Absorption Cycle Research Articles

Experiment investigation on a LiBr-H2O concentration difference cold storage system driven by vapor compression heat pump

Solar-powered LiBr absorption cooling system is of potential in the application of air-conditioning. A LiBr-H2O concentration difference cold storage system driven by vapor compression heat pump was proposed. This cold storage process is not affected by the environmental conditions, since the main energy input is low price electricity at night. The experimental results show that the energy storage density (ESD) can reach 77.8 kWh/m3 and the energy storage coefficient of performance (ESCOP) is 2.81 with low heat loss. The ESCOP means the energy stored in the cold storage process divided by the total electricity consumption in the absorption and heat pump subsystem. The heat transfer in the condenser of the absorption subsystem approximately equals that in the evaporator of the heat pump, and the electricity consumption of the circulating pump in the absorption subsystem is low. Therefore, the value of ESCOP should be slightly lower than the COP of the heat pump system but for higher than 1. These results indicate the feasibility of improving the system efficiency, the operation cost, and long term operation of the solar air conditioning system by coupling the absorption and vapor compression cooling cycles. Finally, the influence of working parameters on the system performance is discussed based on the experimental and simulation analyses. The energy balance between the absorption cycle and the heat pump cycle in the cold storage system is analyzed. It is found that the coefficient of performance of the heat pump (COPele,HP) and ESCOP increase with a low initial LiBr-H2O solution concentration. The ESCOP decreases by 34.4% when the initial concentration increases from 52% to 57%. The average ESD increases to 140.2 kWh/m3 with a concentration difference of 8%. Based on the experiment results, the payback period of the proposed system is estimated as 2.4 years comparing with the traditional LiBr-H2O absorption system.

Techno-Economic Investigation of an Integrated Boiler–Solar Water Heating/Cooling System: A Case Study

With the increase in oil prices, developing nations end up paying expensive electricity and heating bill. This leading study investigates the experimental development of a new energy-saving system by integrating a solar water heater and solar cooling absorption cycle with a conventional boiler for domestic hot water and heating purposes. The heating and cooling load calculations for space heating of the building were calculated using TRNSYS 14.1 computer software and the results were used in calculating the energy-saving value. A 65 flat plate solar collector-chiller system with a total surface area of 130 m2 was integrated with the boiler and used to supply heating and cooling for a three-story building (1500 m2) in Al Bayt University, Jordan. The integrated system helped to save energy, reduced the emission of CO2 into the atmosphere, supplied hot water, and space heating/cooling requirements to the building year-round, and reduced the overall energy cost of heating and cooling by 55% and 48%, respectively. Moreover, the techno-economic analysis showed that the payback period of the combined system with a total cost of $18,650 is roughly 2.5-year. The solar water heating/cooling system has the potential to provide more than 50% of the house energy demand free of charge with a significant reduction in carbon footprint.

Integration of solid-oxide fuel cells and absorption refrigeration for efficient combined cooling, heat and power production

Abstract Combined cooling, heating and power (CCHP) systems are characterized by a substantially higher energy-utilization efficiency compared to standalone systems. In this study, an integrated system comprising a solid-oxide fuel cell (SOFC), hot-water storage tank (HWST) and absorption refrigeration (AR) cycle is considered. The SOFC model was developed in Aspen Plus®. It was used to determine the thermodynamic properties of the exhaust gas that was then used to provide heat for the HWST and to drive the AR cycle. Thermodynamic models for the AR cycles were developed in Engineering Equation Solver, considering LiBr–H2O and NH3–H2O as working fluids. The sensitivity analysis of a number of SOFC output parameters has been carried out. The most optimal case was characterized with the coefficient of performance (COP) and CCHP efficiency of 0.806 and 85.2% for the LiBr–H2O system, and 0.649 and 83.6% for the NH3–H2O system, respectively. Under such optimal operating conditions, the SOFC was characterized by the net electrical efficiency of 57.5% and the net power output of 123.66 kW. Data from the optimal solution were used to perform the thermodynamic study and sensitivity analysis to assess the influence of different absorption cycle operating conditions and to identify possible applications for the considered integrated systems.

