Double-effect Cycle Research Articles

Numerical study of a double-effect elastocaloric cooling system powered by low-grade heat

• A double-effect heat-driven elastocaloric cooling cycle was proposed. • The double-effect eC cycle can harvest low-grade heat at 120 to 160 °C. • Driving temperature difference is used to design the transition temperature of SMAs. • COP of the double-effect eC cycle is three times better than single-effect eC cycle. Elastocaloric cooling technology is a novel solid-state cooling technology based on the latent heat associated with martensitic phase transformation in shape-memory alloys. Heat-driven elastocaloric cooling cycle could harvest low-grade thermal energy other than consuming electric power, and was proposed as a new direction in this field. To improve the heat-to-cooling efficiency of heat-driven elastocaloric cooling systems, a double-effect elastocaloric cooling cycle with two beds of actuator shape-memory alloys and two beds of refrigerant super-elastic alloys is proposed in this study. The double-effect cycle utilizes the input heat two times and thus provides improved efficiency. Numerical simulations are carried out to study the characteristics of the phase transformation in both the actuators and refrigerants. The impact of phase transition temperatures of the actuator alloys, the heat source temperature, and the operating parameters on the phase transformation and cooling performance of the system is investigated. If the phase transition temperatures are properly designed, the double-effect heat-driven elastocaloric cooling system is three times more efficient than the baseline single-effect heat-driven elastocaloric cooling system.

On the rational development of advanced thermochemical thermal batteries for short-term and long-term energy storage

Thermal energy storage is an important means for achieving carbon neutrality. Absorption thermal battery is a promising solution for renewable energy utilization due to its excellent energy storage performance and operational flexibility. This study conducts comparative investigations among different absorption thermal battery cycles from a multi-criteria perspective, including energy storage efficiency, energy storage density, exergy efficiency, charging temperature, and initial cost. Except for the existing cycles (i.e., basic cycle, compression-assisted cycle, double-stage cycle, and double-effect cycle), a novel double-effect compression-assisted cycle is also included to cover a wider range of design options. The effects of charging/discharging/cooling temperatures on the storage performance are analyzed in three scenarios, i.e., short-term cold storage, short-term heat storage, and long-term heat storage. Results indicate that the compression-assisted cycle and the double-stage cycle can improve the energy storage density and lower the charging temperatures (e.g., below 70 °C); the double-effect cycle can enhance the energy storage efficiency; the double-effect compression-assisted cycle can achieve improvements in energy storage efficiency and density simultaneously, with a maximum energy storage efficiency above 1.30 and energy storage density over 300 kWh/m3, and bridge the temperature gap (i.e., 100 °C–140 °C) between the single-effect and double-effect cycles. The maximum energy storage efficiency, energy storage density, and exergy efficiency are 1.53, 365.4 kWh/m3, and 0.61, achieved by the double-effect cycle, the compression-assisted cycle, and the basic cycle, respectively. This work aims to facilitate the rational development of absorption thermal battery cycles for high-density and high-efficiency thermal energy storage towards carbon neutrality.

A novel double-effect compression-assisted absorption thermal battery with high storage performance for thermal energy storage

Thermal battery plays a key role in increasing the utilization of renewable energy. The absorption thermal battery stands out due to its better comprehensive performance and higher application flexibility. However, the energy storage efficiency and density still need improvement, and the performance attenuation in the discharging process also needs mitigation. Thus, a novel double-effect compression-assisted absorption thermal battery is proposed in this study. The dynamic characteristics and storage performance of the novel cycle are compared with various absorption thermal battery cycles using a validated dynamic model. Results indicate that the novel cycle recovers the condensation heat like the basic double-effect cycle, which leads to an increase in energy storage efficiency. Besides, strengthened and modulated by the auxiliary compression, the energy storage density is enhanced, the charging temperature is lowered, and the discharging rate is stabilized. Under a charging temperature of 130 °C, the energy storage efficiency and density of the novel cycle are enhanced from 1.00 to 1.24 and 94.6 kWh/m3 to 240.0 kWh/m3, compared with the double-effect cycle without compression. This paper aims to provide theoretical references and suggestions for the advancement of absorption thermal batteries.

Development Of Absorption Cooling System Work By Using Solar Energy

This paper is devoted to optimize the performance of absorption cooling system working with on solar energy .It aims at reducing the cost of the absorption cooling system and reducing the temperature of the generator to enable the cooler to work with solar collector more economical and to reduce the energy consumption compared with classical cooling system.The COP has been studied for four absorption systems which using water and lithium- Bromide. The temperature of the generator for each cycle was determined according to the (pressure – temperature –concentration) diagram. The COP has been determined by drawing it’s the change with the change of temperature of the generator after determination of condensation and evaporation temperature. The results of this work indicated that, the COP. for double effect cycle is high respectively, but it requires expensive solar receivers.

