Humidification-dehumidification System Research Articles

Techno-economic optimization of a geothermal multi-product layout composed of a CO2 trans-critical Rankine-LNG system integrated with ejector cooling system and HDH desalination unit

This current research introduces and examines a new multi-product configuration based on geothermal energy, using energy, exergy, and exergy-economic perspectives. The configuration under consideration aims to maximize the use of geothermal energy. A cascading trans-critical CO2 Rankine cycle (TCRC)/LNG subsystem functions as the primary system, and a cascading ejector cooling system (ECS)/humidification-dehumidification (HDH) desalination unit functions as the secondary system. The LNG subsystem's output power is transferred to an alkaline electrolyzer for the manufacture of hydrogen once the output power is retrieved from the TCRC. The HDH system and ECS provide the necessary cooling and freshwater. Thus, the suggested plan is transformed into a poly-generation scheme. The addressed research gap lies in the integration of these subsystems to create a novel poly-generation arrangement that simultaneously produces electricity, hydrogen, cooling, and freshwater using geothermal energy—a configuration not yet explored in existing studies. The novelty of this work lies in optimizing this unique system through a comprehensive exergy-economic approach. In the parametric analysis section, geothermal heat source temperature, the hot side temperature difference of TCRC heater, upper pressure of TCRC, and lower temperature in the TCRC are chosen for sensitivity analysis. In conclusion, when taking into account exergy efficiency and the payback period as two opposing objective functions, they are determined to be 16.99 % and 0.616years, respectively, in the optimization process. At this stage, the suggested configuration is capable of generating 435.9 kW of power, 251.5 kW of cooling, 3.68 kg/h of hydrogen, and 0.0493 kg/s of freshwater.

Comprehensive performance analysis and optimization of an ORC-HDH system for power and freshwater production driven by marine exhaust gas

Freshwater serves as a vital energy source for ships, underscoring the paramount importance of research into desalination systems in facilitating diverse and reliable energy supply for maritime vessels. Aiming at numerous waste heat of marine engines and the shortage of freshwater resources on board, this paper designs an innovative waste heat recovery (WHR) system. It includes an organic Rankine cycle, a compression refrigeration cycle, and a humidification-dehumidification (HDH) desalination system to recover waste heat from exhaust gases in cascades, which can effectively produce power, cooling, and freshwater, respectively. A parametric study of the co-generation system in terms of the freshwater production, gained output ratio (GOR), cost per unit of freshwater production, net power output, and per unit of output power cost, are conducted to identify the key operating parameters. A set of operating parameters is determined for the HDH system with a temperature of the humidifier outlet of 358.15 K and a mass flow rate ratio (MR) of seawater to humid air of 4.5. The effect of the relative humidity and temperature of the humid air, as well as the salinity and temperature of the seawater, on the performance of the HDH subsystem are analyzed. And the optimal operating conditions of the co-generation system are obtained through multi-objective cuckoo search optimization. The results demonstrate that the co-generation system can produce an output-power of 1479.8 kW, 500 kW, and 0.49 kg/s for cooling and freshwater production by using the working-fluid R365mfc/Cyclopentane with a mixing ratio of 33:67 under optimal conditions. The GOR and cost per unit of HDH subsystem are 1.62 and 1.70 $/m3, with a capital payback period of 4.18 years. The equivalent output-power of the co-generation system is 9.5 % higher than that of an ORC system.

Optimized irrigation through solar desalination: Exploring the impact of water temperature in wastewater treatment and phosphate fertilizer removal

Could rationalizing irrigation techniques be accomplished with solar desalination? This practical and theoretical study explores the optimization of a solar desalination unit employing the novel Humidification Dehumidification (HDH) method to evaluate its potential in irrigation to provide an answer to that topic. The performance of the system is examined in the first section of the research concerning raising the evaporator temperature and the ensuing temperature difference. The daily distillate production rate for the HDH system is 25 kg/m², and the results show that it has a global efficiency of 58 %. Using wastewater and saltwater polluted with phosphate fertilizers, the HDH system is evaluated in the second section of the study. The findings show that more than 98 % of ionic species were removed, besides presenting a potentially effective response to the complicated water treatment issues facing the agricultural industry.

