Absorption Refrigeration Research Articles

Triple effect absorption refrigeration systems for the deep recovery of low grade waste heat

With regard to energy conservation, low grade waste heat recovery technology is attracting significant interest. The absorption refrigeration can significantly utilize waste heat. The current researches have devoted little attention to the recovery of waste heat at lower temperature. This paper presents three triple effect absorption refrigeration systems for the deep recovery of low grade waste heat, which can make use of more waste heat as low as 60 °C. The involvement of absorption heat transformer cycle enables the proposed systems to exploit waste heat at lower temperature. The models of three systems are established using EES software. Energy, exergy and economic analysis of three systems are conducted. The results indicate that the best of three systems can achieve a coefficiency of performance of 0.178 and the maximum exergy efficiency is 0.190. The triple effect absorption refrigeration systems not only generate more cold energy, but also demonstrate better economic performance than the previous cascade absorption refrigeration system. Except for the first system, the other two systems achieve reductions of 8.7% and 15.2% in the cost of unit cold energy respectively. This paper provides three novel approaches for producing high grade cool energy from lower temperature of waste heat.

Investigation of a Biomass-Driven Cogeneration System Integrated with an Externally Fired Gas Turbine, Organic Rankine Cycle, and Absorption Refrigeration Cycle: Thermodynamic and Exergoeconomic Analyses and Optimization

Investigation of a Biomass-Driven Cogeneration System Integrated with an Externally Fired Gas Turbine, Organic Rankine Cycle, and Absorption Refrigeration Cycle: Thermodynamic and Exergoeconomic Analyses and Optimization

Enhancing the efficacy of humidifier-dehumidifier desalination in humid regions through the use of an absorption refrigeration cycle (an economic and experimental investigation)

This experimental study investigates the performance of a novel humidifier-dehumidifier (HDH) desalination system integrated with a vapor absorption refrigerator (VAR) and photovoltaic (PV) panels for humid regions. The effects of air mass flow rate (m˙a) and inlet air temperature on key performance indicators were evaluated. Increasing m˙afrom 0.0039 kg/s to 0.0071 kg/s led to a 73 % increase in freshwater output, a 35 % increase in Coefficient of Performance (COP), a 100 % increase in Gain of Output Ratio (GOR), and a 75 % increase in Recovery Ratio (RR), but a 20 % decrease in dehumidifier efficiency. The maximum freshwater production rate of 870 g/h and a GOR of 1.4 were obtained at m˙a= 0.0071 kg/s and inlet air temperature of 50 °C, representing a 117 % increase compared to the lowest temperature and flow rate tested. The cost of freshwater for solar and electric operation modes was 0.075 and 0.094 USD/kg, respectively. The system's novelty lies in the integration of HDH desalination with a VAR and PV system, enabling continuous freshwater production even under cloudy or nighttime conditions. The findings demonstrate the potential of the proposed system for sustainable freshwater production in humid areas.

Thermoeconomic analysis of a novel configuration of a biomass‐powered organic Rankine cycle for residential application with consideration the effect of battery energy storage

AbstractIn this article, the energy, exergy, and economic analysis of an organic Rankine cycle (ORC) system powered by biogas to provide electricity, heating, and cooling loads for a residential building in Munich city is investigated. Two methods have been proposed to meet the heating and cooling needs of the residential building. In the first method, heating and cooling needs are provided by a heat pump and mechanical refrigeration (System I), and in the second method, these needs are provided by a radiator and absorption refrigeration cycle (System II). In both modes of this system, the effects of battery energy storage (BES) have been analyzed for peak shaving. The working method of this research is that the residential building's electricity, heating, and cooling needs are calculated by Homer and Carrier software, respectively. Engineering equation solver software models the main local power generation system. A new method has been proposed to select the required number of units to meet the needs of the building with and without BES. The results showed that for System I with and without BES, 3 and 1 ORC units with a nominal power of 2 kW can meet all the needs of the building, respectively. In contrast, for System II, the number of 1 unit with 2 kW and 1 unit with 1 kW is needed to meet the energy needs of a residential building with and without BES. It can be concluded that heating and cooling the building with a radiator and absorption chiller cycle is more cost‐effective. The energy and exergy efficiency of ORC is reported as 11.3% and 65.7%, respectively, and the highest exergy destruction rate is related to the heater and boiler. From the economic point of view, the payback period of System II compared with System I is reduced from 18.4 to 5.66 years without using BES. With the use of BES, the payback period is reduced to 5.3 and 5.66 years, respectively. The lowest and highest electricity prices belong to System I with and without BES, which are 3.11 and 0.36 US$/kWh, respectively.

