with a gained-output-ratio (GOR) value of 9.1. On the other hand, when a single air extraction is applied, about 20 kg/h of desalination water is produced by the system for 0.0042 $/l and 29 GOR. Increasing the number of air extractions to two yields a freshwater production rate of approximately 40 kg/h for 0.0026 $/l and a GOR value of 57. A considerable positive effect of the HDH unit’s performance is found on the system’s performance on both thermodynamic and economic scales. For better desalination performance, it is found that the feed water temperature should be maintained between 25 °C and 30 °C. Finally, the theoretical ceiling of the proposed system’s GOR is estimated.

Performance analysis of a novel two-bed adsorption humidification-dehumidification desalination system using Metal-organic framework 801

Adsorption desalination techniques have been increasingly studied over the last century as a sustainable option for meeting the rapidly growing demand for fresh water. One of the attractive factors for using adsorption desalination systems is the use of low-grade thermal energy normally wasted in the atmosphere. The current study introduces a novel adsorption desalination system integrated with a humidification dehumidification system for producing potable water. Four system configurations are presented. The main distinction between them is the source of hot water used for the humidifier. Scheme #1 utilizes the heat of condensation, Scheme #2 applies the heat of condensation plus the heat of adsorption, while Scheme # 3 adds the outlet of heating water from the desorber as a source of heat to the humidifier. Scheme #4 is a standalone adsorption desalination system that applies chilled water to cool the condenser. The novelty of this system is the application of the chilled water from the evaporator to the dehumidifier to create the highest possible temperature difference necessary for the humidification and dehumidification process. This advantage allows larger water productivity, especially in hot humid regions. In this case, it is possible to extract water vapour in the ambient humid air, water vapour gained from the humidification process and water vapour condensed in the condenser of the adsorption desalination system. Moreover, we have used a novel material Metal Organic Frameworks 801 as an adsorbent for a highly efficient process. Based on the results, Scheme #3 produced the maximum amount of fresh water, 210 kg/h while Scheme #2 obtained the maximum gained output ratio, 4.4 with a minimum cost of 0.0079 $/L. A standalone adsorption system produced the minimum amount of distillate water and the lowest gained output ratio. It is not advisable to use a standalone adsorption system to produce distillate water; as the full desalination potential is not achieved.

A Novel Configuration of Hybrid Reverse Osmosis, Humidification–Dehumidification, and Solar Photovoltaic Systems: Modeling and Exergy Analysis

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.

Experimental investigation of a desalination system using porous carbon tube as a humidification media with swirl flow

Humidification-dehumidification (HDH) technology is a technique for small-scale water desalination applications based on carrier gas humidification motivated by thermal energy. The present work introduces an experimental investigation of a desalination unit based on HDH method. The main objective of this study is to evaluate the heat and mass transport properties of porous carbon tubes (PCT) as a humidification medium with swirl flow for HDH unit. Processes for transferring heat and mass are investigated at varied the temperatures of water and air, water-to-air mass ratios (MR), and helical flow channel pitch (HCP). The performance analysis is investigated based on some of performance metrics such as gained output ratio (GOR), humidification efficiency (ηH), exergy efficiency (ηex), sustainability indicator (SI), and water cost (WC). Results indicate that the increase in MR and HCP increases all of performance parameters. High values of MR based on low air flow rate decrease the entropy generation and enhance the exergy efficiency. The humidity efficiency and GOR improve with the rise in the MR based on the water flow rate. The study of sustainability indicator shows that the proposed system has possibilities of doing business. It still has room for energy improvement and losses, though. The system's usability will increase after these modifications are made. When the process temperature associated with heating the feed water or/and input air rises, more freshwater is produced. The proposed system's maximum hourly yield reaches about 0.225 L with cost 0.078 cent. The best value of GOR, exergy efficiency, humidification efficiency and suitability indicator performed by the current system are about 3, 51.67 %, 48.72 % and 2.07 respectively.

Study on the Heat and Mass Transfer Characteristics of Humidifiers in Humidification–Dehumidification Desalination Systems

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 (tw), mass flow rate of spray water (mw), air temperature (ta), and air mass flow rate (ma) 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 tw can significantly improve the humidification performance. To achieve higher humidification energy efficiency, it is recommended to increase the tw to above 80 °C. (3) With the increase in the mw, although the humidification efficiency (εhum) decreases slightly, the humidification rate (mhum) increases, and the specific humidification energy ratio (ηhum) decreases accordingly. To maintain a high mhum and a low ηhum, it is advisable to control the mw at not less than 0.5 kg/s. (4) Increasing the humidifier inlet ta can improve the mhum, εhum, and ηhum, although not as effectively as increasing tw. (5) Increasing the ma can improve mhum and εhum. However, it simultaneously increases the ηhum. 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.

Thermodynamic comparison of the operation of the HDH system with water heating or air heating in closed water circulation and semi-open-air circulation

The present study focuses on doing a thermodynamic analysis of a desalination system that utilizes the humidification–dehumidification (HDH) process with semi-open-air (SOA) circulation. The HDH desalination system is a notable example of a developed system utilized for freshwater production. This system has the advantage of being able to derive its energy from solar sources. The categorization of desalination units is determined by the configuration of their components, the direction of water and air movement, and the kind of heating employed for each stream. The present study noted that the utilization of this particular air circulation strategy, while maintaining a constant maximum system temperature, leads to enhanced system efficiency when combined with water heating. However, no substantial impact was detected when this method was employed in conjunction with air heating (AH). Each type of HDH desalination system has a different ratio of mass flow rates (MFRs) for the streams. This means that the efficiency of the system stays the same, no matter how the air moves through the system. The examination of temperature and relative humidity characteristics in the environment has indicated that this particular desalination unit is applicable in places characterized by both arid and humid conditions. Furthermore, in both air and water heating modes, it has been observed that the system employing SOA circulation has superior efficiency when the environment temperature is elevated. In the context of water and/or air heating, when a specific value is assigned to the MFR ratio of the two streams, modifying the mode of air circulation does not have an impact on the overall efficiency of the system. It is shown in this article for HDH with air heater the highest GOR is attained at either FCR = 1 or FCR = 0, depending on the operational temperature of the system. Also The system clearly works at its most efficient (GOR = 3.4) when it's in a Semi-open-air mode (FRC = 0.77) and the temperature is 50 °C. On the other hand, the system efficiency is 2.94 when the air exchange system is closed (FRC = 1). In the same way, the overall efficiency is 2.88 if the air flow is open (FRC = 0).