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The perfect combination of renewable energy and desalination technologies is the key to meeting water demands in a cost-effective, efficient and environmentally friendly way. The desalination technique by humidification-dehumidification is non-conventional approach suitable for areas with low infrastructure (such as rural and decentralized regions) since it does not require permanent maintenance. In this study, this technology is implemented by using solar energy as a source of thermal power. A seawater desalination unit is considered, which consists of a chamber with two evaporators (humidifiers), a wetted porous material made of a corrugated cellulose cardboard and a condenser (dehumidifier). The evaporation system is tested with dry bulb temperature and relative air humidity data. The results of numerical simulations indicate that higher inlet air velocities (from 0.75 to 3 m/s) lead to a decrease in the ΔT, ΔRH, and effectiveness. With the air remaining within the evaporator for 30 cm, the temperature differential increases to 5.7°C, accompanied by a 39% rise in relative humidity contrast. These changes result in a significant enhancement in humidification efficiency, achieving a remarkable efficiency level of 78%. However, a wettability value of 630 m2/m3 leads to a smaller reduction of these parameters. Increasing the pad thickness, particularly to 0.3 m, improves performance by boosting ΔT, ΔRH, and effectiveness, especially for pads with a wettability of 630 m2/m3, for which superior performances are predicted by the numerical tests. [ABSTRACT FROM AUTHOR]

The introduction of fresh air into the indoor space leads to a significant increase in cooling or heating loads. Solid desiccant heat pump fresh air unit which can handle the latent and sensible load of fresh air efficiently have been proposed recently. To improve the performance of the solid desiccant heat pump fresh air unit in the fresh air handling process, in this paper, the application of composite silica gel in a heat pump fresh air unit was investigated. The comparison between silica gel coating (SGC) and composite silica gel coating (CSGC) shows that the adsorption rate and water uptake capacity of CSGC are more than two times higher than those of SGC. An experimental setup for the solid desiccant heat pump fresh air unit was established. The performance of SGC and CSGC was tested in the setup successively. Results show that under summer conditions, compared with the solid desiccant heat pump fresh air unit using silica gel (SGFU), the average moisture removal and COP of the one using composite silica gel (CSGFU) increased by 15% and 30%, respectively. Under winter conditions, compared with SGFU, the average humidification and COP of CSGFU increased by 42% and 17%. With optimal operation conditions of 3 min switchover time and 40 r/s compressor frequency, the COP of CSGFU under summer conditions can reach 7.6. Results also show that the CSGFU and SGFU have higher COP and dehumidification rate under higher outdoor temperature and humidity ratio. [ABSTRACT FROM AUTHOR]

The latest research progress of water vapor separation membrane technology is summarized, first introduces the classification of water vapor separation membrane materials, and the characteristics and research progress of different membrane materials are described・ Besides, the three categories and working principles of water vapor separation membranes with different structures in gas dehumidification and humidification are described systematically, and discusses the application and research status of water vapor separation membrane in the field of gas dehumidification at home and abroad・ The future research and development direction of membrane separation technology in the field of gas dehumidification and humidification are prospected. [ABSTRACT FROM AUTHOR]

The condenser's rejected heat in a vapour compression refrigeration system when thrown into the surrounding air results in its thermal pollution and gets wasted, while it has the potential to be recovered. Another major targeted concern is freshwater scarcity which is faced by the population in many areas. Addressing these difficulties, a double-stage integrated humidification-dehumidification and air conditioning system that recovers the condenser's waste heat and is assembled in a novel duct architecture is proposed. The obtained results of the developed model are established using the experimental data. The analysis explores the outcomes of the integrated system and investigates the influences of saline water temperature, humidifier efficiency, ambient temperature, and relative humidity on the output and performance metrics. The system provides air conditioning of 31.410 kJ and desalination of 65.020 mL from a unit volume of air using 0.661 kW of power and mitigates the environmental impact of existing technology. The coefficient of energy performance, cooling performance, gained output ratio, and exergy efficiency at the specified working situations are 0.958, 1.320, 6.809, and 2.701 %, respectively. A litre of freshwater costs $ 0.0068486. [ABSTRACT FROM AUTHOR]

Present work characterizes a spray tower-based desalination system, designed to simultaneously provide fresh water by condensation and supply dehumidified air to occupied spaces. Its configuration is open air-open water, with Celdek 7090 packing in the humidification section and water-cooled helical coils for dehumidification. The performance parameters calculated are: gained output ratio, recovery ratio, coefficient of performance, specific electrical energy consumption, mass ratio, humidification, and dehumidification efficiency. This performance is analyzed for varying air Reynold's number and water flow rate. The best results were obtained for the sea water flow rate tested of 18 liters per hour, and showed maximum humidification efficiency, dehumidification efficiency, COP, freshwater rate, gained output ratio and concentration factor equal to 87.14%, 94.56%, 3.34, 0.9 liters per hour and 1.05, respectively. Exit air meets the thermal comfort requirements which avoids the ventilation thermal loads in the space cooling. • A spray tower desalination unit with a venturi is designed. • The maximum COP of the system is found to be 3.34 which signifies energy efficiency. • Reynolds number of 50519 & water flow rate of 18 LPH yielded maximum fresh water of 0.9 LPM. • Air supply values PMV & PPD obtained are − 0.51 & 10.41 which are within the thermal comfort range. [ABSTRACT FROM AUTHOR]

• A desiccant coated humidification/dehumidification heat pump system is established. • The feasibility of the system has been theoretically analyzed. • The COP of the system for humidification and dehumidification are both more than 5. • The performance of the system under different operation conditions is tested. Widely used vapor-compression heat pump system can provide both heating and cooling capacity, considering it cannot realize humidification and efficiency of condensation dehumidification is relatively low. In this paper, a fresh air humidification and dehumidification system based on desiccant coated heat pump is established. In which the condenser and evaporator of the heat pump system are replaced by desiccant coated heat exchangers. By using the 4-ventilation valve, the system is very compact. The feasibility of humidification and dehumidification of the system has been theoretically analyzed. The performance of the system under GB Shanghai summer conditions and GB winter conditions is experimentally verified. The results show that the system can realize dehumidification and humidification in summer and winter efficiently and the COP under these two conditions is 5.16 and 5.06 respectively. The dehumidification and humidification rates of the system in the two chosen conditions are 2.99 L h −1 and 1.99 L h −1 respectively. The results also show that under Shanghai summer conditions, by changing the compressor frequency, the system can get a dehumidification of 2.40 L h −1 to 3.05 L h −1 with a COP of 7.80 to 3.56. The optimized switchover period is 6 min. [ABSTRACT FROM AUTHOR]

