Humidification-dehumidification Unit Research Articles

Innovative and efficient integrations of desalination plants coupled absorption, adsorption, and humidification-dehumidification desalination units employing external heat recovery techniques

Thermal desalination technologies have been developed recently to solve some pressing problems, such as high energy expenditure, increasing fuel costs, and environmental problems related to conventional plants. However, these technologies still need to be enhanced in terms of water production and gain output ratio (GOR). This paper presents innovative and efficient combined thermal desalination plants consisting of absorption (ABDS), adsorption (ADDS), and humidification-dehumidification (HDH) desalination units to enhance energy utilization, water production, and overall system performance. Four innovative combined desalination plants employing different external heat recovery scenarios are presented and compared. The result from each scenario is evaluated and compared with those of the standalone ABDS and with other studies found in the literature at the same heat source temperatures. The heat source is mainly utilized to drive the ABDS plant. The ADDS and HDH are driven by the heat rejection from the ABDS components with different external heat recovery scenarios. Results illustrated that the maximum freshwater production generated from the proposed scenarios ranges between 1.57 and 2.94 m3.day−1 with a GOR of between 1.38 and 1.75 at 120 °C. Raising heat source temperatures from 55 to 120 °C decreased the improvement in the water productivity from 618.5 to 224 % and decreased the enhancement in the GOR from 222.8 to 99 %. In scenarios where the ADDS and HDH are driven by the heat rejection from the absorption and condensation process of the ABDS, the maximum freshwater production results from the ABDS unit. On the other hand, in scenarios where the ADDS and HDH are driven by the outlet hot water from the ABDS-generator, the maximum freshwater production is obtained from the HDH unit. The finding provided that the proposed innovative scenarios have an effective improvement in overall system performance indicators.

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

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

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

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

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

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

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

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

Solar powered hybrid desalination system using a novel evaporative humidification tower: A numerical investigation

This research describes a hybrid solar desalination system that includes a humidification-dehumidification unit as well as a solar still unit. The current system is being studied numerically. A one-dimensional model of the important heat and mass exchanges, as well as the flow field, was built using the finite difference method. Freshwater productivity is calculated under various operating and weather conditions. The model has been modified to investigate the steady-state behavior of the system components. Four major parameters that have a significant impact on system water production are investigated: the feed flow rate of cooling water through the dehumidifier unit, the airflow rate, and the number and height of packing columns. According to the results, the proposed hybrid desalination system provides appropriate operational compatibility between HDH technology and solar energy. The system can provide a daily production of up to 35 liters per day. Increasing the number of packing columns results in a higher increase in fresh water productivity than increasing the height of the packing columns. The optimal air flow rate at a constant saline-water flow rate is obtained. For high airflow rates, the packing column height doesn't significantly affect the daily water production. System performance is investigated by four main parameters: gained output ratio (GOR), humidifier efficiency, exergy efficiency, and system efficiency. The system efficiency reached about 65% and the GOR reached 3.1. The humidifier’s efficiency varied between 50% and 75%. The maximum exergy efficiency reached about 5.2%.

Design and thermal performance of an innovative greenhouse

The study presents the design and thermal performance evaluation of a novel solar greenhouse with humidification-dehumidification unit, water-cooled heat exchanger and variable mixing ratio in the Mediterranean climate. The greenhouse is designed to provide proper microclimatic conditions for crops, produce fresh water through condensing water vapor released from the plants, and save energy using the semitransparent PV panels. Results showed that on a typical summer day, the solar greenhouse ensures proper microclimatic conditions all day long by reducing the temperature by 11.14 °C compared to conventional greenhouses, while maintaining acceptable values of relative humidity and producing 70 L of fresh water per day. An operation schedule was established based on varying return-to-fresh air ratio to ensure optimal system performance. The operation schedule showed that proper microclimatic conditions can be reached through ventilation for 13 h per day. To enhance the net-energy performance, the produced water can be used for irrigation and the return air can be used for cooling the PV panels.

