The performance assessment of a combined organic Rankine-vapor compression refrigeration cycle aided hydrogen liquefaction

In this study, the performance of the combined cooling cycle with the Organic Rankine power cycle, which provides cooling of the hydrogen at the compressor inlet which compresses the constant temperature in the Claude cycle used for hydrogen liquefaction, on the system is examined. The Organic Rankine combined cooling cycle was considered to be using a geothermal source with a flow rate of 120 kg/s at a temperature of 200 °C. The first and second law performance evaluations of the whole system were made depending on the heat energy at different levels taken from the geothermal source. The thermodynamic analysis of the equipment making up the system has been done in detail. The temperature values at which the hydrogen can be effectively cooled were determined in the presented combined system. The efficiency coefficient of the total system was calculated based on varying pre-cooling values. As a result of the study, it was determined that cold entry of hydrogen into the Claude cycle reduced the energy consumption required for liquefaction. Amount of hydrogen cooled to specified temperature increase by increase in mass flow of geothermal water and its temperature. Liquefaction cost is calculated to be 0.995 $/kg H₂ and electricity produced by itself is calculated to be 0.025 $/kWh by the new model of liquefaction system. Cost of the liquefaction in the proposed system is about 39.7% lower than direct value of hydrogen liquefaction of 1.650 $/kg given in the literature.     

Performance analysis of a waste‐heat‐powered thermodynamic cycle for multieffect refrigeration

A multieffect refrigeration system that is based on a waste‐heat‐driven organic Rankine cycle that could produce refrigeration output of different magnitudes at different levels of temperature is presented. The proposed system is integration of combined ejector–absorption refrigeration cycle and ejector expansion Joule–Thomson (EJT) cooling cycle that can meet the requirements of air‐conditioning, refrigeration, and cryogenic cooling simultaneously at the expense of industrial waste heat. The variation of the parameters that affect the system performance such as industrial waste heat temperature, refrigerant turbine inlet pressure, and the evaporator temperature of ejector refrigeration cycle (ERC) and EJT cycles was examined, respectively. It was found that refrigeration output and thermal efficiency of the multieffect cycle decrease considerably with the increase in industrial waste heat temperature, while its exergy efficiency varies marginally. A thermal efficiency value of 22.5% and exergy efficiency value of 8.6% were obtained at an industrial waste heat temperature of 210°C, a turbine inlet pressure of 1.3 MPa, and ejector evaporator temperature of 268 K. Both refrigeration output and thermal efficiency increase with the increase in turbine inlet pressure and ERC evaporator temperature. Change in EJT cycle evaporator temperature shows a little impact on both thermal and exergy efficiency values of the multieffect cycle. Analysis of the results clearly shows that the proposed cycle has an effective potential for cooling production through exploitation of lost energy from the industry. Copyright © 2014 John Wiley & Sons, Ltd.     

Development of an alternative refrigeration cycle

The paper describes the experimental development of an alternative regenerative refrigeration cycle. The cycle attempts to overcome the inefficiencies caused by flash gas entering the evaporator by a novel use of the main compressor. The system incorporates an extra vessel in place of the traditional expansion valve. The vessel is filled with high temperature, high pressure refrigerant from the condenser. The compressor is then switched from the evaporator, thus reducing the pressure. As the pressure is lowered, it is hoped that the flash gas is removed. The cycle is compared, both theoretically and practically, with the standard vapour compression cycle. The problems encountered and their solutions are also presented were possible.     

Performance improvement of the vapour compression refrigeration cycle by a two‐phase constant area ejector

The performance of a vapour compression system that uses an ejector as an expansion device was investigated. In the analysis, a two‐phase constant area ejector flow model was used. R134a was selected as the refrigerant. According to the obtained results, for any operating temperature there are different optimum values of pressure drop in the suction chamber, ejector area ratio, ejector outlet pressure and cooling coefficient of performance (COP). As the difference between condenser and evaporator temperatures increases, the improvement ratio in COP rises whereas ejector area ratio drops. The minimum COP improvement ratio in the investigated field was 10.1%, while its maximum was 22.34%. Even in the case of an off‐design operation, the performance of a system with ejector is higher than that of the basic system. Copyright © 2008 John Wiley & Sons, Ltd.     

