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Modeling and performance of a forced flow solar collector/regenerator using liquid desiccant
Abstract
A forced flow solar collector/regenerator is one of the effective ways of regenerating the weak liquid solution in an open cycle liquid desiccant air conditioner using solar energy. In this system, the weak solution flows over the absorber plate of a tilted collector/regenerator as a thin liquid film. The forced air stream, which flows parallel or counter to the solution film, removes the moisture which is evaporated from the liquid solution due to absorption of solar energy. The absorber plate of the collector/regenerator is blackened and glazed to enhance the solar energy absorption and protect it from the environment. To evaluate the thermal performance of the solar collector/regenerator, a computer model has been developed using calcium chloride as the desiccant. A parametric analysis of the system has been performed to calculate the rate of evaporation of water from the solution as a function of the system variables and the climatic conditions.
... After that, several attempts have been made to study the forced°o w collectors as regenerators extensively. 9,15 In few cases, the performance of natural convection collectors as regenerators also has been investigated. However, the forced°ow type has been reported to be more e®ective. ...
... In this system, a°at plate solar collector with forced°ow, as put forth by Alizadeh and Saman, 15 has been employed to regenerate the desiccant (shown in Fig. 4). The system also incorporates two simple heat exchangers to cool the dry air leaving the dehumidi¯er and the hot concentrated desiccant solution to come out of the collector. ...
... Equation (12) represents the relation between desiccant concentration, the desorption rate, the mass°o w rate of desiccant and the initial desiccant concentration. 15 1 ...
Traditional air conditioning systems run on the vapor compression cycle, which utilizes electricity generated from fossil fuels, the reserves of which are fast depleting. Moreover, the refrigerants used in such systems have exacerbated ozone layer depletion and climate change. Liquid desiccant air conditioning (LDAC) systems appear as a favorable option in light of these drawbacks. This paper has developed the numerical model of an LDAC system using a dehumidifier that is internally cooled and has a finned coil. The study of this particular model has been limited in the past. The model has been validated against a reference study available in the literature. Moreover, the commonly used desiccant materials tend to be corrosive and detrimental to the air quality. Therefore, the feasibility of an ionic liquid (65% [Emim]OAc) and an organic salt solution (73% HCOOK) as desiccant materials has also been investigated in this paper. With the proposed scheme for room air conditioning, the air temperature and humidity levels within the range of comfort (21 ∘ C, 53% R.H.) could be supplied to the conditioned space. Performance analysis revealed that the eco-friendly desiccants could achieve dehumidifier and regeneration effectiveness similar to that of the traditionally used corrosive salt solution of calcium chloride (CaCl 2 ). Furthermore, the estimated dehumidifier efficiency of about 76% is found to be higher than that available in the previous studies. Economic analysis provides a comparison of total cost between the conventional and the novel desiccant air conditioning systems and also reveals HCOOK to be a more economical choice as desiccant material.
... Although regeneration can be carried out in packed beds [14,[19][20][21][22], direct contact solar regenerators, where the solution itself is the fluid collecting the heat from a surface exposed to solar radiation, are preferred due to its higher effectiveness and lower overhead of system components [18,23]. Recent studies on the use of direct solar regenerators in LDCS have been reported by several authors in the literature [23][24][25][26][27][28]. Alizadeh and Saman [28] presented a theoretical model of a forced parallel flow solar regenerator using an aqueous solution of CaCl 2 as the desiccant and an experimental study on the same reported by Alizadeh and Saman [23] confirmed the accuracy of the theoretical model developed previously and the results were also consistent with other findings reported in the literature. ...
... Recent studies on the use of direct solar regenerators in LDCS have been reported by several authors in the literature [23][24][25][26][27][28]. Alizadeh and Saman [28] presented a theoretical model of a forced parallel flow solar regenerator using an aqueous solution of CaCl 2 as the desiccant and an experimental study on the same reported by Alizadeh and Saman [23] confirmed the accuracy of the theoretical model developed previously and the results were also consistent with other findings reported in the literature. ...
... The regeneration of the LDS is carried out with the help of a forced parallel flow solar regenerator [23,28]. The scheme of a regenerator unit is shown in Fig. 2. It is made of a flat inclined blackened copper plate electroplated with a nickel layer underneath and a thin black chrome coating at the top. ...
In this paper, we provide thermal analysis and design methodology of a liquid desiccant assisted dew point indirect evaporative cooling system. The purpose of the system is to serve as an alternative for conventional vapour-compression based building air conditioning systems in providing satisfactory human thermal comfort conditions in the hot and humid climatic regions. The main features of the study are the following: i) novel incorporation of a forced parallel flow direct solar regenerator and a dew point indirect evaporative cooler within the same air conditioning unit; ii) detailed thermal modelling of each of the system components with lesser simplifying assumptions with respect to earlier works; iii) large cooling capacity (∼18.8 TR) under harsh climate; and, iv) a comprehensive year-around case study for system operation in a hot and humid location (Kolkata, India). Our thermal model is validated with a reference model study. The maximum room air temperature predicted by the current system for yearlong analysis is 26.7 °C. The thermal COP of the system for diurnal operation in the most humid month of a calendar year (July) varied between 0.40-0.96. The cooling system can prevent overheating of the conditioned space, as specified by ASHRAE Standard 55-2017, throughout the year.
... Yang and Wang (2001) performed a computer simulation for the collector/regenerator (C/R) using a radiation processor which makes use of the statistical meteorological data for the summer season at Kaohsiung, Taiwan. Alizadeh and Saman (2002) developed a computer model using Calcium Chloride (CaCl 2 ) as the working desiccant to study the thermal performance of a forced parallel flow solar regenerator. A parametric analysis of the system has been performed to calculate the rate of evaporation of water from the solution as a function of the system variables and the climatic conditions. ...
... where a, b and c are empirical constants (Alizadeh and Saman, 2002) . ...
... As shown in Fig. 5, the vapor pressure difference has a maximum for a given length of the regenerator. The results obtained by Alizadeh and Saman (2002) were compared with that presented in Fig. 5. The trend of the results of both the vapor pressure difference and evaporation rate agree very well along with the regenerator length, which validates the present model. ...
This paper presents the modeling and simulation of solar-powered desiccant regenerator used for open absorption cooling cycles. The input heat, which is the total radiation incident on an inclined surface, is evaluated via a solar radiation model in terms of the location, day of the year, and time of the day. Calcium Chloride (CaCl2) is applied as the working desiccant in this investigation. The solar radiation model is integrated with the desiccant regenerator model to produce a more realistic simulation. A finite difference method is used to simulate the combined heat and mass transfer processes that occur in the liquid desiccant regenerator. The system of equations is solved using the Matlab-Simulink platform. The effect of the important parameters, namely the regenerator length, desiccant solution flow rate and concentration, and air flow rate, on the performance of the system is investigated. It has been found that the vapor pressure difference has a maximum value for a given regenerator length. It is also shown that for specified operating conditions, a maximum value of the coefficient of performance occurs at a given range of air and solution flow rates. Therefore, it is essential to select the design parameters for each ambient condition to maximize the coefficient of performance of the system.