Study on the heating performance of absorption-compression hybrid heat pump in severe cold regions

Traditional heating methods are polluted and inefficient, more than, conventional air source absorption heat pump has poor heating performance at low temperature. To overcome these shortcomings, by sharing evaporator and condenser from absorption and compression heat pump, the novel air source absorption-compression hybrid heat pump (ASACHHP) is proposed. The thermodynamic models of ASACHHP are established and verified. Under different internal thermodynamic parameters, the coefficient of performance (COP) and exergy coefficient of performance (ECOP) of ASACHHP are compared. The maximum COP that can be achieved under given research conditions is 1.241–1.420, the maximum ECOP is 0.697–0.756. In comparison with common absorption heating systems, ASACHHP can provide hot water above 60 °C when the ambient temperature is below −10 °C, which shows better low-temperature applicability than single-stage ASAHP. When the ambient temperature is suitable, ASACHHP can be switched to a single-stage absorption cycle. Although the heating range and environmental application range of ASACHHP are slightly reduced compared with the high-pressure compression-assisted absorption system, ASACHHP has the highest COP among the common absorption heating improved systems, the improving rate can be 1.5–13.0%. In general, ASACHHP is a kind of clean and efficient alternative heating technology in severe cold regions.

DESIGN, CFD ANALYSIS AND PERFORMANCE EVALUATION OF COMBINED STEAM EJECTOR SINGLE EFFECT LIBR/H2O ABSORPTION REFRIGERATION SYSTEM

The objective of this work is to develop the efficiency of vapour absorption system by addition the steam ejector cycle. Computational fluid dynamics (CFD) is a numerical implement that is greatly accurate to simulate a high number of applications and developments. The CFD analysis has appeared as a viable skill to provide dynamic and efficient design solutions. In this work a CFD analysis concentrate on the mathematical simulation of the operating of a steam ejector to develop the Efficiency of vapour absorption cycle using LiBr/H2O as a working refrigerant for this system and operating under steadystate conditions. The overall design steam ejector technique that follows ASHRAE and ESDU recommended are considered in this study, throat nozzle diameter of 4.13 mm, and suction maxing chamber diameter of 10 mm. The effect of different operational settings on the performance of the steam ejector operating in combination with a single effect absorption system was measured. The geometrical model and meshing is done with solid works and ANSYS FLUENT solver is used for the analysis. In this research study, development to the system is achieved by utilizing the potential kinetic energy of the ejector to enhance refrigeration efficiency. The effects of the entrainment ratio of the ejector, primary and secondary operating temperature, on the condition condenser pressure and temperature and system performance have been studied. The results showed that the entrainment ratio is found to increase with the decrease of secondary pressure (evaporator pressure) and consequently, the entrainment ratio is also found to increase with increase of generator temperature keeping the evaporator temperature and condenser pressure constant. The entrainment ratio does not vary much with the condenser pressure until the critical condenser pressure. The COP of the established system is developed by up to 45% compared with that Basic system at the given condition.

Effect of Mischmetal Introduction on Hydrogen Storage Properties in Impure Hydrogen Gas of Ti-Fe-Mn-Co Alloys

The research aims to study the effect of adding mischmetal (Mm) to the TiFe0.86Mn0.07Co0.07 alloy on its hydrogen storage performance and cyclic stability. The results show that TiFe0.86Mn0.07Co0.07 + x% Mm (x = 0,4,6,8) alloys can be easily activated. The hydrogen absorption capacity of TiFe0.86Mn0.07Co0.07 + 4% Mm reaches 1.76 wt% (mass fraction) at 298 K. With the increase of Mm addition, the hydrogen storage capacity decreases slightly. Furthermore, after 40 absorption and desorption cycles in hydrogen containing 250 ppm O2, the alloy still has 36% of its initial hydrogen storage capacity, and the alloy can recover 93% of its hydrogen storage capacity through heat treatment.

