Effect of an Internal Heat Exchanger on the Performances of a Double Evaporator Ejector Refrigeration Cycle

A theoretical investigation is presented about a double evaporator ejector refrigeration cycle(DEERC).Special attention is paid to take into account the influence of the sub-cooling and superheating effects induced by an internal heat exchanger(IHX).The ejector is introduced into the baseline cycle in order to mitigate the throttling process losses and increase the compressor suction pressure.Moreover,the IHX has the structure of a concentric counter-flow type heat exchanger and is intentionally used to ensure that the fluid at the compressor inlet is vapor.To assess accurately the influence of the IHX on the DEERC performance,a mathematical model is derived in the frame of the dominant one-dimensional theory for ejectors.The model also accounts for the friction effect in the ejector mixing section.The equations of this model are solved using an Engineering Equation Solver(EES)for different fluids.These are:R134a as baseline fluid and other environment friendly refrigerants used for comparison,namely,R1234yf,R1234ze,R600,R600a,R290,R717 and R1270.The simulation results show that the DEERC with an IHX can achieve COP(the coefficient of performance)improvements from 5.2 until 10%.

Performance of an irreversible quantum refrigeration cycle

A new model of a quantum refrigeration cycle composed of two adiabatic and two isomagnetic field processes is established. The working substance in the cycle consists of many non-interacting spin-1/2 systems. The performance of the cycle is investigated, based on the quantum master equation and semi-group approach. The general expressions of several important performance parameters, such as the coefficient of performance, cooling rate, and power input, are given. It is found that the coefficient of performance of this cycle is in the closest analogy to that of the classical Carnot cycle. Furthermore, at high temperatures the optimal relations of the cooling rate and the maximum cooling rate are analysed in detail. Some performance characteristic curves of the cycle are plotted, such as the cooling rate versus the maximum ratio between high and low ＂temperatures＂ of the working substances, the maximum cooling rate versus the ratio between high and low ＂magnetic fields＂ and the ＂temperature＂ ratio between high and low reservoirs. The obtained results are further generalized and discussed, so that they may be directly applied to describing the performance of the quantum refrigerator using spin-J systems as the working substance. Finally, the optimum characteristics of the quantum Carnot and Ericsson refrigeration cycles are derived by analogy.

Performance Analysis and Evaluation of a Supercritical CO2 Rankine Cycle Coupled with an Absorption Refrigeration Cycle

The utilization of sensible waste heat such as flue gas and industrial surplus heat is essential for energy saving. Supercritical CO2 power generation cycle is a promising way to be used in this field. In this paper, a new supercritical CO2 Rankine cycle coupled with an absorption refrigeration cycle is proposed, which consists of a reheating supercritical CO2 cycle, a mixed-effect Li Br-H2O absorption refrigeration cycle and solar subsystem including evacuated-tube collector and a hot water storage tank. The system has four variants according to the presence or absence of solar subsystem and net cooling energy output. The thermodynamic model of the proposed system was established and its performance was evaluated. The proposed system is able to realize cascade utilization of flue gas waste heat and efficient conversion of solar energy. It has much higher thermodynamic efficiency than the reference system(i.e., the conventional supercritical CO2 Brayton cycle). Taking combined power and cooling system driven by flue gas waste heat and solar energy as an example, its thermal efficiency and exergy efficiency are 20.37% and 54.18% respectively, compared with the 14.74% and 35.96% of the reference system. Energy Utilization Diagrams(EUD) are implemented to investigate the irreversible losses and variation of the exergy destruction in the energy conversion process. Parametric analysis in two key parameters is conducted to provide guidance for the system optimal design.

Experimental Investigation of the Ejector Refrigeration Cycle for Cascade System Application

Ejector refrigeration cycle(ERC)with advantages of simple structure and low cost holds great application potential in cascade/hybrid cycles to improve the overall system performance by removing or recovering the heat from the main cycle.In this paper,a theoretical and experimental investigation of the ERC as a part of a cascade system was carried out.The operating parameters were optimized.The experimental ERC test rig was designed,developed and investigated at high evaporating temperatures and wide ranges of operating conditions.The influence of operating conditions on the efficiency of the ejector and ERC was analyzed.Experimental results and analysis in this study can be helpful for the application and operating condition optimization of ERC in cascade/hybrid refrigeration systems.

