Vapour Absorption Refrigeration Cycle Research Articles

Enhancement of Condenser Performance in Vapor Absorption Refrigeration Systems Operating in Arid Climatic Zones—Selection of Best Option

Generators and condensers are the two vital equipment items that determine the output of vapor absorption refrigeration systems. Arid weather conditions produce a significant reduction in the performance of the vapor absorption refrigeration cycle due to low condenser heat dissipation despite high generator temperatures. Although numerous studies on condenser cooling methods in vapor compression systems have been reported in the literature, solar-operated vapor absorption systems have not been studied. Limitations in generator temperatures of solar-operated vapor absorption systems necessitate a focused study in this area. This study makes the selection of the best choice for condenser cooling from among four different condenser cooling methods which have an impact on the performance of the vapor absorption refrigeration system for effective cooling using solar energy. A solar vapor absorption refrigeration system working with low-grade heat using a compound parabolic collector is considered in this study. Analysis of a vapor absorption refrigeration system for cooling in arid weather conditions is carried out using different condenser cooling methods with Engineering Equation Solver. Initially, the model used in the study is compared with a similar study reported in the literature. Techniques considered are air, water, evaporative, and hybrid cooling techniques. The performance of the vapor absorption cooling system was analyzed using experimental values of a solar compound parabolic collector obtained from real-time measurements for simulating the model. Results show that water cooling can provide suitable condenser cooling and improve the coefficient of performance of the solar vapor absorption refrigeration system using the solar collector. The water-cooled condenser has 1.9%, 3.3%, and 2.1% higher COP when compared to air-cooled condensers for spring, summer, and autumn seasons respectively, whereas the water-cooled condenser cooling recorded 6%, 14%, and 8% higher COP relative to the evaporative cooling method. Cost comparison showed maximum cost for water-cooled condensers and minimum cost for hybrid-cooled condensers. The effect of each cooling method on the environment is discussed.

Investigations on Solar Powered Vapour Absorption Refrigeration based Air Conditioning

A solar-operated vapor absorption refrigeration cycle is environment-friendly refrigeration system that holds the potential to be used for refrigeration and air conditioning systems. Such a system requires a solar concentrator to run the vapor absorption refrigeration cycle using LiBr-H2O-based refrigeration/air conditioner for small capacity applications. With the solar-powered pumping process, this refrigeration system becomes completely free from electricity requirements. However, the limitations of all time solar radiation availability, low-pressure maintenance requirement of the LiBr-H2O system, low efficiency, and low COP as compared to other vapour compression refrigeration based air conditioning system are the key deterrents. In the present study, the modeling and analysis of various components used in the proposed arrangement of solar vapor absorption refrigeration - air conditioning system has been carried out to improve the performance It is seen that altering the geometrical property of the bubble pump, as well as heat input through a solar concentrating collector, use of hydrogen as a third fluid increases the rate of evaporation which in turn increases the cooling effect as well as COP of the cycle. At 54% concentration of LiBr and 4.5kW heat input, the COP of the proposed layout is found to be 0.61.

Thermodynamic analysis for novel vapor compression/absorption cascade refrigeration system for LNG liquefaction processes in Egypt