Design a novel solar based system integrated with humidification-dehumidification unit and re-compression sCO2 cycle for sustainable development

This paper discusses thermodynamic modeling of a power generation cycle, cooling, and freshwater with the employment of solar energy. The introduced system has different subsystems; solar dish collector, a re-compression sCO2 Brayton cycle integrated with a combined Rankine power-ejector refrigeration system and humidification and dehumidification desalination unit driven with a solar dish system. The considered system is analyzed in the context of thermodynamics index and criteria such as irreversibility, freshwater production, energy and exergy efficiencies, and environmental metric. The performance-affecting primary variables are determined through a parametric evaluation of the suggested system. According to the results, the system is capable of producing 83.3 kW of electrical power at the design point and 3.1 kW of cooling as well as 41.54 kg/h of freshwater. A more accurate analysis of exergy destruction shows that solar dish and heat exchanger-4 have the most significant rate of exergy destruction. In addition, parameters such as solar radiation intensity, compressor pressure ratio, and entrainment ratio are parametrically analyzed. The results indicated that increasing entrainment ratio from 0.3 to 0.6, will increase the refrigeration capacity from 2.33 kW to 4.66 kW and the operation of Turbine 2 from 15.96 kW to 18.63 kW. Also, enhancing the solar radiation intensity from 650 W/m2 to 950 W/m2 has different influences the system outputs so that increasing the solar intensity will reduce the performance of the cooling cycle and increase the freshwater produced.

Discovering a robust machine learning model for predicting the productivity of a solar-driven humidification-dehumidification system

This work introduces a complete study of freshwater productivity prediction of a solar-driven humidification-dehumidification unit (HDH) based on experimental and machine learning methods. Freshwater productivity besides other operational variables was first measured under a series of twenty outdoor experiments each lasted for 4 h. According to these experiments, average accumulated productivity reached up to 10.8 L/m2. Furthermore, these recorded data were used to construct machine learning models for predicting the hourly freshwater productivity, cost, and GOR of the HDH system. Four types of machine learning algorithms were constructed including artificial neural network, random forest, linear support vector machine, and support vector machine. More importantly, the hyperparameters of these algorithms were optimized based on Bayesian optimization algorithm (BOA). Measured variables of solar radiation, meteorological conditions, carrier air flow rate, and temperatures of air and water paths were used as inputs for prediction models. The important feature of these descriptors on output was also estimated and presented based on the trained random forest (RF) model. As a comparsion, the artificial neural network (ANN) and RF model can achieve a more accurate prediction of the system hourly productivity, cost, and GOR than the other models, where these values of MSE and R2 reached (0.0999, and 0.975) and (0.088, and 0.977), respectively. Accordingly, the ANN-BOA model can provide benefits for modeling of hourly productivity and RF-BOA can provide accurate strategies for optimizing the performance of the solar-driven HDH unit.

Cooling and Water Production in a Hybrid Desiccant M-Cycle Evaporative Cooling System with HDH Desalination: A Comparison of Operational Modes

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

Analysis of a novel solid desiccant evaporative cooling system integrated with a humidification-dehumidification desalination unit

A new configuration of a solid desiccant evaporative cooling system integrated with a humidification-dehumidification (HDH) desalination unit was proposed, and its performance was numerically evaluated. In the proposed system, the humid exhaust air from the desiccant wheel and M-cycle IEC was recycled and supplied to an HDH unit to improve the water production rate. Two operation modes were proposed depending on climate conditions. The system with two operation modes was evaluated under various operating conditions. A case study was performed under Australian climatic conditions. The results showed that Mode 1 had a better cooling performance than Mode 2, with a maximum cooling capacity of 4.76 kW. However, Mode 2 was more energy efficient, with an average COP of 0.71, as no regeneration heat was needed. With the HDH unit, the freshwater produced by the system could fully cover the water usage of the M-cycle IEC in both modes. When the heat source temperature of the HDH unit increased to 70 °C, the water productivity of the system could reach 148.5 kg/h and 42.0 kg/h for Mode 1 and 2, respectively. The findings indicated that the proposed system had good potential for producing freshwater and cooling simultaneously.

