Humidification-dehumidification Cycle Research Articles

A novel solar-powered thermal desalination unit coupled with a reverse osmosis plant to increase overall water recovery

The global water crisis could be alleviated by converting saline water to potable water through desalination technologies. Reverse osmosis is the dominant technology in the market. However, its brine disposal is challenging. This paper proposes and investigates a novel hybridization between a solar-driven reverse osmosis plant and a solar-driven thermal desalination unit to enhance the water recovery ratio (freshwater produced/feed saline water). The thermal desalination unit combines an adsorption cycle, ejectors, and a humidification-dehumidification cycle. The brine from the reverse osmosis unit is used as a feed for the thermal desalination unit to produce higher amounts of freshwater. The extra-high saline water discharged from the proposed system can be used for salt extraction in a solar pond as a byproduct. Theoretical and economic models are developed to evaluate the performance and cost of the proposed system. It is found that the recovery ratio of standalone reverse osmosis and the proposed hybrid desalination plant is 40.8% and 70.5%, respectively, having a feed salinity and brine salinity limit of 32,500 ppm and 110,000 ppm. The recovery ratio of the hybrid system could reach 84%, with brine disposal of 220 ppm (which is valid for salt crystallization processes). The reduction in freshwater cost by using the hybrid plant is 23% to 27% compared to the standalone reverse osmosis plant for 40,000 to 50,000 ppm feed salinity and 10 m3 plant capacity. The suggested system can produce freshwater of 83 and 47 m3 per ton of silica gel per day at the gained output ratio of 2.71 and 2.6 in June and December, respectively.

Experimental thermal and electrical performances of a PVT-air collector coupled to a humidification-dehumidification (HDH) cycle

Despite their low electrical efficiencies, PVs are widely used to generate electricity from abundant solar energy. In order to maximize the utilization of incident solar energy, PVT collectors have been used to simultaneously generate electricity and thermal energy. Furthermore, combining PVTs with humidification-dehumidification (HDH) cycles can provide electricity and potable water in remote, arid rural areas that are not connected to the grid. In this paper, a PVT-air collector was coupled to an air-heated closed HDH cycle. Air was heated within the PVT collector and humidified by saline water spray inside the humidifier. Fresh water was produced by cooling humid air inside a dehumidifier that is cooled by saline water. The thermal and electrical performances of the PVT-HDH system were experimentally studied and compared to the electrical performance of a PV module with similar characteristics. The results demonstrated a significant decrease in PV temperature within the PVT-HDH system, which resulted in a 20% increase in the output power of the PVT-HDH system at midday compared to the identical PV module. In addition, the PVT-HDH system produced about 3.8 liters of water distillate for a PV module surface area of 1.48 m × 0.68 m, which contributed about 38% to the overall efficiency of the PVT-HDH system.

THERMODYNAMIC ANALYSIS OF THE OPEN SYSTEM OF THERMAL WATER DESALATION WITH AIR HEATING

With the increase in the world population and industrialization, the use of water resources for industry and domestic needs is also increasing. At the same time, the impact of the water sector on climate change is increasing due to emissions of greenhouse gases associated with the energy processes of water production, transportation and purification. Given that efforts aimed at mitigating the consequences of climate change are not enough today, it is very important to develop new ambitious strategies for sustainable development and decarbonization. The purpose of the work is a mathematical study of the air humidification-dehumidification cycle to obtain fresh water and the search for optimal parameters that will ensure the maximum efficiency of the desalination process. The principle of operation was considered and a mathematical model of the thermal water desalination system with air heating at the entrance to the humidifier in the solar heater was developed. A comprehensive thermodynamic analysis of the proposed scheme was made. The temperatures of air and salt water at the outlet of the heat exchangers were determined. The main energy parameters of the system were calculated with the help of balance equations. Graphical dependences of energy indicators on the operating parameters of the installation were constructed and analyzed. The change in performance and energy efficiency as a function of temperature and air velocity at the inlet to the humidifier is shown. The effect of air and salt water consumption on the energy efficiency and geometric dimensions of the humidifier was revealed. A comparison of the efficiency of open water desalination schemes with heating of air and water at the entrance to the humidifier is given. It was established that, under the same conditions, water heating provides higher energy parameters than air heating. The expediency of simultaneous heating of water and air at the entrance to the humidifier to further increase the efficiency of thermal desalination using the air humidification-dehumidification cycle was noted.