A psychrometric energy process desalination unit has been experimentally tested. The system is based on humidification and dehumidification process where seawater is heated and then sprayed to humidify the incoming air in the humidification chamber. The humidified air enters the dehumidification chamber and is cooled by the incoming cold seawater. The moisture is condensed out and the pure water is accumulated at the base of the chamber, and the dehumidified air is discharged to the outside. The seawater was heated to temperature between 60 - 90°C using a 2.4kW electric heater. Performance data on temperature, seawater mass flow rate, air flow rate and the amount of fresh water produced were obtained, and the maximum coefficient of performance (COP) of the system was calculated based on the data obtained. The result achieved indicates the system had a maximum fresh water production of 13kg/h with a maximum COP of 3.6. The initial test shows that the system has great potential with room for improvements and further optimisation.

The aim of this work is to design and analyze solar humidification and dehumidification desalination plant that is integrated with an energy tower. The proposed integrated water production plant (IWPP) utilizes the waste humid air of the energy tower for the production of potable water as an added benefit in bonus apart from the power production through energy tower. The layout of the proposed desalination plant has been presented which is configured with 100 solar humidification dehumidification desalination units and capable to fulfill potable water demand of 800 liters per day that may be sufficient for a small community of remote area. The seasonal and annual performance of the plant has been analyzed in the climatic condition of Jamnagar which is hot and humid city in western Indian state, Gujarat. The optimum values of air and water mass flow rate have been identified with the help of mathematical simulations in summer, rainy and winter season. The results showed that air mass flow rate 118–120 kg/hr through solar air heater is suitable for water production throughout the year. The water mass flow rate of 125–130 kg/hr in humidifier and 120 kg/hr−122 kg/hr in dehumidifier has been found optimum for potable water production. The seasonal variation in gain output ratio is 0.32−0.45 however it can be increased to 0.62 at optimized operating condition. Finally, the economic and environmental analysis of the proposed plant resulted Rs 0.93/kg (US $ 0.011/kg) cost of potable water, payback period of 0.49 year and 146.8 t/annum reduction in CO2 emission, respectively. Mini desalination plant capable to fulfill water needs of small community. Utilization of waste humid air of energy tower Clean source of potable water. Numerical analysis for time dependent behavior. Annual performance, economic and environment analysis. [ABSTRACT FROM AUTHOR]

This paper presents a vapor compression heat pump-driven humidification–dehumidification process with energy recovery option. Two systems with different applications of recovered energy are proposed. System A recovers energy for preheating inlet feed water to the heat pump condenser, while system B recovers energy for preheating the humidifier inlet air. The system performance metrics such as gained output ratio (GOR), recovery ratio (RR), productivity, specific electrical energy consumption (SEEC) and the cost of freshwater production are investigated based on variations in mass flowrate ratios, humidifier effectiveness, seawater temperature, brine heat exchanger effectiveness, unit cost of electricity and expected plant life. The thermo-economic performance of the proposed system is compared with system "C" without energy recovery option. Findings reveal the need to recover thermal energy associated with the discharged brine for humidification and dehumidification desalination system having ineffective/poor component effectiveness, especially the humidifier. The proposed system shows that the cost of freshwater for system C can be reduced by about 15.23% with energy recovery in system A. The GOR of system C is improved by about 23.1%, whereas the RR, productivity and SEEC of system C are improved by about 23.3% each. The conditions at which the energy recover is effective are also shown in the results. [ABSTRACT FROM AUTHOR]

Fresh air system is getting more and more important nowadays. The heat pump fresh air system based on the desiccant coated heat exchanger (DCHE) that can handle the latent and sensible load of fresh air efficiently has a large energy saving potential. To improve the performance of the heat pump fresh air system based on DCHE, in this paper, a control system based on PLC is established and the operation strategies of the system are investigated. An operation strategy including automatic control of the opening of the electronic expansion valve based on the suction superheat of the compressor, control of the switchover period based on the relative humidity of supply air, and control of compressor frequency based on evaporation and condensation temperature is established. By using the optimal operation strategies, the dehumidification rate and COP of the system can reach 4.42 kg/h and 6.2 in summer, compared with the unoptimized strategy it increased 8% and 25%, respectively. The two performance indices can reach to 3.04 kg/h and 6.98, with an increase of 89% and 78%. • A control system for Heat pump fresh air system based on DCHE is established. • The optimal operation strategy of the system is proposed. • The dehumidification rate and COP of the system reach 4.42 kg/h and 6.2 in summer. • The humidification rate and COP of the system reach 3.04 kg/h and 6.98 in winter. [ABSTRACT FROM AUTHOR]

The main objective of the present work is to treat tannery effluent with a total dissolved content of 150 g/L using solar energy by humidification and dehumidification process using a roof even type greenhouse evaporator. This system not only helps to effectively treat the tannery effluent by increasing its total dissolved solids content to 350 g/L but also helps to generate potable water from tannery effluent by using solar energy. In this study, the performance of the effluent was tested in six different modes. It was found that the tannery effluent total dissolved solids content increased to 350 g/L in just 2.5 days when the greenhouse evaporator was operated in Mode 6 which is the shortest duration when compared to other modes of operation. The specific fuel consumption of the roof even type greenhouse system to treat tannery effluent is 22.55 kW h/ m3 which is 8.3 % of the energy consumed by the zero liquid discharge plant. Meanwhile, the land area required to dehydrate 1 m3 of tannery effluent got decreased by 43 % when the roof even type greenhouse evaporator was used. [ABSTRACT FROM AUTHOR]