This research demonstrates a novel vapour compression/absorption cascade refrigeration system for LNG liquefaction process to replace the air-cooled condenser equipped in Propane precooling refrigeration circuit, via either seawater or cooling towers to remove the heat rejected from precooling cycle of propane. The current investigation focuses on the novel configuration consists of ConocoPhillips optimised cascade cycle using three vapour compression refrigeration circuits which are Propane, Ethylene and Methane, besides one vapour absorption refrigeration cycle. The first aim of this paper is to perform thermodynamic analysis of LNG plant produces 50 kg/s of LNG. The second aim is to present a comparative parametric study for different number of stages which are 6, 7, 8 and 9 stages to evaluate and enhance the coefficients of performance of these design configurations. The results of design configurations for LNG plant conclude that number of stages has significant effects on both Coefficients of performance and the liquefaction efficiency. The Coefficients of performance is strengthened by using the design configurations consist of nine and eight compression stages. The coefficient of performance for vapour compression/absorption cascade for LNG plant can be slightly reduced rather than tradition vapour compression cascade cycles in LNG production from 0.741 to 0.704 for nine stages and from 0.838 to 0.709 for eight stages. The specific power consumptions in (kWhr/kgLNG) can be optimized and adopted from 0.1875 to 0.225 kWhr/kgLNG, for the highly recommended design configurations consist of nine and eight stages. The novelty of this study introduces economical and energy-analysis comparative studies to assess and optimize the performance of several design configurations for LNG plant regarding both economics and thermal performance. The conclusions can support the practical application.

Thermodynamic investigations on PDC based solar air conditioning system

Global warming is raising the ambient temperature and thus resulting in increased air conditioning requirements. The increase in power requirements of air conditioning systems, in turn, burdens the electricity needs and more electricity generation further adds to global warming. In such situations, the availability of solar energy and its utilization for air conditioning systems appears a potential solution to a certain extent. This paper deals with the thermodynamic analysis of a parabolic dish based air conditioning system working on vapour absorption refrigeration cycle for the H2O and LiBr combination as working fluid. Thermodynamic modelling was used to assess the impact of changing the initial concentration of lean solution and the varying condenser temperature under the atmospheric conditions of that region during peak air conditioning demand months on several parameters such as coefficient of performance, cooling effect, and exergetic efficiency of the system. At 45 percent of the initial LiBr concentration in weak solution, the system’s highest coefficient of performance is attained.

Thermo-economic and environmental assessment of hybrid vapor compression-absorption refrigeration systems for district cooling

District cooling plants are predominantly based on vapor compression refrigeration cycles with detrimental environmental impacts due to fossil-based electricity. Vapor absorption refrigeration cycles promise operating improvements and emission reductions in vapor compression-absorption refrigeration system configurations. However, the use of conventional vapor absorption refrigeration working fluids and the limited studies of systems with capacities that are relevant to district cooling plants, prohibit their scaling-up. This work compares the thermodynamic, environmental, and economic performance of seven configurations of the vapor compression refrigeration cycle with a double-effect vapor absorption refrigeration cycle that employs either the conventional ammonia/water or the novel acetaldehyde-N,N-dimethylformamide working fluid. These three cycles are compared with the cascade and parallel vapor compression-absorption refrigeration system configurations, with ammonia/water or acetaldehyde-N,N-dimethylformamide in the vapor absorption refrigeration. The coefficient of performance of the vapor compression refrigeration unit in the cascade configurations is 252% higher than the stand-alone vapor compression refrigeration configuration. The stand-alone vapor absorption refrigeration coefficient of performance with the novel fluid acetaldehyde-N,N-dimethylformamide is 9.1% higher than that of the vapor absorption refrigeration with ammonia/water. The cost per ton of cooling and the total equivalent warming potential of the cascade vapor compression-absorption refrigeration system with acetaldehyde-N,N-dimethylformamide are 65% and 67.8% lower than those of the stand-alone vapor compression refrigeration. The electrical energy utilization factor is 30.5% lower for the acetaldehyde-N,N-dimethylformamide fluid compared to ammonia/water, in the cascade configuration.