A novel dual-heated water and power cogeneration system using solar driven humidification-dehumidification cycle

A novel dual-heated water and power cogeneration system using solar driven humidification-dehumidification cycle

Experimental Performance of Single-Slope Basin Solar Still Coupled with a Humidification–Dehumidification Cycle

Despite their low distillate yield, single-slope basin solar stills incorporate a simple and cheap technique to secure potable water in arid and rural areas away from fresh water resources and the power grid. Nevertheless, recovering a portion of the inevitable thermal losses from the still will significantly contribute to enhancing its daily distillate productivity and thermal performance. In this manuscript, the latent heat of condensation in single-slope basin solar still was partially recovered and utilized as the thermal energy source for an auxiliary humidification–dehumidification (HDH) distillation cycle. The thermal performance of the resultant SS-HDH distiller was experimentally tested side by side with a separate single-slope basin still of the same basin area. The results showed an increase of about 2 L/m2 in the daily distillate production of the SS-HDH distiller over that of the conventional single-slope basin still. In addition, the thermal efficiency of the SS-HDH distiller was 57% greater than that of the conventional single-slope basin still.

Exergetic analysis of the humidification-dehumidificationdesalination cycle involving variation in top temperature

• Effects of the top temperature variation on the HDH cycles is presented. • CAOW cycles involving zero or single air and water extractions were analysed. • Gain-out put ratio and exergetic efficiency parameters were studied in detail. • For extraction cycles, peak GOR corresponds to maximum exergetic efficiency point. Saline water desalination is attaining a prime focus to meet the challenges of water scarcity in the developing countries. Solar energy could be effectively utilized for desalinating the saline/sea water. In this respect, humidification dehumidification (HDH) cycle could prove as a promising solar driven desalination technology. In this paper, exergy analysis of single extraction air heated and water heated HDH desalination cycles are examined in detail. The top temperature and extraction rate parameters are considered crucial for any typical single extraction HDH cycle. Analysis of the effects of varying top cyclic temperature keeping fixed extraction/injection rate of 70% water/air stream is carried out. The top temperature is varied between 60 °C−80 °C range. For the air heated air extraction cycle, total exergy destroyed is higher at lower top temperatures, resulting in lower exergetic efficiency. A similar trend is also followed by the air heated water extraction cycle for the top temperatures ranging up to 70 °C. The total exergy destroyed registered an increase above 70 °C because of the significant rise in exergy destruction for the heater component. In the water heated cycle with water/air extraction, exergy destroyed decreases at lower top temperatures, thereby yielding higher exergetic efficiencies. For each HDH cycle configuration, correlation between the gain output ratio (GOR) and exergetic efficiency is additionally obtained. The results revealed that at the given top temperature, sub-component effectiveness, mass flow rate ratio and bottom temperature parameters, the GOR increases with the exergetic efficiency of the cycle.

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.

Effect of effluent gas composition on characteristics of graphene oxide film based relative humidity sensor

Nitrogen and synthetic air have been used as standard effluent gases in relative humidity (RH) sensing experiments, especially to characterise the dynamic sensing capabilities of RH sensors utilising graphene oxide (GO) as the sensing material. In the present work, we have used GO coated quartz crystal microbalance (QCM) as a tool to investigate the mass adsorption characteristics of samples subjected to multiple humidification-dehumidification cycles using N2 or synthetic air as the effluent gas. We identified that the residual mass adsorbed and retained by the GO film is on average 71.6% higher when using N2 in the initial humidification-dehumidification cycle and this subsequently impacted the hysteresis characteristics until the GO film saturated. To negate the impact of the effluent gas, the GO-based sample should be treated with multiple humidification and dehumidification cycles using either effluent gas.