Application of Spinel MgMn2-X Al x O4 As Cathode for Mg Rechargeable Battery

【Introduction】Lithium-ion battery (LIB) has mainly used in our life, but its high price due to Li and Co metals are crucial problem. Magnesium rechargeable battery (MRB) has been recently studied as a post LIB due to elemental abundant supply and superior theoretical volumetric energy density of magnesium. For cathode materials, spinel oxides is one of a candidate of MRB due to its high redox potential and three-dimensional diffusion paths.[1] Especially, MgMn2O4 is expected to perform high theoretical capacity because utilization of both Mn3+/Mn4+ and Mn2+/ Mn3+ redox is possible in the potential window of the common electrolyte.[2] But structural change from tetragonal to cubic occurs due to Jahn-Teller effect of Mn3+ ion during charge/discharge, which decreases reversibility. In this study, we tried to enhance reversibility of MgMn2O4 spinel by substituting Al for Mn to release its Jahn-Teller distortion, and the optimal substitution ratio and their electrochemical property were evaluated.【Experimental】MgMn2-xAlxO4 (x = 0, 0.1, 0.2, 0.5) were synthesized by Pechini method[3] with an annealing process of 400 ºC, 10 hour. Cathodes were prepared by mixing the obtained samples with acetylene black and polytetrafuluoroethylene at a weight ratio of 60/30/10 . Mg alloy (AZ31) was used for an anode. Galvanostatic charge/discharge profiles were obtained by using a coin cell with a 0.3 M Mg[B(HFIP)4]2/triglyme electrolyte at 25 ºC, 10 mA/g.【Results and discussion】According to X-ray diffraction(XRD) patterns, MgMn2-xAlxO4 (x = 0, 0.1, 0.2, 0.5) spinel were obtained and their crystallinity become lower by Al substitution. In MgMn1.5Al0.5O4, the crystal structure changed from tetragonal to cubic phase, suggesting that the Jahn-Teller effect is suppressed by the formation of the solid solution of tetragonal MgMn2O4 and cubic MgAl2O4. The Al-substituted MgMn2O4 exhibited higher discharge capacities compared with MgMn2O4 (64.0 mAh/g), and especially MgMn1.9Al0.1O4 showed the highest discharge capacity of 92.3 mAh/g. In the poster session, X-ray absorption spectroscopy (XAS) and cycle characteristics will be reported.【Acknowledgment】This work was supported by JST ALCA-SPRING Grant Number JPMJAL1301, Japan.【References】[1] S. Okamoto, T. Ichitsubo, T. Kawaguchi, Y. Kumagai, F. Oba, S. Yagi, K. Shimokawa, N. Goto, T. Doi and E. Matsubara, Adv. Sci., 2015, 2, 1500072[2] H. Kobayashi, K. Yamaguchi and I. Honma, RSC Adv., 2019, 9, 36434-36439.[3] J. Yin, A. B. Brady, E. S. Takeuchi, A. C. Marschilok and K. J. Takeuchi, Chem. Commun., 2017, 53, 3665-3668.

Hydrogen absorption and desorption properties of Mg/MgH2 with nanometric dispersion of small amounts of Nb(V) ethoxide

A study to determine the optimal content of Nb(V) ethoxide required to efficiently catalyze the H2 sorption kinetics in the Mg/MgH2 system is reported. The materials were synthesized by hand mixing different amounts of additive (from 0.10 to 1 mol%) to pre-milled MgH2. Considering kinetics and capacity the best performance corresponds to a 0.25 mol% of Nb ethoxide concentration. With this material, a remarkable kinetic behavior with excellent reversibility is obtained: 5.3 wt% and 5.1 wt% of hydrogen are absorbed and desorbed respectively at 300 °C in 3 min. At 250 °C the material absorbs 5.2 wt% of hydrogen and releases 3.7 wt% in 10 min. Thermal desorption starts at 247 °C and peaks at 268 °C. The H2 sorption properties of all the materials remain unchanged after 10 cycles of absorption and desorption at 300 °C, and the best material reversibly takes in and releases 5.3 wt% of H2 during a 10 min combined cycle. The kinetic improvement of the hydrogen desorption and absorption properties is attributed to an enhancement of the kinetic processes that occur on the surface of the material, due to the excellent spreading of the liquid additive at nanometric level, as revealed by SEM/EDS and TEM/EELS.