... Yang and Wang (2001) performed a computer simulation for the collector/regenerator (C/R) using a radiation processor which makes use of the statistical meteorological data for the summer season at Kaohsiung, Taiwan. Alizadeh and Saman (2002) developed a computer model using Calcium Chloride (CaCl 2 ) as the working desiccant to study the thermal performance of a forced parallel flow solar regenerator. A parametric analysis of the system has been performed to calculate the rate of evaporation of water from the solution as a function of the system variables and the climatic conditions. ...
... where a, b and c are empirical constants (Alizadeh and Saman, 2002) . ...
... As shown in Fig. 5, the vapor pressure difference has a maximum for a given length of the regenerator. The results obtained by Alizadeh and Saman (2002) were compared with that presented in Fig. 5. The trend of the results of both the vapor pressure difference and evaporation rate agree very well along with the regenerator length, which validates the present model. ...
Theoretical investigation on the performance of lithium chloride (LiCl) absorption cooling system using an artificial neural network (ANN) model is presented. Tabulated data from the literature are used to construct the ANN model. Solar collector desiccant/regenerator is applied to re-concentrate the working solution. Using the proposed model, the effect of system design parameters; namely regenerator length, and air flow rate on the performance of the system is demonstrated. The variation of the thermo-physical parameters along the regenerator length is highlighted.
... So heated dry air is passed to the liquid desiccant to regenerate and humid air exit from the desiccant regenerator. For examining the regeneration process various designs of regenerator have been analyzed and different theoretical models have been applied [3][4][5][6]. Kakabayev and Khandurdyev [7] developed an analytical process in terms of the properties of solution and conditions of climate to calculate the evaporated mass from the weak solution in the regeneration process. Utilizing a radiation processor that uses the statistical meteorological data for summer season at Kaohsiung, Taiwan, Yang and Wang [5] accomplished a computer based simulation for the collector/regenerator systems. ...
... To stimulate the performance of solar powered open absorption system for cooling, numerous studies on theoretical modeling have been done [3][4]. To analyze the performance of a forced parallel flow solar regenerator, Alizadeh and Saman [6] displayed a computer model where CaCl2 was used as the working desiccant. An examination of the framework was introduced to ascertain the evaporation rate of liquid (water) from the desiccant solution as a function of the factors of the system and the atmospheric conditions using aqueous solution of lithium bromide in M-cycle indirect evaporative cooling system. ...
Experimental investigation on the performance of liquid desiccant regeneration system using solar water heater has been exhibited in this analysis. Hot water from the tank having in the solar powered heating system has been flowed to a heat exchanger through piping system and returned back to the storage tank. Atmospheric air has been passed through the heat exchanger. The heated air from the heat exchanger has been blown into a CaCl2 solution for the purpose of regeneration of CaCl2 which has been considered as the working desiccant in this analysis. In this experiment different concentrations of CaCl2 solution such that 32.67 gm/kg-water, 39 gm/kg-water, 66.67 gm/kg-water, 150 gm/kg-water and 231.12 gm/kg-water have been used to evaluate the performance. Air flow rate, specific humidity, cooling rate of the desiccant cooling system, evaporation rate have been calculated. The effect of different concentrations of the CaCl2 solution at the air velocity of 2 m/s on evaporation rate and cooling rate have been analyzed. Evaporation rate and cooling rate decrease with the increase of concentration. For 39 gm/kg-water, 66.67 gm/kg-water, 150 gm/kg-water and 231.12 gm/kg-water solutions the water evaporation rate and cooling rate decrease about 2.33%, 28.33%, 46.55% and 55.44% respectively comparing to 32.67 gm/kg-water solution.
... So heated dry air is passed to the liquid desiccant to regenerate and humid air exit from the desiccant regenerator. For examining the regeneration process various designs of regenerator have been analyzed and different theoretical models have been applied [3][4][5][6]. Kakabayev and Khandurdyev [7] developed an analytical process in terms of the properties of solution and conditions of climate to calculate the evaporated mass from the weak solution in the regeneration process. Utilizing a radiation processor that uses the statistical meteorological data for summer season at Kaohsiung, Taiwan, Yang and Wang [5] accomplished a computer based simulation for the collector/regenerator systems. ...
... To stimulate the performance of solar powered open absorption system for cooling, numerous studies on theoretical modeling have been done [3][4]. To analyze the performance of a forced parallel flow solar regenerator, Alizadeh and Saman [6] displayed a computer model where CaCl2 was used as the working desiccant. An examination of the framework was introduced to ascertain the evaporation rate of liquid (water) from the desiccant solution as a function of the factors of the system and the atmospheric conditions using aqueous solution of lithium bromide in M-cycle indirect evaporative cooling system. ...
... A forced flow flat plate solar collector has been used as the regenerator for the system (shown in Fig. 4). The collector prototype similar to what has been proposed by Alizadeh and Saman [8] has been adopted for the present study. The water from a cooling tower which supplies chilled water at 12 0 C [9] has been used in the heat exchangers to cool desiccant and air. ...
... The system could achieve dehumidifier efficiency of about 64%, significantly higher than 49% as presented in [7]. This increase in efficiency can be attributed to higher concentration of desiccant (45% CaCl2 solution) and higher mass flow rates of water and desiccant (0.28 kg/s and 0.1 kg/s).The evaporation rates achieved by the model for the set parameters is higher than that achieved by [8]. The cooling capacity has been found to be approximately 3 kW. ...
A novel scheme of a solar assisted, liquid desiccant supported comfort air conditioning system has been proposed in this paper. The primary intent of the system is to supply air at 25°C and 52% relative humidity, even during the hot and humid summer months prevailing in the plains of sub-tropical countries like India. A mathematical model has been put forward to predict the output air temperature, humidity ratio and the effectiveness of dehumidifier as well as the regenerator. The predicted air humidity ratio has been validated against data available in the literature. The model has been used to predict the optimum mass flow rates required to achieve the desired output conditions for the selected location (Kolkata). The study thus strengthens the need and feasibility of solar assisted desiccant based air conditioning systems for the sub-tropical climates as a replacement of the traditional VCR (vapor compression refrigeration) systems.
... Saman carried an early works in the field of the solar desiccant cooling systems (Saman, 1993). Alizadah, publications 2000-2005 enriched the knowledge in this technology in Australia (Alizadeh and Saman, 2002b;Alizadeh and Saman, 2002a;Saman and Alizadeh, 2001b;Saman and Alizadeh, 2001a;Saman and Alizadeh, 2002). Fig.7. ...
... Many studies have been done since the earlier days of absorption chillers when Mouchot produced Ice cubes utilizing the solar thermal energy in 1878 ,Trombe and Fox (Alizadeh and Khouzam, 2005) reported a successful test for a lab experimental to operate an absorption chillers with solar thermal powered, followed by many researchers, e.g. Nakahara (Alizadeh and Saman, 2002b), now days many researches cover the different aspects of the different solar refrigeration technologies, these studies can be significant in decision making in the first stage of Solar cooling system choosing process. ...