Different configurations of humidification-dehumidification desalination systems: Thermal and economic assessment

Drought has hit several water-stressed regions, with serious consequences for water and food security. In this regard, the low-cost and low-grade thermally driven humidification-dehumidification desalination cycle has good potential to provide freshwater in arid regions. From energy and economic point of view, different configurations of the humidification-dehumidification cycle have been proposed in the literature without a comprehensive comparison to identify the most suitable one. Thus, this paper investigates the thermal and economic performance of several multi-humidifier water- and air-heated humidification-dehumidification cycles. Thermodynamic models are structured to study the behavior of each cycle. The models rely on heat and mass transfer balances for each component. The effectiveness method is implemented for humidifiers and dehumidifiers to evaluate heat and mass exchangers. The models are validated using previously published data. The series seawater flow, triple humidifier, water-heated humidification-dehumidification cycle could deliver 151.2 kg/h of fresh water at a maximum temperature of 70 °C, with a gain output ratio of 1.995 and a specific cost of 2.73 $/m3. This cost rises by around 16% when a maximum temperature of 60 °C is employed. Results reveal that using a double-humidifier in an air-heated humidification-dehumidification cycle produces freshwater of 102.2 kg/h at the lowest price of $2.06/m3. It is concluded that the multi-humidifier water-heated humidification-dehumidification cycle produces more freshwater and less gain output ratio than the multi-humidifier air-heated humidification-dehumidification cycle.

Thermodynamic analysis of thermal desalination system with humidification–dehumidification cycle

Problems. Today desalination of seawaterprovides a worldwide fresh water productionof 24.5 million m 3 perday.One of the promising desalination methods is thermal humidification-dehumidification process. In spite of significant benefits this technology, it has a key drawback – high thermal energy consumption.The aim of the study. Determine the optimal thermodynamic parameters of working substances (air and water) in elements of desalination system with humidification–dehumidification cycleto obtain maximum performance with a minimum energy consumption.Methodology of implementation. Mathematical modeling of the humidification-dehumidification cycle at different input parameters.The thermodynamic model was createdusing equations of mass and energy balances of the desalination system.Research results. System Gain output ratio(GOR) increases with increasing salt watertemperature at the outlet of the dehumidifier.Maximum valuesof GORand recovery ratio (RR) are observed at the maximum temperature difference (maximum heating) of salt water in the dehumidifier. It is shown that values of GOR and RR increasewith increasing salt water temperature at the inlet to the humidifier. It is found that GOR value is independent of the temperature and humidity of the air at the inlet to the humidifier.Conclusions.The maximum valuesof GOR and RR for the humidification-dehumidification cycle with additional water heating are 3.75 and 6%, respectively. To obtain such results,the temperature of salt water at the inlet tothe system (dehumidifier) should be equal to 10 °C, and the temperature of salt water at the inlet to the humidifier – 70 °C. At the same time, temperature and humidity of the airсan have any values. The use of renewable energy for heating salt water in the heater will significantly increase system GOR

Performance analysis of humidifier packing for humidification dehumidification desalination system

The Humidification Dehumidification (HDH) desalination system is a promising method for production of potable water in isolated locations. Among different component constituting the HDH desalination system, humidifier and its packing are paramount factors in determining system productivity. Several experimental investigations were conducted to study the influence of packing on humidifier performance. However, numerical analysis dealing with performance of humidifier packing is still not available. Such an investigation will be useful to select the optimized packing for a humidifier. In the present work, performance analysis of 15 different types of random packing have been carried out using Scilab software. From this study, it is concluded that metal packing with highest surface area to volume ratio, lowest packing factor and smallest packing diameter functions as the best humidifier packing. Experimental study was also conducted in a pilot plant of open air open water HDH cycle using pall ring 25 mm diameter metal packing, which has shown the highest performance index in the numerical study. Experimental results obtained were found to be in agreement with the numerical results. Present work is a useful tool in designing new packing material of desired properties since the packing performance is a strong function of its geometrical properties.

Thermal design of a humidification-dehumidification desalination cycle consisting of packed-bed humidifier and finned-tube dehumidifier