Performance analysis of compressor-assisted two-stage triple effect absorption refrigeration cycle for power and cooling

Ammonia-water absorption and power cycles offer a viable option for the effective use of low and medium temperature heat sources for sub-zero cooling and power generation. The proposed system is a compressor assisted two-stage triple effect absorption cycle for power and cooling. This system comprises of power sub-system and absorption-compressor sub-system and both systems utilize ammonia-water mixture as the working fluid. The power generated by the cycle is used for the compression required to enhance the performance of the cycle. The mathematical model of the proposed system is analyzed using first and second law of thermodynamics. The engineering equation solver (EES) software is employed to analyze the model. Thermodynamic performance of the combined cycle was evaluated based on the compression ratio and the heat source inlet temperature. The pressure ratio (Prcom) of the integrated compressor is varied between 1.0 and 1.6 to observe the effect on the operation, output, and performance of the system. The simulation result shows that the heat source inlet temperature can be reduced by 50 °C compared to the traditional two-stage triple effect absorption system. The effective energy and exergy efficiencies are 17% and 76% respectively while the cooling load was 165.4 kW. The results also showed that asorber1 and absorber 2 have the highest rate of exergy destruction of 30.91% and 37.32% followed by condenser 1 with 16.3% and solution heat exchanger 2 with 7.89%. It is observed that the proposed system performs better in comparison to its counterparts operated at medium temperature heat sources.

The absorption of SO2 by morpholine cyclic amines with sulfolane as the solvent for flue gas

The absorption properties of N-(2-hydroxyethyl) morpholine (HEM), morpholine (MP) and N-(2-aminoethyl) morpholine (AEM) for SO2 were studied using sulfolane (SUL) as solvent in this work. Among these solvent combinations, HEM/SUL shows the best cyclic absorption performance, and the capacity of HEM-SUL-40 (40 wt% of HEM and 60 wt% of SUL) to absorb 8580 mg/m3 SO2 (the remainder is N2) is 192.18 mg/g at 293.15 K. The absorption capacity of the second cycle is 97.5% of the first absorption cycle, which is higher than 70% of the Cansolv amine solution in a commercial application with similar experimental conditions. However, MP/SUL is difficult to desorb at high temperature, and the absorption capacity of AEM/SUL is much lower than HEM/SUL and MP/SUL. According to the FTIR, 1H NMR and 13C NMR, all three cyclic amines have charge transfer effects with SO2. The structure of HEM/SUL can be recovered after heating, but MP cannot be recovered. ΔrGm° in the reaction against HEM with SO2 increases significantly with increasing temperature. The ΔrGm° of HEM-SO2 and MP-SO2 at 353.15 K is −12.56 kJ/mol and −16.29 kJ/mol, respectively, which further explains the easy desorption of HEM-SO2 and the difficult desorption of MP-SO2 at high temperature.

