Absorption Refrigeration System Research Articles

CFD simulation approved by an experimental validation of the diffusion absorption refrigeration system evaporator

The evaporation process has a considerable impact on the operation of a diffusion absorption refrigeration system (DAR). However, there have been few studies that have focused on this specific issue. In this paper, a numerical investigation of the evaporator region in a DAR system was conducted using CONVERGE CFD software and the RANS approach. The aim of this study is to validate an accurate CFD model by analysing the flow behaviour and thermal parameters within the evaporator. The computational results show high agreement with the experimental data, with slight deviations often remaining under 3 %. The current study additionally investigated the effect of ammonia presence at the hydrogen inlet, specifically at 5 % and 10 % ratios. The results demonstrate that the average deviation is less than 1 % when using 5 % ammonia. This study sheds light on the evaporation process, which is important for enhancing the design and operational efficiency of DAR systems. For this purpose, the validated numerical model will be of great use.

Thermodynamic Modeling and Performance Evaluation of Absorption Refrigeration System with Graphene Nanofluid

The study presents a comprehensive computational analysis of an absorption refrigeration system that employs graphene nanofluids as the secondary fluid. The system's tube-type evaporator, utilizing copper tubes, was optimized and analyzed under varying nanofluid concentrations through thermodynamic modeling. Key thermal and design parameters were thoroughly examined, including evaporation area, heat flux, conductive and convective coefficients, and overall heat transfer coefficient. The findings demonstrate notable enhancements in the analyzed parameters when employing nanofluids in the system, with improvements of 5.2% in the pumping power of the secondary system and 0.8% in the evaporation area. These outcomes highlight the potential benefits of incorporating graphene nanofluids in absorption refrigeration systems, paving the way for more efficient and sustainable cooling solutions.

An efficient and compact integrated microchannel membrane-based absorption refrigeration system

Microchannel membrane-based absorption refrigeration system (MMARS) is an efficient and compact solution for delivering cooling capacity, driven by renewable and waste thermal energy. This study introduces a novel integrated MMARS (I-MMARS), featuring integrated evaporator-absorber and desorber-condenser, to further enhance the system compactness. By analyzing the influence of the gap distance within these two integrations on the system efficiency (COP) and compactness (volumetric cooling capacity, Rqv), the advantages of the new system are highlighted. The highest Rqv (136.765 kW/m3) and corresponding COP of 0.6994 are found to be achieved with a 0-mm gap in the evaporator-absorber integration and a 0.2778-mm gap in the desorber-condenser integration. The performance of the I-MMARS, with these optimal gap distances, is further examined under various operating conditions. Our findings indicate that the system COP can be enhanced by increasing both the heat source temperature and the chilled water temperature. Simultaneously, reducing the heat source and solution flow rates, or the cooling water temperature also contributes to COP improvements. Finally, a comparison with conventional MMARS shows that the novel I-MMARS can boost system compactness by 37.88 %. The innovative I-MMARS paves the way for the development of small-scale absorption refrigeration systems in a highly efficient and space-saving manner.

Low-temperature ammonia absorption refrigeration system based on the temperature difference uniformity principle: Optimization analysis

AARS (ammonia absorption refrigeration system) is one of the effective ways to utilize low-temperature waste heat below 100 °C for industrial applications. This novel system of LT-AARS is designed based on the principle of temperature difference uniformity for improving the overall COP. The partial condenser at the distillation section is adopted to achieve the purity of ammonia to more than 99.9 % with a small reflux ratio. A thermodynamic model is established to analyze the influence of the optimized distillation process on system performance and exergy loss. These modifications reduce the temperature difference uniformity factor from 1.12 to 1.025 and improve the COP from 0.414 to 065. Meanwhile, it is proved that the LT-AARS protocol is reasonable and effective by comparing the experimental values with the theoretical model. The exergy loss of the absorber and distiller accounts for about 55 % of the total exergy losses of LT-AARS. With the increases in refrigeration temperature from −15 to 5 °C and heat source temperature from 80 to 100 ℃, the COP can reach a maximum of 0.77. ECOP first increases sharply and then decreases slowly with the increase of refrigeration and heat source temperature, and ECOP has a maximum value. The optimal range of △x for LT-AARS varies from 5 % to 10 %. The COP and ECOP of the LT-AARS are more than 0.6 and 0.3, respectively.