The R-? characteristics of a three-heat-source refrigeration cycle

The influence of irreversibilities of finite-rate heat transfer and heat leak on the performance of a refrigerator driven by ‘low-grade’ heat energy rather than ‘high-grade’ work is investigated by means of an endoreversible three-heat-source cycle model. The cooling rate and coefficient of performance are adopted to be objective functions for optimization. The optimal performance of the refrigeration cycle is analyzed. Some new results are obtained. For example, the maximum cooling rate and corresponding coefficient of performance are determined. The maximum coefficient of performance and corresponding cooling rate are shown. The curves indicating the performance characteristics of the refrigeration cycle are presented. The results obtained here will play an instructive role in the exploitation of real refrigerators.     

Parametric analysis and optimization for a combined power and refrigeration cycle

A combined power and refrigeration cycle is proposed, which combines the Rankine cycle and the absorption refrigeration cycle. This combined cycle uses a binary ammonia–water mixture as the working fluid and produces both power output and refrigeration output simultaneously with only one heat source. A parametric analysis is conducted to evaluate the effects of thermodynamic parameters on the performance of the combined cycle. It is shown that heat source temperature, environment temperature, refrigeration temperature, turbine inlet pressure, turbine inlet temperature, and basic solution ammonia concentration have significant effects on the net power output, refrigeration output and exergy efficiency of the combined cycle. A parameter optimization is achieved by means of genetic algorithm to reach the maximum exergy efficiency. The optimized exergy efficiency is 43.06% under the given condition.     

First and second laws analysis of the heat pipe/ejector refrigeration cycle

Integration of the heat pipe with an ejector will result in a compact and high performance system. The concept of the heat pipe/ejector refrigeration cycle is discussed, in this paper. The needed driving capillary forces are firmly established. The basic characteristics of the system, such as entrainment ratio, coefficient of performance, exergy efficiency and thermal efficiency of the system are evaluated. Also, the zero-dimensional constant pressure mixing theory is applied to ejector. In this study, water is used as the working fluid. Whenever the mixed flow is supersonic, a normal shockwave is assumed to occur upstream of diffuser inlet. The simulation results indicate that, the coefficient of performance can reach about 0.30 at T_e = 10 °C, T_c = 30 °C and T_g = 100 °C. Also, the second law efficiency of the heat pipe/ejector refrigeration cycle increases with increasing evaporator temperature and decreasing condenser temperature. It is seen that, the maximum heat pipe cooling capacity obtains for large heat pipe diameters, near the small heat pipe lengths. It has proven that, this refrigeration system can be widely used in many areas, especially in renewable energy utilization such as solar energy.     

Performance analysis and optimization of a new two-stage ejector-expansion transcritical CO2 refrigeration cycle

In this paper, a new two-stage configuration of ejector-expansion transcritical CO₂ (TRCC) refrigeration cycle is presented, which uses an internal heat exchanger and intercooler to enhance the performance of the new cycle. The theoretical analysis on the performance characteristics was carried out for the new cycle based on the first and second laws of thermodynamics. Based on the simulation results, it is found that, compared with the conventional two-stage transcritical CO₂ cycle, the COP and second law efficiency of the new two-stage cycle are about 12.5–21% higher than that of conventional two-stage cycle. It is also concluded that, the performance of the new two-stage transcritical CO₂ refrigeration can be significantly improved based on the presented new two-stage cycle. Hence the new two-stage refrigeration cycle is a promising refrigeration cycle from the thermodynamically and technical point of views. A regression analysis in terms of evaporator and gas cooler exit temperatures has been used, in order to develop mathematical expressions for maximum COP, optimum discharge and inter-stage pressures and entrainment ratio.     

An improved absorption refrigeration cycle driven by unsteady thermal sources below 100°C

This paper deals with an improved absorption refrigeration cycle with staged absorption. Instead of having only one absorber, the improved cycle uses a series of absorbers among which one is cooled by the external medium and the others are cooled by refrigerant at staged pressures between the evaporation pressure and condensation pressure. Ammonia–lithium nitrates (NH₃–LiNO₃) are selected as the working fluids and the calculation results for the two‐staged cycle and the three‐staged cycle are analysed in detail. It is demonstrated that the improved cycle is able to steadily run when driven by low‐grade thermal sources as low as 65°C, and to produce deep refrigeration temperature as low as −40°C. Copyright © 2000 John Wiley & Sons, Ltd.     