Effective design of sustainable energy productivity based on the experimental investigation of the humidification-dehumidification-desalination system using hybrid optimization

Reliable and cost-effective industrial-based sustainable desalination technologies are crucial for efficient and effective desalination of saline water. Seawater desalination emerges as a vital treatment, with humidification-dehumidification identified as a promising technology due to its simple, low-maintenance design and compatibility with renewable energy sources. The present work was developed using a large-scale experimental test rig based on the performance of a humidification-dehumidification system operated by the heat pump. As such, the study presents an advanced approach for optimizing humidification-dehumidification desalination systems using hybrid machine learning optimization techniques. The effectiveness of a neuro-fuzzy model, a decision algorithm based on a boosted tree, and a simple averaging ensemble in enhancing the performance of humidification-dehumidification systems were investigated. Experimental data includes cold water flowrate (L/min), hot water flowrate (L/min), inlet air temperature (°C), inlet cold water temperature (°C), inlet hot water temperature (°C), and inlet air relative humidity (%) as input variables combination and freshwater productivity (L/h), recovery ratio (%) as target variables. Several statistical indicators were used to evaluate the models’ prediction skills; similarly, a 2-dimensional Taylor diagram and error-radial plot were also utilized. In the calibration phase, boosted tree models slightly outperform neuro-fuzzy models, particularly for recovery ratio, demonstrating high accuracy and low bias. However, all models exhibit robust predictive accuracy in the verification phase, especially for recovery ratio, emphasizing their potential in generalizing to unseen data. The result indicated that the boosted tree outperformed others with Nash–Sutcliffe Efficiency = 94 % and 88 % for recovery ratio and freshwater productivity, respectively. The simple averaging ensemble shows marginal improvement with 95 % accuracy for the recovery ratio. Integrating hybrid artificial intelligence optimization with humidification-dehumidification desalination systems marks a transformative step in addressing freshwater shortages. By utilizing cutting-edge machine learning techniques, we achieve a more efficient, accurate, and reliable prediction of desalination performance.

Off-design behaviors of a solar-powered HDH system for water and power cogeneration

A solar-powered humidification-dehumidification (HDH) desalination system offers flexible water and power cogeneration, promising in addressing energy crisis. However, the system’s operation frequently deviates from the on-design condition, making it crucial to study its off-design behaviors. This paper develops an off-design model to investigate the operation performance in response to variations in liquid–gas mass flow rate ratio (MFRR) and solar intensity. Furthermore, the heat and mass transfer mechanisms in humidifier and dehumidifier are inquired under specific conditions. The results exhibit that the system performance sensitivity to changes in the liquid–gas mass flow rate ratio and solar intensity aligns with the expectations under on-design conditions. The combined heat and mass transfer process weakens first and then strengthens from the bottom to the top in the humidifier, and vice versa in the dehumidifier. Notably, a higher freshwater flow rate enhances dehumidification efficiency, raising gained-output-ratio (GOR) by 7.13% and water production by 1.5%. Validation experiments confirm the off-design model’s accuracy and credibility, to offer methodological insights for the effective prediction of off-design behaviors.

Primarily experimental study of the energy performances of a humidification-dehumidification seawater desalination system coupled with a heat pump

The study presented in this article explores a comprehensive analysis of a humidification-dehumidification (HDH) seawater desalination system integrating a heat pump for heating seawater intended for distillation, and incorporates additional condensation plates supplied with cold seawater. This system was the subject of an experimental investigation to simultaneously evaluate the energy performance of the heat pump and the thermal behavior of the desalination unit, focusing on seawater and condensation wall temperatures, as well as the stratification of temperatures of humid air inside the unit compared to the evaporation surface. Experimental results showed an average daily production of distilled water of approximately 32.75 kg/m² per day, with an electrical consumption of 37.68 kWh/day, which was reduced to 26.72 kWh/day through the integration of photovoltaic solar energy. Based on heat and mass balance equations of all the system’s components, the study used a detailed thermodynamic model. The system's energy performance was analyzed by calculating the coefficient of performance (COP), the specific energy consumption (SEEC), and the gain output ratio (GOR), reflecting the overall energy efficiency of the HDH system coupled with the heat pump, as well as the recovery ratio (RR), indicating the proportion of the recovered water compared to the input water.