This study investigates the performance of a novel humidification dehumidification (HDH) desalination system integrated into a vapor compression (VC) heat pump. The integrated heat pump delivers the necessary heating and cooling loads to the HDH desalination unit. Three different layouts (system A, system B, and system C) of water desalination plants are proposed and evaluated analytically at different operating conditions, such as water temperature, water flowrate, mass flowrate ratio (MR), and humidifier effectiveness. The investigated performance metrics of the proposed HDH desalination system are the gained output ratio (GOR), freshwater production rate, specific electrical energy consumption (SEEC), recovery ratio (RR) and cost of freshwater production. System A is without heat recovery, system B has heat recovery through preheating feed inlet saline water, while system C has heat recovery through preheating inlet air to the humidifier. The parametric analysis indicates that GOR, water productivity, and RR improve with increasing water temperature and humidifier effectiveness, while the specific electrical energy consumption decreases at the same conditions. The findings show the existence of an optimum mass flowrate ratio (MR) at which system performances are maximized. Results also reveal that the systems with the option of energy recovery provide the highest gained output ratio, recovery ratio and productivity, and the least specific electrical energy consumption. Additionally, depending on various system and cost parameters, the price of freshwater production from the proposed systems varies from 34.27 $/m3 to as low as 7.33 $/m3 of freshwater. [ABSTRACT FROM AUTHOR]

• Combination of wind tower with solar humidification dehumidification desalination system. • Thermal comfort and production of potable water together. • Conservation of energy and water both. • Numerical analysis for time dependent behavior. • Humidification and de-humidification for closed and open water cycle. The world which is hot and arid strives for fresh water and thermal comfort, thus there are two basic requirements. In this work, performance of wind tower in combination with solar air heater assisted humidification-dehumidification desalination system working with closed and open air water cycle is analysed numerically for cooling effect and fresh water production. The behaviour of system has been studied by different air flow rate in tower, temperature drop due to energy stored in wall and clay conduits, temperature drop due to evaporative cooling, humidity of moist air available for cooling, amount of potable water produced in dehumidifier and its variation with design and operating variables. A mathematical model based on fluid flow, heat transfer, energy and mass balance in components of system has been developed. Study reveals that comfort condition is achieved mainly by evaporative cooling in wind tower. Optimized column height is found as 8–9 m suitable to design the wind tower with 65% decrease in air velocity, 31% decrease in air temperatures and change in relative humidity up to 90%, however 42% reduction in water requirement in humidifier is also achieved at 5 m height with a cooling effect of 3.5 kW. Air mass flow rate of 0.032–0.035 kg/sec in solar air heater found suitable with maximum productivity of 5 and 4.2 kg/day for closed and open water cycle respectively. Water mass flow rate of 0.035–0.038 kg/sec in dehumidifier has been found suitable for 200% increase in productivity. [ABSTRACT FROM AUTHOR]

In the current status, an Adsorption Desalination System (ADS) has been found to have lower water production capacity than conventional desalination technologies. This study proposes a hybrid desalination system integrating the Adsorption (AD) and Open air cycle Humidification-Dehumidification (OHD) process to overcome the challenge of lower water production capacity in ADS. This hybrid system known as AD-OHD system comprises of a single bed ADS and a Humidification-Dehumidification (HDH) unit. The main objective of this work is to analyse the performance of the hybrid AD-OHD system based on parameters such as Gain Output Ratio (GOR) and amount of desalinated water production. The performance of the hybrid AD-OHD system is studied under three different operating conditions of switching (t swt) and sorption time (t spt), namely, t swt > t spt , t swt = t spt , and t swt < t spt. The results indicate that the optimal working condition is achieved when the hybrid AD-OHD system operates at condition t swt < t spt. The amount of desalinated water and GOR under the optimal condition is found to be 1.12 l/h and 0.78, respectively. The study also conducts experimental investigations to evaluate the GOR of the hybrid AD-OHD system under different operating conditions, including the temperature of the water entering the evaporator and the temperature of the hot and cooling water input to the adsorbent bed. Experimental data indicates a positive correlation between GOR and hot water temperatures, while increased cooling water temperature reduce GOR due to reduced adsorption behaviour. Although the evaporator inlet water temperature initially boosts GOR, it declines as the adsorption capacity diminishes. The study highlights the superior performance of the hybrid AD-OHD system compared to both the standalone single-bed ADS and open cycle HDH desalination systems. The hybrid AD-OHD desalination system exhibits an 80 % improvement over the single-bed ADS system and a 50 % improvement over the open cycle HDH system in desalinated water production. Additionally, a theoretical model of the adsorption desalination cycle is developed and validated, demonstrating the viability of the AD-OHD system for desalination applications. • A small scale hybrid adsorption desalination incorporating open air cycle HDH unit. • Amount of desalinated water and GOR of the hybrid AD-OHD system is analyzed. • GOR is found to be 0.78 with desalinated water production of 1.12 l/h. • The hybrid AD-OHD system outperforms the single bed ADS and HDH unit in desalinated water production. [ABSTRACT FROM AUTHOR]

A solar powered desalination unit which is working on a humidification –dehumidification technique (HDH) is one of the most important techniques used in seawater desalination in remote and rural areas. It is easy to design, operate and maintain. In this paper, a theoretical study based on a design methodology for a solar assisted desalination unit working on a HDH principle under the prevailing conditions of Tajoura-Libya is carried out. The main target is to study the effect of different design and operating parameters that influence the performance of the unit and its productivity under different design scenarios; (spring, summer, autumn and winter). Results show that the productivity of the unit is increased with a corresponding increase in the inlet air mass flow rate to the solar air heater, inlet water mass flow rate to the humidifier and cooling water mass flow rate to the dehumidifier. A significant increase in the productivity of the unit is achieved when the initial water temperature and the initial mass of water inside the storage tank were increased. Moreover, Gained Output Ratio, GOR, values vary between (0.27 and 0.79) for winter and spring designs and (1.94 and 2.75) for autumn and summer designs respectively. In general, the productivity of the unit is estimated to be within a range from a minimum of (2 ~ 4) kg/m2.day, in winter to a maximum of (10 ~ 12) kg/m2.day, in summer, which makes it very convenient for using in rural and remote areas.