Optimal Scheduling for a District Cooling System with Chilled Water Storage: Comparative Assessment of Vapour Compression and Absorption Refrigeration Cycles

District cooling (DC) systems are able to exploit locally available energy in order to supply cooling to local end-users through an integrated DC network. The present work aims at obtaining the critical decisions in the performance of a DC network at the operating level. End-users can be of different type (e.g., residential or commercial) with different demand profiles and an optimal strategy needs to be employed in order to satisfy the demand and minimise energy usage. In published literature the vast majority of the studies employ simplified mathematical models in order to describe the thermodynamic cycle used and only a handful of studies take into account the actual dynamics of the system transition from one state to the other as well as the time delay attributed to the cooling medium transfer through the network. The critical decisions involve the operating conditions and optimal allocation for the cooing of existing units in a suitable time interval, which form the basis for the satisfaction of requirements in cooling under demand variability. Although reduced order models of the process of ABR cycle are used, the time delay of the cooling medium transfer through the pipes is considered through the employment of validated first order plus time delay models. The proposed optimisation framework enables the identification of demand driven, highly performing solutions through the direct consideration of all interacting factors over a pre-defined time horizon. Optimal results include the definition of the optimal allocation of produced cooling effect in such way that cooling demand is always satisfied.

Thermo-environmental analysis of a new molten carbonate fuel cell-based tri-generation plant using stirling engine, generator absorber exchanger and vapour absorption refrigeration: A comparative study

This study aims to present a novel tri-generation plant consisting of a molten carbonate fuel cell (MCFC) unit coupled with a Stirling engine (SE), a heat recovery steam generator (HRSG), and two types of absorption refrigeration cycles (ARCs), i.e., Generator Absorber eXchanger (GAX) and Vapour Absorption Refrigeration (VAR). The proposed system is evaluated from energy, exergy, as well as environmental impact (3E) points of view. To carry out the parametric study, three sub-models are also introduced for the whole system. The sub-model (1) investigates the solo MCFC with the new configuration. In the sub-model (2), the SE and HRSG are added to boost the power generation and overall system efficiency through employing the heat wasted in the sub-model (1). In the last sub-model, for cooling purposes, the surplus heat of MCFC is reutilized using an absorption refrigeration cycle. Besides, to make a comparative study between GAX and VAR systems, the sub-model (3) is classified into two different schemes: (a) with a VAR cycle, and (b) with a GAX cycle. The results reveal that the exergy efficiency and CO2 emissions of the sub-models (1), (2), and (3) are 48.04%, 51.24%, 52.35% (VAR cycle), 52.12% (GAX cycle), 0.388 t/MWh, 0.364 t/MWh, 0.357 t/MWh (VAR cycle), and 0.358 t/MWh (GAX cycle), respectively. Either with GAX or VAR cycle, the proposed system indicates an acceptable standard of functionality in thermodynamic and environmental perspectives.

Parametric evaluation of solar driven combined supercritical organic Rankine cycle and vapor absorption refrigeration cycle for trigeneration

Current study deals with the parametric evaluation of combined supercritical organic Rankine cycle and vapour absorption refrigeration cycle driven by solar power tower. It was obtained from the results, exergy and thermal efficiency of the combined system improved with solar irradiation. Maximum thermal and exergy efficiency were obtained 46.60% and 68.25% respectively at 950 W/m 2 while maximum exergy destruction was obtained 7589.46 kW at 500W/m 2. COP of the system decreased with generator and condenser temperature. The maximum COP for heating and cooling were found 1.4452 and 0.4448 respectively at 90°C of generator temperature.

Comparative Energetic and Exergetic Assessment of Different Cooling Systems in Vegetable Cold Storage Applications

In this study, four different cooling systems have been thermodynamically analysed for vegetable cold storage application, considering a fixed cooling demand of 10 kW. Both vapour absorption refrigeration (VAR) and compression refrigeration (VCR) cycles are considered, each with two different working fluids. For the VCR cycles, R410A and R134a are considered as refrigerants, whereas for the VAR cycles, NH3–water and LiBr–water solutions are considered as refrigerant–absorbent pairs. Both energetic and exergetic performances are assessed and compared between the cycles. The system performances are assessed by varying the conditions of the evaporator and condenser. The effects of ambient temperature on the system performances are also studied. The study reveals that VAR systems can provide feasible alternatives to VCR systems for the cold space temperature range applicable for vegetable storage with the exception that LiBr–H2O cycle cannot be used for cold space temperature below 2 °C. Exergetic performance (ECOP) of the LiBr–H2O-based cooling system matches well with that of VCR systems for evaporator temperature 2–5 °C, and it exceeds the ECOP of R410A cycle at 2 °C evaporator temperature. When the ambient temperature is reached above 35 °C, the exergetic performance of LiBr–H2O-based system is better than that of both the VCR systems. For higher condenser temperature also (40 °C and above), the VAR and VCR cycles show closer ECOP values.