Thermodynamic analysis and comparison of different absorption cycles driven by evacuated tube solar collector utilizing hybrid nanofluids

The utilization of hybrid nanofluids is the most attractive way to improve the heat transfer rate of solar thermal applications. Evacuated tube solar collector is one of the most important solar collector that is being utilized in thermal applications. The objective of the present study is to thermodynamically investigate and compare four different absorption cycles (namely, single, double, triple and quadruple effect absorption cycles) driven by evacuated tube collector and hybrid nanofluids are used as a heat transfer fluid. The operating parameters for instance, inlet temperature, direct normal irradiation, evaporator and generator temperatures are varied to assess the performance of different systems. Results showed that the efficiency of collector is higher for hybrid nanofluids as compared to the other heat transfer fluids. In addition, the coefficient of performance of quadruple effect absorption cycle is found to be 2.287, while it is 1.752 for triple effect system. The coefficient of performance of single and double effect cycles is found to be 169% and 88% less than the quadruple effect absorption cycle. The coefficient of performance of all systems increase with rise in the weak solution percentage due to the more vapor generated, while reduce as the generator temperature increases. Furthermore, hybrid nanofluid has the highest percentage of exergy destruction of 114.93 kW and quadruple effect absorption cycle is found to have the lowest exergy destruction rate, approximately 82.2 kW.

Design screening and analysis of gas-fired ammonia-based chemisorption heat pumps for space heating in cold climate

Abstract Thermally-driven ammonia-based chemisorption heat pumps (CSHP) have the potential to provide high-efficiency space heating in cold climates. Using the reversible chemical bond between sorbent salt and ammonia, CSHP thermochemically pumps heat from the cold ambient to the end-uses of space heating at 50 °C. The heating coefficient of performance (COP) of a CSHP is largely dependent on the selection of the sorbent salts, cycle configuration, and the system operation. This study uses a thermodynamic model to investigate the performance of six CSHP system configurations, including four single-effect and two double-effect cycles. The feasibility and performance of 121 available NH3/salt reactions are studied for each configuration. The thermal COP of the cycles and the primary energy COP of the gas-fired CSHP systems are evaluated assuming 50 °C supply temperature for building space heating and the optimal system designs are identified. The highest thermal COP for single-effect and double-effect cycles under −25 °C ambient temperatures are predicted to be 1.22 and 1.57, respectively. The corresponding primary energy COPs are above 1.0 and 1.15, which are 30% higher than condensing furnaces and is sustained into the same cold temperatures.

Performance evaluation of compressor assisted multi-effect absorption refrigeration cycles for power and cooling using evacuated tube collectors

To improve the thermal energy utilisation performance of an absorption cycle, compressor-assisted single, double and triple effect absorption refrigeration cycles for power and cooling using thermal energy from evacuated tube collector was proposed in this study. The power generated by the cycles is used to power the compression required to enhance the performance of the cycles. For prcom = 1.5 (base case), the simulation results show that the net power output decreased by 88%, while the cooling output increased slightly by 5.2% for the single effect cycle. The effective energy efficiency decreased from 14% to 13% and the effective exergy efficiency increased from 61% to 66% respectively. A further analysis of multi-effect cycles showed that the system can be operated at low temperatures, with the desorber temperature of double effect cycle decreasing by 32% while the desorber temperature for triple effect cycle decreases by 23% for a compression ratio of 1.5.

Analysis of Hybrid Ejector Absorption Cooling System

In this paper, a hybrid ejector single-effect lithium-bromide water cycle is theoretically investigated. The system is a conventional single-effect cycle activated by an external steam-ejector loop. A mathematical model of the whole system is developed. Simulations are carried out to study the effect of the major parameters of the hybrid cycle on its performances and in comparison with the conventional cycle. The ejector performance is also investigated. Results show that the entrainment ratio rises with steam pressure and condenser temperature, while it decreases with increasing generator temperature. The effect of the evaporator temperature on ejector performance is negligible. It is shown also that the hybrid cycle exhibits better performances than the corresponding basic cycle. However, the performance improvement is limited to a specific range of the operating parameters. Outside this range, the hybrid system behaves similar to a conventional cycle. Inside this range, the COP increases, reaches a maximum, and then decreases and rejoins the behavior of the basic cycle. The maximum COP, which can be as large as that of a conventional double-effect cycle, about 1, is obtained at lower temperatures than in the case of single-effect cycles.