In this work, a solar desalination system working through cyclic humidification and dehumidification and also utilizing waste hot air of air conditioner is analyzed numerically for the production of potable water during day and night both operations. The productivity of the proposed system is investigated for different operating and design variables and compared with a conventional system by simulation of a mathematical model based on energy and mass conservation of considered components in transient behavior using MATLAB. During simulations, climatic and geographic condition of Mumbai (India) is used due to the availability of saline water, humid air and the high annual operation of air conditioners. In proposed system air is heated by a double pass solar air heater whereas the saline water is heated by the hot air coming out from the air-cooled condenser of air conditioning unit particularly during day hour operation. The same arrangement is used to heat both air and water during night hours. The use of hot air from the condenser of air conditioner proved beneficial by increasing the yield by 21%-31% per day that depends under different operating and design conditions. Air mass flow rate of 0.032-0.035 kg/s in air heater found suitable and resulted in maximum productivity of 6 kg/d. The mass flow rate of cooling water at 0.038 kg/s has been found suitable with a maximum productivity of 7 kg/d. Need for higher Initial water temperature in a storage tank with a productivity of 8.2 kg/d at water temperature 46°C and low temperature of cooling water in a dehumidifier with a maximum productivity of 10 kg/d found by the analysis. Productivity variation in the range 4-10.2 kg/d has been found as the heater area varied from 0.5 to 2.5 m2. The proposed system found suitable to work in a region with higher wind speed and ensured better utilization of thermal energy with gained output ratio close to 1. [ABSTRACT FROM AUTHOR]

The performance of a hybrid humidification-dehumidification (HDH) desalination system operated through the waste heat recovered from vapour compression refrigeration (VCR) based household air-conditioning unit is investigated in the present study. The paper deals with the design and simulations aspects to examine the desalination system's performance for hot and medium climatic conditions considering various ranges of space conditioning temperatures (20 °C, 24 °C and 28 °C) respectively. The heat and mass transfer mechanisms in the various components of the system were established using TRNSYS software with experimental validation of the major components of the desalination system. The model operates using the real meteorological data to predict the performance of the hybrid HDH desalination system. Sequence of experiments was conducted and the obtained experimental results were compared with the simulated results. It was found that the average condensate production rate decreased with increase in space conditioning temperature. Further, economic analysis indicated that cost of freshwater produced from the present system is about $0.1658/kg. The obtained results depicted that the developed model could be used to design and predict the behaviour of the desalination system when installed in various meteorological conditions. • A HDH system using waste heat from household air conditioning system is studied • Performance was investigated for summer and pre-monsoon seasons • Respective maximum average freshwater yield is 4.63 kg/h and 4.13 kg/h • Fresh water yield is highly dependent on atmospheric air temperature and RH • Cost of freshwater generated from waste heat was $0.1658/kg [ABSTRACT FROM AUTHOR]

Rapid growth in urbanization, industrialization and decrease in rainfall rates all over the world demands more fresh water for human use, industries and agriculture purpose. The novel desalination technologies for converting saline water into fresh water have more value and demand. Present work aim at evaluating the performance of an integrated air cooling and two stage desalination system using humidification dehumidification (HDH) technology experimentally by varying flow rate and temperature of saline water. The components of the proposed system are designed, developed and carried out experiments for different operating conditions to get optimum operating conditions. The plant consists of a solar water heater (SWH), two air preheaters, two humidifiers, two dehumidifiers with a normal and a vapour compression refrigeration water chiller. The influence of saline water temperature and flow rate on air temperature, desalination yield, recovery ratio, energy utilization factor (EUF), air cooling effect and coefficient of performance (COP) of the cooling system are studied. The experimental observations recommend higher saline water temperature with high flow rates to air preheaters and humidifiers, circulating and chilled water to dehumidifiers with lower possible temperatures. The integrated plant yields 240 W of cooling energy and a maximum fresh water of 2180 ml/h with 15 m³/h air flow at saline water temperature of 54.5°C with a flow rate of 200 LPH. Experimental results show a maximum EUF of 0.5 for the hybrid plant and 0.45 for conventional plant single stage plant. A maximum COP of 2.2 with a recovery ratio of 0.78 is observed from the experimental results. [ABSTRACT FROM AUTHOR]

In this paper, a numerical investigation of a direct-contact humidification-dehumidification desalination system is presented. The system functions in an open loop for both the air and the water and does not have packing materials inside the humidifier and dehumidifier. The air is humidified by spraying hot seawater into it and then dehumidified by spraying cold freshwater. Both processes occur in a counterflow arrangement. The mass and energy conservation equations at steady-state conditions were solved through a finite difference scheme. During the solution, the properties of the fluids were evaluated for each discrete element. The influence of the geometry was also examined through the variation of the humidifier and dehumidifier height ratio. From the results, it was observed that for a fixed geometry, the freshwater production is enhanced through small droplet diameter and velocity and high seawater temperature and mass flow rate. The largest production achieved was 242.2 kg/h at a height ratio of 2.0. Increasing the height ratio was in general beneficial; however, the gains after it exceeded 1.5 were not significant. Since no attempt of heat recovery was done for this system, the gained output ratio was consistently low for all the cases analyzed. The largest value obtained was 0.58. [ABSTRACT FROM AUTHOR]

The humidification–dehumidification method (HDH) is a thermal desalination process. The process is viewed as a promising technique for small-capacity production plants. The process has many features, which include operation at low temperatures and the ability to combine with a sustainable solar-energy source. This paper demonstrates the design, modeling, simulation, economy, and optimization of an HDH desalination unit simulated within one hour of operation. The designed unit has continued water circulation across the humidifier (HD), a cross-flow oil heater, and closed air circulation. The effects and economic impact of a circulating air-mass flow rate and HD-inlet water temperature on unit productivity are studied. Other parameters, such as energy consumption, heatto-mass transfer ratio, humidifier enthalpy difference, humidifier thermal efficiency, gained-output ratio (GOR), and annual production costs, are evaluated. Experimentally obtained mass-transfer coefficients in the humidifier were used to simulate the desalination unit. The study reveals that increasing air-mass flow rate has a significant effect on improving unit productivity. Moreover, highest productivity was obtained at the maximum simulated humidifier-inlet water temperatures. Packing with a higher mass-transfer coefficient gives higher unit productivity. The unit was optimized to achieve the best operating conditions, with higher productivity, at lower operating costs, maintaining best energy use at the highest attainable GOR. The optimal operating air-mass flow rate for all conditions ranged between 0.131 and 0.1998 kg/s for both the experimental and the simulated conditions. The lowest production cost obtained was at the HD-inlet water temperature of 50°C. The best experimental production costs were US$/0.07/L compared to US$0.066/L for the simulation. Finally, the simulation process showed good agreement with the experimental results, which can be a useful tool to further evaluate the unit when coupled with a renewable-energy source. [ABSTRACT FROM AUTHOR]