Across the world, governments, organisations and individuals are seeking to obtain the most effective, cheapest and environmentally clean power sources. During the last decade, air conditioning systems that use renewable energies have undergone significant development. This expansion has been driven, in large part, by successive periods of extreme solar heat and increased demand for the comfort of summer air conditioning in residential and commercial buildings. Most of Australia’s greenhouse gas emissions (about 50%) come from the burning of fossil fuels for energy (e.g., for electricity and transport). For this reason, looking for a reduction in the energy used in buildings as well as looking for alternative power sources to fossil fuels should be explored.
This project presents approaches to increasing the performance of a solar cooling system by improving the energy efficiency of the building for a typical small-sized Australian office building in Sydney, New South Wales (NSW). Solar cooling systems with a thermally driven LiBr-H₂O single-effect absorption chiller that utilises the solar thermal energy provided through evacuated tube solar thermal collectors and thermal back-up is a popular system among solar cooling applications around the world. In this study, the performance of a similar system is evaluated and compared with a conventional cooling system in terms of energy, economic and environmental aspects.
The aim of this project was to examine a solar air conditioning system with absorption chiller contributions in a small office building cooled in different thermal efficiency scenarios by demonstrating and evaluating specific architectural improvements to the basic model of the building. These improvements took the form of double-glazed windows, overhanging window shades, and a combination of double-glazed windows and overhanging shades in the environment of Sydney, NSW.
TRNSYS and OpenStudio/EnergyPlus software with the graphical interference of Google SketchUp for building energy modelling and simulation were used. To achieve an efficient usage for the building under consideration, the project was divided into two main blocks. The first block included the design and simulation of the building to evaluate a set of proposed architectural improvements, with the aim of achieving optimal intake. For the second block, energy and economic assessments were performed to choose the best alternative application. The building underwent simulation under four different scenarios: the baseline scenario (i.e. the current situation); the introduction of an overhang on the north side of the building; the modification of existing glazing of 4 mm to a double glass and finally a combination of the two modifications: overhang and glazing options.
The analysis of the energy and environmental performance of the solar cooling system was based on the system solar fraction and the CO₂ foot print. The modelling and simulation of the solar cooling system was carried out by the TRNSYS program in the four different scenarios.
The results show that the combination of double glazing with overhang shade is the best option for increasing the thermal efficiency of the building and reducing the cooling load. The favourable assessment of performance of the solar cooling system is indicated by both the equivalent natural gas saved rate (3307 m³/year) and the solar fraction (0.804). In addition, the environmental performance of the system shows positive results by saving more than 69 Tonnes of CO₂/year, which is the optimum value compared to other scenarios.
Economically, the window overhang shade is the preferred option as an architectural modification in terms of initial cost, net present value and payback period. However, the economic performance of the solar cooling system studied was not competent when compared to the reference system (vapour compression).
The LCC (life cycle cost) calculations show that the solar cooling system values are 40% more than those of the reference system. However, the NPV (net present value) results were found to be negative values after the 25-year life span, indicating that there is no significant profit reward at the end of the term of operation. The PBP (payback period) results, by contrast, show that the solar cooling system will return its value in a lesser period than the proposed life span of 25 years.
In conclusion, by applying different architectural modifications for the building envelope, cooling loads can be reduced significantly. However, the window overhang shade is found to be the best option in terms of economic performance. The contribution of the solar cooling system shows that the system is not practical in all four scenarios. This may be due to the high initial cost of the system, even though it is found to be efficient in saving energy and is capable of reducing greenhouse gas emissions.
... These systems include sorption systems containing liquid/vapor or solid/vapor absorption/adsorption, vapor compression systems, and hybrid desiccant vapor compression systems [23]. Different regenerator designs have been examined and a variety of theoretical models have been employed to analyze the regeneration process2425262728. An analytical procedure for calculating the mass of water evaporated from the weak solution in the regenerator in terms of climatic conditions and solution properties at the regenerator inlet has been developed by Kakabayev and Khandurdyev [21]. ...
... The regeneration chamber is also eliminated. Forced parallel flow type solar C/R is designed and tested by Alizadeh and Saman [27] . The regenerator has been designed and optimized and the prototype of the solar C/R has been built and tested. ...
In the present work, a novel configuration of solar-powered desiccant dehumidification system is demonstrated. A rotating wick made of double layered cotton-cloth has been applied as a desiccant solar regenerator. The blackened wick-surface, which is impregnated with calcium chloride solution, moves between two rotating pulleys at an inclination angle of 20 degrees. Solar radiation incident on the wick surface regenerates the liquid desiccant in the wick. In the experimental study, instantaneous values of the desiccant solution concentration is evaluated and recorded with time. Apparent values of system coefficient of performance around 2 could be attained in the dry climate of Taif city. Instantaneous as well as average values of mass transfer coefficient are evaluated from the experimental measurements. System operational problems are discussed and highlighted.
... Yang and Yan [20], and Yang and Wang [21] performed a computer simulation for the collector/regenerator using a radiation processor which makes use of the statistical meteorological data for the summer season at Kaohsiung, Taiwan. Alizadeh and Saman [22] developed a computer model using calcium chloride as the working desiccant to study the thermal performance of a forced parallel flow solar regenerator. A parametric analysis of the system has been performed to calculate the rate of evaporation of water from the solution as a function of the system variables and the climatic conditions. ...
... where a, b and c are empirical constants [22]. For lithium chloride solution, an artificial neural network (ANN) model is used to extract the required parameter from tabulated data available from the literature [28] as follows, ...
This paper presents the modeling and simulation of solar-powered desiccant regenerator used for open absorption cooling system. The input heat, which is used to re-concentrate the desiccant solution, is estimated via a real-time solar radiation model in terms of the location, day of the year and time of the day. Lithium chloride (LiCl) and calcium chloride (CaCl 2) solutions are applied as the working desiccants in this investigation. To compute the thermo-physical properties, a state equation is used for the calcium chloride desiccant while tabulated data along with an artificial neural network (ANN) model is used for the lithium chloride desiccant. A finite difference method is used to simulate the combined heat and mass transfer processes that occur in the liquid desiccant regenerator using the Matlab–Simulink platform. Using the proposed model, the effect of the important parameters, namely the regenerator length, desiccant solution flow rate and concentration, and air flow rate, on the performance of the system is investigated. It has been found that the vapor pressure difference has a maximum value for a given regenerator length with higher values obtained with the calcium chloride desiccant than those obtained with the lithium chloride desiccant. The proposed model can be successfully used for investigating the effect of different operating parameters under different ambient conditions and for predicting the overall performance of the system.
... The experimental results show a regeneration efficiency varying between 38% and 67%. Alizadeh and Saman [20,21] developed a computer model to evaluate the thermal performance of the solar collector and regenerator. They used a forced parallel flow prototype of a solar collector and regenerator and conducted experimentation. ...
