Showing papers on "Thermodynamic cycle published in 2012"

Working medium and heat cycle system

Abstract: To provide a working medium for heat cycle, of which combustibility is suppressed, which has less influence over the ozone layer, which has less influence over global warming and which provides a heat cycle system excellent in the cycle performance (efficiency and capacity), and a heat cycle system, of which the safety is secured, and which is excellent in the cycle performance (efficiency and capacity). A working medium for heat cycle comprising 1-chloro-2,3,3,3-tetrafluoropropene and a mineral oil is employed for a heat cycle system (such as a Rankine cycle system, a heat pump cycle system, a refrigerating cycle system 10 or a heat transport system).

First and second law investigation of waste heat based combined power and ejector-absorption refrigeration cycle

Abstract: In the proposed cogeneration cycle, a LiBr–H2O absorption refrigeration system is employed to the combined power and ejector refrigeration system which uses R141b as a working fluid. Estimates for irreversibilities of individual components of the cycle lead to possible measures for performance improvement. Results of exergy distribution of waste heat in the cycle show that around 53.6% of the total input exergy is destroyed due to irreversibilities in the components, 22.7% is available as a useful exergy output, and 23.7% is exhaust exergy lost to the environment, whereas energy distribution shows 44% is exhaust energy and 19.7% is useful energy output. Results also show that proposed cogeneration cycle yields much better thermal and exergy efficiencies than the previously investigated combined power and ejector cooling cycle. Current investigation clearly show that the second law analysis is quantitatively visualizes losses within a cycle and gives clear trends for optimization.

Evaluation of Design Performance of the Semi-Closed Oxy-Fuel Combustion Combined Cycle

Abstract: This study aims to present various design aspects and realizable performance of the natural gas fired semi-closed oxy-fuel combustion combined cycle (SCOC-CC). Design parameters of the cycle are set up on the basis of component technologies of today’s state-of-the-art gas turbines with a turbine inlet temperature between 1400°C and 1600°C. The most important part in the cycle analysis is the turbine cooling which affects the cycle performance considerably. A thermodynamic cooling model is introduced to predict the reasonable amount of turbine coolant to maintain the turbine blade temperature of the SCOC-CC at the levels of those of conventional gas turbines. Optimal pressure ratio ranges of the SCOC-CC for two different turbine inlet temperature levels are searched. The performance penalty due to the CO2 capture is examined. Also investigated are the influences of the purity of oxygen provided by the air separation unit on the cycle performance. A comparison with the conventional combined cycle adopting a post-combustion CO2 capture is carried out taking into account the relationship between performance and CO2 capture rate.© 2012 ASME

Thermodynamic model for prediction of performance and emission characteristics of SI engine fuelled by gasoline and natural gas with experimental verification

Abstract: In this study, a thermodynamic cycle simulation of a conventional four-stroke SI engine has been carried out to predict the engine performance and emissions. The first law of thermodynamics has been applied to determine in-cylinder temperature and pressure as a function of crank angle. The Newton-Raphson method was used for the numerical solution of the equations. The non-differential form of equations resulted in the simplicity and ease of the solution to predict the engine performance. Two-zone model for the combustion process simulation has been used and the mass burning rate was predicted by simulating spherical propagation of the flame front. Also, temperature dependence of specific heat capacity has been considered. The performance characteristics including power, indicated specific fuel consumption, and emissions concentration of SI engine using gasoline and CNG fuels have been determined by the model. The results of the present work have been evaluated using corresponding available experimental data of an existing SI engine running on both gasoline and CNG. It has been found that the simulated results show reasonable agreement with the experimental data. Finally, parametric studies have been carried out to evaluate the effects of equivalence ratio, compression ratio and spark timing on the engine performance characteristics in order to show the capability of the model to predict of engine operation.

Multi-Objective Optimization of a Combined Power and Cooling Cycle for Low-Grade and Midgrade Heat Sources

Abstract: Optimization of thermodynamic cycles is important for the efficient utilization of energy sources; indeed it is more crucial for the cycles utilizing low grade heat sources where the cycle efficiencies are smaller compared to high temperature power cycles. This paper presents the optimization of a combined power/cooling cycle, also known as the Goswami Cycle, which combines the Rankine and absorption refrigeration cycles. The cycle uses a special binary fluid mixture as the working fluid and produces power and refrigeration. In this regard, multiobjective genetic algorithms (GA) are used for Pareto approach optimization of the thermodynamic cycle. The optimization study includes two cases. In the first case the performance of the cycle is evaluated as it is used as a bottoming cycle, and in the second case as it is used as a top cycle utilizing solar energy or geothermal sources. The important thermodynamic objectives that have been considered in this work are, namely, work output, cooling capacity, effective first law and exergy efficiencies. Optimization is carried out by varying the selected

Optimization on a three-level heat engine working with two noninteracting fermions in a one-dimensional box trap

Abstract: We setup a three-level heat engine model that works with two noninteracting fermions in a one-dimensional box trap. Besides two quantum adiabatic processes, the quantum heat engine cycle consists of two isoenergetic processes, along which the particles are coupled to energy baths at a high constant energy EH and a low constant energy EC, respectively. Based on the assumption that the potential wall moves at a very slow speed and there exists a heat leakage between two energy baths, we derive the expressions of the power output and the efficiency, and then obtain the optimization region for the heat engine cycle. Finally, we present a brief performance analysis of a Carnot engine between a hot and a cold bath at temperatures TH and TC, respectively. We demonstrate that under the same conditions, the efficiency η=1-(EC/EH) of the engine cycle is bounded from above the Carnot efficiency ηc=1-(TC/TH).

Carbon dioxide refrigeration cycle

Abstract: A refrigeration cycle is operated in conjunction with various thermodynamic cycle working fluid circuits to cool a target fluid that may be used in a separate system or duty. In one embodiment, the refrigeration cycle includes an ejector that extracts a motive fluid from the working fluid cycles in order to entrain a suction fluid that is also extracted from the working fluid circuits. Expanding the suction fluid reduces the pressure and temperature of the suction fluid for cooling the target fluid in an evaporator, which evaporates the suction fluid before being entrained into the ejector by the motive fluid. A mixed fluid is discharged from the ejector and injected into the working fluid circuits upstream from a condenser that cools the mixed fluid and the working fluid circulating throughout the working fluid circuits.

Design Methodology of Supercritical CO2 Brayton Cycle Turbomachineries

Abstract: The supercritical CO2(S-CO2) Brayton Cycle is gaining attention due to its high thermal efficiency at relatively low turbine inlet temperature and compactness of turbomachineries. For designing turbomachineries of the S-CO2 Cycle, however, most of existing codes based on ideal gas assumption are not proven yet to be accurate near the supercritical condition. Furthermore, many of existing design computer programs usually focuses on a specific type of turbomachinery, e.g. axial or radial, which makes hard to compare performance of both types at the same design condition. Since both axial and radial types of turbomachineries were pointed out as an equally possible candidate for the S-CO2 Brayton cycle, in order to compare and determine the best effective type of turbomachinery requires considering both types under the same design conditions. Taking into consideration of these facts, some modifications to the conventional design methodology of gas cycle turbomachinery are necessary to design a turbomachinery for the S-CO2 cycle. Especially, a modified design method should consider non-linear property variation of CO2 near the critical point to obtain an accurate result. Thus, the modified design method for the S-CO2 Brayton cycle turbomachineries is suggested in this paper and the method was implemented in the in-house code. In addition, some preliminary results will be discussed with the plan for validation and verification of the code.© 2012 ASME