Absorption Heat Transformer Cycle 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.

Performances of an absorption heat transformer cycle with water/deep eutectic solvents working fluids: Modelling and screening using a multiscale approach

In this work, a tool was developed to evaluate the performances of working fluids composed of deep eutectic solvents as absorbents and water as refrigerant in a single-stage absorption heat transformer. The thermophysical properties required for the simulation were obtained using a multiscale approach involving the COSMO–SAC(+OH–ClBr) model for the vapour-liquid equilibria and group contribution models for the densities and heat capacities of the DESs. The predictive power of the model was assessed by comparing the results with the ones obtained with a conventional approach based on the non-random two-liquid model and empirical correlations derived from experimental data. The performances of the absorption heat transformer were evaluated using several criteria including the coefficient of performance, the circulation ratio and the heat input. The results are in agreement with the ones obtained with the classical approach. The performances of 32 deep eutectic solvents as well as the influence of the different temperatures of the process on the results are investigated. Results show that the best performances are obtained with deep eutectic solvents composed of ethylene glycol, glycerol, tetramethylammonium chloride, choline chloride and betaine, with coefficient of performance values comprised between 0.438 and 0.441, circulation ratio between 14.75 and 9.66 and heat input between 1982.11 and 2006.77 kJ.kg−1. In particular, the best performances were achieved with the pair water/{ethylene glycol:[tetramethylammonium][chloride]}, ratio [2:1]. Overall, the deep eutectic solvents with a higher ratio of hydrogen bond acceptor and lower molar masses showed better performances as absorbents in absorption heat transformers.

Development and performance assessment of a novel combined power system integrating a supercritical carbon dioxide Brayton cycle with an absorption heat transformer

This study aims to investigate the system performance enhancement brought by an absorption heat transformer (AHT) on the supercritical carbon dioxide (sCO2) Brayton cycle. In the proposed sCO2/AHT system, the AHT cycle serves as a bottoming cycle to upgrade the energy level of the waste heat in the sCO2 system, producing high-quality thermal energy output to preheat the CO2 at the main compressor outlet. System performance is evaluated through the established and validated model. The variation trends of system performance with four key parameters are determined from the parametric analysis. Moreover, optimization and comparative analysis are performed for the sCO2 system, sCO2/ORC system and sCO2/AHT system. The results suggest that the sCO2/AHT system shows the best system performance. The exergy efficiency of the proposed system is 64.013%, which is 4.96% and 1.87% higher than that of the sCO2 system, sCO2/ORC system. The total product unit cost of the proposed system is 18.903$/GJ, which is 3.66% and 2.24% lower than that of the other two systems. Exergy analysis indicates that compared with the sCO2 system, the proposed system can effectively reduce the exergy destructions in the pre-cooler (4.97 MW to 1.32 MW) and get a strengthened regeneration effect for the sCO2 cycle.

Investigating the effects of integrating an absorption heat transformer with a combined cooling, heating and power system: A thermodynamic and economic analysis

Regarding the significance of low-temperature heat sources in combined cooling, heating, and power (CCHP) systems, it is necessary to find practical and economical ways to maximize the efficient use of available energies. Integrating the auxiliary cycle with the main system and changing the configuration are among the useful solutions to achieve this purpose. In this work, a combination of both solutions is presented, accordingly, an absorption heat transformer cycle (AHT) is integrated with a conventional CCHP system, which is made of organic Rankine cycle, absorption refrigeration cycle, and a heat exchanger. Three conventional CCHP systems with sequential (Configuraion1), parallel (Configuraion2) and a combination of sequential and parallel (Configuraion3) configurations are considered. It is shown that among the Configuraion1, Configuraion2, and Configuraion3, Configuraion1 has the highest energy efficiency; therefore, it is selected to be compared with the proposed integrated system with AHT. This integration affects the outputs production and also energy consumption; therefore, four different modes (standpoints) are taken into account to compare the production of power (mode A), cooling (Mode B), heating (mode C), and energy consumption (mode D) of these two systems. Also, from the exergy, environmental, and economic aspects, these two systems are compared. Regarding mode D, it is indicated that the energy and exergy efficiencies, energy consumption and carbon emission of the proposed system are improved 17.68%, 17.68%, 15.03%, and 15.02%, respectively. It is noted that for the heat source stream temperature range of 90 °C–120 °C, the proposed system has better performance than the Configuration1. Despite the additional costs of integrating AHT with the CCHP system, the proposed system has 517018.1 US$/year cost saving (which is 32.65% of the investment cost of Configuration1) if biomass is used as a heat source, which indicates its higher economic advantage than the Configuration1. Also, comparing the proposed system with Configuration1, the amount of power, cooling and heating productions are improved 27.98%, 102.15%, and 36.87%, respectively.