Solar thermal energy-powered air conditioning technologies are receiving increased attention. Among the solar energy-driven cooling technologies, open type liquid desiccant air conditioning (AC) system is emerging as a promising technology, which has a solar driven desiccant solution regenerator. In this type of system, the evaporation of water and concentrating the desiccant or regenerator performance determines the cooling performance of the AC system, which necessitates its development and experimental performance testing under actual operating conditions. The setup is made of a black painted corrugated solar collector of area 0.8 m × 1.84 m covered with glass, and a liquid desiccant solution tank and distribution system over the absorber. Solar regeneration experiments on calcium chloride–water solution were carried out on the setup and a total of five sets of meteorological, collector and solution property data were collected through concentrating the desiccant from 32.9 initially to 51.3% in five days. The evaporation of water from the regenerator was analyzed using energy and desiccant mass conservation. For a typical day, the mass of water evaporated was estimated to be 3.10 and 3.16 kg over a day, as estimated by conservation of mass and energy principles from a 34.8 kg of calcium chloride solution with initial desiccant concentration of 43.6% stored in the tank.
... To stimulate the performance of solar powered open absorption system for cooling, numerous studies on theoretical modeling have been done (Yang and Yan 1992). To analyze the performance of a forced parallel flow solar regenerator, Alizadeh and Saman (2002) displayed a computer model where CaCl2 was used as the working desiccant. An examination of the framework was introduced to ascertain the evaporation rate of liquid (water) from the desiccant solution as a function of the factors of the system and the atmospheric conditions using aqueous solution of lithium bromide in M-cycle indirect evaporative cooling system. ...
Solar based air conditioning systems are becoming more and more popular in warmer and humid regions keeping in mind the environmental issues. The implementation of liquid desiccant in air conditioning system reduces the application of environment unfriendly refrigerants. Experimental investigation on the performance of air humidifying system with desiccant regenerator using solar water heater has been exhibited in this analysis. Hot water from the tank having in the solar powered heating system has been flowed to a heat exchanger through piping system and returned back to the storage tank. Atmospheric air has been passed through the heat exchanger. The heated air from the heat exchanger has been blown into a CaCl2 solution for the purpose of regeneration of CaCl2 which has been considered as the working desiccant in this analysis. In this experiment different concentrations of CaCl2 solution such that 32.67gm/kg-water, 39gm/kg-water, 66.67gm/kg-water, 150gm/kg-water and 231.12 gm/kg-water have been used to evaluate the performance. Air flow rate, specific humidity, cooling rate of the desiccant cooling system, evaporation rate have been calculated. The effect of different concentrations of the CaCl2 solution at the air velocity of 2m/s and 3m/s on evaporation rate and cooling rate have been analyzed. Evaporation rate and cooling rate decrease with the increase of concentration of the solution. The evaporation rate and cooling rate increase about 25%-49.5% with the increase of the air velocity from 2m/s to 3m/s.
... Renewable energies such as solar energy [6] and wind energy [7] can generate the energy demanded in LDAC systems. Alizadeh and Saman [8] studied a solar collector's thermal performance as a regenerator and used a computer model for CaCl2. They found that the theoretical model and experimental results had a good agreement [9]. ...
Corrosive fluids such as lithium chloride are often used in liquid desiccant air conditioners. Corrosion in enthalpy exchanger is one of the design problems. Some solutions are studied in this research, and based on them; an experimental setup is investigated. In this design, a counter-flow enthalpy exchanger is used to exchange moisture between the air and the liquid desiccant. First, the inlet air is preheated or precooled by an aluminium heat exchanger. Then, the liquid desiccant is preheated or precooled by thin-walled plastic tubes. By contacting this processed air and liquid desiccant, heat, and mass exchanging occurs. The variation of the air moisture content is investigated in laboratory conditions, and the rate of regeneration and dehumidification is studied. The results indicate that in general, the ambient air moisture content decreased around 20% during the dehumidification process and it enhanced around 14.28% during the regeneration process. Furthermore, the moisture content variation in the dehumidification process improved at least 9.92%, but the regeneration process decreased at least 10.76% compared to the previous study. In addition, utilizing the particle swarm optimization algorithm is desirable to identify the system's transient behavior and obtain the fitting parameters of a curve that is closely similar to the experimental data of the rate of dehumidification and regeneration and the average errors of the fitted curve were 10.43 and 1.52%, respectively.
... a p and s p refer to the temperature (°C), fraction of return air in process air, specific humidity, mass flow rate (kg/s), specific enthalpy (J/kg), effectiveness of DEH, specific area of packing (m 2 /m 3 ), packed bed height (m), ratio of vapor pressure depression of the LDS to the vapor pressure of pure water, partial pressure of water vapor in the air (Pa) and vapor pressure of the LDS respectively. The REG is modeled based on the work of Alizadeh and Saman[8]. The governing equations are given in equations (6) through(12). ...
In this paper, exergy analysis of a novel solar powered liquid desiccant assisted air
conditioning system is presented and simulated. The system aims to provide suitable thermal
comfort conditions inside large office buildings with high internal loads situated in the hot and
humid tropical/subtropical countries of the world. The system consists of process and
regenerating air streams, a liquid desiccant solution loop and a cooling water loop. The primary
objective of this study is to present the exergy of cooling capacity along with the overall
exergy efficiency of the proposed system. The study helps to quantify the optimum operating
and design parameters for system operation based on the second law of thermodynamics. For
the base case, which is representative of a hot and humid climatic condition, the proposed
system is able to maintain the room air conditions within the moderate thermal acceptability
criterion. The exergy of cooling capacity and exergy efficiency for the base case is about 2900
W and 2 % respectively. Parametric analyses show that the system performs the best under
conditions of high ambient insolation and temperature, low ambient humidity and a process air
to desiccant solution mass flow rate of about 3 in the dehumidifier.
... Alizadeh and Saman (2002a) designed, optimized and provided an experimental study of a forced parallel flow solar regenerator using calcium chloride solution as liquid desiccant. They compared the experimental results with those obtained from a reference model study available in literature (Alizadeh and Saman, 2002b). The study showed that the rate of evaporation of water from diluted desiccant solution increases as water vapour stripping air mass flow rate increases and rate of water loss generally decreases with increasing solution mass flow rate. ...
In this paper, a novel scheme of a partially closed solar regenerated liquid desiccant assisted evaporative cooling system has been proposed. The objective of the system is to provide suitable conditions inside greenhouses for cultivation of high value temperate crops like lettuce throughout the year in hot and humid climates of tropics and subtropics. The partially closed system re-circulated a fraction of return air from the greenhouse and ventilated a certain amount of ambient air. A forced parallel flow solar regenerator has been used to re-concentrate the weak desiccant solution. A thermal model has been developed to predict the greenhouse air temperature, vapour pressure deficit and the coefficient of performance of the system. The predicted greenhouse temperature has been compared with that of a reference model study available in literature. A very good agreement is established on comparing the temperatures predicted by the two models with a root mean square error of 0.82 °C and average percentage difference being 2.4%. The COP of the cooling system varied between 0.64 and 0.74 for daylong operation in the most humid month of the year (July). The maximum greenhouse temperature predicted using our proposed model was about 27 °C for year round system operation for the place under consideration (Kolkata). The predicted vapour pressure deficits were also in the optimum range. Thus, optimum or viable lettuce growing conditions were predicted by our model all year around. The study consequently reinforces the viability of cultivation of target plantation (lettuce) in hot and humid climates prevailing in the tropical or subtropical countries like India with our model.