Eco-friendly atmospheric water generation: A novel desiccant-based variable pressure humidification-dehumidification system

This study introduces a zero-brine discharge approach, eliminating the necessity for continuous seawater input and brine disposal—major drawbacks in traditional desalination methods. This research’s core is a humidification-dehumidification (HDH) system operating under variable pressures, significantly boosting efficiency. The system comprises two synergistic components: a variable-pressure HDH unit and a desiccant-based moisture extractor utilizing a lithium chloride solution. After freshwater is extracted, the concentrated desiccant cycles through the moisture extractor to absorb atmospheric water vapor, diluting it for reuse and thus completing the desiccant loop. The heat and mass transfer processes were scrutinized through mathematical modeling, and parameters for maximizing the Gain Output Ratio (GOR) were optimized. The results underscore the system’s capacity for sustainable, efficient freshwater production. This methodology offers a feasible solution to challenges in desalination and significantly contributes to alleviating global water scarcity, particularly in coastal areas. Further analysis shows that systematic optimization of key parameters, such as pressure ratios and desiccant temperatures, considerably improves performance metrics. Adjusting the pressure ratio from 1.22, where the GOR peaks at 2.44, to 1.56 directly impacts system efficiency. Modulating the maximum desiccant temperature at an optimal pressure ratio of 1.25 reveals that the GOR can increase from 1.635 at 0.7 to 2.44 at an effectiveness of 0.8. Optimized manipulation of these parameters can potentially enhance the GOR by up to 50% and improve mass transfer efficiency by about 20% within the HDH process.

On the selection of humidification dehumidification desalination system cycle for high productivity, low energy consumption and low capital cost

Humidification Dehumidification (HDH) desalination is a convenient process to produce drinking water from low temperature saline water in waterfront areas. High energy consumption of the system remains as a limiting factor, besides many enhancements done in improving the system performance. Though HDH system cycles are classified on the basis of air and water cycles, detailed performance analysis of different HDH cycles is absent till date. The present study aims at carrying out parametric analysis of possible HDH layouts and finally proposing a layout with high Gain Output Ratio (GOR) and Recovery Ratio (RR) at the low equipment volumes. Simulations are carried out using the Scilab® software. Simulation results are validated using the experimental data obtained from a pilot plant of open-air open-water single stage system. Variation of system parameters like humidifier volume, dehumidifier volume, GOR and RR were analysed in detail for each individual layouts. Out of the eight different layouts investigated, Layout 8 is found to be the best based on GOR, RR, equipment volume and specific energy consumption. Hence it is recommended to use Layout 8 with an inlet temperature of 74 °C and MFR of 2.4 for productivity of 90 LPH.

Investigation of thermodynamic process in a humidifier of humidification–dehumidification system based on a computational fluid dynamics model

Humidification–dehumidification is well-suited for solar-powered operation. Packed bed humidifier is an essential system component for water evaporation. Computational fluid dynamics (CFD) simulation of the packed bed humidifier is a challenging multiscale task. The simultaneous capture of micro flow properties and macro transfer performance by existing CFD models is inadequate. This paper presents a novel CFD model for a structured packed bed humidifier. The Eulerian method is applied to the multiphase flow and several simplified models are proposed to evaluate the influence of the microstructure on the transfer properties. The model can predict the overall transfer performance and partially reflect the micro flow characteristics. It is found that the air temperature increases rapidly when the packing height is < 0.3 m, while the liquid temperature decreases rapidly when the height is > 1.65 m or <0.45 m. Under different conditions, the outlet relative humidity of the air is all between 95 % and 99 %. The maximum evaluation error of gained output ratio of the humidification–dehumidification system can reach 10 % under the saturated air assumption. With a maximum of 10.85 % and a minimum of 3.46 %, the proportion of sensible heat transfer in the total energy transfer decreases with the packing height.

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.

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.