Review on Performance Optimization of Absorption Heat Pump Systems Based on Finite-Time Thermodynamics

Most of industrial processes use a lot of thermal energy by burning fossil fuel to produce steam or heat for the purpose. After the processes, heat is rejected to the surrounding as waste. The absorption heat pump is becoming more important because it can be powered by these industrial energy wastes and hence, it poses no danger to the environment. In this paper, a literature review of the theoretical finite-time thermodynamic-based performance optimization of absorption heat pump systems independent of the used mixtures is presented. The review describes and discusses the performance objective functions for the various absorption heat pump cycle models. It covers the endoreversible and irreversible three-heat-source cycle models, four-heat-source cycle models and absorption heat transformer cycles with respect to the following aspects: the heat transfer law models, the effect of heat resistance and other irreversible loss models on the performance. Findings from published works considering the heating load, the coefficient of performance, the total heat transfer area, the thermo-economic function, the ecological function, the exergy-based ecological function and the ecological coefficient of performance as objective functions have been summarized in a table. It appears that design parameters based on the maximum of the ecological coefficient of performance conditions represent a best compromise between the heating load and the loss rate of availability.

Energetic and exergetic analyses of a new energy system for heating and power production purposes

Energetic and exergetic analyses are performed for a proposed cogeneration cycle of heat and power. The cycle includes a STC (steam turbine cycle) to produce power and saturated steam, an AHT (absorption heat transformer) cycle to produce hot water and a HCCI (homogeneous charge compression ignition) engine as prime mover. Furthermore, the cooling water of the engine is used for heating purposes. The effect of variation of the cycle variables on the performance of the STC and AHT cycles are evaluated in details. The results show that the integrated system improves the energy utilization factor from 44.65% for the HCCI engine to 86.01% for the proposed system. Also, the exergy efficiency of the system increases from 39.49% for the HCCI engine to 48.56% for the proposed system. The maximum exergy destruction for the HCCI engine happens in the combustion chamber and for the STC occurs in turbine and for the case of the AHT cycle takes place in the absorber. Results of parametric study show that the exergy efficiency increases by increasing pressure ratio of the STC. The COP (coefficient of performance) of the AHT cycle increases as the condenser and absorber temperatures increase, but slightly decreases by increasing the evaporator temperature.

Experimental evaluation of a membrane contactor unit used as a desorber/condenser with water/Carrol mixture for absorption heat transformer cycles

A conventional desorber in the Absorption Heat Transformer (AHT) cycle requires a constant heat flux and vacuum pressure conditions to boil the working mixture and separate the working fluid. In this paper, an Air Gap Membrane Distillation (AGMD) unit was adapted as desorber/condenser with water/Carrol mixture in order to demonstrate the feasibility of the desorption process at atmospheric pressure conditions. Two membranes with 0.22 and 0.45μm pore sizes were used and three temperature levels were tested. The maximum increase in the concentration (ΔX) was 1.54% w/w (from 60.63 to 62.17% w/w) with a membrane with pore size up to 0.45μm and a solution temperature of 82.7°C. The maximum thermal process effectiveness was 17.7% (on average) with a membrane with pore size up to 0.22μm and a solution temperature of 84.4°C. Due to the corrosion process, a fouling particle by iron oxide was found on the membrane; this fouling layer could promote the “wetting” process in the membrane after a long operating time.

Performance analysis of absorption heat transformer cycles using ionic liquids based on imidazolium cation as absorbents with 2,2,2-trifluoroethanol as refrigerant

A detailed thermodynamic performance analysis of a single-stage absorption heat transformer and double absorption heat transformer cycles using new working pairs composed of ionic liquids (1-ethyl-3-methylimidazolium tetrafluoroborate ([emim][BF4]) and 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4])) as absorbent and 2,2,2-trifluoroethanol (TFE) as refrigerant has been studied. Several performance indicators were used to evaluate and compare the performance of the cycles using the TFE+[emim][BF4] and TFE+[bmim][BF4] working pairs with the conventional H2O+LiBr and organic TFE+TEGDME working pairs. The obtained results show that the ionic liquid based working pairs are suitable candidates to replace the conventional H2O+LiBr working pairs in order to avoid the disadvantages associated with it mainly crystallization and corrosion and also they perform better (higher gross temperature lift) than TFE+TEGDME working pair at several operating conditions considered in this work.

Finite Time Thermodynamic Studies on Absorption Thermodynamic Cycles: A State-of-the-Art Review

The state-of-the-art on the thermodynamic optimization of absorption thermodynamic cycles is presented in this paper. The review covers the endoreversible and irreversible three-heat-reservoir cycle models, four-heat-reservoir cycle models, four-temperature-level cycle models and other related cycles and methods on absorption refrigeration cycles, absorption heat pump cycles and absorption heat transformer cycles coupled to finite and infinite heat capacity reservoirs.

