Absorption Refrigeration System Research Articles

Novel working fluid pair of methanol/betaine-urea for absorption refrigeration system driven by low-temperature heat sources

An absorption refrigeration system (ARS) designed for low-temperature heat sources like industrial waste heat, solar-heated water, or geothermal heat can offer substantial energy-saving benefits. This study explores a novel working fluid pair comprising methanol and betaine-urea (BE-UR), forming a deep eutectic solvent (DES) system. This design capitalizes on methanol's high enthalpy of vaporization, the low heat capacity of the working pair, and the appropriate intensity and strength of the hydrogen bonding network within the solution. The proposed fluid pair shows full solubility of BE-UR in methanol at a mole ratio of 1.81 to 1 (methanol to BE-UR), with an equilibrium vapor pressure dropping to 8.59 kPa at 303.15 K. Molecular dynamics simulations unveil a microscale solution structure, showcasing a hydrogen bond network and unbonded methanol in the concentrated working fluid pair. This configuration enhances the absorption process of methanol vapor in the ARS absorption unit. Aspen Plus simulations predict a coefficient of performance (COP) exceeding 0.85, comparable to H2O/LiBr in single effect-ARS and outperforming NH3/H2O in SE-ARS by approximately 30 %, while maintaining a lower cycle ratio of about 2.

Machine learning-based Nusselt number prediction for falling-film evaporators in absorption refrigeration systems

The evaporator serves as a pivotal component of an absorption refrigeration system (ARS), bolstered by improved wettability and mitigation of the irregular arrangement of the liquid film. The complexities of the evaporation heat transfer characteristics of falling films have led to numerous empirical correlations for falling-film Nusselt number (Nu) estimation, demanding substantial computational resources and experimental expenses and limiting their universal applicability. This study used machine learning to predict Nu of a falling-film evaporator. Artificial neural network (ANN) and random forest regression (RFR) models were used to predict heat transfer characteristics and establish a novel Nu correlation using an experimentally derived dataset. Correlations of falling-film Nu were established for six tube types using empirical data, ANN, and RFR predictions and then compared based on experimental falling-film Nu. The ANN and RFR provided high prediction performance within 10 % error and an R2 of 0.985 and 0.999, respectively. The Nu correlations derived from ANN and RFR demonstrated satisfactory agreement, typically within ±15 % error of experimental results lower than that of the empirical correlations. The optimized ANN and RFR demonstrates their promising ability to predict heat transfer characteristics and establish Nu correlations, thereby reducing the need for immense experimental efforts.

Economic optimization and thermodynamic analysis of a novel nuclear district cooling system

“Yanlong” pool-type low-temperature heating reactor (DHR-400) stands at a highly promising nuclear heating technology. However, its annual utilization duration faces constraints when exclusively employed for winter heating. To cope with this challenge, a novel nuclear district cooling system driven by DHR-400 is proposed for the first time in this paper. As the core component of the proposed nuclear district cooling system, single-effect double-lift LiBr-H2O absorption refrigeration system (SDARS) can significantly increase the temperature difference between the supply and return of the primary heating network (PHN), thereby reducing the transmission energy consumption. Despite the significant potential, the optimization design of SDARS has received limited attention. An optimization model for SDARS with the annual cost (AC) as the objective function is developed. Focusing on a real district cooling scenario in Xi'an High-tech Zone, the heat transfer areas of all process units and the operating parameters of all streams in SDARS are optimized. Results demonstrate that the optimal annual average coefficient of performance (AACOP) is improved by 10.63 % and AC is reduced by 5.44 % compared with the Benchmark case. The dynamic payback period for the combined heating and cooling system driven by DHR-400 is reduced by 5.53 years compared to the heating-only system.

Energetic performance of a solar driven absorption refrigeration system integrated with humidification dehumidification desalination system

Integrating cooling and desalination systems with a single heat source is a shortcut technique to meet the shortage of fresh water and energy as well as enhancing the efficiency of energy utilization. In this paper, the energetic performance of a double effect vapor absorption refrigeration system integrated with humidification-dehumidification desalination system has been optimized·H2O–LiCl achieves higher system primary energy ratio and needs lower heat source temperature by 5 °C and 11 °C at evaporation temperature of 10 °C and 4 °C, respectively as compared with H2O–LiBr. Therefore, a parametric study has been performed to get the optimum operating conditions for the integrated system using H2O–LiCl as working pair by varying generation, condensation, and evaporation temperatures. The optimum system conditions are generation, condensation, and evaporation temperatures of 103 °C, 103 °C and 7 °C, respectively. The corresponding system COP, GOR and EUF are 1.471, 2.391 and 3.863, respectively. Finally, the transient performance of the proposed integrated system assisted by solar energy has been evaluated for Marsa-Matrouh city in Egypt. The proposed integrated system could save 71.2 % of the input energy without solar assistance and 88.5 % with solar assistance as compared with separated systems.