Thermodynamic and Optimization Comparison of a Solar-Powered Compressor-Assisted Combined Absorption Refrigeration and Power Systems

Thermodynamic and Optimization Comparison of a Solar-Powered Compressor-Assisted Combined Absorption Refrigeration and Power Systems

Compression-assisted absorption refrigeration cycle employing organic working pairs for ultra-low grade heat recovery

Solar absorption refrigeration technology is considered an ideal alternative to energy-intensive refrigerated warehouses due to its decarbonization and environmental friendliness. However, it faces challenges in competing with vapor compression refrigeration, such as high driving heat source temperature (>100 °C) and a long payback period. In this paper, we address these challenges by focusing on cycle structure and working pair, and propose a compression-assisted absorption refrigeration cycle (CARC) using R32/dimethylacetamide (DMAC) as working pair. The aim is to significantly reduce driving heat source temperature by adjusting absorption pressure utilizing an auxiliary compressor, enabling the cycle to be connected to low-cost and efficient non-concentrating solar collectors, thereby effectively shortening its payback period. This cycle includes two operating modes: CARC mode powered by solar energy during the daytime and vapor compression refrigeration cycle mode driven by off-peak electricity at night, ensuring 24-hour cooling capacity for refrigerated warehouses. The results indicate that this cycle can flexibly utilize 60∼80 °C solar hot water easily obtained as driving heat source and its evaporation temperature decreases to -20 °C. To assess its performance benefits, a compression-assisted absorption refrigeration system is developed and implemented. By utilizing the limited roof area of a refrigerated warehouse, it can achieve an 18.2 % reduction in electricity consumption and a 24.2 % reduction in carbon emissions compared to the vapor compression one annually. Additionally, during peak electricity demand periods in summer, the system exhibits significant energy-saving effects, and its payback period is about 4.2 years. Ultimately, this cycle provides a viable solution for energy-saving and emission reduction in refrigerated warehouses.

Evaluation of a concentrated solar power-driven system designed for combined production of cooling and hydrogen

The current technique of hydrogen generation and cooling production raises climatic problems, which calls for the investigation of cleaner alternatives. No research has been conducted to propose and analyze a solar thermal power cycle-based water electrolysis for on-site production of hydrogen and the detailed exergy analysis of a series flow double-effect absorption chilling machine employed for large solar cooling. In this regard, a helically coiled tube embedded central receiver is used in the heliostat field for the simultaneous production of solar cooling and green hydrogen to meet the increasing needs of energy and fuel sustainably. The combined system is composed of four sub-systems including a heliostat field, LiBr–H2O operated series-flow double effect absorption refrigeration cycle (DEARC), organic Rankine cycle (ORC), and proton exchange membrane (PEM) electrolyzer. The system was examined from energy and exergy perspectives in the Engineering Equation Solver (EES) using library data of REFPROP for obtaining the thermodynamic properties of working fluids. The results of the thermodynamic model for the combined system are validated. Furthermore, the effect of ambient temperature, solar irradiation, and type of ORC working fluid on the hydrogen and cooling production, and the overall energy and exergy efficiency of the combined system are examined. A computational fluid dynamics simulation applying ANSYS-FLUENT was used to examine how coil curvature ratio and coil torsion affect solar heat transfer fluid (SHTF) pressure and temperature leaving the receiver. The coil curvature ratio affects temperature increase more than coil torsion. Solar heat transfer fluid outlet temperature increases by 36.9 % when the coil curvature ratio increases from 0.063 to 0.095 at direct normal irradiations (DNI) 1200 W/m2, input temperature of 92°C, and coil torsion of 0.032. The response of the cogeneration cycle to varying operating parameters is examined. Application of R141b as the ORC fluid results in a large increase of cooling exergy efficiency from 14.98 % to 63.48 % when the ambient temperature is increased from 15 °C to 45 °C whereas the exergy efficiency of the combined system is marginally improved. The exergy distribution presents for ORC operating on R141b, out of 100 % input solar exergy, 16.42 % is generated as hydrogen exergy and 13.67 % cooling exergy, 66.79 % is the exergy destroyed, and the rest 3.12 % is exergy loss. Exergy analysis is utilized to identify the sources of losses in useful energy within the components of the system considered and provides a more realistic and meaningful assessment than the traditional energy analysis. The results justify a need for the promotion of exergy analysis through policy decisions in the context of the global energy and environment crisis.