Humidification-dehumidification desalination (HDH) systems have been found to be ideal for treating seawater at a smaller scale. It requires thermal energy to drive the processes inside the HDH system which can be supplied by a renewable source of energy (such as solar energy). For this purpose, a nanofluid-based direct absorption solar collector (DASC) can be used which has a relatively higher thermal efficiency, as compared to the conventional surface absorption-based solar thermal collector. In this study, these two sub-systems—HDH and DASC, are coupled through a heat exchanger. In this paper, a numerical model has been prepared for DASC-based HDH system which aims to evaluate the energy efficiency of this combined system by calculating gained output ratio as a function of various parameters, related to the DASC, such as particle volume fraction (fv), height (H) and length (L) of the collector, mass flow rate of nanofluid inside the collector (m˙nf) and amount of solar energy incident (q) on the collector. The performance of the combined or integrated system has also been verified against the various parameters related to HDH system such as ratio of mass flow rate of the saline water to the dry air (m˙w/m˙da), effectiveness of the humidifier (εH) and dehumidifier (εD) and the bottom temperature (Tw1). Also the results of the numerical model prepared in this study have been compared with those available in the literature. Finally, the applicability and benefits of using nanofluids in various thermal desalination techniques have been presented. [ABSTRACT FROM AUTHOR]

Abstract Water scarcity has resulted in a pressing need to develop an inexpensive and efficient desalination technology for fresh water production, especially in developing countries. Apart from other effective desalination technologies, humidification-dehumidification desalination process is predominantly adopted in the past decade to meet water deficiency due to its varied advantages in system construction, maintenance and operation. In this paper, a comprehensive review of the various advancements carried out experimentally for improving the performance of the solar humidification-dehumidification desalination system has been presented. The major factors contributing for enhanced system performance such as mass flow rate of heat transfer fluid, forced convection mechanism, multi-pass technique, recirculation mechanism, use of nano heat transfer fluid and phase change material are discussed. Further, the effect of solar intensity, ambient temperature, wind velocity, stage-wise heating and cooling on freshwater productivity is also reported. It was found that easy construction and maintenance of flat plate collector and higher performance index of evacuated tube collector make them as the predominant technologies adopted for heating the water and air heat transfer fluid's in solar humidification-dehumidification desalination system respectively. Further, it is identified that there exists a large potential for improving the fresh water yield through hybrid systems which involve use of geothermal or biomass energy, integration of solar stills with humidification-dehumidification desalination system, coupling of solar still, Fresnel lens solar collector and parabolic trough collector respectively with the flat plate collector and evacuated tube collector systems. The scope for further improvement in individual system and process parameters have been discussed. Highlights • Specified solar technologies adopted for HDH desalination are studied. • Effect of water and air preheating are examined. • Significant system factors for performance improvement are identified. • Scope for system design improvement has been provided. [ABSTRACT FROM AUTHOR]

Abstract Experimental investigation on the performance of novel composite desiccant Silica Gel and Sodium Acetate Coated Heat Exchanger (SASCHE) is conducted for typical summer and winter seasons in the city of Shanghai, China. First, effects of main parameters such as regeneration temperature, hot and cooling water temperature, inlet air velocity, thermal coefficient of performance ( COP th ) and energy efficiency are experimentally investigated in summer and winter for dehumidification-cooling and humidification-heating application, respectively. Then, its performance is compared with Single Silica Gel Coated Heat Exchanger (SCHE), and Potassium Formate and Silica Gel Coated Heat Exchanger (PSCHE). In the summer season, the experimental results showed that the new composite desiccant material can handle dehumidification-cooling process with an excellent performance regarding cooling capacity and efficiency. The dehumidification capacity of SASCHE is improved by 10% and 30% in comparison with that of PSCHE and SCHE, respectively. In the winter season for humidification-heating process, the average humidification capacity of SASCHE is two times higher than PSCHE and SCHE. Additionally, indoor comfort conditions are satisfied with high hot water temperature and low inlet air velocity for summer season, while low hot water temperature and high inlet air velocity are recommended for winter season. Highlights • A novel composite desiccant heat exchanger Silica Gel-Sodium Acetate is presented. • Performance is experimentally investigated during summer and winter season. • Experimental results are compared with different types of DCHEs. • Dehumidification amount is improved by 10% and 30% in comparison with PSCHE and SCHE. • Humidification capacity is two times higher than PSCHE and SCHE. [ABSTRACT FROM AUTHOR]

In this study, exergo-economic analysis of two layouts of humidification-dehumidification (HDH) desalination systems driven by a vapor compression heat pump (HP) is presented and discussed. The systems are closed-air open-water water-heated cycle coupled with a heat pump (HP-HDH-WH), and modified air-heated cycles integrated with a heat pump (HP-HDH-AH). For the purpose of comparison, a conventional closed-air open-water (CAOW) electric water heated HDH system (E-HDH-WH) is also presented. Exergy destruction, exergetic efficiency and product cost are evaluated for these systems. The influence of input parameters such as mass flowrate ratio, dehumidifier effectiveness, compressor isentropic efficiency, and feed water temperature on second-law efficiency and exergy destruction associated with the major components of the systems are analyzed. The impact of input cost parameters is investigated using two different approaches. The analysis shows that evaporator and compressor are the components with the largest exergy destruction. The exergy efficiency for the HP-HDH air-heated unit, HP-HDH water-heated unit, and E-HDH water-heated unit is found to be 1.097%, 0.06965% and 0.05795%, respectively. The cost of desalinated water evaluated by current analysis for HP-HDH air-heated system, HP-HDH water-heated cycle, and E-HDH water-heated unit is found to vary from 4.61$/m 3 to 5.49$/m 3 , 6.00$/m 3 to 7.14$/m 3 , and 4.44$/m 3 to 14.95$/m 3 , respectively. The results generally reveal that HP-HDH air-heated cycle shows better performance both from energetic and exergetic viewpoints. [ABSTRACT FROM AUTHOR]