Exergy analysis of Joule–Thomson cryogenic refrigeration cycle with an ejector

In this paper, exergy method is applied to analyze the ejector expansion Joule–Thomson (EJT) cryogenic refrigeration cycle. The exergy destruction rate in each component of the EJT cycle is evaluated in detail. The effect of some main parameters on the exergy destruction and exergetic efficiency of the cycle is also investigated. The most significant exergy destruction rates in the cycle are in the compressor and ejector. The ejector pressure ratio and compressor isothermal efficiency have a significant effect on the exergetic efficiency of the EJT cycle. The exergy analysis results show the EJT cycle has an obvious increase in the exergetic efficiency compared to the basic Joule–Thomson refrigeration cycle. A significant advantage from the use of the ejector is that the total exergy destruction of the EJT cycle can be reduced due to much more decreasing of the exergy destruction rates in the compressor and expansion valve. The exergy analysis also reconfirms that applying an ejector is a very important approach to improve the performance of the Joule–Thomson cryogenic refrigeration cycle.     

Thermodynamic assessment of a lab-scale experimental copper-chlorine cycle for sustainable hydrogen production

An integrated lab-scale copper-chlorine (Cu-Cl) thermochemical cycle for hydrogen production at the University of Ontario Institute of Technology (UOIT) is presented and analyzed in this paper. In a practical operation of the Cu-Cl cycle, besides the main steps of hydrolysis, thermolysis, electrolysis and drying, the oxidized anolyte (consumed anolyte at the electrolyzer cell) needs to be recycled to be concentrated sufficiently for the electro-chemical process. Recycling of the oxidized anolyte through the separation processes is achieved by distillation of anolyte, drying unit, separation cell, pressure swing distillation and CuCl₂ concentrator. This study examines the thermodynamic performance of all unit operations in the lab-scale Cu-Cl cycle. A process simulation model with Aspen Plus is used to assess the system by energy and exergy analyses. For the specific system design characteristics, the cycle is capable of producing 100 L/h of hydrogen. From the simulation results, the overall energy and exergy efficiencies of the lab-scale Cu-Cl cycle are determined to be 11.6% and 34.9%, respectively. Furthermore, after the thermolysis and hydrolysis reactors, the quench cell and CuCl₂ concentrator have the highest exergy losses with thermal energy transferred through CuCl solidification and water vaporization phase-change processes at relatively high temperature. Additional results of the processes are presented and discussed.     

Exergetic life cycle assessment of a hydrogen production process

Exergetic life cycle assessment (ExLCA) is applied with life cycle assessment (LCA) to a hydrogen production process. This comparative environmental study examines a nuclear-based hydrogen production via thermochemical water splitting using a copper–chlorine cycle. LCA, which is an analytical tool to identify, quantify and decrease the overall environmental impact of a system or a product, is extended to ExLCA. Exergy efficiencies and air pollution emissions are evaluated for all process steps, including the uranium processing, nuclear and hydrogen production plants. LCA results are presented in four categories: acidification potential, eutrophication potential, global warming potential and ozone depletion potential. A parametric study is performed for various plant lifetimes. The ExLCA results indicate that the greatest irreversibility is caused by uranium processing. The primary contributor of the life cycle irreversibility of the nuclear-based hydrogen production process is fuel (uranium) processing, for which the exergy efficiency is 26.7% and the exergy destruction is 2916.3 MJ. The lowest global warming potential per megajoule exergy of hydrogen is 5.65 g CO₂-eq achieved a plant capacity of 125,000 kg H₂/day. The corresponding value for a plant capacity of 62,500 kg H₂/day is 5.75 g CO₂-eq.     