Exergy analysis of single to triple effect lithium bromide-water vapour absorption cycles and optimization of the operating parameters

This paper deals with a review on exergy analyses of lithium bromide-water based single to triple effect direct and indirect fired vapour absorption systems. The analysis carried out by various investigators on exergy of the absorption cycles have been discussed. To fill the gap in the knowledge on exergy destruction rate in the absorption system, optimization of the single to triple effect direct and indirect fired absorption cycles have been conducted for a wide range of operating conditions. Hence optimum parameters in various components of the systems for maximum exergy coefficient of performance and minimum exergy destruction rate have been determined. The indirect fired systems have been optimized for different temperatures of the energy source related to the main generator temperature. While the direct fired systems have been optimized considering exergy destruction rate during the combustion process of energy sources. The energy sources selected in the present analysis are compressed natural gas and liquefied petroleum gas. Double effect cycle yields better exergy performance when the difference in temperatures of the energy source and the generator is between 6 to 37 °C, while triple effect cycle performs well when it is beyond 37 °C.

Experimental study of a new ejector-absorption refrigeration cycle driven by multi-heat sources

This paper proposes a new ejector-absorption refrigeration cycle driven by two heat sources at different temperature levels to realize the economic optimization in low-grade heat recovery application. The cycle uses the exergy of steam from a high-pressure generator and entrains the steam out of a low-pressure generator. The quantity of the steam that comes out of the low-pressure generator for the new cycle is greater than that of a conventional double-effect cycle, which means that more low-temperature-level heat, such as non-focused solar thermal heat, can be used. Therefore, the heat required to input into the system and the temperature level required to drive the cycle declines. In this study, water-lithium bromide as the working pair and a hot air temperature level ranging from 185 °C to 215 °C is used as the high level driving heat source, while the hot water heated by a solar energy collector is the low level driving heat source. In some conditions of the new cycle’s COP, 0.95 can be achieved for refrigeration, which is about 20% higher than that of the single-effect cycle. Besides this, the proposed chiller requires lower driven temperature than that of a conventional double-effect cycle.

Optimization of operating temperatures in the gas operated single to triple effect vapour absorption refrigeration cycles

Thermodynamic analysis of LiBr–H2O single, double and triple effect vapour absorption cycles has been carried out using LPG and CNG as sources of energy. Optimization of operating temperatures in single to triple effect cycles has been carried out for maximum COP of the system and minimum gas requirement in it at desired temperatures in evaporator, absorber and main condenser using iterative technique. In single effect cycle, optimum temperatures in main generator have been obtained, while in double effect cycle, low pressure generator, high pressure condenser and main generator temperatures have been optimized. In triple effect cycle having three condensers and three generators, condenser temperatures (Tc3 and Tc4) and generator temperatures (Tg2, Tg3 and Tg) have been optimized. The maximum COP of triple effect cycle goes up to 1.955 which is around 132% higher than single effect cycle with its gas requirement reduced to around 122% at the same conditions.

Energy and Exergy Analyses for Optimization of the Operating Temperatures in Double Effect Absorption Cycle

Abstract Energy and exergy analyses of double effect lithium bromide-water vapour absorption cycle has been carried out to optimize the operating temperatures in the main generator and the secondary condenser/ generator for maximum coefficient of performance (COP) and exergetic efficiency. There exists maximum COP and also maximum exergetic efficiency as the temperature in the secondary generator and the main generator are varied, thus leading to the optimum temperatures. Because of two generators in the double effect cycle, the optimization has been done in two steps. Since the secondary generator operates by using the heat of condensation release in the secondary condenser, the temperature in the secondary condenser will be nearly same as in the secondary generator. The analysis has been done for fixed temperatures in the evaporator, main condenser and the absorber. Results show that the COP increases while the exergetic efficiency decreases with increases in the evaporator temperature. The optimum parameters such as temperatures in the main generator, secondary generator and condenser, including the LiBr-Salt concentrations in the two generators, are presented for different values of the evaporator, main condenser and the absorber temperatures. A computer program has been developed for simulating the cycle.

