Humidification Dehumidification Desalination System Research Articles

An experimental investigation of a novel design air humidifier using direct solar thermal heating

In this study, a novel solar heated multi-stage bubble column humidifier is designed and tested. The overall objective of this work is to investigate the main operating parameters of the new humidifier. The study addresses the significance of the perforated plate geometric features, optimum balance of air superficial velocity and water column height, and the influence of inlet water temperature and inlet air relative humidity on the performance of the humidifier. The day round performance of the humidifier is investigated in single stage, two stage, and three stage configuration, in which each configuration was tested with and without the integration of the Fresnel lens. Findings show that the average day round absolute humidity, without Fresnel lens, increased up to 9% for the two stage configuration and 23% for the three stage configuration as compared to the single stage configuration of the humidifier. The integration of the Fresnel lens further increased the absolute humidity up to 25% as compared to the results obtained without the integration of the Fresnel lens under the same prevailing conditions, which is significant. Moreover, the current humidifier shows a higher humidification efficiency in the climatic conditions that have a lower inlet air relative humidity. Furthermore, the finding demonstrates that the newly developed multi-stage bubble column humidifier has better performance as compared to the conventional single stage bubble column humidifier. The findings from this study are of pivotal importance to understand the optimum operating conditions of the humidifier for its possible integration with the dehumidifier. Consequently, an improved humidification-dehumidification desalination system attained.

Development of an active solar humidification-dehumidification (HDH) desalination system integrated with geothermal energy

This paper investigates the technical and economic feasibility of using a hybrid solar-geothermal energy source in a humidification-dehumidification (HDH) desalination system. The newly developed HDH system is a modified solar still with air blower and condenser used at its inlet and outlet respectively. A geothermal water tank in a temperature range 60–80°C which imitates a low-grade geothermal energy source was used to supply heat to water inside the humidification chamber. The experiments were conducted in January 2015 under the climatological conditions of Madinah (latitude: 24°33′N, longitude: 39°36′0″E), Saudi Arabia to study the effect of geothermal water temperature and flow rate on the performance and productivity of proposed desalination system. Analytical model was also developed to compare the effect of solar energy and combined solar-geothermal energy on accumulated productivity. Daytime experimental accumulated productivity up to 104L/m2 and daily average gained output ratio (GOR) in the range 1.2–1.58 was achieved using the proposed desalination system. Cost of fresh water produced using the presented desalination system is 0.003USD/L.

Design and performance improvement of a solar desalination system by using solar air heater: Experimental and theoretical approach

This paper focuses on the design and performance improvement of a recently developed solar humidification-dehumidification (HDH) desalination system comprising centrifugal air blower, humidification chamber equipped with two electric water heaters (500W each) and a condenser. To improve the design and performance of this desalination system, a solar air heater was used before the humidification chamber to pre-heat the induced ambient air. Two sets of experiments (I and II) were performed in January 2015 under the similar ambient conditions for all the test days in Madinah (24° 28′ 06″ N, 39° 36′ 51″ E), Saudi Arabia. Experiment set-I was performed without solar air heater and with two electric water heaters whereas experiment set-II was performed with solar air heater and one electric water heater. The results show that daily productivity and Gained Output Ratio (GOR) significantly increased in experiment set-II compared to experiment set-I whereas the Specific Energy Consumption (SEC) and cost per liter of fresh water produced in experiment set-II was greatly reduced compared to that of experiment set-I for the studied range of induced air flow rates.

Parametric analysis of an air-heated humidification-dehumidification (HDH) desalination system with waste heat recovery

Industrial waste heat is effective to provide power for the desalination system to acquire distilled water. In this paper, exhaust gas is drawn into the plate heat exchangers (PHEs) to heat the circulated humid air within the humidification dehumidification (HDH) desalination unit. Based on the governing equations of the components and the fixed-effectiveness model, key parameters are prescribed to accomplish the performance analysis of the HDH desalination system, and the relevant recovery results of the waste heat are also attained. The simulation results present that the balance condition of the dehumidifier is inaccessible due to a negative specific entropy generation of the dehumidifier in spite of the obtained best performance at such point. It is summarized that high values of the component effectiveness and the initial temperature as well as the vacuum environment are beneficial to raise the performance of the desalination system and reduce the heat transfer surface area for the PHEs. Moreover, the elevation of the top temperature contributes to a slight elevation of the gained-output-ratio (GOR), while the relevant heat transfer surface area of the PHEs increases.