Thermodynamical Analysis of the Distillation Column for Targeting Minimum Energy in Ammonia–Water Absorption Refrigeration Cycle

In this study, a comprehensive method to optimize distillation columns in ammonia–water absorption refrigeration, power, and cogeneration cycles is introduced. The novelty of this work lies in a comprehensive analysis of the distillation column's thermal performance and the introduction of a new design framework that maximizes heat integration. Key findings include the critical role of the solution heat exchanger, especially at lower generation and evaporation temperatures. Using a saturated liquid or two‐phase feed can achieve up to 80% efficiency at a feed composition of 0.3. Moreover, in the results, the substantial potential for improving the coefficient of performance (COP) through strategic design is highlighted. Notably, minimizing the pinch point temperature difference to 0 °C can boost the COP by 6%, while optimal feed placement can increase it by 9%. Incorporating feed preconditioning and side exchangers can lead to a 22% COP enhancement, indicating the significance of heat integration to the distillation column. In this study, a graphic guideline for selecting cycles that can achieve a minimum of 10% COP improvement without introducing unnecessary complexity is delivered and it suggests that distillation columns can be simplified by using a combination of separators, heaters, and coolers in certain cases.

Performance optimization and techno-economic analysis of a novel geothermal system

A novel geothermal system that has high efficiency and economic benefits was proposed in this study. The proposed geothermal system includes an organic Rankine cycle, absorption refrigeration subsystem, and heating/hot water subsystem. The selection of working fluid, performance optimization, and techno-economic analysis of the geothermal system were conducted by establishing mathematical models. The thermodynamic performance was enhanced by using evaporators in series and the separation-flash process. And the thermodynamic performance of the proposed system was investigated with five working fluids. The ratio of mass flow rate, separate pressure, and flash pressure were optimized using the stepwise multi-objective optimization technology. The results show that R245fa was the optimal working fluid. The system can reach its optimal operating state when the ratio of mass flow rate is 2.5, separate pressure is 2500 kPa and flash pressure is 1000 kPa. The largest power generation, thermal efficiency, exergy efficiency, and the lowest irreversible loss of the optimized system are 962.5 kW, 13.64 %, 35.74 %, and 4248 kW, respectively. The techno-economic analysis shows that the total investment cost of the novel geothermal system is 8.173–9.132 million dollars, the annual revenue is 2.451–2.608 million dollars per year, and the static payback period is 3.134–3.726 years.

Retrofitting of a solar cooling and heating plant by employing PCM storage and adjusting control strategy

A solar cooling and heating plant with a 1000 l hot water storage tank has been operated since 2018. Two main problems were observed: (1) a fluctuating operation of the absorption chiller due to a high number of stat-up and shut-down procedures; (2) high electricity consumption caused by a low solar fraction SFn of 50.9% during the cooling period. In 2021, the solar plant was retrofitted by employing a shell and tube heat exchanger based on a PCM melting at 64 °C and by adjusting the control strategy. The system performance was evaluated and compared before and after retrofitting based on the operational data in 2021 and 2022. The total number of switch-on times of the chiller shrank by 33.5% and the operation time was increased by 65% in 2022 due to the stable hot water inlet temperature. Contributing to the high heat storage capacity of the PCM storage, more solar thermal energy was utilized and the average SFn reached 75.6% during the cooling period in 2022, leading to a 24.4% reduction in the total electricity consumption compared to 2021.

Proposal of a geothermal-driven multigeneration system for power, cooling, and fresh water: Thermoeconomic assessment and optimization

The depletion of fossil fuel reserves and environmental challenges have prompted the exploration of alternative energy sources. Geothermal energy, extractable from within the Earth's crust, emerges as a reliable renewable option throughout the mentioned shift. In this regard, the presented study introduces a geothermal-powered multigeneration system designed to generate power, manage cooling loads, and produce fresh water. This comprehensive system incorporates an organic flash cycle, a half-effect absorption refrigeration unit, a Kalina cycle, and a humidification-dehumidification desalination unit. Evaluating the system's thermoeconomic performance involves considering input parameters and simplifying assumptions to determine the performance profitability of the presented system. Furthermore, a parametric examination is conducted which is followed by the employment of an optimization analysis across three diverse scenarios to identify the most favorable operating conditions. The results of the presented research reveal that the suggested system can deliver power, cooling capacity, and freshwater production at rates of 342.3 kW, 301.7 kW, and 0.233 kg/s, respectively. Additionally, the system demonstrates an exergy efficiency of 31.52 % and achieves a payback period of 5.85 years.

