scholarly journals Performance Analysis of an Irreversible Regenerative Brayton Cycle Based on Ecological Optimization Criterion

2014 ◽  
Vol 09 (1) ◽  
Keyword(s):  
Power Output ◽  
Thermal Efficiency ◽  
Ecological Function ◽  
Dominant Factor ◽  
Entropy Generation Rate ◽  
Working Fluid ◽  
Brayton Cycle ◽  
Regenerative Heat ◽  
Environment Temperature ◽  
Ecological Optimization

An ecological optimization along with a detailed parametric analysis of an irreversible regenerative Brayton cycle with finite heat capacity of external reservoirs have been carried out. The external irreversibilities due to finite temperature difference and internal irreversibilities due to fluid friction losses in compressor / turbine, regenerative heat loss, pressure loss are included in the analysis. Ecological function is thermodynamically optimized which is defined as the power output minus the product of environment temperature and entropy generation rate. A detailed analysis shows that the ecological function and corresponding power output / thermal efficiency can be maximized with judicious selection of parameters such as efficiency of turbine and compressor, effectiveness of various heat exchangers, heat source inlet temperature, pressure drop recovery coefficients and heat capacitance rate of the working fluid. It is found that the regenerative effectiveness is more prominent for maximum ecological function and corresponding thermal efficiency while cold side effectiveness is dominant factor for corresponding power output. It is also found that the effect of turbine efficiency (ηt) is more than the compressor efficiency (ηc) on the thermodynamic performance of an irreversible regenerative Brayton heat engine cycle. The model analyzed in this paper gives lower values of various performance parameters as expected and replicates the results of an irreversible regenerative Brayton cycle model discussed in the literature at pressure recovery coefficients of α1=α2=1.

scholarly journals Four-Objective Optimizations for an Improved Irreversible Closed Modified Simple Brayton Cycle

Entropy ◽  
2021 ◽  
Vol 23 (3) ◽  
pp. 282 ◽  
Author(s):  
Chenqi Tang ◽  
Lingen Chen ◽  
Huijun Feng ◽  
Yanlin Ge
Keyword(s):  
Power Density ◽  
Power Output ◽  
Thermal Efficiency ◽  
Variable Temperature ◽  
Ecological Function ◽  
Cycle Performance ◽  
Heating Process ◽  
Brayton Cycle ◽  
Nsga Ii ◽  
Deviation Index

An improved irreversible closed modified simple Brayton cycle model with one isothermal heating process is established in this paper by using finite time thermodynamics. The heat reservoirs are variable-temperature ones. The irreversible losses in the compressor, turbine, and heat exchangers are considered. Firstly, the cycle performance is optimized by taking four performance indicators, including the dimensionless power output, thermal efficiency, dimensionless power density, and dimensionless ecological function, as the optimization objectives. The impacts of the irreversible losses on the optimization results are analyzed. The results indicate that four objective functions increase as the compressor and turbine efficiencies increase. The influences of the latter efficiency on the cycle performances are more significant than those of the former efficiency. Then, the NSGA-II algorithm is applied for multi-objective optimization, and three different decision methods are used to select the optimal solution from the Pareto frontier. The results show that the dimensionless power density and dimensionless ecological function compromise dimensionless power output and thermal efficiency. The corresponding deviation index of the Shannon Entropy method is equal to the corresponding deviation index of the maximum ecological function.