Humidification-dehumidification (HDH) desalination technology is an ideal technology for off-grid and remote locations where fresh water requirement is approximately between 1-100 m3/day. The principal components of the HDH system such as humidifier and dehumidifier have already been utilized in various industrial applications for some time and are readily available in the market. But the actual thermal performance of the HDH system depends on the specific type and size of the components used. In the present study, a detailed heat and mass transfer model has been prepared for a closed-air open-water (CAOW) and water-heated type HDH cycle which uses a counter-flow packed-bed cooling tower for humidification of air and finned-tube heat exchanger for dehumidification purpose. With the help of transport model, the optimum sizes of the humidifier and dehumidifier have been obtained for a desired thermal performance of the cycle, measured in terms of gained output ratio (GOR) and recovery ratio (RR). Additionally, a very basic thermodynamic model for the same HDH cycle is also prepared in order to validate the results of the transport model and results from both the models are found to be in close agreement with each other. Parametric study reveals that for fixed sizes of the humidifier and dehumidifier, there always exists an optimum value of mass flow rate ratio, top brine temperature and feed water temperature at which the GOR of the cycle is maximum. It is also concluded that the thermal performance of the system is greatly influenced by the performance of the dehumidifier as compared to the performance of the humidifier. Finally, the present work will be helpful to design a similar HDH system as per the required GOR and RR.

STUDY ON MECHANICAL PROPERTIES AND MICROSCOPIC DAMAGE OF UNDISTURBED LOESS UNDER DRY AND WET CYCLES

Humidification-dehumidification cycle is one of the main causes of engineering diseases in the loess area. It is of great theoretical and engineering significance to explore the mechanism of the humidification-dehumidification cycle to damage the loess structure. In this paper, the loess in Yan'an area is taken as the research object. The undisturbed loess humidification-dehumidification cycle tests with different water contents and different times are carried out to analyze the change rules of porosity, shear strength and parameters of loess induced by dry and wet cycles. NMR technology is used to obtain the damage evolution of crack development in loess. The results show that with the increase of the times of dry-wet cycling, the soil exhibits a gradual increase in porosity, a decrease in the liquid limit and plasticity index, and a basically constant plastic limit. The reason is the dynamic changes in the internal particles loess damage. The increase of dry-wet cycling times and water content weakens the cementation of the soil particles, which reduces the shear strength, cohesion, and internal friction angle. When the water content of the sample exceeds the plastic limit, the decline becomes more obvious. The NMR of the loess shows that with the increase of the times of dry-wet cycling, micropores smaller than 0.025 μm inside the sample gradually transits to small pore groups of 0.025~0.63 μm and new pores begin to occur.

Performance evaluation of a novel compact humidification-dehumidification desalination system coupled with a heat pump for design and off-design conditions

In this study, the theoretical investigation of a novel heat pump assisted humidification-dehumidification desalination system has been carried out. The conventional dehumidifier of the humidification-dehumidification system was removed and the evaporator of the heat pump was utilized for direct dehumidification of air. Besides, the heat pump condenser was used as the saline water heater of the humidification-dehumidification cycle. First, the sizes of the components were calculated at design conditions for fixed input operational conditions namely the ambient air temperature, relative humidity, and inlet saline water temperature. However, the input operating conditions vary at off-design conditions resulting in changes in heat pump performance. Since the performance of a heat pump is a function of its refrigerant saturation temperatures, to examine the performance of the designed system at off-design conditions, the system performance balancing was carried out through the method of characteristics for a given set of fixed-size components. It was observed that the gained output ratio and hourly yield of the proposed system reach 2.476 and 0.91 kg/h, respectively. The economic analysis indicated that the cost per liter of the proposed system is 0.014 $/L.

Water Desalination Using Renewable Energy in a Humidification–Dehumidification Cycle for Bahrain Climate Conditions

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Performance evaluation of humidification-dehumidification (HDH) desalination systems with and without heat recovery options: An experimental and theoretical investigation

Humidification dehumidification (HDH) desalination system is a thermal-based desalination technology that is suitable for small-scale water desalination applications. In this paper, we present an experimental and thermodynamic analysis of the energetic performance of two HDH cycles. The HDH cycles considered are the basic open-air open-water (OAOW) cycle and the modified closed-water open-air (CWOA) cycle with the options of brine recirculation. An experimental investigation is performed on the modified cycle to validate the theoretical model that is used to assess the energetic performance of both the basic and modified cycles. The theoretical model is found to be in a good agreement with the experimental data with a maximum percentage deviation of 5% from the experimental data. Furthermore, limiting cases of the system are explored. Within the limiting cases, the modified cycle recorded about 100% improvement in the energy performance over the basic cycle due to heat recovery process associated with the modified cycle. Additionally, a cost analysis was performed to determine the cost of freshwater production by the presented desalination cycles. Results show that the freshwater price varied from 4.10 to 6.55 $/m3 and 0.79 to 2.25 $/m3 for the basic OAOW HDH cycle and the modified CWOA HDH cycle, respectively.