Model of irreversible finite-heat capacity heat reservoir absorption heat transformer cycle and its application

An irreversible four-temperature-level absorption heat transformer cycle model with variable-temperature heat reservoirs is established, which considers the heat resistances between the heat reservoirs and the working fluid, the internal irreversibility due to internal dissipation of the working fluid, and the heat leakages between the heat reservoirs and the surrounding. The general relations between the heating load and the coefficient of performance are derived, and the general performance characteristic and the optimal performance characteristic are obtained using numerical examples. Moreover, the cycle model and the derived general relations are confirmed by comparing the prediction results of the model and engineering analysis results for real absorption heat transformer, and the cycle performance characteristic are discussed. The results obtained herein can provide some guidance for the optimal design of absorption heat transformer.

Performance of real absorption heat-transformer with a generalized heat transfer law

An irreversible four-temperature-level absorption heat-transformer cycle model with a generalized heat transfer law of Q ∝ Δ( T n ) ( n ≠ 0) is established, which considers effects of heat resistance, heat leak and internal irreversibilities. The general relation between the COP (coefficient of performance) and the heating load is deduced. The fundamental optimal relation and the performance limit, the optimal temperatures of working substance, as well as the optimal heat transfer surface area distributions with linear phenomenological heat transfer law are derived. Moreover, effects of heat transfer law, heat leak, and internal irreversibilities on the performance of absorption heat-transformer are analyzed; and the performance comparison is performed for the distribution of the total heat transfer surface area is optimized or not by numerical example. The results obtained herein are useful for optimal design and performance improvement of absorption heat-transformer cycles.

PERFORMANCE OF AN ABSORPTION HEAT-TRANSFORMER WITH DIFFERENT HEAT TRANSFER LAW

An irreversible four-heat-temperature absorption heat-transformer cycle model is established by taking account of the heat leakage, internal irreversibilities and heat resistances between working substance and heat reservoirs with heat transfer law of Q ∝△(Tn). The general relation between the heating load and COP (coefficient of performance) with Q ∝△(Tn) is deduced. The fundamental optimal relation, the maximum heating load, the maximum COP, the optimal temperatures of working substance, as well as the optimal heat transfer surface areas distribution with linear phenomenological heat transfer law are derived. Moreover, effects of heat transfer law, heat leak and internal irreversibilities on the performance of absorption heat-transformers are analyzed, and the performance comparison is performed for the distribution of the total heat transfer surface area is optimized or not by numerical example.

Performance of an endoreversible four-heat-reservoir absorption heat-transformer with a generalized heat transfer law

SYNOPSIS An endoreversible four-heat-reservoir absorption heat-transformer cycle model with a generalised heat transfer law Q α Δ(Tn) is established. The general relationship between coefficient of performance (COP) and heating load with Q α Δ(Tn) is deduced. The fundamental optimal relationship, the maximum heating load and the corresponding COP, the optimal temperatures of the working substance, as well as the optimal heat transfer surface area distributions with linear phenomenological heat transfer law, are derived. Moreover, the effects of the heat transfer law on the performance of an absorption heat-transformer are analysed, and the performance comparison is performed for the distribution of the total heat transfer surface area, optimised or not, by numerical example.

Optimization between heating load and entropy-production rate for endoreversible absorption heat-transformers

For an endoreversible four-heat-reservoir absorption heat-transformer cycle, for which a linear (Newtonian) heat-transfer law applies, an ecological optimization criterion is proposed for the best mode of operation of the cycle. This involves maximizing a function representing the compromise between the heating load and the entropy-production rate. The optimal relation between the ecological criterion and the COP (coefficient of performance), the maximum ecological criterion and the corresponding COP, heating load and entropy production rate, as well as the ecological criterion and entropy-production rate at the maximum heating load are derived using finite-time thermodynamics. Moreover, compared with the heating-load criterion, the effects of the cycle parameters on the ecological performance are studied by numerical examples. These show that achieving the maximum ecological criterion makes the entropy-production rate decrease by 77.0% and the COP increase by 55.4% with only 27.3% heating-load losses compared with the maximum heating-load objective. The results reflect that the ecological criterion has long-term significance for optimal design of absorption heat-transformers.