Mapping of optimum operating condition for LiBr–water refrigeration cycles

In this work, optimum operating condition maps are generated covering wide ranges of refrigeration and sink temperatures for single- and double-effect LiBr–water vapour absorption refrigeration cycle. These optimum condition maps will be useful to choose optimum operating conditions while designing LiBr–water cycle for desired applications. Methodology for generating such maps is discussed in detail, which can also be used for other absorption refrigeration cycles with various working fluids. Three configurations of LiBr–water absorption refrigeration cycles, single effect, double-effect series flow and double-effect parallel flow, are analysed with the most accurate thermodynamic property correlation available in the literature. Sensitivity of cycle performance to various operating variables such as generator, absorber and condenser temperatures is determined. Second law analysis shows that when a higher temperature heat source is available, double-effect cycles are more effective over single effect as they have higher coefficient of performance.

Static analysis of triple-effect adsorption refrigeration with compressor

In order to improve the efficiency of the adsorption refrigeration cycle, this study proposes a triple-effect adsorption refrigeration cycle equipped with a compressor. This cycle can run in order to create a large variation in adsorbent concentration range by the compressor, even if there is little temperature variation in the desorption and adsorption processes. The objective of this study is to clarify the effect that regulating adsorption pressure using a compressor has on the adsorption refrigeration cycle, and to that end cycle efficiency was calculated using a static analysis based on a state of equilibrium. As a results from the simulation, the triple-effect cycles can operate by regulating adsorption pressure. Both COP and exergy efficiency can be improved by a factor of 1.2 if the cycled is regulated the adsorption pressure of each cycle rather than using a shared adsorption pressure. For heat sources in the temperature range of 70–100°C, this method is superior in terms of COP and exergy efficiency. COP values of approximately 1.7–1.8 can be obtained, which is three times higher than single-effect cycles. The triple-effect cycles have one-third the SCE of single-effect cycles but about the same SCE as double-effect cycles.

Performance analysis of an absorption double-effect cycle for power and cold generation using ammonia/lithium nitrate

The performance of a two-stage double-effect absorption machine for combined power and cold generation is proposed and studied theoretically, generating innovative schemes. The ammonia/lithium nitrate solution allows this cycle, consuming either solar thermal or residual heat. The machine is represented by means of a thermodynamic steady-state cycle. First, only power generation and only cold production are separately studied as function of the main internal temperatures, introducing the concepts of mixed and unmixed vapour and of virtual temperatures for allowing comparison. The results indicate that for producing power the efficiency of the cycle increases when rising the maximum pressure while for producing cold is the contrary. The maximum efficiency obtained for only power production with no superheating is 19.5% at a high generation temperature of 173°C and at a moderate 20.3bars of maximum pressure. The solution crystallization avoids a higher efficiency. The combined power and cooling cycle allows adapting the energy production to cold demand or to power demand by splitting the vapour generated. At a generation temperature of 132°C, when splitting the vapour generated into half for power and half for cooling, the cycle obtains an electric efficiency of 6.5% and a COP of 0.52. This cycle is compared to a conventional double-effect cycle configured in parallel flow, obtaining the same electric efficiency but with a 32% higher COP.

Evaluation of the Characteristic of Adsorption in a Double-Effect Adsorption Chiller with FAM-Z01

Here, we propose a double-effect adsorption chiller with a zeolite adsorbent (FAM-Z01) for utilization of waste heat. The FAM-Z01 adsorbent has the potential to recover waste heat in low temperatures ranging from 353 to 333 K and shows good potential in the adsorption chiller in terms of the high cooling output. A double-effect adsorption chiller could provide a higher Coefficient Of Performance (COP) than that of a single-effect chiller. In this paper, we developed a measuring method for the amount of adsorption in the first and second adsorber in a double-effect adsorption chiller and measured the adsorption and desorption rate based on the volumetric method. We calculated the COP of the adsorption chiller with the quantity of adsorbent obtained in the experiment. In the experiments, the quantity of adsorbent in the first adsorber was 0.14 g-H2O/g-Ads at the pressure 20 kPa and a desorption temperature over 100℃. The amount of adsorbent in the second adsorber was equal to that of the first adsorber. By analyzing the COP with the experimental results, the COP value was calculated to be over 1.0 (–) at any desorption temperature. The COP of the double-effect cycle was higher than that of single-effect cycle.