Investigation of a solar energy driven and hollow fiber membrane-based humidification–dehumidification desalination system

A solar energy driven and membrane-based air humidification–dehumidification desalination (MHDD) system is proposed. A test rig is designed and constructed to investigate the performance of the system. The test rig consists of a U-tube evacuated solar collector, a heat storage water tank, a membrane-based humidifier (hollow fiber membrane module) and a dehumidifier (a fin-and-tube heat exchanger). A theoretical model for the whole system simulation is developed and validated. Performance indices of the system, such as the specific water production rate on the basis of unit area of membrane (SWR), specific electric energy consumption on unit volume of water production (SEC), coefficient of performance (COP) and electric coefficient of performance (COPE) are investigated. The effects of various parameters including the saline water flow rate, the air flow rate and the packing fraction of the membrane module, etc., on system performance are examined. It indicates that solar energy accounts for 92.0% of the energy consumption by the whole system. Sensible heat losses account for most of the energy losses from the system. High-purity water is produced by this system at a SWR of 25.88kgm−2d−1, a SEC of 19.23kWh/m3, a COP of 0.75 and a COPE of 36.13. The feasible operating parameters investigated are: hot saline water flow rate, 236L/h for per unit area of membrane; air flow rate, 25m3/h for per unit area of membrane; module packing faction, 30%.

Performance analysis of an air-heated humidification–dehumidification desalination plant powered by low grade waste heat

Humidification dehumidification desalination system has shown advantages to satisfy small scale freshwater demand. In this paper, an air-heated humidification dehumidification desalination system powered by low grade waste heat, coupled with plate heat exchangers, is constituted. Working mechanisms of the air-heated HDH desalination system are revealed, and performance for both the humidification dehumidification desalination unit and the plate heat exchangers is obtained and analyzed based on the established mathematical models. Entropy generation of both the components and the whole humidification dehumidification desalination system is calculated to judge the feasibility of the system cases and demonstrate the energy loss. Simulation results show that despite the top value of the gained-output-ratio, 3.51, at the balance condition of the dehumidifier with a negative specific entropy generation of the dehumidifier, the actual maximum value is 3.04 when the mass flow rate ratio between the seawater and the dry air is ṁsw/ṁda=1.28. Based on the elevation of the heat transfer rate and the descendant trend of the heat transfer coefficient, the heat transfer area of the plate heat exchangers rises from A=5.25m2 to A=15.90m2. Furthermore, it is summarized that the pressure drop of the plate heat exchangers will result in a very limited adverse influence on the energy utilization efficiency of the whole humidification dehumidification desalination system.

Thermodynamic investigation of waste heat driven desalination unit based on humidification dehumidification (HDH) processes

Humidification dehumidification (HDH) technology is an effective pattern to separate freshwater from seawater or brackish water. In this paper, a closed-air open-water (CAOW) desalination unit coupled with plate heat exchangers (PHEs) is applied to recover the waste heat from the gas exhaust. Sensitivity analysis for the HDH desalination unit as well as the PHEs from the key parameters including the top and initial temperature of the seawater, operation pressure, and the terminal temperature difference (TTD) of the PHEs are accomplished, and the corresponding performance of the whole HDH desalination system is calculated and presented. The simulation results show that the balance condition of the dehumidifier is allowed by the basic thermodynamic laws, followed by a peak value of gained-output-ratio (GOR) and a bottom value of total specific entropy generation. It is concluded that excellent results including the system performance, heat recovery effect and investment of the PHEs can be simultaneously obtained with a low top temperature, while the obtained desalination performance and the heat recovery effect from other measures are always conflicting. Different from other parameters of the desalination unit, the terminal temperature difference of the PHEs has little influences on the final value of GOR.

Comparative analysis of regenerative and air-extraction multi-stage humidification–dehumidification desalination system using pinch technology

To reduce energy consumption, the multi-stage type is a promising technology used in the humidification–dehumidification desalination system. Two types of multi-stage desalination system (regenerative and air-extraction multi-stage desalination) were proposed, and were studied and improved relatively separately. So, this paper comparatively investigated the two typical desalination systems based on the pinch technology. The pinch analysis models of regenerative and air-extraction multi-stage desalination were established and numerically analyzed. Subsequently, the effects of the pinch point temperature difference and the number of stage on the performance of the two desalination systems were comparatively analyzed. The result showed that the Gained Output Ratio (GOR) of regenerative multi-stage desalination was worse than that of air-extraction multi-stage desalination, while the Recovery Ratio (RR) of regenerative multi-stage desalination was better. Furthermore, when the single-stage system upgraded to two-stage system, the performance was significantly improved. But as the number of stage increases further, the enhancement effect is gradually weakened and even the performance becomes worse. The research content of this paper will help to select the device in the design of the desalination system.