Techno-economic assessment of a biomass-based combined power and cooling plant for rural application

This paper presents techno-economic assessment of a biomass-based combined power and cooling plant suitable for off-grid rural areas. The proposed plant employs an indirectly heated air turbine cycle drawing heat from combustion of biomass-derived producer gas. The installation capacity of 50 kW is determined based on the present electricity demand and taking into account the possible demand growth over next 10 years. The gas turbine operating condition is optimized at pressure ratio 10 and turbine inlet temperature 1100 °C, where it shows maximum efficiency. Waste heat of the power generation unit is utilized by a 120 metric ton (MT) cold storage facility that runs on NH3–water vapour absorption refrigeration cycle. Both electrical and thermal storage units are included in the plant to cater to the hourly variations in power and heat demands. Lithium-ion battery is chosen for electrical storage, and Hitec salt-based phase change material is chosen for thermal storage, their storage capacities being estimated at 250 kWh and 220 kWh, respectively. The paper proposes a new method of determining effective cost of electricity, taking into account the avoided electricity for conventional cooling. The effective price of electricity is found to be 0.08 USD/kWh. Estimated payback period of the plant, without subsidy, is 14.4 years, and with 50% capital subsidy this is reduced to 6.6 years. Cost of storage as well as the discount rate is seen to influence the plant economy and payback period considerably. Based on the analysis, a policy recommendation has also been outlined in the paper.

Parametric Study of Combined Cooling and Power (CCP) Plant Integrated with Parabolic Trough Solar Collectors (PTSCs)

This study presents a detailed energy analysis of a Combined Cooling and Power (CCP) plant operated by Parabolic Trough Solar Collectors (PTSCs). The integrated cycles; Vapor Absorption Refrigeration Cycle (VARC) and Organic Rankine Cycle (ORC) are used to produce cooling and power, respectively. Six organic working fluids, namely, R113, R141b, R123, R245fa, R142b, and isobutane were selected for ORC, while LiBr-H2O solution used in VARC. Four key energetic parameters, useful heat gain, work output, cooling rate, and energy utilization factor (EUF) were examined during varying direct normal irradiance (DNI). A parametric study was carried out in three modes of operation, power only, combined power and cooling and cooling only under the limits of DNI from 0.6 kW/m2to 0.88 kW/m2recorded on the yearly-average basis in two cities of Pakistan, Lahore, and Quetta respectively. Results enunciated that R113 given the highest thermal efficiency of 17.12%, while isobutane gave the least thermal efficiency of 7.88%, hence R113 was chosen as organic working fluid for further study. The maximumEUF was found in the cooling mode of operation which increased from 63.95% to 66.79% at 0.6 kW/m2 and 0.88 kW/m2 respectively. During the combined cooling and power mode, maximum cooling rate, power output, and EUF were 3456 kW, 822.5 kW, and 41.34% respectively at 0.88 kW/m2.

