Vapour Absorption System Research Articles

Performance comparison of solar-driven single and double-effect LiBr-water vapor absorption system based cold storage

The solar-assisted vapor absorption system provides a promising alternative to the vapor compression system for cold storage applications. In the present work, a comparative performance assessment of a single-effect and a double-effect vapor absorption system has been carried out for the operation of a cold storage facility. The proposed cold storage is powered through a combination of a grid-interactive solar photovoltaic system and parabolic trough collectors. A thermal model of the VAR systems is developed based on the first law and the second law of thermodynamics. An economic model has also been developed to compute the payback period. The maximum coefficient of performance of the double-effect VAR system (for the present case) for a calendar year is found to be 1.32, which is about 80% higher than that of the corresponding single-effect system. Also, the exergy efficiency of the double-effect VAR system is estimated to be about 16% higher than that of the single-effect system. The payback period of the double-effect VAR system-based multi-commodity cold storage powered through the solar thermal-PV system is found to be about six months lesser than the corresponding single-effect system. Thus, the double-effect VAR system is a more feasible option to operate a cold storage facility from the energy, exergy, and the economic point of view.

Experimental heat and mass transfer studies on horizontal falling film absorber using water-lithium bromide

Vapour absorption systems are more viable technology option in energy and environmental perspective in cooling and heating applications. Among the four major components of vapour absorption system, the absorber plays a vital role in deciding the performance, size and cost. Horizontal falling film absorbers comparatively contain good heat and mass transfer characteristics than other type of absorbers for working fluids such as water-lithium bromide. Literature shows that experimental approach of performance evaluation of absorber is more realistic and accurate than the theoretical approach. Hence in the present work, a detail experimental study has been done on horizontal tube falling film absorber using water-lithium bromide as a working fluid. The set-up consists of two major components viz. absorber and generator. Absorber contains three columns of tubes, with eight rows in each column. Detailed parametric study has been done by considering influence of spray density, cooling water-flow rate, cooling water temperature and concentration on solution temperatures, cooling water temperatures, inlet and outlet concentrations, heat flux, mass flux, heat transfer coefficient, and mass transfer coefficient with the help of plots. Results have been validated and literature gaps have been discussed.

Feasibility studies on alternative aqueous salt mixture in vapour absorption cooling

Current years, the research is based on renewable energy resources, especially solar-based applications, due to its promising energy resource. Vapour absorption refrigeration system widely accepted as an environmentally friendly, prospective innovation for the economic and efficient use of solar heat for refrigeration purposes. The extensive search for coolant-absorbing varieties is underway that can be made to operate at a solar energy temperature range. However, Thermodynamic analysis shall check the compatibility of a coolant-absorbing mixture for a particular operation. Detailed thermodynamic analysis of H2O-(LiBr + LiI + LiNO3 + LiCl) cooling systems with a single-effect and a capacity of one ton is carried out in the current work. It also established the sustainability of systems for solar and air-cooled applications. A thermodynamic evaluation was conducted based on all aspects of the device that are conserved in mass, concentration, and energy. The impacts on output parameters of the working variables are explored through performance plots. Possible temperature variations are defined for optimum system operation. Generator temperature range represents the suitability of the system for solar thermal applications. Absorber/ Condenser temperature range shows the suitability of the system for air-cooled applications to carry away rejected heat. It shows the possibility of reduction in size and cost of the system. It has been found that H2O-(LiBr + LiI + LiNO3 + LiCl) COP is nearly 9% more than the H2O-LiBr system in every operating temperature. The alternative salt mixture is best adapted for solar and air-cooled vapour absorption systems with higher COPs.

Comparative Study of Improvements in Multiple Effect Vapor Absorption Systems using Loop Heat Pipes

Comparative Study of Improvements in Multiple Effect Vapor Absorption Systems using Loop Heat Pipes

A state of the art on solar-powered vapor absorption cooling systems integrated with thermal energy storage.