Performance investigation of a novel water–power cogeneration plant (WPCP) based on humidification dehumidification (HDH) method

Humidification dehumidification (HDH) technology was well applied to produce freshwater in the desalination system. However, besides the demand of freshwater, power is also required simultaneously in most situations. In the paper, a novel water–power cogeneration plant (WPCP) based on the HDH desalination system coupled with the organic Rankine cycle (ORC) is proposed. Energy analysis for the proposed combined system at different appointed operation parameters is achieved, and the corresponding performance correlation between the HDH desalination and ORC power system are revealed. It is verified that the production of freshwater and electricity can be gained synchronously in the suggested novel platform, and the performance of the whole system is really sensitive to the operation parameters of the HDH desalination system. It is found that after the regulation of the operation pressure, p, and the seawater temperature at the outlet of the seawater heater, Tsw,2, for the HDH desalination from p=0.1MPa, Tsw,2=353.15K to p=0.3MPa, Tsw,2=383.15K, a maximum elevation, 25.46kgh−1 for the freshwater production, 4.17kW for the electricity and 2% for the extended gained output ratio (EGOR) is obtained. Furthermore, owing to the asynchronism between the specific production and the final energy utilization efficiency, the balance should be optimized among the demand of the freshwater and power and the efficiency of the novel WPCP.

Humidification–dehumidification desalination process driven by photovoltaic thermal energy recovery (PV-HDH) for small-scale sustainable water and power production

Humidification–dehumidification (HDH) desalination technology with the use of recovered photovoltaic (PV) thermal energy could be viable for the production of small-capacity sustainable water and improvement of PV electric power generation efficiency. This paper investigates the technical feasibility and environmental friendliness of an air-cooled PV system integrated with ambient seawater inflow into a HDH desalination system. The technical analysis of the PV-HDH desalination process was carried out through the modeling of the physical and thermodynamic properties involved in the recovery of PV thermal energy and determination of the effect of this recovery on water produced under the environmental conditions of Abu Dhabi, UAE. The results showed that the heat recovered from the PV resulted in the production of a daily average of 2.28L of fresh water per m2 of PV. On the other hand, the environmental impact assessment of this PV-HDH power and desalination technology was also carried out for the first time in order to determine its viability for small-scale sustainable water and energy production. The PV-HDH system resulted in 83.6% decrease in environmental impacts when compared with PV-Reverse Osmosis (PV-RO) system. In conclusion, the integrated PV-HDH desalination technology is promising and expected to play a key role in the field of water desalination.

A parametric study of a humidification dehumidification (HDH) desalination system using low grade heat sources

Humidification dehumidification (HDH) desalination system is applicable to recover the low grade heat source to heat the seawater before the humidifier. In the paper, plate heat exchangers are integrated to recover the waste heat from the exhaust in the water heated closed air open water (CAOW) HDH desalination system. The performance of the HDH desalination system as well as the plate type of low grade heat collector (LGHC) is investigated at different operation pressures. Gain investment ratio (GIR) is proposed and defined to depict the overall consumption of the whole system. The simulation results show that the modified heat capacity ratio of the dehumidifier (HCRd) is vital for the performance of the HDH desalination system as well as the plate LGHC with a top value of gain output ratio (GOR) at the balance point, HCRd=1, and the maximum GOR, GOR=2.44, results from the raised pressure of p=0.15MPa. Furthermore, taking the cost for the heat transfer surface area of the LGHC and the air and seawater pipes into consideration, it is revealed that the conditions, HCRd>1, are more economical due to the increase of GIR, which indicates the profit of unit consumption is more significant.