Ammonia/ionic liquid based double-effect vapor absorption refrigeration cycles driven by waste heat for cooling in fishing vessels

To use high-temperature waste heat generated by diesel engines for onboard refrigeration of fishing vessels, an ammonia-based double-effect vapor absorption refrigeration cycle is proposed. Non-volatile ionic liquids are applied as absorbents in the double-effect absorption system. In comparison to systems using ammonia/water fluid, the complexity of the system can be reduced by preventing the use of rectification sections. In this study, a multi-scale method is implemented to study the proposed system, including molecular simulations (the Monte Carlo method) for computing vapor-liquid equilibrium properties at high temperatures and pressures, thermodynamic modeling of the double-effect absorption cycles, and system evaluations by considering practical integration. The Monte Carlo simulations provide reasonable vapor-liquid equilibrium predictions. 1-butyl-3-methylimidazolium tetrafluoroborate is found to be the best performing candidate among the investigated commercialized ionic liquids. In the proposed cycle, the best working fluid achieves a coefficient of performance of 1.1 at a cooling temperature of −5 °C, which is slightly higher than that obtained with generator-absorber cycles. Integrated with the exhaust gas from diesel engines, the cooling capacity of the system is sufficient to operate two refrigeration seawater plants for most of the engine operating modes in high-latitude areas. Thereby, the carbon emission of onboard refrigeration of the considered fishing vessel could be reduced by 1633.5 tons per year compared to the current practice. Diagrams of vapor pressures and enthalpies of the studied working fluids are provided as appendices.

Preliminary conceptual design and thermodynamic comparative study on vapor absorption refrigeration cycles integrated with a supercritical CO2 power cycle

Combined cooling and power system has gained extensive attention from government and publics throughout the world due to fuel saving, high energy utilization efficiency and different energy forms output. In this paper, a novel combined cooling and power system comprising a supercritical CO2 (sCO2) power cycle and a vapor absorption refrigeration cycle with lithium bromide as the working fluid is proposed. A comparative study is conducted between this system and the combined sCO2/ammonia-water system to show its advantages and potential on the basis of the self-built thermodynamic simulation platform. The influence of different variables including turbine inlet temperature, pressure ratio in sCO2 cycle and evaporating temperature on the system performance is analyzed. Single-objective optimization relying on the genetic algorithm and multi-objective optimization based on the NSGA-II method are used to further investigate and compare the performance of above two cycles. Optimization results reveal that compared with the combined sCO2/ammonia-water system, the proposed sCO2/LiBr-H2O system could gain improvement on CORP by 0.3112 at the expensive of COPP drop by 0.0004 excepting the advantage of extreme low pump outlet pressure in bottoming cycle. Besides, sCO2/LiBr-H2O system is relatively easier to reach the balance between power and cooling.

Optimization of operating temperatures in the gas operated single to triple effect vapour absorption refrigeration cycles

Thermodynamic analysis of LiBr–H2O single, double and triple effect vapour absorption cycles has been carried out using LPG and CNG as sources of energy. Optimization of operating temperatures in single to triple effect cycles has been carried out for maximum COP of the system and minimum gas requirement in it at desired temperatures in evaporator, absorber and main condenser using iterative technique. In single effect cycle, optimum temperatures in main generator have been obtained, while in double effect cycle, low pressure generator, high pressure condenser and main generator temperatures have been optimized. In triple effect cycle having three condensers and three generators, condenser temperatures (Tc3 and Tc4) and generator temperatures (Tg2, Tg3 and Tg) have been optimized. The maximum COP of triple effect cycle goes up to 1.955 which is around 132% higher than single effect cycle with its gas requirement reduced to around 122% at the same conditions.

Computational Model of a Biomass Driven Absorption Refrigeration System

The impact of vapour compression refrigeration is the main push for scientists to find an alternative sustainable technology. Vapour absorption is an ideal technology which makes use of waste heat or renewable heat, such as biomass, to drive absorption chillers from medium to large applications. In this paper, the aim was to investigate the feasibility of a biomass driven aqua-ammonia absorption system. An estimation of the solid biomass fuel quantity required to provide heat for the operation of a vapour absorption refrigeration cycle (VARC) is presented; the quantity of biomass required depends on the fuel density and the efficiency of the combustion and heat transfer systems. A single-stage aqua-ammonia refrigeration system analysis routine was developed to evaluate the system performance and ascertain the rate of energy transfer required to operate the system, and hence, the biomass quantity needed. In conclusion, this study demonstrated the results of the performance of a computational model of an aqua-ammonia system under a range of parameters. The model showed good agreement with published experimental data.