Modeling and Parametric Analysis of a Large-Scale Solar-Based Absorption Cooling System

This study investigates the thermodynamic performance of a solar-powered absorption cooling system. The system uses a lithium bromide-water (LiBr-H2O) absorption refrigeration system (ARS) integrated with evacuated solar collectors (ETSC) and thermal energy storage (TES) to provide a 3 kTR cooling capacity for a university campus. The paper examines the performance of the integrated system under different design and operating conditions as well as the performance of each subsystem, i.e., ETSC, TES, and ARS. Furthermore, a parametric energy and exergy analysis is applied, where different parameters are studied, such as the temperatures of the generator, the condenser, the evaporator, and the absorber. In addition, the system performance is examined with the variation in environmental conditions. The coefficient of performance (COP), exergetic efficiency, exergy destruction, and fuel depletion ratio (FDR) are used to evaluate the system’s performance. The ETSC and the TES are studied under the variation in solar radiation through the day in two seasons: summer and winter. The results revealed that the increase in generator temperature positively impacts the COP of the ARS while lowering the condenser and absorber temperature gives the same positive effect. Furthermore, the main reason for the exergy destruction is found to be the solar collector, which is responsible for destroying 89% of the input solar exergy. Additionally, 4.7% of the inlet exergy is destroyed in the generator, which makes 4.5% of the total exergy loss. The TES destroyed 4.8% of the total solar exergy input. The energy analysis shows that the ARS achieves an energetic COP of about 0.77, while the exergy analysis revealed that the exergetic COP is 0.21.

Research on geothermal-driven single-effect absorption refrigeration systems with different working fluids: energy and exergy analysis

Abstract Geothermal energy is not only environmentally friendly and has low carbon but also represents a nonintermittent technology. It is anticipated that its utilization in human society will experience rapid growth in the coming decades. Absorption refrigeration can be employed for the recovery of geothermal resources. However, the low performance of absorption refrigeration systems has hindered their development. In order to advance absorption refrigeration technology suitable for geothermal energy recovery, this study developed a mathematical model for an absorption refrigeration system using 55% lithium bromide (LiBr) and 35% lithium chloride (LiCl) solutions as working fluids. The impact of various parameters, including cooling water conditions, chilled water conditions, heat source parameters, and working fluid concentration, on the thermodynamic performance, system efficiency, and exergy efficiency of a single-effect absorption refrigeration system was analyzed. The results reveal that the cooling water inlet temperature and flow, chilled water inlet temperature, heat source inlet temperature, and working fluid concentration are the primary factors affecting the thermodynamic performance and exergy efficiency of the absorption refrigeration system. The coefficient of performance (COP) of the system increases with higher cooling water flow, chilled water inlet temperature, and working fluid concentration, but decreases with higher cooling water inlet temperature. Within a certain temperature range, the COP increases with higher heat source temperature. The effective COP (ECOP) increases with higher cooling water inlet temperature, cooling water flow, chilled water inlet temperature, and working fluid concentration, while it decreases with higher heat source temperature. The highest COP values for the LiBr and LiCl solution single-effect absorption refrigeration systems are 0.795 and 0.785, respectively, while the highest ECOP values are 0.694 and 0.684, respectively.

Dynamic model of a solar powered absorption refrigeration system

This paper focuses on the analysis of a dynamic simulation model used to describe the operation of a solar cooling system located in Jaén (Spain). The dynamic model has been developed using the simulation environment TRNSYS. The main goal of this paper has been to analyze separately the dynamic behaviour of each components of the installation and have been shown the differences between the temperatures of input and output of each of them, discussing and justifying the phenomena that appear. During the analysis phase and using and detailed model of the solar cooling system, it has been dedicated a special interest in showing the differences in all components between the initial transitional period and the period of stabilization of their operation.

A Review of Multistage Vapor Absorption Refrigeration System Under Different Heat Sources

This review paper systematically analyzes the state-of-the-art developments, innovations, and applications of multistage vapour absorption refrigeration systems, emphasizing their adaptability to various heat sources. The manuscript navigates through the fundamental principles of vapor absorption refrigeration, highlighting the advantages and drawbacks of single-stage systems. It then delves into the intricacies of multistage systems and their potential to enhance performance and efficiency. Various configurations are explored, offering insights into the key factors influencing system performance. The core of the review revolves around the compatibility of multistage vapor absorption refrigeration systems with a diverse range of heat sources, including waste heat, solar energy, geothermal sources, and industrial processes. Furthermore, this review paper addresses the challenges, limitations, and future prospects of multistage vapor absorption refrigeration systems, paving the way for an informed discussion on the advancement of sustainable cooling technologies. Key Words: Gas energy sources, VARS, VCRS, Absorption cooling system.