PV and CSP solar technologies & desalination: economic analysis

This paper presents an overview of using solar energy in running desalination systems, called solar desalination. Solar energy can be converted directly to electric energy, which can operate electrically driven desalting systems such as reverse osmosis (RO), electrodialysis (ED), and mechanical vapor compression systems. Solar energy can also be converted to the thermal energy that can operate the mainly used thermally operated desalination system such as multistage flash (MSF), conventional multieffect (ME), and multieffect thermal vapor compression (ME-TVC), and emerging membrane distillation and humidification–dehumidification desalination systems. The thermal energy converted from solar energy can also be used to produce high-pressure steam running power plant producing electric power to operate mechanically driven desalting systems, and/or extracted steam at relatively low pressure to operate thermally driven desalting system. The main obstacle that hinders the use of solar desalination is the initial investment cost. This paper discusses the use of the solar desalination and calculates the investment cost to install solar desalination plants. These include photovoltaic (PV)-driven RO system, and thermally driven MSF and ME plants by steam directly generated by solar collectors, or by steam extracted from solar steam power plants operated by the concentrated solar collectors. The results revealed that PV-RO desalting system has the highest specific capital cost, among the considered systems, because the expensive storage of the electric energy in batteries, and the fact solar energy supply lasts about one third of the day. It showed also that using the thermally generated energy from concentrated solar collectors operating power plant is much cheaper than using this thermal energy when directly operating the desalination system.

Energy and exergy analysis for a humidification–dehumidification desalination system integrated with multiple inserts

An experimental analysis is conducted to accelerate the productivity of the humidification dehumidification (HDH) desalination system. In the air heater region of the HDH desalination system, inserts namely (i) twisted tape in short length with tapered form, (ii) cut out conical turbulators integrated with internal fins arranged in convergent and divergent mode and (iii) half perforated circular inserts with an orientation angle of 45°, 90°, and 180° are tried out respectively with pitch ratio (PR) of 3, 4 and 5 to enhance the heat transfer rate in the air heater. Two types of packing materials, such as gunny bag and saw dust, are tested in the humidifier region accommodating the mass transfer rate. Also an attempt has been made to augment the overall heat transfer coefficient in the dehumidifier with spring insert for PR of 3 and 4. An energy and exergy analysis construed the quantity of effective utilization of energy with the modified HDH desalination system. The enhanced system produced 45% increase of productivity compared to conventional system of 0.340kg/h. For the same input power, the modified system enhanced the heat output and productivity equivalent to a power saving of 40% and 13% respectively.

Performance analysis of proposed hybrid air conditioning and humidification–dehumidification systems for energy saving and water production in hot and dry climatic regions

Performance of integrative air-conditioning (A/C) and humidification–dehumidification desalination systems proposed for hot and dry climatic regions is theoretically investigated. The proposed systems aim to energy saving and systems utilization in fresh water production. Four systems with evaporative cooler and heat recovery units located at different locations are proposed, analyzed and evaluated at different operating parameters (fresh air ratio, supply air temperature and outside air wet bulb temperature). Other two basic systems are used as reference systems in proposed systems assessment. Fresh water production rate, A/C cooling capacity, A/C electrical power consumption, saving in power consumptions and total cost saving (TCS) parameters are used for systems evaluations and comparisons. The results show that (i) the fresh water production rates of the proposed systems increase with increasing fresh air ratio, supply air temperature and outdoor wet bulb temperature, (ii) powers saving of the proposed systems increase with increasing fresh air ratio and supply air temperature and decreasing of the outdoor air wet bulb temperature, (iii) locating the evaporative cooling after the fresh air mixing remarkably increases water production rate, and (vi) incorporating heat recovery in the air conditioning systems with evaporative cooling may adversely affect both of the water production rate and the total cost saving of the system. Comparison study has been presented to identify systems configurations that have the highest fresh water production rate, highest power saving and highest total cost saving. Numerical correlations for fresh water production rate and total system energy consumption are developed and presented in terms of the controlling parameters.

Enhancement of productivity of humidification–dehumidification desalination using modified air heater

Experimental investigation on humidification–dehumidification (HD) desalination system is carried out with half-perforated circular inserts incorporated in the air heater. These half-perforated circular inserts are provided with the orientation angle of 45, 90, and 180° with two pitches, 114 and 152 mm. Experiments are conducted in the HD desalination unit for various combinations of parameters in the air heater. The productivity of the HD desalination system is based on the mass flow rate, temperature of air and saline water, and also the pitch ratio and orientation angle of the circular inserts. Maximum productivity of 0.82 kg/h is obtained for the orientation angle of 180°, pitch ratio (pitch length/diameter of the pipe) of 3 and the air flow rate of 21 kg/h. The economic analysis is also carried out and the payback period of such a system is found as 171 d.