Energy, exergy, and exergoeconomic evaluation of a novel CCP system based on a solid oxide fuel cell integrated with absorption and ejector refrigeration cycles

An innovative cogeneration power and cooling system is presented in which a solid oxide fuel cell (SOFC) is integrated with absorption and ejector refrigeration cycles. To assess the practicality of the suggested system, it is evaluated from energy, exergy, and exergoeconomic vantage points. The effects of key design parameters including SOFC input temperature, ammonia concentration, evaporation temperature, and hot temperature difference of the generator on the system’s technical and economic performance are determined. The results revealed that the suggested system can generate overall electricity, and cooling load of 398.4 kW, 51.31 kW, respectively. Further, the energy and exergy efficiencies, and product cost rate of the system are 55.46%, 47.29%, and 106.7$/GJ, respectively. Heat exchanger 3 is indicated as the major source of inefficiency by an exergy destruction rate of 106.2 kW. Furthermore, the results demonstrated that higher energy productivity is achievable by increasing the ammonia concentration, SOFC input temperature, and evaporation temperature. Moreover, results revealed that the higher the input temperature of the fuel cell, and the hot temperature difference of the generator are, the higher the exergy efficiency is obtainable. Considering the exergoeconomic assessment, it is observed that the product cost rate of the suggested CCP system can be decreased by the augmentation of the fuel cell input temperature, ammonia concentration, and evaporation temperature.

Simultaneous Removal of NO and SO2 from Flue Gas Using [Bmim]2FeCl4/Sulfolane Binary Mixtures.

NO and SO2 are the major pollutants of coal combustion. As superior absorbents, ionic liquids are environmentally friendly, are reusable, and can clean flue gases, such as CO2, SO2, and NOx. However, NO and SO2 absorption with low concentration in flue gases under normal conditions is rarely studied. In this work, [Bmim]2FeCl4 was synthesized and mixed with sulfolane for NO and SO2 removal from flue gas. The investigated concentrations of NO and SO2 were 1100 and 2500 ppm, respectively, which are close to real fuel gas conditions. Results showed that 30 wt % [Bmim]2FeCl4/sulfolane mixture performed the best absorption behavior. The presence of SO2 could promote NO absorption by [Bmim]2FeCl4/sulfolane mixture. The 30 wt % [Bmim]2FeCl4/sulfolane mixture had removal efficiencies of 93.6 and 76.2% for NO and SO2, respectively. This mixture also showed great reusability for NO and SO2 after six cycles of absorption. Fourier transform infrared (FTIR) spectrum indicated that SO2 and NO removal by [Bmim]2FeCl4/sulfolane binary mixture was due to the chemical reaction between NO and [Bmim]2FeCl4 and the physical absorption between SO2 and sulfolane.

Energy and exergy evaluation of triple-effect H2O/LiBr absorption cooling system

This paper deals with the energy and exergy analysis of triple-effect LiBr–water absorption system. Mathematical models have been developed using an engineering equation solver (EES) to simulate the triple-effect absorption cycle. The coefficient of performance, exergy efficiency and total exergy destruction are determined by varying generator, absorber and evaporator temperatures. The operating parameters are selected as generator temperature (170–200°C), absorber temperature (25–40°C) and evaporator temperature (5–11°C). Findings illustrate that COP of triple-effect absorption cycle increases at absorption temperatures 35°C and 40°C. For a given evaporator and generator temperature, COP and exergy efficiency of triple absorption cycle increase. The total exergy destruction rate decreases with an increase in evaporator temperature. Largest exergy destruction and exergy percentage are found in absorber and smallest in medium pressure generator.

Design and performance evaluation of a double ejector boosted multi-pressure level absorption cycle for refrigeration

In this work, a multi-pressure double ejector boosted absorption refrigeration system (DEBARS) is designed and analyzed; two vapor and liquid ejectors are implemented simultaneously before the condenser and absorber components and both of the solution and refrigerant heat exchangers are included in the cycle. Vapor and liquid ejectors are simulated and analyzed in details and the shock circle method is used for the vapor ejector simulation. The characteristics inside the vapor ejector involving the chocking phenomenon and the irreversible shock process are also considered comprehensively. The proposed system is compared with the basic and three-pressure level absorption refrigeration cycles. The results show that the multi-pressure level cycle has the superior performance to both of the previous cycles; The maximum Coefficient of performance (COP) and second law efficiency (ηII) in the new cycle is improved up to 108.35/33.11 and 31.61/46.62 percent in comparison with the basic and three-pressure level cycles, respectively. The generator activation temperature of the DEBARS is in the range of basic cycle and 36–55 °C lower than the three-pressure level cycle; Also, the evaporator start-up temperature in the DEBARS is considerably lower than both of the basic and three-pressure level cycles.