The effects of solar energy and Phase Change Material (PCM) on the energy saving of a desiccant air conditioner have been numerically investigated. Three configurations of desiccant air conditioner (Type A, Type B, and Type C) are investigated at the same ambient conditions to get beater configurations for the energy-saving potential. The difference between the three configurations represents the source of thermal energy used for heating the regeneration air used for reactivation the desiccant material. For Type A the electrical air heater represents the thermal energy source for heating the regeneration air. For Type B the solar energy and electric air heater represent a source of thermal energy for heating the regeneration air. For Type C the solar energy, PCM, and electric air heater represent a source of thermal energy for heating the regeneration air. The numerical results of these simulations are validated by published experimental data, which resulted great agreement between numerical results and experimental data. Also, the economic analysis has been studied to get the beater configurations. The results show that, the average percentage savings in the electrical energy which consumed about 20.85% for Type B and 75.82% for Type C as compared to the Type A. [ABSTRACT FROM AUTHOR]

Humidification-dehumidification is a carrier gas based thermal technique that is ideal for small-scale water desalination applications. One advantage of humidification-dehumidification systems is the ability to utilize low grade and renewable energies as heat source to drive the system. This work presents theoretical investigation of humidification-dehumidification desalination system operated by a heat pump. The model is based on the first law of thermodynamics, describing heat and mass transfer in the combined humidification-dehumidification-heat pump cycle. The model predicts the performance of closed-air open-water water-heated, and modified air-heated cycle coupled with a heat pump. To improve the Gain output ratio and energy recovery of the system, a heat pump is used as the source of heating and cooling for the humidification-dehumidification desalination system. Energy rejected in the condenser is used as a source of heat in the humidifier whereas the cooling effect of the evaporator is used to cool incoming seawater for effective condensation of humid air in the dehumidifier. A parametric study is conducted to investigate the influence of system operating parameters, including water and air flowrate, seawater temperature, and refrigerant flow rate on the system performance. Results indicate a maximum Gain output ratio of 8.88 and 7.63 obtained at 80% components effectiveness and mass flow rate ratio of 0.63 and 1.3 for modified air heated and water heated cycle, respectively. A maximum gain output ratio greater than 10 can be achieved for humidifier and dehumidifier effectiveness of 100% leading to more energy efficient systems. The cost of desalinated water production is calculated and the effect of major parameters on its variation is also presented. [ABSTRACT FROM AUTHOR]

Desalination by air Humidification Dehumidification (HDH) is one of the upcoming technologies of converting brackish water into freshwater. It works by evaporating the brackish water and humidifying air passing over it, leaving the salts behind. The humidified air is then passed through the condensers to recover the water it carries by condensation of water vapour. This condensed water is free from salts and can be directly used or can be further treated for use. The use of a compact finned tube heat exchanger for the purpose of the 2nd dehumidifier in a two stage HDH process is carried out by using computational fluid dynamics (CFD) analysis. The boundary condition for the computational work is obtained from experimental setup in a pilot plant. As CFD models can take up very large computational power for solving fin structures, the model is solved by modelling the fins side of the dehumidifier as a porous medium. The water yield obtained from condensation, thermal characteristics of the fluid model are obtained is compared with experimental results. The yield of water obtained is 3848 ml/hour for the first set of experimental observations. [ABSTRACT FROM AUTHOR]

In recent years, liquid desiccant air-conditioning system (LDAC) has shown a great potential alternative to the conventional vapor compression systems. LDAC not only greatly improves the indoor air quality by controlling the humidity and temperature independently, but also deceases the electrical energy consumption of the conventional air conditioner. In this work, the liquid desiccant and humidification cycle is driven by the exhaust heat of the compressor. Cycle performance of a small-scale heat pump type air conditioner coupled with a liquid desiccant/humidification cycle has been theoretically and experimentally evaluated by the present study. Parametric analysis on cycle performance of the present cycle is carried out through both theoretical and experimental methods, and lithium chloride aqueous solution is used as the working fluid of the solution cycle. The thermodynamic analysis results show that while the evaporating temperature of the present cycle increases to 15 °C, the energy consumption decreases by about 22.64% when compared with conventional air conditioner. Theoretical results also indicate that the coefficient of performance (COP) of the novel system has a potential improvement of about 35.3%. Based on the theoretical results, experimental analyses of this novel cycle under summer and winter working conditions are carried out. In addition, comparison of the humidification and dehumidification ability as well as COP of the present novel system and the traditional one are carried out. Researching results of the present study provide important reference for investigator of this field. [ABSTRACT FROM AUTHOR]

Humidification–dehumidification (HDH) desalination works based on a water cycle principle and involves air humidification and condensation (dehumidification). The cooling of humid air with chilled water increases the desalination and results in cold air suitable for air conditioning process. The merits of the proposed HDH desalination and cooling are not analyzed and compared in the literature. Therefore, the performance results of HDH with normal water (current technology) and HDH with chilled water (proposed idea) are compared to highlight the merit of this cycle. The combined cycle for desalination and cooling has been solved thermodynamically with psychrometric properties. The results are validated with a laboratory experimental setup. The examined operational process conditions are hot water inlet temperature, efficiency of humidifier, and vapor absorption refrigerator's (VAR's) evaporator exit temperature. The focused results are desalination, cooling and energy utilization factor (EUF). The comparative study recommends the use of chilled water in the final stage. The two stage desalination with dehumidification by normal water in the first stage and chilled water in combined two stages improves the cycle EUF from 0.18 to 0.33. Out of 300 W of cooling generation, 100 W is used for dehumidification and the remaining 200 W is available for air conditioning process at 15 N⋅m 3  h −1 of air. [ABSTRACT FROM AUTHOR]