Energy and environmental assessment of a novel multigeneration plant powered by infectious medical waste

This study highlights the energy and environmental impacts of a multigeneration system for infectious medical waste -to-energy (IMWtE). Thermal performance and life cycle assessment (LCA) are investigated via the energy conservation, ReCiPe method, SimaPro database, and situation of environmental issues in Thailand and worldwide. A lifespan of 20 y is considered in this study. The energy results show that the multigeneration system can produce a net power of 15.80 kWe from an organic Rankine cycle (ORC), 4.62 kW of cooling power from an absorption chiller, and 13.21 kW of heating power from a drying room. An overall system efficiency of 13.40% is directly driven from an infectious medical waste (IMW) of 81.98 kg/s. According to the LCA results, the construction phase has the highest emissions (81%), followed by the operation phase (6%) and the landfill (1%). The recycling process reduces the environmental impact by 12%. The total lifetime midpoint impact is 3.88E-01 kg emission-eq/kWh. The endpoint includes 4.33E-07 DALY/kWh of human health, 1.50E-06 Species·y/kWh of ecosystem, and 3.81E-03 USD/kWh of resources. The LCA single score is approximately 6.08E+02 Pt/lifespan or 5.63E-04 Pt/kWh.

Exergy and exergoeconomic comparative analysis of three NH3–NaSCN absorption refrigeration cycles driven by solar collector

Exergy and exergoeconomic comparative analysis of three NH3–NaSCN absorption refrigeration cycles driven by solar collector

Exergoeconomic evaluation and multi-objective optimization of a novel geothermal-driven zero-emission system for cooling, electricity, and hydrogen production: capable of working with low-temperature resources

Geothermal energy is an abundant natural resource in many regions around the world. However, in some areas, the temperature of the geothermal energy resource is too low to be efficiently harvested. Organic Rankine cycles (ORCs) are known for recovering heat from low-temperature resources and generating electricity. Furthermore, half-effect absorption chillers (HEACs) are designed to produce cooling with low-temperature resources. This study proposes a novel configuration that utilizes an ORC for electricity generation, a HEAC for cooling production, and a PEM electrolysis system to produce hydrogen. The power section consists of two turbines, one driven by the vapor produced from the geothermal flow expansion, which powers the PEM section, while the other turbine in the ORC is used to drive pumps and electricity production. First, the system is thermoeconomically analyzed for an initial set of inputs. Then, various parameters are analyzed to determine their influences on system performance. The analyses reveal that the system can work with geothermal source temperatures as low as 80 °C, but the exergy and energy (thermal) efficiencies decrease to around 17% under the base settings. Furthermore, the system is capable of working with resource temperatures up to 170 °C. Ten parameters are found to affect the system’s efficiency and effectiveness. To optimize the system, the Non-dominated Sorting Genetic Algorithm II (NSGA-II) is implemented to find the optimum conditions. The objective functions are exergy efficiency and unit polygeneration cost (UPGC), which can conflict. The optimization shows that the exergy efficiency of the system can reach 48% in the optimal conditions (for a heat source temperature of 112 °C and a mass flow rate of geothermal fluid of 44 kg/s), with a hydrogen production rate of 1.1 kg/h.

Techno-economic analysis of blue ammonia synthesis using cryogenic CO2 capture Process-A Danish case investigation

Ammonia is a vital chemical with numerous applications. Currently, the primary methods for generating the necessary reactants for ammonia production involve steam methane reforming (SMR) and cryogenic air separation unit (CASU), while the Haber-Bosch process converts these reactants into ammonia. However, the SMR process releases substantial amounts of CO2, making it imperative to employ an efficient and cost-effective CO2 capture technology to mitigate emissions. This investigation focuses on evaluating the cryogenic CO2 capture (CCC) process for blue ammonia production and provides a thorough economic analysis, estimating both the initial investment costs and operational expenses involved in producing blue ammonia. The results indicated that the CCC process can capture 90% of the CO2 content in the flue gas emitted by the SMR, incurring an energy penalty of 0.724 MJe/kgCO2 while capturing CO2 in the liquid phase with purities exceeding 99.9%. In this case, the estimated CO2 capture costs would be 18.05, 45.1, and 16.65 USD/ton in 2021, 2022, and 2023, respectively. This represents a 40% reduction compared to the CO2 capture costs associated with conventional amine-based technology. The results of this study indicate that the annual electricity costs for ammonia production increase by 38.5% and 64.2% when employing the CCC and amine-based processes, respectively. This investigation employed an isothermal reactor for ammonia synthesis, using the heat from the exothermic reaction in a water ammonia absorption refrigeration cycle (ARC) to condense and purify ammonia. The results show that the ARC system can effectively condense ammonia at −6 °C, producing a liquid ammonia stream with 99.3% purity. This leads to a 95% reduction in power consumption compared to a vapor compression refrigeration cycle (VCRC). Consequently, this method has the potential to decrease the annual operational costs for ammonia production by 2.92%, 2.69%, and 3.13% in 2021, 2022, and 2023, respectively. This study indicated that the hydrogen production unit incurs the highest initial investment costs, as well as operating costs, in the blue ammonia production process, followed by CASU and the Haber-Bosch process.