Power generation from waste heat: Ionic liquid‐based absorption cycle versus organic Rankine cycle

AbstractAspen Plus® simulations using the Peng‐Robinson (PR‐EOS) and the COSMO‐SAC models were performed to study absorption power cycles (APCs) using mixtures of R‐134a with two ionic liquids, [C2C1im][Tf2N] or [C6C1im][Tf2N], and compared against an R‐134a organic Rankine cycle (ORC) operating under similar conditions. The PR‐EOS results were in agreement with calculations from a PR model fitted to the R‐134a + IL experimental phase equilibrium data. The APCs have similar efficiencies and outperform the ORC by 3%–46%, with the largest differences observed when operating with lower grade (lower TH) heating sources, lower quality cooling (higher TL), and lower subcooling in the pump inlet stream. The PR‐EOS and the Conductor‐like Screening Model Segment Activity Coefficient (COSMO‐SAC) results follow similar trends, but numerical discrepancies are observed in the cycle efficiencies and stream flow rates and compositions due to differences in solubilities and enthalpy changes between both models, suggesting that improvements are needed to increase the accuracy of COSMO‐SAC for these systems.

K2CO3-containing composite sorbents based on a ZrO2 aerogel for reversible CO2 capture from ambient air

Abstract In this work, K2CO3-containing composite materials were synthesized based on a mesoporous zirconia aerogel prepared by an epoxide-assisted sol-gel method using supercritical drying in ethanol. The porous ZrO2 was impregnated with an aqueous solution of potassium carbonate to obtain composite materials with K2CO3 weight content ranging from 9 to 29 wt%. All the composites were tested in the process of CO2 absorption from the air with a relative humidity of 25% followed by thermal desorption at 200 °C. The samples after the CO2 absorption step were characterized by Fourier transform infrared spectroscopy and X-ray diffraction methods. Among the materials studied, the composite sorbent containing 23 wt% K2CO3 demonstrated the highest dynamic CO2 absorption capacity (4.6 wt%) in the temperature-swing absorption (TSA) cycles. The results indicate that a certain part of K2CO3 loaded into zirconia mesopores forms surface species which do not actively participate in the CO2 absorption and desorption processes. For the composite K2CO3/ZrO2 material with the optimal K2CO3 loading, CO2 absorption capacity is higher compared to the values obtained for K2CO3/γ-Al2O3 composite sorbents studied under the same conditions. Taking into account that this material demonstrates stable CO2 absorption capacity values in the consecutive TSA cycles and needs a relatively low temperature for regeneration, it should be considered for application in Direct Air Capture units.

Research Progress on the Anti-Disproportionation of the ZrCo Alloy by Element Substitution.

Hydrogen-induced disproportionation (HID) during the cycles of absorption and desorption leads to a serious decline in the storage capacity of the ZrCo alloy, which has been recognized as the biggest obstacle to its application. Therefore, the prerequisite of a ZrCo application is to solve its anti-disproportionation problem in the field of rapid hydrogen isotope storage. Beyond surface modification and nanoball milling, this work systematically reviews the method of element substitution, which can obviously improve the anti-disproportionation. From a micro angle, as hydrogen atoms that occupy the 8e site in the ZrCoH3 lattice are instable and are considered to be the driving force of disproportionation, researchers believe that element substitution by changing the occupation of hydrogen atoms at the 8e site can improve the anti-disproportionation of the alloy. At present, Ti/Nb substitutions for the Zr terminal among substitute elements have an excellent anti-disproportionation performance. In this work, up-to-date research studies on anti-disproportionation and its disproportionation mechanism of the ZrCo alloy are introduced by combining experiments and simulations. Moreover, the optimization of the alloy based on the occupation mechanism of 8e sites is expected to improve the anti-disproportionation of the ZrCo alloy.