Evaluation of two-stage humidification-dehumidification desalination systems operated by a modified heat pump

The humidification-dehumidification desalination system operated by a heat pump is ideal for the decentralized small-scale desalination plant, due to its advantages of low investment and stable freshwater provision. To overcome the heat source limitation of multi-stage humidification-dehumidification system, a modified heat pump with a subcooler is used to operate the two-stage humidification-dehumidification system. With the difference of heated object, two layouts of the heat pump operated two-stage humidification-dehumidification systems are proposed, which are twice water-heated system and twice air-heated system. A parametric study is conducted to analyze the effect of feed seawater temperature and water/air mass flow ratio on the thermodynamic and economic performances of the proposed systems. A performance comparison is also carried out to analyze the difference between water heating and air heating, together with advantages over the reported systems. According to the results, it can be concluded that optimal feed seawater temperature and water/air mass flow ratio exist for the proposed systems. The twice water-heated system outperforms the twice air-heated system with the maximum freshwater productivity and gain output ratio of 34.69 kg/h and 7.69, while the lowest specific electricity consumption and freshwater production cost of 89.18 kWh/m3 and 14.52 $/m3. These results are also superior to those of previously reported HP-HDH systems, fully demonstrating the value of research and development for this novel system and its promising market application prospects.

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.

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.

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.

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).

Experimental analysis on hybrid adsorption and open air cycle humidification dehumidification (AD–OHD) desalination system

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 (tswt) and sorption time (tspt), namely, tswt > tspt, tswt = tspt, and tswt < tspt. The results indicate that the optimal working condition is achieved when the hybrid AD-OHD system operates at condition tswt < tspt. 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.

Experimental study on optimum performance of two-stage air-heated bubble-column humidification–dehumidification system

An experimental investigation of a small-scale air-heated humidification–dehumidification (HDH) desalination system with bubble-column humidification and dehumidification units was conducted. The study addressed the performance of the multistage air-heated bubble-column HDH system, which has limited coverage in the literature, by operating two bubble-column humidifiers in series for the air humidification process with air reheating. The effect of operating parameters such as airflow rate, air temperature, and saline water levels in both humidifiers on the performance metrics of the system were investigated. The product distillate rate, energy consumption, gain output ratio (GOR), and specific energy consumption (SEC) are the main indicators of performance for the proposed desalination system. Response surface methodology (RSM) was applied to the current system using the design of experiment (DoE) for the prediction of variables that greatlyaffect productivity and energy input. The airflow rate, air temperature, and water level of the second humidifier have a favourable effect on the distillate rate and GOR of the system. In contrast, the effect of the water level inside the first humidifier is insignificant. Furthermore, the RSM optimization approach was used to obtain the optimum distillate productivity. An optimized distillate rate of 0.45 L/h and a GOR of 0.4 are achieved at 1.5 SCFM (standard cubic feet per minute) of airflow rate, and 6.5 cm of water level in the second humidifier with 140°C air inlet temperature. The numerical optimization reveals the optimal operating parameters, that correspond to maximum distillate production of 0.3 L/h with minimum input energy of 0.71 kW, to be 139°C air temperature, 1.13 SCFM of airflow rate, 6.5 cm and 3 cm water levels of second and first humidifier, respectively.

Energy and exergo-economic analysis of a parallel feed multi-effect system integrated with humidification–dehumidification system for brine recovery

Desalination technologies reject large amounts of brine with significant value back to sea. The concept of hybridization of different desalination technologies has proven that it can be effective in terms of reducing rejected brine and increasing the freshwater production rate as well as reducing the freshwater cost. In this work, brine recovery to improve water production through a simple modified configuration of integrating a multi-effect desalination (MED) system with humidification–dehumidification system (HDH). The rejected brine of the MED system is used as the feed for the HDH system without the need for preheating the rejected brine since it leaves the MED at a suitable temperature for HDH application. The study focuses on investigating the effect of different operating conditions on the increase in system freshwater production rate and recovery ratio as well as the exergetic efficiency. Parameters investigated include steam temperature, feed salinity, number of brine streams, cooling water flow rate, and ambient temperature. An exergo-economic analysis has also been conducted using the cost flow method to evaluate the freshwater production cost for the modified system. Results indicate that the integration of HDH can increase the water production rate by a maximum of 7.82% and produce fresh water at 2.08 $/m3 compared to 2.094 $/m3 when using the standalone system under the same conditions.