The intermittent nature of solar energy is a dominant factor in exploring well-designed thermal energy storages for consistent operation of solar thermal-powered vapor absorption systems. Thermal energy storage acts as a buffer and moderator between solar thermal collectors and generators of absorption chillers and significantly improves the system performance. Vapor absorption chillers are available in half, single, double, and triple-effect modes of operation and operate at temperatures ranging from 75 to 220°C to produce a cooling effect with COPs ranging from 0.3 to 1.8. Thus, the selection of appropriate solar collectors and thermal energy storages are two significant decisions affecting the consistency of output of a vapor absorption refrigeration system. The present review of state of the art is focused on the appropriate selection, from among different types of solar collectors available to meet the demand of capacity and degree of thermal energy required in operating absorption chillers at optimum performance. Characteristics of various thermal energy storage systems and their integration with solar thermal collectors and absorption chillers are also investigated to meet the demand for heat during non-sunshine hours or periods of low solar intensity. In the latter section, economic feasibility is explored so that a sustainable solar cooling system can be proposed which can work consistently with the best performance throughout its entire life.

Simulation of Lithium Bromide- Water (LiBr-H2O) Vapor Absorption System (VAS) powered by Solar Flat Plate Collector (SFPC)

Solar energy may probably prove to be best option for future in air conditioning system. With growing need of energy consumption, the solar air conditioning system stands as a useful alternative. The objective of this work is to simulate a single effect LiBr-H2O absorption system, coupled with solar flat plate collector (SFPC), to supply heat to the generator of Vapor Absorption System (VAS). Case studies have been taken from India, particularly New Delhi and Mumbai, which are, respectively, known for their hot and humid climate. The influence of different parameters like inlet generator temperature, heat supplied to the generator and cooling load have been investigated. The design day of 15th of April, May and June has been considered. The thermodynamic analyses have also been carried out. An outlet solar collector temperature between 68°C and 78°C was maintained for New Delhi, whereas between 67°C and 79°C for Mumbai. The maximum efficiency of SFPC was found to be 50 percent and 51 percent in case of New Delhi and Mumbai, respectively, on 15th April and 15th of May. A coefficient of performance of 0.857 was obtained at 4.1033 kWof heat supplied to the generator, at an inlet generator temperature of 68°C and cooling load of 3.5167 kW. It was observed that at constant ??????, any increase in supply heat, increases the flow rate of vapor and cooling load. Furthermore, the analysis for various stages of single effect LiBr-H2O (VAS) is presented including the design of the evaporator, absorber, condenser, heat exchanger and generator.

Design Analysis and Fabrication of Solar Vapour Absorption

Solar energy is one of the greenest sources of electricity and the idea of using it to power transportation is not new. In this work, parabolic dish is used to collect the solar irradiation, instead of Photo voltaic cells (PVC). This radiation is focused on to a point, where the water is heated to the required temperature and this heat energy is transferred to vapour absorption unit through the heat exchanger. In vapour absorption system (Three fluid systems) consists of a combination of three fluids ammonia and water and hydrogen. These fluids complete the vapour absorption cycle and provide the sufficient cooling. The experiments are conducted on the Solar Vapour absorption unit from 9:00A.M to 5:00P.M. For two days. Temperature readings of generator, Evaporator are taken on an hourly basis and C.O.P of the system at the minimum evaporator temperature is calculated. The system had attained a minimum evaporator temperature of 23⁰C at its peak generator temperature of 92⁰C.

Performance analysis of PTC field based ejector organic Rankine cycle integrated with a triple pressure level vapor absorption system (EORTPAS)

The Proposed system consists of an ejector organic Rankine cycle (EORC) integrated with a triple pressure level absorption system (TPAS) based on parabolic trough collector (PTC) solar field. This system produces power and refrigeration output at two different temperatures simultaneously. A thermodynamic analysis is conducted to discover the effect of various design parameters such as solar beam radiation (SBR), turbine inlet pressure (TIP), turbine extraction pressure (TEP), and ejector evaporator temperature (EET) on the performance of the proposed system (EORTPAS). It is found that with the addition of TPAS in EORC, the energy efficiency of EORTPAS increases considerably but exergy efficiency decreases. It has also been observed that energy efficiency increases with the increase in TIP, TEP and, EET while decreases with the increase in SBR for both the systems. On the other hand, the exergy efficiency of both the systems increases with increase in SBR or TIP and with the decrease in TEP. It is also noticed that there is a slight decrease in exergy efficiency of both the systems with the increase in EET.