Study and development of a technique for measuring concentration and mass flow rate for saline solutions

The purpose of this work is the design and construction of a non-invasive meter for concentration in saline solutions and the proposal of a low-cost mass flow meter for absorption refrigeration systems with LiBr/H2O. The proposed meter makes use of a capacitive sensor relating the electrical capacitance of the LiBr/H2O mixture to the mass fraction of LiBr in the solution. Thus, an experimental apparatus composed of a capacitive sensor with cylindrical geometry, high-frequency oscillators, and a temperature control system was built. Tests involving samples of the solution at concentrations from 50 to 64% LiBr were conducted to reproduce the typical operating conditions of the absorption chiller, establishing correlations between concentration, voltage, and temperature. The matches of these correlations between concentration and density were very good with maximum relative errors of less than 2.5%. The same procedure was performed for the density measurement, achieving a density, voltage, and temperature relationship with errors of less than 0.27%. For the determination of the volumetric flow rates, a turbine-type meter, equipped with a Hall effect sensor W1305347 and an Arduino microcontroller (MEDY FLOW), was adopted, which proved to be effective when dealing with the LiBr/H2O salt solution and good accuracy when compared to conventional meters, showing statistically proven relative errors of less than 4%. The results showed a satisfactory level of repeatability and accuracy with errors of 0.4% and 2.5%, for the range of operation evaluated.

Investigation of a Hybridized Cascade Trigeneration Cycle Combined with a District Heating and Air Conditioning System Using Vapour Absorption Refrigeration Cooling: Energy and Exergy Assessments

The insufficiency of energy supply and availability remains a significant global energy challenge. This work proposes a novel approach to addressing global energy challenges by testing the supercritical property and conversion of low-temperature thermal heat into useful energy. It introduces a combined-cascade steam-to-steam trigeneration cycle integrated with vapour absorption refrigeration (VAR) and district heating systems. Energetic and exergetic techniques were applied to assess irreversibility and exergetic destruction. At a gas turbine power of 26.1 MW, energy and exergy efficiencies of 76.68% and 37.71% were achieved, respectively, while producing 17.98 MW of electricity from the steam-to-steam driven cascaded topping and bottoming plants. The cascaded plant attained an energetic efficiency of 38.45% and an exergy efficiency of 56.19%. The overall cycle efficiencies were 85.05% (energy) and 77.99% (exergy). More than 50% of the plant’s lost energy came from the combustion chamber of the gas turbine. The trigeneration system incorporated a binary NH3–H2O VAR system, emphasizing its significance in low-temperature energy systems. The VAR system achieved a cycle exergetic efficiency of 92.25% at a cooling capacity of 2.07 MW, utilizing recovered waste heat at 88 °C for district hot water. The recovered heat minimizes overall exergy destruction, enhancing thermal plant performance.

Conceptual design and 4E analyses of a tetrageneration system in two different configurations based on poplar sawdust as a local woody biomass fuel

ABSTRACTIn this study, an innovative woody biomass‐fueled hybrid tetrageneration system composed of a single‐effect lithium bromide‐water absorption refrigeration system, a reverse osmosis desalination system, two organic Rankine cycle for the production of cooling, heating, power, and freshwater in two distinct configurations (configurations A and B), compared and discussed using energy, exergy, economic, and exergoeconomic analyses. The poplar sawdust used as a local woody biomass fuel was a by‐product of the Iran Wood and Paper Industries Company, located in northern Iran. The results revealed that the highest heating production and lowest exergy destruction were related to configuration B. The overall cost of configuration A was higher than that of configuration B. A detailed sensitivity analysis was also developed to study the effect of various factors on the thermodynamic and economic performance of the proposed configurations. By increasing the turbine inlet temperature of ORC1 from 625 to 692 K, the total sum unit costs of product of the system in configurations A and B decreased by 20 and 23 $ GJ−1, respectively (about 21%).

Utilizing an Artificial Intelligence Model to Estimate Performance Coefficients in Absorption Cooling Systems

Absorption cooling system is a cooling method used to transfer heat from one environment to another. In this system, the refrigeration cycle is based on a chemical reaction between two different fluids that absorb and expel heat. Generally, the absorption refrigeration system includes a refrigeration fluid and an absorbent heat absorbing fluid. Artificial intelligence is a field of science and engineering that aims to enable computer systems to have human-like intelligence. Artificial intelligence aims to enable computers to perform tasks such as data analysis, pattern recognition, learning, problem solving and decision making. In this study, the change of the inlet and outlet pressure values of the generator in the absorption cooling system and the prediction of the system performance (COP) value with the artificial intelligence model were studied.

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.

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.

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