Technical evaluation of solar-activated absorption refrigeration systems and operating conditions: a case study in Culiacán-Mexico

This research shows the methodology for technical evaluations of the energy performance of absorption refrigeration systems activated with solar energy. This document determines the optimal installation angle of the solar thermal collectors that activate the chiller. Also, the cooling energy Qe, Coefficient of Performance (COP), and hourly Seasonal Coefficient of Performance (SCOP) are determined for each month of the year and recommendations are made for operation in the city of Culiacán, Mexico. The absorption cooling system achieved a Qe of 400.9 kW, a COP of 0.778, and a SCOP of 0.557.

Investigation of Solar Powered Single Effect Absorption System

Cooling processes like refrigeration and air conditioning are known for their high energy consumption. Since most Indian states experience abundant sunshine year-round, solar refrigeration is a suitable technology for the country. Solar-powered absorption refrigeration systems offer a viable alternative to traditional refrigeration, providing not only cooling and ice-making capabilities but also energy savings and environmental benefits. However, further research is necessary to enable widespread industrial adoption and the replacement of conventional refrigeration systems with solar powered absorption system. Using solar energy for an air-conditioning system is typically more cost-effective, when it can fulfil both heating and cooling needs. This research focuses on the thermodynamic modelling of a system, specifically the effect of various temperature on COP. Thermodynamic modelling was done with the help of first law of thermodynamics. Using engineering equation solver software, study simulated the cycle and equations were developed for energy and mass flow for each component. Further, before proceeding to analysis some assumptions were also made. We then analysed how the Coefficient of Performance (COP) changed when varying the temperatures across each component. Our findings show that COP increases with increase in condenser, evaporator, and absorber temperatures, but it is declined with decrease in generator temperature.

Development of an Integrated Solar-Biomass Energy System for Near-Zero Energy Buildings: A Technical and Environmental Study

The present study aims to satisfy the energy demands of a set of Norwegian residential structures with the least carbon dioxide and most renewable energy. Real-time data on building domestic hot water (DHW), heating, and electricity usage is used to plan and expand the renewable energy supply side. PVT panels provide DHW and electricity in the hybrid solar and biomass energy system. Heat is produced by the digester and heat pump. Also used is a twofold effect absorption refrigeration system for cooling. Rule-based regulation manages heat streams and redirects flows on the supply side. We provide the plant's size and execute the dynamic energy simulation. Electricity and biomass expenses determine building heating. The system is then tuned for operational conditions and compared to the design point. PVT may generate over 80% of annual DHW. Summertime radiation is more intense and can be turned into cooling energy, therefore 64.8% of cooling output comes from it. Digester/CC heats 66.55% of the structure, suggesting designers use biomass in winter due to increased energy costs. A parametric analysis shows that increasing PVT duration and tank size affects efficiency and emissions differently. Cost, efficiency, and emission index at TOPSIS are 9.73 $/hr, 36.8%, and 7.75 kg/MWh, according to optimization findings.

Design and Fabrication of a LiBr Absorption Refrigeration System to Utilize the Waste Heat of Engine Exhaust Gas for Vehicle Cabin Cooling Application

Design and Fabrication of a LiBr Absorption Refrigeration System to Utilize the Waste Heat of Engine Exhaust Gas for Vehicle Cabin Cooling Application

Vapor-liquid equilibrium measurements of ionic liquid [DEME][TFSI] with different hydrofluorocarbon refrigerants R152a, R32, and R143a

To overcome the shortages of traditional working pairs (LiBr/H2O and NH3/H2O) for absorption-refrigeration systems (ARSs), novel working pairs consisting of low global warming potential (GWP) hydrofluorocarbons difluoroethane (R152a) and difluoromethane (R32) plus low-viscosity ionic liquid N,N‑diethyl-2‑methoxy-N-methylethan-1-aminium bis((trifluoromethyl)sulfonyl)amide ([DEME][TFSI]) are studied. Firstly, solubilities of R152a and R32 in [DEME][TFSI] are measured by the isochoric saturation method in the temperature range of 293 K ∼ 343 K and pressure range of 0.14 MPa ∼ 1.664 MPa with the relative expanded uncertainty of 0.03. A high-GWP hydrofluorocarbon 1,1,1-trifluoroethane (R143a) is involved in the experiment for further comparison. The non-random two-liquid model is used to correlate the vapor-liquid equilibrium data with average absolute relative errors of 0.55 % (R152a), 0.58 % (R32), and 0.94 % (R143a), respectively. [DEME][TFSI] shows its low viscosity and good solubility of hydrofluorocarbons by contrast with conventional ionic liquids. A refrigerant solubility rank order in [DEME][TFSI]: R152a > trans-1,3,3,3-tetrafluoropropene (R1234ze(E)) > R32 > 2,3,3,3-tetrafluoro-1-propene (R1234yf) > R143a is obtained from the comparison. This work provides the possibility to apply low-GWP working pairs R152a/[DEME][TFSI] and R32/[DEME][TFSI] in ARSs.