An Assessment of Biofuel Potential in Fulfilling the Energy Requirements of Cold Storage in India

Every year in India, approximately 18% of fruits and vegetables are wasted due to the absence of post-harvest storage infrastructure. The UN’s Food and Agriculture Organization (FAO) found that 40 per cent of India’s fresh fruits and vegetables worth an annual $8.3 billion perish before reaching consumers. This is despite the fact that India is the second largest producer of fruits and vegetables, producing around 83 million tonnes of fruits and 121 million tonnes of vegetables annually. In order to overcome the above losses, effective post-harvest storage infrastructure is required. Since cold storage is a power gulping monster and in order to develop the infrastructure for the same, large electric requirements needs to be addressed. It can be met by the conventional electricity production, but it will further increase our dependence on crude oil imports and it will have an impact on environment. In order to solve the above scenario two different sustainable approach are proposed. One of the approach is of integrated vapour absorption system driven by biofuel based combustion chamber. Second approach is to run vapour absorption system on the waste heat rejected by the internal combustion (IC) engines powered by biofuels. Coefficient of performance (COP) based analysis has been done to determine the yearly requirements of different biofuels for meeting this requirements. Biofuel used in the study are biogas, ethanol and biodiesel. On the basis of result obtained biodiesel is proposed for first system and biogas & ethanol is proposed for second system.

Performance analysis of alternative HVAC systems incorporating renewable energies in sub-tropical climates

Over the past 40 years, energy consumption has increased dramatically to become a significant crisis faced today. The peak demand is growing at approximately 50% greater than the demand base growth in many Australian cities, which, in turn, requires greater finite resources and infrastructure to meet the required generation capacity needed. Currently, approximately 40% of electrical energy is consumed by HVAC systems in commercial building. This level of energy consumption emphasizes the necessity of developing an eco-friendly air-conditioning system, where possible, harnessing low-grade thermal energy such as solar energy rather than electricity. In this paper, a comparison of energy performances of three different HVAC is undertaken. Mathematical models are developed with TRNSYS17 to simulate the HVAC system within a typical small commercial building with various cooling options. The model is implemented to provide a comparative analysis across various cooling systems such as Vapour Compression System, Vapour Absorption System and Desiccant Evaporative Cooling System. This paper implements the developed model to investigate and compare the energy consumption and running costs over an eight-month cooling period of the widely used Vapour Compression System against alternative solar assisted cooling options for a sub-tropical location of Brisbane, Australia.

Experimental analysis of triple fluid vapour absorption refrigeration system driven by electrical energy and engine waste heat

In this study, performance analysis of absorption refrigeration cycle has been carried out under variable power sources namely electrical and thermal energy sources. The triple fluid vapour absorption system was used in this work. The temperatures at each point in the cycle such as generator, absorber, evaporator and condenser have been measured. The coefficient of performance of the system was calculated and then compared. The results showed that when the cycle driven by electricity, the coefficient of performance varied from 0.28-1.6 along the test time and the generator temperature changed from 66?C to 106?C. When thermal energy used to generate power, the coefficient of performance varied between 0.16 and 0.6 under the generator temperature of 98?C and 150?C. It was observed that the waste heat energy from engine exhaust can be used efficiently and can replace the conventional power source to drive the absorption refrigeration unit.