... Different regenerator designs have been examined and a variety of theoretical models have been employed to analyze the regeneration process [7][8][9]. An analytical procedure for calculating the mass of water evaporated from the weak solution in the regenerator in terms of climatic conditions and solution properties at the regenerator inlet has been developed by Kakabayev and Khandurdyev [1].Alizadeh and Saman [10] developed a computer model using Calciu m Chloride as the working desiccant to study the thermal performance of a forced parallel flo w solar regenerator. A parametric analysis of the system has been performed to calculate the rate of evaporation of water fro m the solution as a function of the system variables and the climatic conditions. ...
Application of Evaporative Air Coolers Coupled With Solar Water Heater for Dehumidification of Indoor Air
... Saman and Alizadeh [76,77] proposed a liquid desiccant cooling system in conjunction with an indirect evaporative cooling system as shown in Fig were defined to observe the system performance for different conditions of weather. The results showed that system has a good performance for hot and humid climates. ...
... The phenomenon was attributed to the fact that though the increasing air flow rate enhances the mass transfer coefficient, excessive flow velocity adversely results in a decrease in the regenerator temperature, and consequently a decrease in the vapour pressure, which may ultimately result in a decrease in performance. This phenomenon has also been reported for parallel flow configuration [132,133]. ...
... These systems include sorption systems containing liquid/vapor or solid/vapor absorption/adsorption, vapor compression systems, and hybrid desiccant vapor compression systems [42]. Different regenerator designs have been examined and a variety of theoretical models have been employed to analyze the regeneration process [43][44][45][46][47][48]. ...
This paper gives a detailed account of the general features of the major desiccant regeneration techniques and configurations of the related systems; meanwhile, attention has been paid to both technological development of solar powered regenerator, which is a key component of the liquid-desiccant dehumidification system. Studies to improve the system performance have been discussed. Benefits and conditions of the use of liquid desiccant for dehumidification purposes have been stated. It is clear from the survey that the desiccant dehumidification is more energy-efficient compared with the conventional vapor compression system. Moreover, new configurations of the solar regenerator, to improve the system performance, have been demonstrated. Some new hybrid systems that greatly expand the desiccant in residential applications, as well as effectively promoting the single system's performance, are also introduced.
... Considerable laboratory experiments, computational analysis and design work has been carried out on a liquid desiccant system at the Sustainable Energy Centre of the University of South Australia [2][3][4][5][6], and the Queensland University of Technology [7,8]. These involved modelling and experimental work on both cross flow and packed-bed dehumidifier as the absorber unit as well as the solar regenerator [9]. ...
... Their analysis led to simple expressions of efficiency that characterise the performance of such systems.Based on Kakabaev's and Collier's studiesKumar and Devotta (1989) modelled the heat and mass transfer taking place in an open type regenerator using correlations of heat and mass transfer coefficients for forced convection found experimentally in an earlier study published byKumar et al. (1985). The predicted water evaporation rate values had a 9.3 average percent error.Extending Kakabaev and Khandurdyev's approach by using the same linear approximation of solution vapour pressure,Alizadeh and Saman (2002) modelled the heat and mass transfer processes taking place in a closed-type forced flow solar regenerator and evaluated the performance of the system under different conditions. The differential equations of the model were solved by the finite difference method. ...
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... Alizadeh and Saman [120] developed a computer model to study the thermal performance of parallel or counterflow to the solution in a solar collector/regenerator using calcium chloride (CaCl 2 ) as the working desiccant. The absorber plate of the collector /regenerator is blackened and glazed to enhance the solar energy absorption and protect it from the environment. ...
... Damper its many advantages (Lof, 1955a,b). The solar C/Rs also helps reduce the number of installed equipment (Collier, 1979; Saman et al., 1987; Alizadeh and Saman, 2002a,b). The strong desiccant leaving the solar C/Rs (24) is cooled by cooling water (31) in a compact heat exchanger before entering the dehumidifier (21) and completes the loop. ...
A solar-regenerated liquid desiccant ventilation pre-conditioning system has been installed and experiments were carried out for a period of nine months covering rainy, cold, and hot seasons in a hot and humid climate (Thailand). A heat exchanger was used to cool the dehumidified air instead of typical evaporative cooling to maintain the dryness of the air. The use of solar energy at the regeneration process and cooling water from a cooling tower makes the system more passive. The evaporation rate at the regeneration process was always greater than the moisture removal rate at the dehumidification process indicating that the concentration of the desiccant in the system would not decrease and so the performance would not drop during continuous operation. The system could reduce the temperature of the delivered air by about 1.2°C while the humidity ratio was reduced by 0.0042kgw/kgda equivalent to 11.1% relative humidity reduction. The experimental results were also compared with models in literature.
... Many studies have been done since the earlier days of absorption chillers when Mouchot produced Ice cubes utilizing the solar thermal energy in 1878 ,Trombe and Fox (Alizadeh and Khouzam, 2005) reported a successful test for a lab experimental to operate an absorption chillers with solar thermal powered, followed by many researchers, e.g. Nakahara (Alizadeh and Saman, 2002b), now days many researches cover the different aspects of the different solar refrigeration technologies, these studies can be significant in decision making in the first stage of Solar cooling system choosing process. The comparing between different technologies should be base on the terms of performance and cost, the performance evaluation of solar cooling technology is based on the efficiency of the solar collectors, the coefficient of performance for the cooling technology (e.g., absorption chillers, evaporative cooler with desiccant wheel, conventional Vapour compression, etc.), also the efficiencies of other system components like the energy storage systems (thermal tank, batteries, etc.) and engine (e.g. ...
The air conditioning sector demand for energy has increased incessantly in Australia in the past few years due to global warming and the increase of life standards. This added more loads on the electricity demand and a significant increase in peak demand due to the use of conventional air conditioning systems, in addition to the environmental impact of energy producing from fossil fuels. Nevertheless, to minimise the environmental impact associated with air conditioning/ refrigeration system operation it is logical to evaluate the alternative options for energy sources and/or refrigerant systems. The solar assisted air conditioning /refrigeration system is presented as an attractive substance utilise the free, clean and sustainable solar energy. In this study, an overview of the different solar assisted air conditioning technologies available and their applications with a brief literature of the current related research and study in Australia, the review cover the solar thermal assisted cooling system (Absorption, Adsorption, Ejector systems, Desiccant cooling, thermo-mechanical) and the Solar electric cooling technology. From the study, the Solar cooling system applied Absorption chillers present as the most promising technology available.
... An analytical procedure for calculating the mass of water evaporated from the weak solution in the regenerator in terms of climatic conditions and solution properties at the regenerator inlet has been developed by Kakabayev and Khandurdyev [6]. Different regenerator designs have been examined and a variety of theoretical models have been employed to analyze the regeneration process [12][13][14][15][16][17]. ...
In the present work, a rotating tilted wick, which is made of a double layer cotton-cloth, has been used as a desiccant regenerator. Calcium chloride solution is applied as the working desiccant. The wick surface, which is impregnated with the desiccant solution, moves between two rotating pulleys at an inclination angle of 20 degrees. The regenerated solution carried by the wick returns to the solution tank at the end of a complete cycle. Desiccant solution concentration in the tank is evaluated and recorded with time. Instantaneous as well as average values of the mass transfer coefficient are evaluated from the experimental measurements. Mathematical model, which can be applied for the prediction of solar radiation intensity and analysis of the proposed system, is developed. Model validation shows a good agreement between measured and predicted values of radiation. Apparent values of system coefficient of performance around 2 could be attained in the dry climate of Taif city. Finally, system operational problems are discussed and highlighted.