Thermodynamic process control of compression-assisted absorption refrigeration using ocean thermal energy

An efficient control method is crucial for the safe and reliable operation of compression-assisted absorption refrigeration using ocean thermal energy. In this study, a dynamic model of 10 kW compression-assisted absorption refrigeration system is developed, and four integrated control strategies containing two cooling-capacity control approaches (Single input control and Cooperation control) and two temperature glide control approaches (Valve-based control and Compressor-based control) are proposed to control thermodynamic process. The proposed control strategies are evaluated in terms of both control and refrigeration performances. The results indicate that the refrigeration system can operate with stability at 50 % cooling load under the proposed control strategies. Moreover, the cooperative control of the flow rates for both warm-seawater and concentrated solution can significantly speed up cooling-capacity regulation. The rotational speed of compressor is a more suitable manipulated variable for regulating the evaporator temperature glide. The equivalent COP for the compressor-based control strategies is greater than 0.12 at 50 % cooling load, while the equivalent COP for the valve-based control strategies is only 0.064.

Use of Ionic Liquid as Crystallization Inhibitor in Water-Lithium Bromide Absorption Chiller

Chillers are used in commercial buildings and industrial plants to provide air conditioning, refrigeration, and process fluid cooling. There are two basic types of chiller cycles: vapor compression and sorption. Sorption chillers are available as either absorption or adsorption designs, depending on the state of the sorbent. Absorption chillers use fluid refrigerants and absorbents (liquid or dissolved), while adsorption chillers employ a solid sorbent (typically silica gel) in combination with a fluid refrigerant. Among the former category, the use of highly hygroscopic LiBr salt as absorbent in combination with H2O as refrigerant comprises LiBr-H2O absorption chillers. Such chillers possess cooling capacities ranging from a few kilowatts (kW) to megawatts (MW) which match with small residential to large scale commercial or even industrial cooling needs. One of the major debilitating factors associated with LiBr-H2O absorption chillers is crystallization. A crystallization event causes a loss of cooling and requires de-crystallization by applying external heat, which results in extensive down-time and requires redundancy designed into a chiller plant. We investigated the use of the imidazolium-based ionic liquid, 1-butyl-3-methylimidazolium bromide ([BMIm]-Br), as crystallization inhibitor additive to LiBr-H2O in the ratio 1:19 [BMIm]-Br:LiBr. It was found that under the operating boundary conditions of 27°C/9°C (cooling water inlet temperature/chilled water outlet temperature), the LiBr-H2O absorption chiller can be operated without modifications and with around 10 K higher heating water inlet temperatures when adding [BMIM]-Br before crystallization occurs compared to pure LiBr-H2O solution. When using the [BMIM]-Br ionic liquid, the refrigeration capacity of the absorption chiller under the above operating conditions and at 85°C heating water inlet temperature exhibited 10% increase after optimizing the solution flow, that lead to higher outputs, such as lower cooling water temperatures. By adding the [BMIM]-Br to the aqueous lithium bromide solution the operating range of the absorption refrigeration system could also be extended to resorption mode, which allows refrigeration below 0 °C. Thus, there is an excellent potential for a significant extension of the application range of LiBr-H2O chillers, e.g. in the field of food cooling and refrigeration processes. Figure 1

Downsizing strategy for an air-cooled indirect-fired single-effect ammonia-water absorption chiller in part-load operation in hot climates