Experimental Analysis of Vapour Absorption Generator integrated with Thermal Energy Storage system

Abstract A vapour absorption Air-conditioning system can run replacing the compressor by a pump, absorber and a generator. The generator can be operated by the low thermal energy like solar, exhaust heat of IC engines etc. But all the period this heat energy will not be available. In this present research the generator part alone considered for experiment. A new model of generator heater is designed and fabricated. The heat transfer capacity and the thermal energy charging and discharging were calculated for analysis. The suitable capacity of generator is integrated with Phase change material is designed to operate a vapour absorption system in the capacity of 3.5 KW. The generator design is modified for Phase change material containment. The average temperature of the heat energy available will be around 60°C to 80°C. In this temperature range suitable Phase change material is selected for thermal energy storage tank. The experiment is conducted on this storage tank for thermal energy charging and discharging by varying the material composition.

Exergy analysis of single to triple effect lithium bromide-water vapour absorption cycles and optimization of the operating parameters

This paper deals with a review on exergy analyses of lithium bromide-water based single to triple effect direct and indirect fired vapour absorption systems. The analysis carried out by various investigators on exergy of the absorption cycles have been discussed. To fill the gap in the knowledge on exergy destruction rate in the absorption system, optimization of the single to triple effect direct and indirect fired absorption cycles have been conducted for a wide range of operating conditions. Hence optimum parameters in various components of the systems for maximum exergy coefficient of performance and minimum exergy destruction rate have been determined. The indirect fired systems have been optimized for different temperatures of the energy source related to the main generator temperature. While the direct fired systems have been optimized considering exergy destruction rate during the combustion process of energy sources. The energy sources selected in the present analysis are compressed natural gas and liquefied petroleum gas. Double effect cycle yields better exergy performance when the difference in temperatures of the energy source and the generator is between 6 to 37 °C, while triple effect cycle performs well when it is beyond 37 °C.

Investigation of a microchannel heat and mass exchanger for absorption systems

An investigation of a microchannel heat and mass exchanger for vapor absorption systems is presented. A sheet with 88 microchannels of depth 0.5 mm and width 0.76 mm is investigated via visual and thermal measurements. The flow in the microchannels is predominantly in the slug-flow regime, with distinct vapor and liquid regions. High rates of heat transfer were observed in the absorber. However, poor liquid mass transfer rates limit the performance of the microchannel absorber. The performance of the microchannel absorber is compared with that of an absorber with serpentine microscale passages containing micro-pin fins. A physics-based model for the absorption of ammonia into a dilute solution of ammonia-water in a microchannel absorber with mixing sections is developed using insights from flow visualization. The model is validated by comparing its predictions with the data. The potential of surfactants to enhance absorber performance is also investigated.

A data driven control strategy for optimal and flexible operation of absorption systems

A novel control strategy for vapor absorption systems with experimental validation is presented. Statistical methods are used to integrate a detailed thermodynamic model and system-specific characteristics into a model based control algorithm. This allows for continuously optimized operation as well as fast response to variations in operating conditions. Autonomous controller performance was tested experimentally for response to changes in heat sink and evaporator temperatures. Continuous turndown with fast response to capacity demand changes, in contrast to suboptimal on/off control, was demonstrated. The thermal compressor concept was employed to develop the variable speed thermal compressor module, with aspects specific to absorption heat pumps, also facilitating cross-applicability of vapor compression system control strategies. The results of this study enable further development and optimization of absorption systems for a wide range of applications.

Investigation of a serpentine micro-pin fin heat and mass exchanger for absorption systems

An investigation of a heat and mass exchanger with micro-pin fins in serpentine passages for vapor absorption systems is presented. A serpentine micro-pin fin absorber sheet with a pin fin diameter of 350 µm and height of 406 µm is used. Visualization of the two-phase mixture flowing through the micro-feature component, and an investigation of the heat and mass transfer mechanisms over a range of temperatures, pressures, concentrations and flow rates are conducted. A model for the absorption of ammonia into a dilute ammonia-water solution in the geometry is developed based on insights from flow visualization results, and validated by comparing its predictions with heat transfer measurements. A computational fluid dynamics study of flow through the serpentine micro-pin fin passages is also used for additional insights. Liquid-phase mass transfer resistance is found to be the bottleneck to improved rates of vapor absorption in these absorbers.