Comparison of energy, exergy, and entropy balance methods for analysing double-stage absorption heat transformer cycles

The energy, exergy and entropy balance methods are used to analyse a double-stage LiBr-water absorption heat transformer cycle. An energy balance comparing component energy transfer is used to determine energy calculations. An exergy balance is employed to evaluate exergy destruction, and an entropy balance to verify entropy generation. A comparison of the results by the second law exergy and entropy balances indicates that they are consistent in identifying the location and relative significance of key non-idealities within the system. The results obtained clearly show the influence of irreversibilities of individual components on deterioration of the effectiveness and the coefficient of performance of the system. The second law analysis offers an alternative view of cycle performance and provides an insight that the first law analysis cannot. The differences between the first law analysis by energy balance method and second law analysis by exergy and entropy balance methods are illustrated quantitatively for the double-stage absorption heat transformer cycle, and the limitations and advantages of these methods are presented and discussed. Copyright © 2004 John Wiley & Sons, Ltd.

Optimal Performance of an Endoreversible Four-Heat-Reservoir Absorption Heat-Transformer

Based on an endoreversible absorption heat-transformer cycle model operating between four temperature levels with linear (Newtonian) heat transfer law, the fundamental optimal relation between the specific heating load and the coefficient of performance, the optimal temperatures of the working substance, and the optimal heat transfer surface areas of the four heat exchangers are derived by using finite-time thermodynamics. Moreover, the effects of the cycle parameters on the cycle characteristic are studied by numerical examples. The results obtained herein can provide some guidance for the optimal design of absorption heat-transformers.

Energy Analysis: Absorption Heat Transformer Cycle with a Combinig Ejector using Lithium Bromide/Water as Working Fluid

Energy Analysis: Absorption Heat Transformer Cycle with a Combinig Ejector using Lithium Bromide/Water as Working Fluid

An absorption heat-transformer and its optimal performance

On the basis of an endoreversible absorption heat-transformer cycle, a generalized irreversible four-heat-reservoir heat-transformer cycle model has been established by taking account of the heat resistances, heat leaks and irreversibilities due to the internal dissipation of the working substance. The heat transfer between the heat reservoir and the working substance is assumed to obey the linear (Newtonian) heat-transfer law, and the overall heat transfer surface area of the four heat-exchangers is assumed to be constant. The fundamental optimal relations between the coefficient of performance (COP) and the heating load, the maximum coefficient of performance and the corresponding heating load, the maximum heating load and the corresponding coefficient of performance, as well as the optimal temperatures of the working substance and the optimal heat-transfer surface areas of the four heat exchangers are derived using finite-time thermodynamics. Moreover, the effects of the cycle parameters on the characteristics of the cycle are studied by numerical examples.

Performance simulation of an absorption heat transformer operating with partially miscible mixtures

This paper proposes to study the thermodynamics performances of a new absorption heat-transformer cycle, where the separation step is obtained by the cooling and settling of a partially miscible mixture at low temperature. This new cycle has been called an absorption-demixing heat transformer (ADHT) cycle. A numerical simulation code has been written, and has allowed us to evaluate the temperature lift and thermal yield of 2 working pairs. Both high qualitative and quantitative performances have been obtained, so demonstrating the feasibility and industrial interest for such a cycle. Moreover a comparison of the simulation results with performances really obtained on an experimental ADHT has confirmed the pertinence of the simulation code.

Performance research of self regenerated absorption heat transformer cycle using TFE-NMP as working fluids

A heat transformer is proposed in order to upgrade low-temperature-level energy to a higher level and to recover more energy in low-temperature-level waste heat. It is difficult to achieve both purposes at the same time using a conventional heat transformer cycle and classical working pairs, such as H 2O–LiBr and HN 3–H 2O. The new organic working pair, 2,2,2-trifluoroethanol (TFE)- N-methylpyrolidone (NMP), has some advantages compared with H 2O–LiBr and NH 3–H 2O. One of the most important features is the wide working range as a result of the absence of crystallization, the low working pressure, the low freezing temperature of the refrigerant and the good thermal stability of the mixtures at high temperatures. Meanwhile, it has some negative features like NH 3–H 2O. For example, there is a lower boiling temperature difference between TFE and NMP, so a rectifier is needed in refrigeration and heat pump systems. Because TFE–NMP has a wide working range and does not cause crystallization, it can be used as the working pair in the self regenerated absorption heat transformer (SRAHT) cycle. In fact, the SRAHT cycle is the generator–absorber heat exchanger (GAX) cycle applied in a heat transformer cycle. In this paper, the SRAHT cycle and its flow diagram are shown and the computing models of the SRAHT cycle are presented. Thermal calculations of the SRAHT cycle under summer and winter season conditions have been worked out. From the results of the thermal calculations, it can be found that there is a larger temperature drop when the waste hot water flows through the generator and the evaporator in the SRAHT cycle but the heating temperature can be kept the same. That means more energy in the waste heat source can be recovered by the SRAHT cycle.