Design, modeling, and thermo-economic optimization of an innovative continuous solar-powered hybrid desalination plant integrated with latent heat thermal energy storage

Ever-increasing needs for freshwater over the globe have made scientists investigate and find out viable solutions to overcome this concern. In line with this fact, multi-objective optimization of a solar-assisted hybrid desalination plant, which encompasses multi-effect distillation with thermal vapor compression and humidification-dehumidification units, was carried out during this study. Parabolic trough solar collectors play the role of a supplier of required input energy to run this system. In addition, there is a heating and storage unit, which includes a latent heat thermal storage tank to store the excess heat gained by solar collectors and an auxiliary boiler to assist in supplying the required heat for desalination units. Design parameters such as Parabolic trough solar collectors rows, phase change materials, number of multi-effect distillation system effects, motive steam flow rate, and last effect brine temperature of multi-effect distillation system which have the greatest impact on the performance of the system are selected. The non-dominated sorting genetic algorithm was employed to conduct multi-objective optimization. According to the optimization results, the total cost rate of the system and the sustainability index is 0.548 $/s and 1.54 respectively. In addition, adding the humidification-dehumidification unit to the system contribute to producing 0.5% more fresh water and brings 0.1% extra cost.

Study on transient performance of geothermal desalination with variable geothermal fluid temperature

Geothermal desalination is one of renewable energy-driven desalination technologies. Due to the continuous decrease of geothermal fluid temperature, desalination rate changes with running of the system. Therefore, this paper presents a theoretical study on the transient performance of geothermal desalination with variable geothermal fluid temperature. Firstly, a comprehensive model coupling with transient geothermal extraction and heat and mass transfer in desalination unit was built to simulate the transient performance. Deep coaxial borehole heat exchanger is used for geothermal extraction and humidification-dehumidification unit is taken for thermal desalination. Then the transient performances of the system, freshwater production rate, geothermal fluid temperature and extraction were studied and the effects on the transient performances were also investigated. The simulation results show that freshwater production rate drops by about 60 % during 20-years operation with continuous declination of geothermal fluid temperature and extraction, and the drop trend is strengthened with BHE depth and geothermal gradient rising, but weakened with increase of rock thermal conductivity. The production rate increases with air flow rate rising but decreases with increase of seawater flow rate. Both production rate and humidifying capacity can be enhanced by improving air temperature at inlet of humidifier and reducing the inlet relative humidity.

The exergo-economic analysis of two novel combined ejector heat pump/humidification-dehumidification desalination systems

Two novel integrated cycles including ejector heat pump (EJR-HP)/humidification-dehumidification (HDH) desalination were investigated. The first scheme (EJR-single) uses the rejected heat of the HP condenser for heating both seawater and dry air streams of the HDH cycle. In the second scheme (EJR-double), the condenser rejected heat only heats the air, and the system includes double HDH units that use the rejected brine of the first HDH as the feed sweater of the second unit. Based on the results, the novel EJR cycles have better exergy efficiency (ηex), gained output ratio (GOR), and lower fresh water cost (COW) over the base cycle without EJR. Moreover, the GOR and ηex of the EJR-double cycle (7.10, 1.1%, respectively) are 1.88% and 12.45% higher than the EJR-single cycle, respectively. However, the electricity consumption of the EJR-single cycle is higher than the other EJR cycle due to higher pumping power. Due to the higher investment costs of the EJR-double scheme, the COW was obtained as 5.33 $/m3 which is slightly higher than that of the EJR-single cycle (5.18 $/m3). The increase of dehumidifier effectiveness (εdh) from 0.87 to 0.97 decreases the COW of the first and second schemes to 4.20 $/m3 and 4.30 $/m3, respectively.

Psychometric study and performance investigation of an efficient evaporative solar HDH water desalination system

The improvement of the evaporation process can significantly improve water production and the overall efficiency of a solar humidification-dehumidification (HDH) system. This study experimentally investigates the use of novel packing materials to improve the performance of the humidification process. Contact time and area between sprayed water and surrounding air are two critical parameters that considerably influence evaporation. Therefore, using selected packing materials inside the humidifier can increase these two parameters. A wet cooling tower facility is used as a humidifier with instrumentations installed to measure the inlet and outlet air and water conditions. Among different materials tested, it is found that fine-grain foam has the maximum specific humidity difference at different operating temperatures. At a high-water flow rate of 80 L/h and low water temperature of 60 °C, the gain output ratio (GOR) is evaluated to be 4.23. Moreover, a solar HDH system includes a solar collector, out of three options, and a thermal storage (TES), and HDH unit is designed and modeled to provide the required heat. For solar collectors, flat-plate, parabolic-trough, and evacuated-tube are considered. It is found that the flat-plate collector has a maximum efficiency of more than 70% while producing over 25 L/d/m2 of distilled water.