Numerical modeling of a confined falling liquid film sheared by a gas flow in a plate heat exchanger of an NH3/H20 absorption chiller

In recent years, the demand for cooling has seen a substantial increase, primarily due to rising summertime temperatures. Conventional mechanical compression air conditioners have played a predominant role in fulfilling this demand, albeit at the cost of significant electricity consumption. In response, absorption chillers have emerged as an eco-friendly alternative, powered by sustainable heat sources like solar energy or industrial waste heat. The present work is conducted within the framework of developing compact absorption chillers incorporating plate heat exchangers. It builds upon prior research by improving an existing numerical model for falling film plate heat exchangers within an NH3/H2O absorption chiller. This former numerical model evaluates the coupled heat and mass transfer between the liquid film and the vapor flow while excluding hydrodynamic interactions at the liquid-vapor interface. The current investigation aims to address compactness and cost-efficiency limitations in absorption chillers. The consequences of operation within confined spaces were numerically evaluated. An innovative analytical model was developed to quantify the influence of the interactions at the liquid-vapor interface. Shear stress and interfacial perturbations were considered compared to the classical Nusselt model, enabling the evaluation of the changes in the average film thickness and the flooding phenomenon. This analytical model was then added to the previously developed heat and mass transfer model. The numerical model was applied to both the desorber and absorber units. The results show that increased confinement has minimal effects on the transfer coefficients. Additionally, an approach is suggested for estimating flooding in confined spaces and the results are compared with various correlations available in the literature.

A multivariable control strategy based on fuzzy logic interference rule for a solar-driven, direct air-cooled H[formula omitted]O-LiBr absorption chiller

The operation of a solar-driven H2O-LiBr Absorption Chiller (AbC) is subjected to various limitations regarding its ability to satisfy efficiently the required cooling demand while avoiding certain internal conditions, such as H2O-LiBr solution crystallization and water freezing. These circumstances would lead to problematic situations and jeopardize the continuous operation of the system. Thus, the development of accurate control strategies is an issue of interest. A new operational control strategy approach is introduced and tested through simulation studies, by employing a transient model of the entire solar cooling application. A prototype under development is used for the parametrization of the direct air-cooled AbC model used in the simulations. The developed control strategy aims to minimize the electrical consumption of the auxiliary components of the AbC (i.e., fan, pumps) during the partial load operation period, by using a fuzzy logic interference rule for determining the cooling capacity demand and then applying an optimization algorithm for determining the velocity of the auxiliary components. Within the proposed control strategy, a fast-calculation model is embedded, which predicts the chiller’s capacity under variable external conditions and partial load operation. The electrical COP is increased up to 2.2 times with respect to a baseline case, based on a basic two-step control strategy, while allowing the chiller to operate smoother, minimizing the crystallization and freezing risk.

Performance characteristics of a hybrid absorption chiller driven by exhaust gas and cooling water from a gas engine

Performance characteristics of a hybrid absorption chiller driven by exhaust gas and cooling water from a gas engine

The Prospect of Using Membrane Devices for Cold Production as an Alternative to the Absorption Refrigerating Installation

The Prospect of Using Membrane Devices for Cold Production as an Alternative to the Absorption Refrigerating Installation

Experimental research of a novel binary solution for diffusion absorption cooling systems

AbstractThe diffusion absorption refrigeration (DAR) systems are driven by heat and utilize a binary solution along with an inert gas as the working fluid. In commercial applications, the choice of binary solutions operating with an auxiliary gas is typically limited to ammonia‐water or water‐lithium bromide combinations. The focus of this study is to explore the viability of using tetrafluoropropene (R‐1234yf, an HFO refrigerant) as the refrigerant, dimethylacetamide (DMAC) as the absorbent, and helium as the auxiliary gas. As the thermodynamic properties of this specific binary solution are yet to be studied, experimental investigations are conducted to obtain these properties. The results allow the establishment of the pressure‐temperature and concentration relationships and determine the mixture‘s enthalpy for various temperatures. Subsequently, both numerical and experimental analyses of the diffusion absorption system are performed. The experimental findings show that, under certain concentrations of the components and with appropriate heat input, temperatures in the evaporator reached below 0 °C. However, the system exhibits low coefficient of performance values, high generation temperatures, and overall inefficiency, suggesting that this particular binary solution may not be well‐suited for diffusion absorption cooling systems.