A modular mathematical model has been created to simulate an ammonia-water absorption refrigeration system indirectly fired and air-cooled. The model includes governing equations based on mass, species, and energy balances, implemented for the main components of the system. It accounts for both thermal and mass resistances in the transfer processes that occur in the system. The study evaluates the performance of the ROBUR® absorption refrigeration system, model ACF60-00 LB, operating under part-load conditions, driven by hot water temperatures ranging between 160 and 210 °C, while the ambient temperature remains up to 40 °C. This refrigeration system is characterised by including an extra valve that allows active control of the pressure levels of the system. The analysis focusses on the effect of its active control on the size of the system. The results show that increasing the pressure loss in this valve reduces the size of the air-cooled absorber to 37.3 % of its nominal size at an ambient temperature of 40 °C, while the reduction in refrigerant mass flow is 18.5 %, while the condenser size decreases 3.1 times. Evaporator, air-cooled absorber and condenser effectiveness are minimally affected. Additionally, contribution of condenser and evaporator to exergy destruction is balanced.

The performance of [Emim]Br/H2O as a working pair in the absorption refrigeration system

The energy efficiency of the single-effect absorption refrigeration systems (ARS) using ionic liquid (IL) [Emim]Br as an absorbent and water as a refrigerant is evaluated in this study. The thermodynamic properties of the mixture, such as vapor pressures and excess enthalpies, are calculated using the non-random two-liquid (NRTL) activity coefficient model. The coefficient of performance (COP) is estimated with fixed temperatures for the evaporator, absorber, condenser, and generator, set at 10, 30, 40, and 100 °C, respectively. It is found that the COP of the single-effect ARS using [Emim]Br-H2O as the working pair is about 0.8, which is slightly lower than that obtained with LiBr-H2O (0.83), but much higher than that of H2O-NH3 (0.65) systems. The effect of generator temperature on COP has the same trend as that of other IL working pairs. The influence of each component temperature on the system’s performance is investigated, and it is found that the single-effect ARS performs very well under different conditions with [Emim]Br - H2O as the working pair.

Exergy-based sustainability analysis of combined cycle gas turbine plant integrated with double-effect vapor absorption refrigeration system

Exergy-based sustainability analysis of combined cycle gas turbine plant integrated with double-effect vapor absorption refrigeration system

Multi-Objective Optimization Research on the Integration of Renewable Energy HVAC Systems Based on TRNSYS

Well-designed passive buildings can drastically reduce building energy consumption, and optimal design of air conditioning systems is the key to achieving low operating energy consumption in near-zero energy buildings. TRNSYS was used to build the simulation model for a near-zero-energy building and its air conditioning system in Beijing. The Taguchi method was used to sort the design parameters that affect system performance according to the degree of influence and find the best combination of design parameters to optimize the system, which increased the solar fraction of the system by 4.6% and reduced the annual operating energy consumption by 7.32%. For the optimized system, a multi-objective optimization function of the life cycle costs and carbon emissions was established. By comparing the energy consumption, life cycle costs, and carbon emissions of the air conditioning system under different system configurations, optimal configuration solutions under different design target weights were obtained. It was found that using a ground source heat pump system + solar collector system had better energy-savings benefits, but the operating costs were slightly higher. The application of absorption refrigeration can reduce the system operating costs but will increase the initial investment. The best economic benefits were achieved using the ground source heat pump system + solar collector system for heating in winter and the ground source heat pump system for cooling in summer, and the best environmental benefits were obtaining using the ground source heat pump system + solar collector system for heating in winter and the ground source heat pump system + solar absorption refrigeration system in summer, which provides a reference for the optimization design and research of air conditioning systems in near-zero energy buildings.

Experimental investigation of diesel engine driven micro-cogeneration system integrated with thermal energy storage for power and space cooling

In this paper the performance and emission characteristics of thermal energy storage integrated micro-cogeneration system was investigated. This system was developed by connecting the vapor absorption refrigeration (VAR) system and thermal energy storage (TES) system with the exhaust gas pipe of a single-cylinder diesel engine. The vapor absorption refrigeration system has the cooling capacity of 500 W. A cabin of 1500 mm length, 1200 mm width and 1500 mm height was fabricated with proper insulation as space for cooling. The cabin temperature drop of 8.6 ℃ was achieved in 45 min. The cooling capacity of the VAR system was 302 W, and the COP of the VAR system was 0.398. The cabin temperature drop decrease with decrease in engine RPM but it was maintain stable (8.6℃) for 25 min by using TES. The overall efficiency of the cogeneration system was 1.79 % higher than the single generation. Hence, the result showed that the small capacity (5 kW) stationary diesel can be successfully converted into a cogeneration system to produce power and space cooling simultaneously.