With the recent development of the independent control of temperature and humidity, the demand for dehumidification has significantly increased, and liquid desiccant dehumidification systems have attracted considerable attention because of a high dehumidification efficiency. This study presents a new design for a liquid desiccant dehumidification system that applies a membrane-assisted dual sump for maintenance the solution concentration with a low solution cooling and heating loads. A detailed heat and mass transfer analysis was conducted to evaluate the feasibility of the membrane for the maintenance the solution concentration according to the mass transfer resistance of the membranes. Moreover, the variation in the solution temperature and concentration was predicted by performing detailed simulations. The simulation results indicated that the low-mass-transfer-resistance membrane requires a large amount of solution load and the high-mass-transfer-resistance membrane cannot be used to maintain the solution concentration. Thus, the mid-mass-transfer-resistance (i.e., 15,000 s/m) membrane is suitable for the liquid desiccant dehumidification system. Compared with the conventional liquid desiccant dehumidification system based on a solution exchange, the membrane-assisted liquid desiccant dehumidification system could save about 19% load for solution cooling and heating owing to the lower heat and mass transfer rate on the absorber and regenerator sump.
In this paper, a self-preheated solar collector/regenerator (C/R) is proposed to conquer the anti-regeneration phenomenon of traditional solar C/R in order to increase its regeneration efficiency. Through numerical simulation, the applicability of the self-preheated C/R in Northern and Southern cities of China and parameter optimization as well as the performance comparisons with the traditional C/R are conducted. The research results show the self-preheated C/R has good applicability for the 24 cities chosen in China, but the length of collector section is selected in the optimum ranges. The optimal proportion of collector length in the southern China is in the range of 0.4–0.55 while it focusing on 0.35–0.5 in the northern China. In the optimization of parameters, the best flow-rates of air and solution for the unit area of C/R fall into the ranges of 50–100 kg/(m²·h) and 3–6 kg/(m²·h) respectively, and the height of C/R glazing should be maintained at 0.04–0.06 m for higher regeneration efficiency of the device. By comparing to the performance of traditional C/R, the self-preheated solar C/R has greater superiority at higher ambient relative humidity, lower solution temperature and higher solution concentration as well as lower solar radiation intensity. The increased extent can reach as much as 22% at ξin = 0.4 kg/kg. The total length of self-preheated C/R has an optimal value on the performance of device. All these results can provide guidance for performance analysis and application of the novel solar collector/regenerator.
The large electricity consumption due to the extensive use of vapour compression machines in the air conditioning and industrial sectors dramatically increases the emissions of greenhouse gases. Besides, the synthetic halocarbon refrigerants used in said machines are responsible for ozone depletion. These environmental concerns give an opportunity to solar thermally-driven liquid sorption systems, whose energy consumption primarily lies on the regeneration heat of liquid sorbents. This paper surveys both theoretical and experimental studies on solar thermal regeneration methods of the hygroscopic solutions used in liquid sorption systems. A brief review of some conventional and alternative liquid desiccants utilised in said systems is firstly presented. Furthermore, information about several configurations of regenerators and their performance is covered in detail, putting special emphasis on solar collector/regenerators, which use directly solar energy to reconcentrate the weak desiccant solution. A comparative assessment of relevant thermophysical properties of some hygroscopic liquids is realised in order to determine their suitability for use in sorption systems. The results show that the aqueous solutions of potassium formate and ionic liquids are very promising desiccants due to their low vapour pressures, specific heat capacities and dynamic viscosities, as well as their non-corrosiveness. A performance comparison between typical regeneration units and solar collector/regenerators is also carried out. It could be shown that solar collector/regenerators have a high potential for enhancing the water desorption rate from a diluted desiccant solution and, consequently, the capacity of the air dehumidification process within the absorber.
This study deals about the investigation of a solar powered desiccant dehumidification system coupled with Variable Frequency Drive (VFD). The proposed design of the system consists of two evaporative air coolers. One cooler performs as an absorber and the other one as desiccant regenerator coupled with solar water heater.The Variable Frequency Drive is connected with the first evaporative air cooler. In this work, using solar energy Zeolite is regenerated as part of the investigation. Regeneration cycle for Hot water .Absorption is explained and analyzed. A simple expression for the cycle is proposed. System efficiency is derived with consideration of flow of work and heat to and from the system. The operating concentration of desiccant used greatly affected regeneration temperature limits and mass of strong solution for unit mass of vapor produced.
Application of the open cycle solar collectors/regenerators (C/R) is an effective way to utilize low-grade solar thermal energy to concentrate desiccant solution for air-conditioning. This paper aims at developing an analytical model for the coupled heat and mass transfer process inside an open cycle solar C/R. Within narrow range of operating conditions, linear approximations were made to find the dependence of equilibrium humidity ratio on the solution temperature, constant properties and coefficients. New parameters, which represent the heat and mass transfer driving forces, were defined and the basic differential equations were rearranged to obtain two coupled non-homogeneous linear equations. The effects of the climate conditions were organized as non-homogenous parts, which allow direct evaluation. The analytical expressions for water evaporative rate and outlet conditions of the desiccant solution and scavenge air were further developed based on the analytical solution. A parametric analysis of the solar C/R has been performed to reveal the effects of climate conditions and system variables on the rate of evaporation of water from the solution. The ratio of the solution to the air mass flow rate was also found to be an important controlling parameter. Based on the simulation results, the possible optimization methods for the solar C/R and operating variables were also discussed. 1979
A regenerator is one of the main components of a solar liquid desiccant cooling system. The regenerator used in this application is a forced counter flow type solar collector/regenerator(C/R). Experimental results of the tests indicate that there occurs a maximum value for regeneration efficiency at some air flow-rate. The regeneration efficiency of solution at ambient temperature decreases with the increase in solution flow-rate, instead of increasing at moderate temperature. The inlet temperature of solution has great influence on the regeneration efficiency and a higher concentration of solution is accompanied by a lower efficiency of regeneration. Compared with the regeneration efficiency at Ya,in = 20 g/kg, the regeneration efficiency was increased by about 40% at Ya,in = 10 g/kg. Higher solar radiation intensity will better regeneration performance of the C/R. Air flow-rate has far more effect on heat and mass coefficients between air and solution than solution flow-rate. The solution inlet temperature and salt concentration have contrary effects on heat and mass transfer coefficients with increase in their values. By Simpson numerical integration, two correlations on heat and mass transfer characteristics were given. Finally, it was concluded that the proposed solar collector/regenerator performs satisfactorily in humid climates of the Southern China.