Mapping of optimum operating condition for LiBr–water refrigeration cycles

In this work, optimum operating condition maps are generated covering wide ranges of refrigeration and sink temperatures for single- and double-effect LiBr–water vapour absorption refrigeration cycle. These optimum condition maps will be useful to choose optimum operating conditions while designing LiBr–water cycle for desired applications. Methodology for generating such maps is discussed in detail, which can also be used for other absorption refrigeration cycles with various working fluids. Three configurations of LiBr–water absorption refrigeration cycles, single effect, double-effect series flow and double-effect parallel flow, are analysed with the most accurate thermodynamic property correlation available in the literature. Sensitivity of cycle performance to various operating variables such as generator, absorber and condenser temperatures is determined. Second law analysis shows that when a higher temperature heat source is available, double-effect cycles are more effective over single effect as they have higher coefficient of performance.

Comparative energetic and exergetic studies of vapour compression and vapour absorption refrigeration cycles

In this study, two types of refrigeration cycles, a vapour compression refrigeration (VCR) cycle and a vapour absorption refrigeration (VAR) cycle, have been modelled and analysed. Both the cycles have same operating cooling loads and both operate between the same temperature limits. R134a has been considered as refrigerant for the VCR cycle whereas LiBr-H2O has been considered as the working fluid for the VAR cycle. Energetic and exergetic performances have been evaluated for both the cycles and compared. The effects of condenser temperature, evaporator temperature and environmental dead state temperature on the performances of these cycles are also discussed. Energy analysis reveals that the coefficient of performance (COP) of the VCR cycle is considerably higher than that of VAR cycle. However, exergy analysis reveals that the exergetic coefficient of performance (ECOP) of the VAR cycle is very close to that of VCR cycle. For environmental dead state temperature beyond 35°C, the exergetic performance of VAR cycle is better than that of VCR cycle. The maximum exergy destruction occurs at the evaporator for the VCR cycle but for VAR cycle, the maximum exergy destruction occurs at the generator.

Comparative energetic and exergetic studies of vapour compression and vapour absorption refrigeration cycles

Comparative energetic and exergetic studies of vapour compression and vapour absorption refrigeration cycles

Design of Solar Thermal Combined Power and Cooling System Using LiBr-Water as Working Fluid

The integration of power and vapor absorption refrigeration cycle overcomes the disadvantages of power used for the compression refrigeration and also produces additional power for other purposes (Low pressure turbine). The integration is done by making the heat exchanger and generator as common and separate super heater and reheater is used to run the high pressure turbine (HPT) and low pressure turbine (LPT). The maximum total power output of 69.78 kW and 31.86 kW is obtained for HPT and LPT at the atmosphere temperature 30 °C and separator temperature 180 °C. At the same collector exit and atmosphere temperature shows the maximum cooling output of 188.88 kW. The additional advantages of integrating the power and cooling cycle’s shows the choice of choosing the need of only power only cooling and both power and cooling. The analyses are done for various separator temperature and strong solution concentration.

Energy and Exergy Analysis of Vapour Absorption Refrigeration Cycle—A Review

In recent years, an energy crisis and the energy consumption have become global problems which restrict the sustainable growth. In these scenarios the scientific energy recovery and the utilization of various kinds of waste heat become very important. The waste heat can be utilized in many ways and one of the best practices is to use it for vapour absorption refrigeration system. To ensure efficient working of absorption cycle and utilization of optimum heat, exergy is the best tool for analysis. This paper provides the comprehensive picture of research and development of absorption refrigeration technology, practical and theoretical analysis with different arrangements of the cycle.