Optimal design of a hybrid thermal- and membrane-based desalination unit based on renewable geothermal energy

• A renewable-based hybrid desalination system consisting of HDH and RO is evaluated. • Two different operating modes of the introduced system are investigated. • Exergoeconomics is used to identify the optimal working condition of the system. • Maximum exergy efficiency of the plant is 28.86% for the second operating mode. • The first operating mode can provide freshwater at a maximum rate of 22070 m 3 /day. In this article, exergoeconomic analysis of a hybrid desalination system driven by renewable geothermal energy source is investigated. Freshwater and electrical power are the products of this system. Humidification – dehumidification (HDH) unit works in parallel with reverse osmosis (RO) unit to produce freshwater and Kalina cycle is the power generator unit. Thermoelectric generator (TEG) is responsible for providing the energy required by RO unit. As both HDH and TEG can operate with low-grade energy, two different modes are suggested for the proposed system. In the first mode, the geothermal low grade energy stream is passed to TEG unit, while in the second, it goes through the HDH unit. The effect of different parameters on four main objective functions is examined in parametric study. Moreover, with the aid of selection maps, the objectives of modes can be compared in different operating conditions. The maximum attainable exergy efficiency is calculated to be 28.86% for mode 2. Single objective optimization studies revealed that the first mode produces the largest amount of freshwater at a rate of 22,072 (m 3 /day), while the minimum achievable freshwater cost and total product cost rate can be obtained in the second mode, which is calculated to be 21.94 (¢/m3) and 37.19 ($/GJ). Besides, Sankey diagrams for exergy flow and mass flow of saline water are presented to unravel the impact of each sub-system on exergy and salinity.

Integrated Capacitive Deionization and Humidification-Dehumidification System for Brackish Water Desalination

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

Seawater Desalination via Waste Heat Recovery from Generator of Wind Turbines: How Economical Is It to Use a Hybrid HDH-RO Unit?

Over recent years, the concept of waste heat recovery from the generators of wind turbines for driving a thermal-driven desalination system was introduced, and its advantages were highlighted. However, any selection of a bottoming thermal-driven desalination system among different existing technologies should be taken under consideration before making an ultimate recommendation. Unfortunately, no comprehensive comparison is available in the literature to compare the performance as well as the cost aspects of using the waste thermal energy of the generator of a wind turbine for desalinating seawater, comparing them with those of a layout where the power of the wind turbine is directly supplied to a mechanically driven desalination system for the same amount of drinkable water production. This study aims at analyzing the economic aspects of waste heat recovery from the generators of wind turbines for seawater desalination via the humidification-dehumidification (HDH) approach, versus the reverse osmosis (RO) unit. For this purpose, a closed-air water-heater HDH unit, directly coupled with a RO unit (called a hybrid HDH-RO unit) is employed, in which thermal energy is provided by the heat dissipating from the generator of the wind turbine while its power is supplied directly by the wind turbine. The energetic and exergetic performance, along with the cost aspects of a hybrid HDH-RO unit driven by the wind turbine, are compared with those of a solo RO unit. The results of the study were extended for six different types of wind turbines, and we concluded that the unit cost associated with the freshwater produced by the waste heat recovery approach is astronomically higher than that of the solo RO system for all wind turbine models, and hence is not practically feasible. It was found that more power can be recovered from the discarded brine from the solo RO unit than the hybrid HDH-RO unit. In addition, the solo RO desalination system, working directly with the power of the wind turbine, has a less complex configuration, and hence its investment cost rate is significantly lower than that needed for setting up an HDH-RO unit. At high wind speeds, however, the cost penalty associated with the freshwater produced by the HDH-RO unit decreases, but it is still huge. Among all screened wind turbines, the GW-136/4.8 is most appealing in terms of greater power generation, but its investment cost rate is the highest among all models due to its high rated power value. However, the freshwater unit cost of the GW-136/4.8 is significantly lower than the values obtained for other models. Finally, the two locations of Manjil and Zabol are selected as a benchmark and the results of the simulation are extended for these locations.