In the present work, novel configuration of solar powered desiccant dehumidification system is investigated. The proposed system comprises two evaporative air coolers. One of the two coolers functions as an absorber and the second, which is coupled with solar water heater, functions as a desiccant regenerator. In the experimental part of this investigation, Calcium Chloride is regenerated using solar energy. Hot water from a solar collector is circulated through an air heater to regenerate the liquid desiccant. Mathematical model, which can be applied for analysis of the proposed system, is developed. Absorption-regeneration cycle for the do humidifier is described and analyzed. An expression for the efficiency of the simple cycle is introduced. Theoretical analysis shows that strong and weak solution concentration limits play a decisive role in the value of cycle efficiency. System efficiency with consideration of heat and work added to the system is well defined. The limits of regeneration temperature and mass of strong solution per kg of produced vapor are found highly dependent on the operating concentration of desiccant. Experimental results show that solution with 30% concentration can be regenerated up to 50% using solar energy. Good agreement is found between the trained data of the ANN model and the experimental measurements for the whole range of the air inlet temperature.
The study history and actualities of solar liquid desiccant cooling systems are introduced systematically. A new solar air pretreatment collector/regenerator flow is put forward. Through theoretical calculation it is found that the solution concentration difference between outlet and inlet of the air pretreatment collector/regenerator increases 90% and the storage capacity increases 50% comparing with the traditional C/R (collector/regenerator). In theory the crafts are constructed on the compound air conditioning system including solar liquid desiccant and radiation cooling and the expressions of mass transfer coefficient on the packed bed dehumidifier and regenerator are gained by experiments. Through thermodynamics analysis, the expressions of theoretical regeneration efficiency and coefficient of performance (COP) are found. When the solution concentration is low, theoretical regeneration efficiency may be larger than 1.0 and when the temperature of heat source rises from 60 to 100°C, COP augments 1.0 with the surrounding temperature of 35°C.
The numerical simulation method was adopted to study the steady performance of solar air pretreatment liquid regenerator. The results show that as effective solution proportion ESP decrease, the solution outlet concentration Cout, regeneration efficiency ηz and storage capacity SC are all improved in a large extent. With lower solution mass flow rate and higher solution inlet concentration in the regenerator, the decrease of effective solution proportion ESP will raise the evap-oration rate G remarkably. With the effect of air mass flow rate on regeneration, except the blind and decrease areas, the decrease of effective solution proportion ESP will also improve the regeneration performance notably. All these show that the air pretreatment liquid regeneration equipment possesses huge potential of improving solution regeneration performance.
Solar liquid collector/regenerator combines solar photothermic transformation and liquid regeneration, effectively achieving liquid regeneration for solar energy-driven liquid desiccant cooling systems. In this paper a group of dimensionless heat and mass transfer equations describing the heat and mass transfer processes in the solar liquid C/R can be obtained by defining total temperature difference (ΔT0) and dimensionless heat loss coefficient (h̄z) and validated by comparing with the related experimental data. Through the analysis of effect of inlet parameters of air and solution on the regeneration performance, it was found that when the air inlet temperature rose by 12°C and humidity ratio decreased by 12 g·kg-1, the increment of outlet concentration of solution increased by above 30% and 70% respectively and when the solution inlet temperature rose by 30°C, the increment of outlet concentration of solution raise increased by above 160%. From the effect of four kinds of variable groups, the increase of number of heat transfer units (NTU), flow rate ratio, total temperature difference ΔT0 and Lewis factor Le could promote the regeneration of solution. Compared to the parallel-current regeneration, the increment of solution concentration in the counter-current regeneration case could increase by about 10%.
A countercurrent solar solution collector/regenerator (C/R) with experiment platform the size of 1 m(wide)×2 m(long)×0.35 m(high) was used for analyzing the factors influencing regeneration efficiency of solar C/R. It is found that there is an obvious two-stage distribution for regenerating solution at normal temperature. The regeneration efficiency of solution increases first and then decreases with the increase of air mass flow rates and there exists a maximum value. The regeneration efficiency always decreases with the increase of solution flow rates. Heating solution leads to an increase of integrated regeneration efficiency; however, heating regeneration air decreases the integrated regeneration efficiency. The regeneration efficiency is decreased by 0.16 by using humid air of 20 g/kg instead of using humid air of 10 g/kg. The regeneration efficiency increases correspondingly with the increase of the solar radiation intensity. The countercurrent solar solution C/R can operate better in dry air and high solar radiation conditions and a suitable air flow-rate should be selected to achieve better performance.
Definition of the Subject and Its ImportanceCooling is needed for two main fields of application. On the one hand, it is needed in buildings and other closed spaces, for example, vehicles, which are occupied by human beings. Cooling assures that occupants feel comfortable. On the other hand, in industrial and commercial applications, cooling is needed to cool commodities or processes. In a wider sense, cooling in buildings refers to both control of temperature and control of humidity. In the following, it is referred to as air-conditioning. Cooling of commodities or processes is referred to as refrigeration. Cooling in a thermodynamic sense means to withdraw heat. Any heat flux is always directed from a source of high temperature to a sink of lower temperature. Unless a natural heat sink is available – such as the ground or outside air – a thermodynamic cycle has to be employed in order to provide a low-tem ...
Solar liquid collector/regenerator (C/R), combining the functions of solar collector and regenerator of absorbent solution together, can be effectively utilized in solar energy-driven liquid desiccant cooling systems. Based on thermal balance of the glazing of solar C/R, a group of modified heat and mass transfer models, validated by experimental results to reflect solution regeneration process more truly, were put forward in this paper. Numerical simulation showed only preheating air stream, keeping an equal humidity ratio, did raise the performance of solar C/R, but preheating solution increased the regeneration efficiencies to reach twice that of preheating air stream. There occurred optimum mass flow rates for both air stream and solution film reaching 36-48 kg m(-1) h(-1) and 4-6 kg m(-1) h(-1) respectively for solar C/Rs of 3 similar to 6 m long. As for effect of the length of solar C/Rs, the regeneration efficiency eta(x) reached a maximum value at about 4 m and shorter or longer solar C/Rs failed to increase solution regeneration efficiencies.
Liquid desiccant dehumidification technology is becoming increasingly attractive due to its high efficient utilization of low-grade heat and its effectiveness in dehumidification. Using this technology, energy-efficient air conditioning systems have been developed, which demonstrated superiority over the traditional vapor compression type system by allowing both temperature and humidity to be controlled independently. This paper presented a state-of-the-art review of the research and development in this field, covering the topics of heat and mass transfer models, performance evaluation of liquid desiccant dehumidification and regeneration, and technology development of dehumidifiers and regenerators as the most important components of liquid desiccant systems. Meanwhile, many detailed systems using solar energy in desiccant cooling was reported, and some new applications of liquid desiccant dehumidification were also introduced.
Experiments and theoretical modelling have been carried out to predict the performance of a solar-powered liquid desiccant cooling system for greenhouses. We have tested two components of the system in the laboratory using MgCl2 desiccant: (i) a regenerator which was tested under a solar simulator and (ii) a desiccator which was installed in a test duct. Theoretical models have been developed for both regenerator and desiccator and gave good agreement with the experiments. The verified computer model is used to predict the performance of the whole system during the hot summer months in Mumbai, Chittagong, Muscat, Messina and Havana. Taking examples of temperate, sub-tropical, tropical and heat-tolerant tropical crops (lettuce, soya bean, tomato and cucumber respectively) we estimate the extensions in growing seasons enabled by the system. Compared to conventional evaporative cooling, the desiccant system lowers average daily maximum temperatures in the hot season by 5.5–7.5 °C, sufficient to maintain viable growing conditions for lettuce throughout the year. In the case of tomato, cucumber and soya bean the system enables optimal cultivation through most summer months. It is concluded that the concept is technically viable and deserves testing by means of a pilot installation at an appropriate location.