Two-stage double-effect ammonia/lithium nitrate absorption cycle

The two-stage configuration of a double-effect absorption cycle using ammonia/lithium nitrate as working fluid is studied by means of a thermodynamic model. The maximum pressure of this cycle configuration is the same as the single-effect cycle, up to 15.8 bars, being an advantage over the double-effect conventional configuration with three pressure levels that exhibits much higher maximum pressure. The performance of the cycle and the limitation imposed by crystallization of the working fluid is determined for both adiabatic and diabatic absorber cycles. Both cycles offer similar COP; however the adiabatic variant shows a larger margin against crystallization. This cycle can produce cold for external inlet evaporator temperatures down to −10 °C, but for this limit the crystallization could happen at high inlet generator temperatures. The maximum COP can be 1.25 for an external inlet generator temperature of 100 °C. This cycle shows a better COP than a typical double effect cycle with in-parallel configuration for the range of the moderate temperatures under study and using the same working fluid. Comparisons with double effect cycles using H2O/LiBr and NH3/H2O as working fluids are also offered, highlighting the present configurations advantages regarding COP, evaporation and condensation temperatures as well as crystallization.

Performance analysis of a triple-effect absorption cooling cycle using aqueous (lithium, potassium, sodium) nitrate solution as a working pair

A triple-effect absorption cooling cycle using aqueous (lithium, potassium, sodium) nitrate solution (Alkitrate) as a working fluid in the high temperature stage is simulated in this work. This cycle takes advantage of the thermal potential of high temperature heat sources and has a configuration consisting of a H2O/LiBr double-effect cycle coupled with a single-effect cycle that uses Alkitrate as a working fluid. Heat is exchanged between the two cycles by thermal fluids which flow in the external circuits. The conventional working fluid H2O/LiBr suffers from serious problems of corrosion and thermal decomposition at temperatures of over 180 °C, which restricts its use in the high temperature components of a triple-effect absorption cooling cycle. At the nominal operating conditions selected, namely a heat source temperature TH of 250 °C and a cooling-water temperature TC of 30 °C the coefficient of performance achieved with the Alkitrate topping cycle is 1.73. The correct operation of the cycle is demonstrated by drawing the cycle in the Dühring diagram, where the safety margin for the crystallization of the working fluid is adhered to.Results show that the Alkitrate triple-effect cycle has a slightly higher efficiency as compared to the H2O/LiBr triple-effect cycle at generator temperatures of over 180 °C. Moreover, the practical operation of a H2O/LiBr triple-effect cycle at temperatures higher than 180 °C suffers from the above mentioned problems related to the thermal stability and corrosion of the working pair.

Multi-Effect Plants and Ionic Liquids for Improved Absorption Chillers

State-of-the-art absorption chillers using conventional working pairs still suffer from problems like crystallization, corrosiveness, and a relatively low efficiency. To improve this technology, different working pairs as well as plant designs are investigated using the simulation tool AspenPlus. The simulation is validated by comparing the results of single-effect absorption chillers using the current commercially applied working pairs water/lithium bromide and ammonia/water with literature data. To increase the efficiency, double-effect absorption chillers are implemented and analyzed. The performance of two kinds of double-effect cycles, series and parallel, is compared using the working pair water/lithium bromide. In addition, ionic liquids (ILs) are investigated as a sorbent in order to improve the technology. So far, ILs have not been implemented in AspenPlus yet. Therefore, a guideline for the implementation of ILs in AspenPlus is outlined and the accordant phase equilibria results are validated with literature data. Simulations of single-effect cycles using the ILs 1,3-dimethylimidazolium dimethylphosphate ([MMIM][DMP]) and 1-ethyl-3-methylimidazolium dimethylphosphate ([EMIM][DMP]) in combination with water as a refrigerant are performed and the results are compared to conventional working pairs. It is shown that by using ILs, similar or even higher coefficients of performance (COPs) can be achieved in comparison to conventional working pairs. Moreover, the findings reveal that the main benefit of using ILs as a sorbent consists in providing a broader operating range with respect to heat source temperature.

Use of low grade heat sources in combined ejector–double effect absorption refrigeration systems

At a particular temperature range, heat sources are not hot enough to drive lithium bromide double-effect absorption refrigeration systems efficiently and are too hot to be used for the single effect systems because of the risk of crystallization. To make effective use of heat sources at this temperature range for refrigeration purposes, a combined ejector–double effect absorption cycles are proposed. A computational model is developed to study and compare the effect of operating parameters on the performance of combined and conventional single- and double-effect cycles from the viewpoints of first and second laws of thermodynamics. In addition, because of the importance of crystallization risk in these systems, the effect of varying working conditions on the possibility of crystallization is investigated too. The results show the advantageous performance of the combined cycle compared to that of the single- and double-effect systems at particular ranges of heat source temperature. These temperature ranges are extended at lower evaporator and higher condenser or absorber temperatures.