Performance comparison of the solar-driven supercritical organic Rankine cycle coupled with the vapour-compression refrigeration cycle

In this study,a parametric analysis was performed of a supercritical organic Rankine cycle driven by solar parabolic trough collectors(PTCs)coupled with a vapour-compression refrigeration cycle simultaneously for cooling and power production.Thermal efficiency,exergy efficiency,exergy destruction and the coefficient of performance of the cogeneration system were considered to be performance parameters.A computer program was developed in engineering equation-solver software for analysis.Influences of the PTC design parameters(solar irradiation,solar-beam incidence angle and velocity of the heat-transfer fluid in the absorber tube),turbine inlet pressure,condenser and evaporator temperature on system performance were discussed.Furthermore,the performance of the cogeneration system was also compared with and without PTCs.It was concluded that it was necessary to design the PTCs carefully in order to achieve better cogeneration performance.The highest values of exergy efficiency,thermal efficiency and exergy destruction of the cogeneration system were 92.9%,51.13%and 1437 kW,respectively,at 0.95 kW/m2 of solar irradiation based on working fluid R227ea,but the highest coefficient of performance was found to be 2.278 on the basis of working fluid R134a.It was also obtained from the results that PTCs accounted for 76.32%of the total exergy destruction of the overall system and the cogeneration system performed well without considering solar performance.

Experiments on an Open-Loop Cycle Carbon Dioxide Refrigeration System

An open loop cycle carbon dioxide(CO2)refrigeration system is established,and the cooling performances of high-pressure CO2 under different storage conditions(25℃,30℃,and 35℃)are investigated.Moreover,the experimental mass flow rates of CO2 are compared with the theoretical values at different conditions and refrigeration capacities.The results indicate that the storage condition of CO2 has a significant impact on the refrigeration performance,and the mass flow rate of CO2 increases with the increasing storage temperature in a given refrigeration capacity.

Conceptual Design of 25-Barrel Pellet Injector with Cycle Refrigerator for HL-2A Tokamak

The preliminary design of a multi-barrels pellet injector with cycle refrigerator as an advanced plasma-fuelling tool for HL-2A tokamak has been proposed. The design aims at precise temperature control, easy operation with high reliability and high flexibility. GM-cycle refrigerator and pipe-gun structure have been employed to produce 25 pellets in 25 gun barrels simultaneously and the design aims. have been accomplished. Prime design principle, engineering parameters, structure and layout of the cryostat components as well as calculation of heat load for the cryostat are presented.

Model Predictive Control for Vapor Compression Cycle of Refrigeration Process

A model predictive controller based on a novel structure selection criterion for the vapor compression cycle （VCC） of refrigeration process is proposed in this paper. Firstly, those system variables are analyzed which exert significant influences on the system performance. Then the structure selection criterion, a trade-off between computation complexity and model performance, is applied to different model structures, and the results are utilized to determine the optimized model structure for controller design. The controller based on multivariable model predictive control （MPC） strategy is designed, and the optimization problem for the reduced order models is formulated as a constrained minimization problem. The effectiveness of the proposed MPC controller is verified on the experimental rig.

Performance Analysis of an Integrated Supercritical CO_(2) Recompression/Absorption Refrigeration/Kalina Cycle Driven by Medium-Temperature Waste Heat

A novel power and cooling cogeneration system which combines a supercritical CO_(2) recompression cycle(SCRC), an ammonia-water absorption refrigeration cycle(AARC) and a Kalina cycle(KC) is proposed and investigated for the recovery of medium-temperature waste heat. The system is based on energy cascade utilization, and the waste heat can be fully converted through the simultaneous operation of the three sub-cycles. A steady-state mathematical model is built for further performance study of the proposed system. When the exhaust temperature is 505℃, it is shown that under designed conditions the thermal efficiency and exergy efficiency reach 30.74% and 61.55%, respectively. The exergy analysis results show that the main exergy destruction is concentrated in the heat recovery vapor generator(HRVG). Parametric study shows that the compressor inlet pressure, the SCRC pressure ratio, the main compressor and the turbine I inlet temperature, and the AARC generator pressure have significant effects on thermodynamic and economic performance of the combined system. The findings in this study could provide guidance for system design to achieve an efficient utilization of medium-temperature waste heat(e.g., exhaust heat from gas turbine, high-temperature fuel cells and internal combustion engine).

Performance Analysis of an Irreversible Refrigerator with Finite Thermal Capacity Reservoirs

To explore the influence of heat reservoirs of total thermal capacity at high and low temperature side heat exchanger of an irreversible refrigeration cycle on the coefficient of performance,the cycle model is established. By using the irreversible thermodynamics,much progress had been made in the studies of thermal resistance,heat leak and irreversible factors on the cycle of the coefficient of performance. The analytical formula of coefficient of performance and the distribution ratio of total thermal capacity are derived when the total thermal capacity at high and low temperature side heat exchanger is a constant. The influences of cycle parameters and different kinds of irreversible factors on the coefficient of performance and the optimal distribution ratio are analyzed by numerical computation. The results indicate that the coefficient of performance increases with the increase of the total heat capacity,and decreases with heat leak and internal irreversible factors. Furthermore,the optimal distribution ratio of total thermal capacity,when coefficient of performance reaches the maximum value,only has a connection with the internal dissipation.