Design of a Helical Coil Dehumidifier for a Novel Gravity-driven Solar Distillation Unit

Solar distillation is a widely researched option for producing potable water in water-starved regions of the globe. Despite its technical simplicity and easiness-to-use, its efficiency has not sufficiently improved to promote its widespread use. The reasons for relative inefficiency of solar distillation are poor energy harvest at solar collectors, poor utilization of the harvested energy for evaporation of the water and suboptimum condensation of the humidified air in the condenser. A novel concept of solar still attempts to optimize the humidification-dehumidification cycle of a solar distillation unit to address these issues related to solar distillation units. The system works in a closed air open water humidification-dehumidification cycle. The energy source is solar irradiation, which heats up an air-water mixture. The driving force in the system is a small suction pressure induced in the system due to an aerator attached to the water inlet. A helical coil dehumidifier achieves efficient dehumidification in the system. The current paper describes experiments conducted to improve the efficiency of the dehumidifier attached to the novel solar distillation unit by optimizing the design parameters. The dehumidifier has the shape of a helical coil heat exchanger, which is cooled by the relatively cold water from a reservoir, which conversely, is heated by the heat of condensation. Even though there are sufficient studies on the design parameters of general helical coil condensers in literature, few studies are done to study their use in a humidification-dehumidification cycle involving non-condensable air. Further, a detailed parameter study of the helical coil dehumidifier is not yet done. The current paper discusses the various design parameters of a helical coil dehumidifier working in conjunction with a solar distillation unit as described above. Different design parameters of a helical coil dehumidifier discussed in this paper are pitch and diameter of the helical dehumidifier. Design insights for helical coil dehumidifier are thus obtained. The study reveals that the overall efficiency of a solar humidification-dehumidification cycle of a solar distillation unit could be considerably improved by optimizing the design of the helical coil dehumidifier used therein.

Experimental Study on Cooling of Solar Collectors Using Air-water Mixture

Large numbers of studies are reported on solar collectors using a single fluid to cool it, be it with water or with air only. The present paper reports a series of experiments that investigate into the performance of solar collectors that are cooled by an air-water mixture, a two-phase heat transfer fluid. This special way of cooling of solar collectors is designed in conjunction with a humidification-dehumidification cycle that produces hot water and saturate air at the same time to run an efficient solar distillation unit. Parameters analyzed in the study include the effects of the air-to-water ratio and the inner diameters of the absorber tubes of the solar collector. A mechanism to control air-water ratio was also developed in the process. The results indicate that the two-phase flows can efficiently cool solar collectors producing better cooling of absorber plates of solar collectors, under suitable operating conditions.

Experimental Study of the Water Depth Effect and the Impact of Condensers Connection in a New Desalination System by HDH Process, Using Solar Energy

This work is part of increasing the profitability of a system of sea water desalination, single stage, held at the laboratory scale, using the method of Humidification Dehumidification (HDH) handset, instantaneous (shorten up the HDH cycle). This is essentially an experimental approach which consists on studying a new combination of HDH system based on the use of a plate condenser cooled by sea water and the envelope of the system cooled by the ambient air, subsequently, we test the effect of changing the water depth and the impact of condenser connection on the quantity of distilled water. The temperature of the free evaporation surface was also analyzed to determine its effect on the flow rate values of the distillate. This is a closed air system using solar energy and the cooling energy provided by the low temperature of sea water and ambient air. The results justify the feasibility of the proposed system, since we got encouraging results and quite comparable to other desalination systems using solar energy, those results also allow us to understand and predict the characteristics required for a new prototype of this desalination system.

Design of a Continuous Solar Desalination System with Humidification-Dehumidification Cycle

A continuous solar desalination system with humidification-dehumidification cycle was devised. Solar energy was chosen as the main heat source, the electric heater the auxiliary heat source, and the hot water reservoir the energy storage unit. To ensure the 24-hour continuous production of fresh water, four specific operation modes were designed and analyzed for the conditions of average, excess, insufficient and no illumination intensity respectively, based on which the methods for the judgment and calculation of process parameters were derived.