Performance investigation of a thermal‐driven refrigeration system

Thermal‐driven refrigeration systems have attracted increasing research and development interest in recent years. These systems do not cause ozone depletion and can reduce demand on electricity. The main objective of this work is to perform tests and theoretical analyses of a thermal‐driven refrigeration system using a new sorbent–sorptive pair as the working pair. The active component of the sorbent used in this study is sodium thiocyanate (NaSCN). Ammonia (NH₃) is chosen as sorptive. Based on the thermodynamic properties of the working solution, a mathematical model is introduced to analyze the system characteristics and performance. A series of experimental data is collected to establish the relationships among different system parameters. The results are compared with those of other thermal‐driven refrigeration systems. It is shown that the advantages provided by this system over others include lower generator and evaporator temperatures and a higher coefficient of performance (COP). Copyright © 2008 John Wiley & Sons, Ltd.     

Performance characteristics of a two-stage irreversible combined refrigeration system at maximum coefficient of performance

A general cycle model of a two-stage combined refrigeration system is established and used for analizing the influence of multi-irreversibilities, such as finite rate heat transfer, heat leak between the heat reservoirs and internal dissipation of the working fluid, on the performance of the refrigeration system. The coefficient of performance is taken as an objective function for optimization. The maximum coefficient of performance is calculated, and other corresponding performance parameters, such as the temperatures of the working fluid in the isothermal processes, the optimal distribution of the heat transfer areas and the power input of the refrigeration system, are determined. The results obtained here are more general than those obtained from a two-stage endoreversible combined refrigeration system and can guide the optimal design and operation of real combined refrigerator systems.     

Performance analysis of a refrigeration cycle using a direct contact evaporator

This research work studies an ice thermal energy storage having an injection of R12 refrigerant into the water to exchange heat directly. The water temperature decreases to the freezing point and ice is formed. The ice is used for creating chilled water for an air-conditioning purpose. The system consists of a compressor, a condenser, an expansion valve and a direct contact evaporator. This system has a capacity of approximately 2 tons of refrigeration. The system simulation created from the mathematical model of each component has been carried out. It was found that the performance of the system depends on two factors, the compressor speed and the mass flow rate of the refrigerant. The suitable conditions are 8–10 rps for the compressor speed and 0.04–0.06 kgs⁻¹ for the mass flow rate. The coefficient of performance is about 3·4–3·6 which is higher than that of the conventional system. © 1998 John Wiley & Sons, Ltd.     

Investigation of a novel combined cycle of solar powered adsorption–ejection refrigeration system

A novel model of the combined cycle of a solar-powered adsorption–ejection refrigeration system (CCSPAERS) is established. By analyzing the theory of this system and its thermodynamics, together with numerical simulation, it is found that it is a feasible method to overcome the intermittent character of a single bed solar adsorption refrigeration system. The estimated coefficient of performance for this combined cycle is about 0.4 under the following operating conditions: condensing temperature 313 K, evaporating temperature 283 K, regenerating temperature 393 K and desorbing temperature 473 K, using zeolite 13X–water as the pair. The higher desorbing temperature can be obtained when a vacuumed tube adsorber or a CPC adsorber is used.     

Maximum equivalent efficiency and power output of a PEM fuel cell/refrigeration cycle hybrid system

With the help of the current models of proton exchange membrane (PEM) fuel cells and three-heat-source refrigeration cycles, the general model of a PEM fuel cell/refrigeration cycle hybrid system is originally established, so that the waste heat produced in the PEM fuel cell may be availably utilized. Based on the theory of electrochemistry and non-equilibrium thermodynamics, expressions for the efficiency and power output of the PEM fuel cell, the coefficient of performance and cooling rate of the refrigeration cycle, and the equivalent efficiency and power output of the hybrid system are derived. The curves of the equivalent efficiency and power output of the hybrid system varying with the electric current density and the equivalent power output versus efficiency curves are represented through numerical calculation. The general performance characteristics of the hybrid system are discussed. The optimal operation regions of some parameters in the hybrid system are determined. The advantages of the hybrid system are revealed.     