A New Approach to Solar Desalination Using a Humidification–Dehumidification Process for Remote Areas

Freshwater supply in remote areas has become a critical issue. This paper aims to introduce a new approach to a solar-powered humidification–dehumidification (HDH) desalination system. The design uses a solar collector, a thermal storage tank, and an HDH unit. The HDH works continuously by feeding water to absorb solar energy during the day and then relaying the desalination units with feed water at a top brine temperature (TBT) at night. The model predicts the amount of solar energy stored for the next day, and based on this, the amount of feed water that should be raised to the TBT is calculated. The system operation is carried out in two phases. During the day, the feed water absorbs the heat of solar energy, thereby increasing its temperature to TBT. This hot feed water is then kept in storage tanks. At night, the tank switches to discharging mode and starts feeding the HDH with the hot feed water. The system is designed so that the roles of the tank are rotated at sunset. To achieve the same TBT every day in response to changes in the available solar energy, the mass of the feed water is adjusted daily. The design is simulated using a dynamic model of the energy and mass balance resulting in an average daily production of 7.6 kg of fresh water per unit area of the solar collector. The daily average of the gain output and the recovery ratios are 0.3 and 0.09 respectively.

Indirect mechanical heat pump assisted humidification‐dehumidification desalination systems

In this study, four new indirect heat pump assisted mechanical vapor compression humidification-dehumidification (HDH) systems are proposed and their superiorities over the reference system are demonstrated from thermodynamics and thermoeconomics viewpoints. The proposed models are configured based on an HDH unit and a simple cascade heat pump, an HDH unit and a heat pump with an ejector, an HDH unit and a cascade heat pump with an ejector, and an HDH unit and a vapor injection heat pump. Although employing a heat pump with cascade and ejector configurations improved gain-output-ratio (GOR) and specific power consumption (SPC) values in comparison with the base system, the performance metrics of such layouts are still inferior to those of the HDH unit coupled with the vapor injection heat pump. It is found that the desalination unit with vapor injection mechanism has the highest GOR and the lowest SPC values of 9.22 and 71.29 kWh/m3, respectively, under constant electrical power of 31.26 kW. Overall, proposal of the cascade heat pump, heat pump with an ejector, cascade heat pump with an ejector, and a vapor injection heat pump instead of the conventional heat pump improved GOR by 4.83%, 10.03%, 11.52%, and 14.25%, respectively. Meantime, the SPC of the HDH unit coupled with a simple heat pump decreased by 4.6%, 9.1%, 10.26%, and 12.46% when a cascade heat pump, a heat pump with an ejector, a cascade heat pump with an ejector, and a vapor injection heat pump were used instead of the conventional heat pump, respectively. Also, it is found that a maximum improvement of 14.13% can be achieved in exergy efficiency with a cost penalty of only 1.59 $/m3. Also, it was found that with the use of a simple cascade heat pump instead of the simple heat pump, the exergy efficiency can be enhanced by 4.9%, while the unit cost of the distilled water (UCDW) was degraded by 51.32%. Likewise, the HDH unit coupled with the cascade heat pump with an ejector was resulted in high UCDW compared to the base system, while its exergy efficiency was not enhanced so significantly. Variation of exergy efficiency versus the intermediate temperature had a maximum value of 1.93% (for the HDH unit coupled with a simple cascade heat pump) and 2.05% (for the HDH unit coupled with a cascade heat pump with an ejector) at Tint = 315 K. Moreover, it was found that the UCDW can be decreased with the rise of the intermediate temperature and cascade heat exchanger temperature difference as the fresh water cost rate decreases as a result, while the exergy efficiency can be increased with the rise of the cascade heat exchanger temperature difference.