Design and analysis of dual mixed refrigerant processes for high-ethane content natural gas liquefaction

Recovery and purification of ethane has a significant impact on economic benefit improvement of the high-ethane content natural gas.However,current LNG-NGL integrated processes mainly focus on conventional natural gas,which are not applicable to natural gas with high ethane content.To fill this gap,three dual mixed refrigerant processes are proposed for simulation study of high-ethane content natural gas liquefaction.The proposed processes are optimized by a combination method of sequence optimization and genetic algorithm.Comparatively analysis is conducted to evaluate the three processes from the energetic and exergetic points of view.The results show that the power consumption of Process 3 which compressing natural gas after distillation is the lowest.For safety or other considerations,some common compositions of the mixed refrigerant may need to be removed under certain circumstances.Considering this,case studies of mixed refrigerant involving six composition combinations are carried out to investigate the effects of refrigerant selection on the process performance.

Thermodynamic analysis on direct air capture for building air condition system:Balance between adsorbent and refrigerant

Direct air capture(DAC)is one of the most potential technologies to mitigate CO_(2) emission.Adsorption technol-ogy is recognized as a promising CO_(2) capture method in view of its desirable characteristics including reusability of adsorbents and low capital investment.To further improve thermal performance,evaporation/condensation heat of vapor compression refrigeration(VCR)cycle in air condition system of buildings is adopted for adsorp-tion/desorption process of DAC.Thermal performance of a 4-step temperature swing adsorption process(TSA)is analyzed at various adsorption/desorption temperatures by using different adsorbents.Analysis on Coefficient of Performance(COP)of VCR cycle is also conducted in search for a balance between adsorbent and refrigerant.Taking both real working capacity and COP into consideration,Mg-MOF-74&R134a is the best choice for more amounts of CO_(2).Real working capacity of Mg-MOF-74 is up to 0.38 mol•kg−1 at 70°C,which is twice as much as that of zeolite 13X.While zeolite 13X&R134a shows the best performance of two cycles in view of exergy efficiency and COP,which could reach 81.9%and 7.21,respectively,at 35°C.These matches will provide some guidelines for the practical application of the combination of DAC with heating,ventilation and air conditioning(HVAC).

Integration of evacuated solar collectors with an adsorptive ice maker for hot climate region

This research study compares the steady-state and dynamic behaviour of a solar-powered activated carbon-35(AC35)/methanol-based vapour adsorption refrigeration system for production of ice at hot climate region.Ther-modynamic comparisons are made with the coefficient of performance(COP),system COP(SCOP),specific refrig-eration capacity(SRC)and critical parameters such as cycle time and ice production rate are quantified.Further,the sustainability of the proposed ice maker has proven by integrating economic and environmental perceptions.The minimum solar flux required to ensure continuous ice production was found 800 W/m^(2).Moreover,the max-imum ice production rate and COP were decreased by 32.36%and 37.63%respectively when the system was operated under real ambient conditions.The proposed solar adsorptive ice maker achieved maximum SRC of 61.6 g m^(−2)during April month and reduced the CO_(2)emissions by 12.82 ton annually.

Development of mobile miniature natural gas liquefiers

With increasing consumption of natural gas(NG),small NG reservoirs,such as coalbed methane and oil field associated gas,have recently drawn significant attention.Owing to their special characteristics(e.g.,scattered distribution and small output),small-scale NG liquefiers are highly required.Similarly,the mixed refrigerant cycle(MRC)is suitable for small-scale liquefaction systems due to its moderate complexity and power consumption.In consideration of the above,this paper reviews the development of mobile miniature NG liquefiers in Technical Institute of Physics and Chemistry(TIPC),China.To effectively liquefy the scattered NG and overcome the drawbacks of existing technologies,three main improvements,i.e.,low-pressure MRC process driven by oil-lubricated screw compressor,compact cold box with the new designed heat exchangers,and standardized equipment manufacturing and integrated process technology have been made.The development pattern of"rapid cluster application and flexible liquefaction center"has been eventually proposed.The small-scale NG liquefier developed by TIPC has reached a minimum liquefaction power consumption of about 0.35 kW.h/Nm^(3).It is suitable to exploit small remote gas reserves which can also be used in boil-off gas reliquefaction and distributed peak-shaving of pipe networks.