Comparison the start-up time of the key parameters of aqua-ammonia and water–lithium bromide absorption chiller (AC) under different heat exchanger configurations

The time that an absorption chiller needs to reach the designed working condition is called start-up. During this time, energy is consumed through the system while efficient refrigeration is not available. So, it’s too important to consider the influencing parameters on this period of time so that reduction in energy consumption is achieved. Also, dynamic analysis is used to reduce the startup time and increase system performance in addition to strategic control purposes. Optimizing an absorption cycle during transient operations, such as start up or shut down is very important. The aim of this study is to investigate and compare the effect of employing refrigerant and solution heat exchangers (RHX and SHX) on dynamic performance of both NH3–H2O and H2O–LiBr absorption chillers (ACs). Also, the effect of solution heat exchanger’s efficiency on the start-up time of the key parameters of both ACs is investigated. To diminish the effect of approximate relations on the results, thermodynamic properties of NH3–H2O and H2O–LiBr solutions are extracted from the EES software. By making a link between MATLAB and EES software, a set of differential equations is solved in MATLAB software. The fourth order Runge–Kutta method is employed to solve the differential equations system. This process is continued until convergence criteria are satisfied. The results show that removing SHX from the cycle increases the start-up time of both NH3–H2O and H2O–LiBr AC’s COPs by 11.76% and 45.16% respectively. The start-up time of the COP of H2O–LiBr absorption chiller is highly affected in comparison with the NH3–H2O absorption cycle, by removing SHX or increasing the SHX efficiency. Also, utilizing the RHX does not affect the dynamic response of the key parameters of the both absorption chillers.

Thermoeconomic analysis and multi-objective optimization of a novel hybrid absorption/recompression refrigeration system

In the present article, thermodynamic, exergoeconomic, economic, and sustainability investigations of a recently developed environmentally friendly hybrid absorption/recompression refrigeration cycle is proposed to evaluate its feasibility for decision making and marketing. The proposed system is a novel hybridization of the conventional vapor compression and absorption cycles, wherein a booster compressor has been used between the generator and condenser of the single-effect absorption cycle to improve its performance. Also, two separate multi-objective optimization models are developed using a combination of the nondominated-storing-genetic algorithm (NSGA-II) and artificial neural network (ANN) to address the optimum performance values concerning the objective functions. The obtained results approve that the proposed cycle is a promising concept from both thermodynamic and economic viewpoints. The results indicate that the system presents a coefficient of performance and exergy efficiency of 4.88 and 37.43% under the optimum working conditions. The overall rate of exergy destruction of the system is 20.23 kW, and a sustainability index of around 1.53 can be achieved at a cooling capacity of 150 kW. The economic results indicate that the reference system has a payback period of 4.17 years, which is reduced to less than 4 years after doing the optimizations.

High-flux thermal management at megawatt scale using a double-effect absorption/vapor-compression cascade refrigeration cycle

Abstract A robust, high-performance, cascaded double-effect absorption/vapor-compression cycle with a high temperature lift was conceptualized and analyzed for a naval ship application. A double-effect LiBr–H2O absorption cycle driven by high-temperature (>275 °C) exhaust heat was coupled to a subcritical CO2 vapor-compression cycle to provide low temperature refrigerant (-40 °C) for high-heat flux electronics applications and medium temperature refrigerant (5 °C) for space conditioning and other low-heat flux applications. The double-effect absorption/vapor-compression cycle outperformed the corresponding single-effect cycle, providing 74.4% higher cooling capacity for the same waste heat input; however, it required more heat exchange area. The improved performance of the double-effect configuration was much higher at lower heat rejection temperatures. A parametric study on the exhaust and heat rejection temperatures showed that the cycle exhibited high COPs over a wide range of operating conditions, indicating the robustness of the cycle.