Solar desalination system using spray evaporation

This paper evaluates a one-stage technique to improve fresh water production from salty water by enhancing the evaporation and condensation. A pilot plant is designed and constructed in an arid area with 1 m2 solar water collector area to evaluate the one-stage process. The effect of main parameters on fresh water production of the unit is studied. The results show that, the productivity, efficiency, productivity rate, and Gained Output Ratio of the desalination unit are strongly affected by the inlet hot water temperature and flow rate. Within the studied ranges, the maximum daily productivity reached to 9 l/m2. According to these results, fresher water production of the present system is higher than that solar humidification–dehumidification desalination system in the previous studies. The maximum daily efficiency in the desalination system is about 87%. A TDS (total dissolved solids) of fresher water is 40 ppm. Finally, the cost of distilled water per liter is $0.029.

Experimental study on a humidification and dehumidification desalination system of solar air heater with evacuated tubes

In this paper, a small scale solar humidification–dehumidification (HDH) experimental setup based on a new kind of solar air heater with all-glass evacuated tubes is designed and tested. Firstly, a new kind of solar air heater with evacuated tubes is designed and tested for the solar HDH desalination process. The test results of solar air heater show that the cut length of efficiency and overall heat loss coefficient is 0.47 and 1.60 respectively, while air flow rate is 140m3/h. Secondly, the humidifier and dehumidifier are designed and optimized by the mathematical design methods. Finally, a desalination pilot plant is designed and built. And then, operation characteristics are tested and analyzed. Test results show that different inlet sprayed water temperature in the pad humidifier from 9°C to 27°C can effectively improve relative humidity of outlet moist air from 89% to 97% and the outlet air temperature from 35°C to 42°C. The results are valuable in the pursuit of the optimal design for a 1000L/day solar HDH desalination system with the new kind of solar air heater.

A parametric study on a humidification–dehumidification (HDH) desalination unit powered by solar air and water heaters

The performance of a solar powered humidification–dehumidification desalination system is theoretically investigated for various operating and design parameters of the system under climatological conditions of Antalya, Turkey. The primary components of the system are a flat plate solar water heater, a flat plate double pass solar air heater, a humidifier, a dehumidifier and a storage tank. The mathematical model of the system is developed and governing conservation equations are numerically solved by using the Fourth order Runge–Kutta method. Daily and annual yields are calculated for different configurations of the system such as only water heating, only air heating and water–air heating.

An experimental study of a solar humidifier for HDD systems

This paper investigates the performance of a solar humidification prototype suitable for using in humidification dehumidification desalination (HDD) systems. This unit replaces the solar air heater, solar water heater and the evaporator of the traditional HDD plants, facilitating compact system designs. The prototype is composed of a solar collector, filled with water, through which air is forced to travel upwards in the form of bubbles. Experiments are conducted under the weather conditions of North Cyprus. It is discovered that the air temperature is found to approach the hot water temperature in the collector (thus increasing the vapor carrying capacity) and the relative humidity is raised to almost 100% at the exit. The collector inlet and outlet temperatures and relative humidity values are recorded for different flow rates in the period between the 1st and the 14th of December, 2012. It was found that for an average intensity of solar radiation of 700W/m2 and a mass flow rate of 12.6kg/h of air; the amount of water evaporated was 0.75kg/h on a square meter basis. Introduction of a reflector mirror at the bottom side of the humidifier increased the average absolute humidity by 32%.

Use of multiple extractions and injections to thermodynamically balance the humidification dehumidification desalination system

Humidification dehumidification (HDH) desalination systems are well suited for small scale, off-grid desalination. These systems are very robust and can tolerate a wide range of feed salinities, making them a good candidate for treating produced water from hydraulically fractured natural gas wells. A primary engineering challenge for these systems is their high thermal energy consumption. In this study, we examine the use of multiple air extractions and injections to thermodynamically balance the HDH system, so as to make it more energy efficient. The effect of the number of extractions on several performance parameters is studied. In addition, we study the effect of the enthalpy pinch, which is a measure of performance for a heat and mass exchanger, on these performance parameters. Finally, we present results that can be used as guidelines in designing HDH systems. These results include the identification of appropriate temperatures for the extracted/injected air streams, the division of the heat duty between stages, and the value of the mass flow rate ratio in each stage at various values of enthalpy pinch.