Solar liquid collector/regenerator combines solar photothermic transformation and liquid regeneration together for solar energy-driven liquid desiccant cooling systems. A group of dimensionless heat and mass transfer equations describing the heat and mass transfer process in the solar C/R(Collector/Regenerator) were obtained by introducing total temperature difference (ΔT0) and dimensionless heat loss coefficient (h¯z). The increment of solution concentration ΔC was increased 2.9–3.5%/°C and 5.3%/°C for increasing unit inlet temperature of air stream and solution respectively and increased about 6.2%/(g/kg) and 0.9%/(g/kg) for decreasing unit inlet humidity ratio of air and solution concentration. Besides, the increasing number of heat transfer units (NTU), air-to-salt mass flow rate ratio (ASMR) and total temperature difference (ΔT0) can increase the performance of solution regeneration significantly. Compared to parallel flow regeneration, the performance of counterflow regeneration was increased about 10%.
A two-stage collector/regenerator (C/R) for the solar liquid desiccant air conditioning system is presented, which adopts a fin-forming absorber plate and where the liquid desiccant flowing process is divided by an isolation board into two stages: regenerating stage I and regenerating stage II. Then a heat and mass transfer mathematical model is established to predict the performance of the two-stage C/R by using calcium chloride as the desiccant. The main results are as follows: (i) The fin-forming absorber plate can increase heat and mass transfer areas and promote turbulence, so that it significantly enhances heat and mass transfer between solution stream and air stream; (ii) Compared with the traditional C/R, a 10 to 25 percent increase in the water evaporation rate for the two-stage C/R can be achieved under the same operating condition.
Theoretical and experimental investigation on the application of flat plate solar water heater coupled with air humidifier for regeneration of liquid desiccant has been presented in this work. The heated water from the storage tank of the solar heating system is circulated in a finned tube air heater. Hot air from the air heater is blown through a packing of a honeycomb type for the purpose of regeneration of calcium chloride (CaCl2) solution. An experimental system has been designed and installed for this purpose. The system comprises a solar water heater with a storage tank connected to an air/water heat exchanger. Hot air from the heat exchanger is blown to the air humidifier, which functions in this study as a regenerator. Calcium chloride solution is applied as the working desiccant in this study. Solution concentration is determined at the end of regeneration process and the mass of evaporated water is evaluated. It is observed that the heating temperature varies, at day time, in a range of about 5 °C. This limited variation in hot water temperature demonstrates the importance of the storage tank to attain a nearly steady state operation of the system. Experimental results show that solution with 30% concentration can be regenerated up to 50% using solar energy. In the theoretical part of this study, a multiple-layer artificial neural network (ANN) model has been applied to study the performance of a solar liquid-desiccant dehumidification/regeneration system when calcium chloride solution is applied as the working desiccant. The experimental results of the present study are used to construct and test the ANN model. Then the model has been utilized to describe and analyze the effect of the inlet conditions of air on the regeneration process. Good agreement between the outputs from the ANN model and the corresponding results from the experimental data has been found. The proposed model can work well as a predictive tool to complement the experiments.
In open cycle liquid desiccant air conditioning, the solar collector regenerator is one of the effective ways of regenerating liquid solution. In this work, the regeneration of liquid solution using cross flow of air stream with flowing film of desiccant on the surface of a solar collector/regenerator has been investigated. To evaluate the effect of cross flow of air stream on the performance of the unit, two identical units are constructed and tested in the same conditions of operation. One of the two units was augmented with air blower. The absorber plate is a black cloth layer. The forced air stream, which flows across the absorber removes the moisture from the liquid solution. The regeneration in the other collector/regenerator unit is free. The results show enhancement of regeneration efficiency for the forced cross flow compared with the free regeneration. The effect of concentration and flow rate on the performance is discussed. Two relations for regeneration efficiency as a function of concentration for the two units are introduced.
A solar liquid regenerator that embodies energy saving effect is a key part in solar liquid cooling air-conditioning system. Solar air pretreatment liquid collector/regenerator as a novel solar C/R (collector/regenerator) can achieve liquid regeneration in lower temperature, which is suitable to be employed in the high humidity area. The heat and mass transfer process was simulated in the novel liquid regenerator and the conclusions show that the increment of solution outlet concentration increases 70%, regeneration efficiency ηz augments 45.7% and storage capacity SC increases 44% as effective solution proportion ESP falls from 100% to 62%. For higher solution outlet concentration needed in the dehumidifier, both lower solution mass flow rate and higher solution inlet concentration all can be adopted in the novel C/R, in which the decrease of effective solution proportion ESP can increase the rate of evaporation G significantly. Along with the augment of air mass flow rate, the rate of evaporation G rises fast firstly and then falls slowly. The simulated results show that there is huge potential of improving and regulating solution regeneration performance by employing the novel C/R.
Two solar collector / regenerators of the air circulation type have been designed, constructed and tested. Two new features are incorporated in a falling film type generator, in one of the designs. They are the use of atomizers to spray the solution and inclusion of wire meshes to increase the wetted area. The second model, which is of a basic falling film type, was used for comparsion purposes. The two models were tested side by side under Baghdad summer conditions. In addition to specifying the effects of the various operating parameters, the regeneration and collection efficiencies for both models are compared.
Preliminary results are presented from an analysis of the forced flow solar regenerator used for regenerating weak absorbent solutions, whose thermal performance depends on the rate of evaporation of water from the weak solution. A simple expression is derived to determine the desorption rate of water, assuming that solution temperature, concentration, and vapor pressure are constant at the arithmetic average of these values at the start and end of the regenerator. It is found that the effect of preheating the solution, or air, increases the rate of desorption due to the mass transfer potential increase, although solution regeneration is more effective while preheating the air than while preheating the solution.
An open cycle absorption refrigeration system is simulated and analyzed. The open cycle differs from the closed cycle in that the open cycle regenerates the weak absorbent solution by evaporating refrigerant to the earth's atmosphere rather than to a condenser. The solar collector used for the open cycle is one in which the weak absorbent solution flows as a fluid film over a flat, open, black surface. The absorbent solution is heated by the black surface and is regenerated by water evaporating to the atmosphere. It was found that the relationship between the collector length and the solution mass flow rate was tied to environmental factors such as wind and humidity when optimizing system performance. The system performance was simulated for five cities using actual weather data. The overall daily cooling COP's (cooling/incident solar) ranged from 0.09 to 0.45 for various conditions.
Refrigeration capacity of an absorption solar refrigeration plant with flat glazed solution regenerator
- Kakabayev
A large scale solar air conditioning pilot plant and its test results
- Kakabayev
Absorption solar regeneration unit with open regeneration of solution
- Kakabayev