Modelling and performance study of a continuous adsorption refrigeration system driven by parabolic trough solar collector

This article suggests a numerical study of a continuous adsorption refrigeration system consisting of two adsorbent beds and powered by parabolic trough solar collector (PTC). Activated carbon as adsorbent and ammonia as refrigerant are selected. A predictive model accounting for heat balance in the solar collector components and instantaneous heat and mass transfer in adsorbent bed is presented. The validity of the theoretical model has been tested by comparison with experimental data of the temperature evolution within the adsorber during isosteric heating phase. A good agreement is obtained. The system performance is assessed in terms of specific cooling power (SCP), refrigeration cycle COP (COP_cycle) and solar coefficient of performance (COP_s), which were evaluated by a cycle simulation computer program. The temperature, pressure and adsorbed mass profiles in the two adsorbers have been shown. The influences of some important operating and design parameters on the system performance have been analyzed.The study has put in evidence the ability of such a system to achieve a promising performance and to overcome the intermittence of the adsorption refrigeration systems driven by solar energy. Under the climatic conditions of daily solar radiation being about 14 MJ per 0.8 m² (17.5 MJ/m²) and operating conditions of evaporating temperature, T_ev = 0 °C, condensing temperature, T_con = 30 °C and heat source temperature of 100 °C, the results indicate that the system could achieve a SCP of the order of 104 W/kg, a refrigeration cycle COP of 0.43, and it could produce a daily useful cooling of 2515 kJ per 0.8 m² of collector area, while its gross solar COP could reach 0.18.     

Exergy analysis on the simulation of a small-scale hydrogen liquefaction test rig with a multi-component refrigerant refrigeration system

This study investigates the simulation of a proposed small-scale laboratory liquid hydrogen plant with a new, innovative multi-component refrigerant (MR) refrigeration system. The simulated test rig was capable of liquefying a feed of 2 kg/h of normal hydrogen gas at 21 bar and 25 °C to normal liquid hydrogen at 2 bar and −250 °C. The simulated power consumption for pre-cooling the hydrogen from 25 °C to −198 °C with this new MR cycle was 2.07 kWh/kg_GH2 from the ideal minimum of 0.7755 kWh per kilogram of feed hydrogen gas. This was the lowest power consumption available when compared to today’s conventional hydrogen liquefaction cycles, which are approximately 4.00 kWh/kg_GH2. Hence, the MR cycle’s exergy efficiency was 38.3%. Exergy analysis of the test rig’s cycle, which is required to find the losses and optimize the proposed MR system, was evaluated for each component using the simulation data. It was found that the majority of the losses were from the compressors, heat exchangers, and expansion valves. Suggestions are provided for how to reduce exergy in each component in order to reduce the exergy loss. Finally, further improvements for better efficiency of the test rig are explained to assist in the design of a future large-scale hydrogen liquefaction plant.     

Performance analysis of a novel eco‐friendly internal combustion engine cycle

The Miller cycle applications have been performed to diminish NO_x released from internal combustion engines (ICEs), in recent years. The Miller cycle provides decreased compression ratio and enhanced expansion ratio; hereby, maximum in‐cylinder combustion temperatures diminish, and NO_x formations slow down remarkably. Another less‐known method is Takemura cycle application, which provides heat addition into engine cylinder at constant combustion temperatures. In this study, a novel cycle including the Miller cycle and the Takemura cycle has been developed by using novel numerical models and computing methods with seven processes and a novel way to decrease NO_x emissions at higher levels compared with the single applications of known cycles. A comprehensive performance examination of the proposed cycle engine in terms of performance characteristics such as effective power (EFP), effective power density (EFPD), exergy destruction (X), exergy efficiency (ε), and ecological coefficient of performance (ECOP) has been conducted. The impacts of engine operating and design parameters on the performance characteristics have been computationally examined. Furthermore, irreversibilities depending on incomplete combustion loss (INCL), exhaust output loss (EXOL), heat transfer loss (HTRL), and friction loss (FRL) have been considered in the performance simulations. The minimum exergy destruction and maximum performance specifications have been observed with 30 of the compression ratio. Maximum effective power values have been obtained at range between 1 and 1.2 of equivalence ratio. The optimum range for exergy efficiency is between 0.8 and 1 of equivalence ratio. Increasing engine speed has provided enhancing effective power. However, an optimum range has been found for the exergy efficiency that is interval of 3000 to 4000 rpm. The results obtained can be assessed by researchers studying on modeling of the engine systems and designs.