Thermal comparison and multi-objective optimization of single-stage aqua-ammonia absorption cooling system powered by different solar collectors

This paper presents the comprehensive thermodynamic modelling to compare the performance and optimization of single-stage NH3–H2O-type absorption cooling system integrated with different solar collector types for the city of Mehsana, India. A 20-kW system at 0 °C is analysed which includes four different solar collectors flat-plate collectors, parabolic-trough collectors (PTC), flat plate with compound parabolic collector reflectors and evacuated-tube collectors (ETC) attached with insulated thermal storage tank to power the NH3–H2O vapour absorption system. The study investigated the effect of heat source temperature on performance aspects of systems. The examined performance parameters are exergetic efficiency, coefficient of performance and area of collector. Exergetic optimization of each system estimated the optimum collecting area requirement for cooling. Differentiation between optimized systems determined that the optimum cost, SCOP and ηII,system of PTC-type system are averagely 30, 11 and 0.5% higher than ETC-type system at different ambient temperatures. For effective comparison and conclusion, key performance indicator is evaluated to select optimum system configuration from both thermodynamic and economic criteria.

Vapor absorption system powered by different solar collectors types: Cooling performance, optimization, and economic comparison

The current article presents the comprehensive thermodynamic modeling to compare the performance and optimization of single-stage LiCl-H2O and LiBr-H2O type absorption cooling system integrated with different solar collector types for the Gujarat, India. A 10 kW system at 7°C is analyzed which includes four different solar collectors (flat-plate collectors, parabolic-trough collectors, flat plate with compound parabolic collector reflectors, and evacuated-tube collectors) attached with insulated thermal storage tank to power the LiCl-H2O and LiBr-H2O vapor absorption system. The study investigated the effect of heat source temperature on performance aspects of systems. Optimum heat source temperature corresponding to energetic and exergetic aspects for LiCl-H2O pair is found to be lower in comparison to LiBr-H2O pair for all collectors type system. The examined performance parameters are exergetic efficiency, coefficient of performance, and area of collector. Exergetic optimization of each system estimated the required optimum collecting area for cooling. At optimum collector areas, capital cost is evaluated. Differentiation between optimized systems determined that evacuated-tube collectors-based technology is most economic and from exergetic point-of-view, parabolic-trough collectors is recommended. For effective comparison and conclusion, key performance indicator is evaluated to select optimum collector and working fluid pair from both thermodynamic and economic criteria.

Study of Improvement in the Performance of Triple Effect Vapor Absorption System Using Loop Heat Pipes

Study of Improvement in the Performance of Triple Effect Vapor Absorption System Using Loop Heat Pipes

Optimum Heat Source Temperature and Performance Comparison of LiCl–H2O and LiBr–H2O Type Solar Cooling System

This comprehensive investigation has been executed to compare the thermodynamic performance and optimization of LiCl–H2O and LiBr–H2O type absorption system integrated with flat-plate collectors (FPC), parabolic-trough collectors (PTC), evacuated-tube collectors (ETC), and compound parabolic collectors (CPC). A model of 10 kW is analyzed in engineering equation solver (ees) from thermodynamic perspectives. Solar collectors are integrated with a storage tank which fueled the LiCl–H2O and LiBr–H2O vapor absorption system to produce refrigeration at 7 °C in evaporator for Gujarat Region of India. The main objective includes the evaluation and optimization of critical performance and design parameters to exhibit the best working fluid pair and collector type. Optimum heat source temperature corresponding to energetic and exergetic aspects for LiCl–H2O pair is lower than that of LiBr–H2O pair for all collectors. Simulation shows that FPC has lowest capital cost, exergetic performance wise PTC is optimum, and ETC requires lowest collector area. On the basis of overall evaluation, solar absorption cooling systems are better to be powered by ETC with LiCl–H2O working fluid pair.