The performance of a desalination unit using humidification-dehumidification technology with new corrugated packing aluminum sheets in the humidifier was experimentally investigated. The influences of operating variables on yield and performance are studied. Operating variables include the air and water temperature at entry to the humidifier, the humidifier water flow rate, the ratio of mass of water to air, and the cooling water flow rate into the dehumidifier. To conduct such a study, an experimental set-up was developed, including a packed bed humidifier, finned tube condenser, water heater, air heater, and other auxiliary devices. The results indicate that increasing the temperature of inlet water in the humidifier, the humidifier water flow rate, and the dehumidifier cooling water rate significantly increases the production of distilled water. However, a slight increase in the production of desalinated water is observed by raising the air temperature, while a specific air mass rate achieves the highest productivity. The inlet cooling water temperature significantly enhances the yield from 10 to 15 L/h as the inlet cooling temperature reduces from 28.5 °C to17 °C. Cost analysis of the developed system indicates that the total cost per one liter of fresh water is about $0.01. [ABSTRACT FROM AUTHOR]

An experimental study of the performance of an air conditioning system, using the concept of humidification-dehumidification is presented and investigated. The technique (AWVP) relies on utilizing the moisture present in atmospheric air and to increase its content to certain extent. The water extracted through this technique is of good standard and can be used for drinking and other purposes. The test setup consists of four loops namely fresh water circuit, air circuit, refrigerant circuit and dirty water circuit. Certain operating parameters like volume flow rate of air, air inlet temperature after heating and relative humidity was varied and its effect on the performance of the system was studied and analyzed. [ABSTRACT FROM AUTHOR]

A novel solar energy driven and membrane-based air humidification-dehumidification desalination (MHDD) system is designed and constructed. To realize a water-salt separation, a hollow fiber membrane module is employed as the humidifier to humidify air with solar energy heated saline water. The humidified air is then cooled and condensed to obtain distilled water. A detailed theoretical model is developed and validated to evaluate the performance of the proposed MHDD system. The whole model includes submodels for the solar collector, the water tank, the membrane humidifier, and the vapor condenser. At a specified membrane area, the effects of the water tank volume and solar collector area on the system performance such as the electric energy consumption for water production ( SEC ), the coefficient of performance ( COP ), etc., are analyzed. The optimal water tank volume and the optimal solar collector area for the desalination system are evaluated. In addition, an economic analysis on the whole system reveals that the system needs a low maintenance cost to make the water production competitive. Generally it provides an attractive alternative to small-scale, stand-alone desalination systems that could provide high purity drinkable water. [ABSTRACT FROM AUTHOR]

The productivity of the humidification-dehumidification solar desalination systems (HDHSDS) significantly increases when the temperature of the feed water increases, so, high temperature solar water collectors as parabolic trough or evacuated tube collectors are recommended for these systems. On the other hand, the effect of air temperature on the productivity of the HDHSDS is insignificant. Thus, the utilization of solar air heater is not recommended in these systems. Based on these recommendations, three research points are suggested for future work: 1) using the recovered PV thermal energy for heating the feed water in the HDHSDS. This will provide an annual fresh water productivity more than 833 L/m 2 of PV in addition to 278 kWh of electricity; 2) using phase change material with melting temperature around 90 ˚C as a thermal energy storage medium to provide feed water with high and almost constant temperature during the day and keeps the system in operation 24 h/day; 3) using the thermal energy rejected from the thermal power cycles for water heating in the HDHSDS. [ABSTRACT FROM AUTHOR]

Recent technological advancements in the HVAC industry enable optimized occupant thermal satisfaction and system efficiency, thanks to better control of the comfort parameter. Current work aims to automatically control the thermal comfort parameters: dry bulb temperature, air-velocity, and relative humidity. This is achieved using an air handling unit (AHU) equipped with a fresh air control for air quality control, a chiller unit that runs on a VCR cycle for cooling and dehumidification, an ultrasonic mist humidification system, and an air volume control system installed in the ductwork for temperature control. These systems are automatically controlled based on the feedback from various sensors installed in the target space to fit to the ASHRAE Standard 55. Experiments are conducted for varying air velocity at different daytime periods in Dubai. Air temperature and humidity are measured at each stage of the AHU. Total time for achieving thermal comfort is recorded. Results indicated that maximum coefficient of performance (COP), dehumidification effectiveness (DE), humidification effectiveness (HE), predicted mean vote (PMV) and bypass factor were 8.60, 0.96, 36%, −0.62 and 0.48 respectively when outdoor conditions reached 42 °C and 50% RH. The operational efficiency of the current adaptive-controlled system is found to be 21.50% more efficient than a conventional system. • Integration of AHU with an adaptive control unit. • A transient analysis to achieve thermal comfort conditions was tested. • Maximum saving of 21% of power for a heat load of 200 Watts. • Operation cost is reduced by 26% compared to a conventional AC unit. [ABSTRACT FROM AUTHOR]

This study was focused on modeling of the integration system of flue gas desulfurization (FGD) and humidification dehumidification desalination (HDD). The study dealt with the development of appropriate models for two alternative process flow structures intended for achieving the target of FCO by seawater while obtaining a fresh water credit. Each of the two schemes was dealt with separately. This included a brief description of the characteristic features of each scheme, models associated with the formulation of overall mass and heat balances, and the design equations used for rating the various components within each process scheme. The proposed model was applied to the operating conditions of the power plants in Kuwait, motivated by the large capacity of these plants and the use of high sulfur oil fuels. The analysis included sizing of the required HDD units, evaluation of the specific amounts of water generated relative to the plant power capacity, the design characteristics, and the performance of the flue gas/seawater heat exchanger and seawater absorption column for sulfur dioxide removal from the flue gases. The two alternative configurations were compared by summarizing the results of the major factors affecting the initial and operating costs associated with the different schemes. [ABSTRACT FROM AUTHOR]

The present work is an experimental study of a solar desalination unit which operates on the principle of humidification-dehumidification using a Scheffler solar parabola. This unit is installed in the National Centre for Studies and Research on Water and Energy, University Cadi Ayyad Marrakesh, Morocco. The system comprises a primary reflector (10 m2 area), secondary reflector, distillation still, condenser and Florentine flasks. In order to describe the studied system, The variations of the debit condensate, the solar radiation and the characteristic temperatures of the system are measured during the day. The gotten results show that this system is very profitable since that it permits to get a mass output of 97%. The average power and efficiency of the solar distillation system were found to be 2.39 kW and 29.67% respectively for an average beam radiation of 987 W/m2. [ABSTRACT FROM AUTHOR]

The present work deals with an experimental study of a solar desalination unit using the humidification-dehumidification (HDH) process. A bench-scale desalination unit was designed and tested in Bizerte, Tunisia. Humidification is achieved through a humidifier with saline water falling on its absorber plate, and dehumidification is realized by means of a tubular heat-exchanger condenser. The desalination unit operates with open-water and open-air cycles. Thermal performances as well as fresh water production of the HDH desalination unit were evaluated via measurements of air and water temperatures and flow rates. Measurements were conducted in free and forced convection. Special attention was focused on the influence of air velocity on the fresh water production of the desalination unit. The optimal air velocity, corresponding to the maximum of fresh water production, was found to be 3.34 m/s. [ABSTRACT FROM AUTHOR]

In this study a desalination system based on air humidification–dehumidification is investigated theoretically and experimentally. To evaluate the productivity of the proposed humidification–dehumidification desalination unit, a mathematical model has been developed for the design of a unit, based on mass and energy balances as well as thermodynamic analysis of cooling tower and condenser. The results obtained from the theoretical model are in very good agreement with those obtained experimentally. [ABSTRACT FROM AUTHOR]

Membrane distillation (MD) and humidification/dehumidification (HDH) are emerging desalination technologies suitable for inland or “zero liquid discharge” (ZLD) applications. A1 m 3 /d pilot MD system desalinated saline groundwaters with up to 6.3% total dissolved solids (TDS) and produced a brine at 10.2% TDS. This brine served as the feed for a pilot HDH crystallizer. The MD unit operated at 40% recovery producing distillate with < 20 mg/L TDS at a stable flux of 5 L/m 2 -h. Pretreatment, either by adding antiscalant or concentrated acid, was critical for stable MD operation. HDH was an effective crystallizer capable of generating solids from the MD brine while producing additional distillate with TDS < 100 mg/L. Total energy input for MD and HDH were 260 kWh/m 3 and 220 kWh/m 3 respectively. Because cooling water is typically not available at inland applications, removal of latent energy is the key challenge faced by inland thermal desalination processes. This paper also describes the distinctly different processes used by MD & HDH for heat removal and presents an enthalpy balance for a 500 m 3 /d MD desalination plant. Pilot results showed MD & HDH to be technically feasible for inland desalination but both processes need to increase energy efficiency to improve process economics. [ABSTRACT FROM AUTHOR]

A solar energy driven and membrane-based air humidification–dehumidification desalination (MHDD) system is proposed. A test rig is designed and constructed to investigate the performance of the system. The test rig consists of a U-tube evacuated solar collector, a heat storage water tank, a membrane-based humidifier (hollow fiber membrane module) and a dehumidifier (a fin-and-tube heat exchanger). A theoretical model for the whole system simulation is developed and validated. Performance indices of the system, such as the specific water production rate on the basis of unit area of membrane (SWR), specific electric energy consumption on unit volume of water production (SEC), coefficient of performance (COP) and electric coefficient of performance (COP E ) are investigated. The effects of various parameters including the saline water flow rate, the air flow rate and the packing fraction of the membrane module, etc., on system performance are examined. It indicates that solar energy accounts for 92.0% of the energy consumption by the whole system. Sensible heat losses account for most of the energy losses from the system. High-purity water is produced by this system at a SWR of 25.88 kg m −2 d −1 , a SEC of 19.23 kW h/m 3 , a COP of 0.75 and a COP E of 36.13. The feasible operating parameters investigated are: hot saline water flow rate, 236 L/h for per unit area of membrane; air flow rate, 25 m 3 /h for per unit area of membrane; module packing faction, 30%. [ABSTRACT FROM AUTHOR]

Important advances have been made in solar water desalination technology but their wide application is restricted by relatively high capital and running costs. Until recently, solar concentrator collectors had usually been employed to distill water in compact desalination systems. Currently, it is possible to replace these collectors by the more efficient evacuated tube collectors, which are now widely available on the market at lower prices. This paper describes the results of experimental and theoretical investigations of the operation of a novel small-scale solar water desalination technology using the psychometric humidification and dehumidification process coupled with a heat pipe evacuated tube solar collector with an aperture area of ∼1.73 m2. Solar radiation during spring in the Middle East was simulated by an array of halogen floodlights. A synthetic brackish water solution was used for the tests and its total dissolved solids (TDSs) and electrical conductivity were measured. A mathematical model was developed to describe the system's operation. A computer program was written to solve the system of governing equations to perform the theoretical calculations of the humidification and dehumidification processes. The experimental and theoretical values for the total daily distillate output were found to be closely correlated. The test results demonstrate that, at temperatures of 55-60°C, the system produces ∼5-6 kg/h of clean water with a high desalination efficiency. Following the experimental calibration of the mathematical model, it was demonstrated that the performance of the system could be improved to produce a considerably higher amount of fresh water. [ABSTRACT FROM AUTHOR]

One of the innovative methods for decentralized low-scale purification of water is the humidification dehumidification (HDH) desalination technology. Many research activities have been carried out recently with the aim of improving this technology. The economic and environmental benefits of the HDH technology are enormous including feasibility of being powered by sustainable energy sources such as solar and geothermal, ability to operate at low temperature, low maintenance requirements, and simple construction needs. The principal HDH components, latest research on HDH systems driven by renewable energy, and recent innovations on HDH design for sustainable water production are discussed in this paper. It is worth noting that the development of the key features and sustainability aspects of HDH desalination technology are still under research and more improvements are needed to optimize process performance parameters in terms of quantity of water produced, specific renewable energy required, and specific cost of water produced. However, HDH technology has been proven to be an inexpensive and reliable desalination system in terms of environmental friendliness for small scale applications. [ABSTRACT FROM AUTHOR]