Performance Comparison and Parametric Analysis of sCO2 Power Cycles Configurations

2018 ◽  
Author(s):  
Ali S. Alsagri ◽  
Andrew Chiasson ◽  
Ahmad Aljabr
Keyword(s):  
Power Output ◽  
Thermal Efficiency ◽  
Performance Comparison ◽  
Specific Power ◽  
Brayton Cycle ◽  
Computationally Efficient ◽  
Power Cycles ◽  
Optimization Study ◽  
Specific Power Output ◽  
Improve Calculation

A thermodynamic analysis and optimization of four supercritical CO2 Brayton cycles were conducted in this study in order to improve calculation accuracy; the feasibility of the cycles; and compare the cycles’ design points. In particular, the overall thermal efficiency and the power output are the main targets in the optimization study. With respect to improving the accuracy of the analytical model, a computationally efficient technique using constant conductance (UA) to represent heat exchanger performances is executed. Four Brayton cycles involved in this compression analysis, simple recaptured, recompression, pre-compression, and split expansion. The four cycle configurations were thermodynamically modeled and optimized based on a genetic algorithm (GA) using an Engineering Equation Solver (EES) software. Results show that at any operating condition under 600 °C inlet turbine temperature, the recompression sCO2 Brayton cycle achieves the highest thermal efficiency. Also, the findings show that the simple recuperated cycle has the highest specific power output in spite of its simplicity.

Thermodynamic Analysis of a Novel Ammonia-Water Cogeneration System for Maritime Diesel Engines

2020 ◽  
Author(s):  
Ziyang Cheng ◽  
Yaxiong Wang ◽  
Qingxuan Sun ◽  
Jiangfeng Wang ◽  
Pan Zhao ◽  
...  
Keyword(s):  
Power Output ◽  
Thermal Efficiency ◽  
System Performance ◽  
Mass Fraction ◽  
Ammonia Concentration ◽  
Working Fluid ◽  
Fluid Temperature ◽  
Kalina Cycle ◽  
Ammonia Water ◽  
Cogeneration System

Abstract This paper proposes a novel cogeneration system based on Kalina cycle and absorption refrigeration system to meet the design requirements of China State Shipbuilding Corporation, which is efficiently satisfy the power and cooling demands of a maritime ship at the same time. Unlike most of the combined systems, this cogeneration system is highly coupled and realizes cogeneration without increasing the system complexity too much. The basic ammonia mass fraction of this novel system is increased, so that the ammonia concentration of ammonia-water steam from the separator can be higher, which contributes to lower refrigerating temperature and thus less heat loss in the distillation process. In addition, higher ammonia concentration solution makes overheating easier, which improves the thermal efficiency. Moreover, the system has two recuperators to make further improvement of the thermal efficiency. Thermodynamic models are developed to investigate the system performance and parametric analysis is conducted to figure out the effects of including working fluid temperature at the outlet of the evaporator, working fluid temperature at superheater outlet, mass fraction of ammonia in basic solution, turbine inlet pressure, temperature of cooling water at the inlet of condensers and the refrigeration evaporation temperature on the system performance. Furthermore, the cogeneration system is optimized with genetic algorithm to obtain the best performance, which achieves 333.00kW of net power output, 28.83 kW of cooling capacity and 21.81% of thermal efficiency. Finally, the performance of the proposed system is compared with an optimized recuperative organic Rankine cycle (ORC) system and an optimized Kalina cycle system 34 (KCS34) using the same heat source. The results show that the thermal efficiency and power output of the novel cogeneration system is 3.89% and 1.05% higher than that of the recuperative ORC system and KCS34 system respectively.

Analysis and Comparison of the Performance of an Inverted Brayton Cycle and Turbo-Compounding With Decoupled Turbine and CVT Driven Compressor for Small Automotive Engines

2016 ◽  
Author(s):  
P. Lu ◽  
C. Brace ◽  
B. Hu ◽  
C. Copeland
Keyword(s):  
Fuel Consumption ◽  
Power Output ◽  
Heat Recovery ◽  
Power Plants ◽  
Waste Heat ◽  
Ambient Pressure ◽  
Working Fluid ◽  
Brayton Cycle ◽  
Partial Load ◽  
Exhaust Heat

For an internal combustion engine, a large quantity of fuel energy (accounting for approximately 30% of the total combustion energy) is expelled through the exhaust without being converted into useful work. Various technologies including turbo-compounding and the pressurized Brayton bottoming cycle have been developed to recover the exhaust heat and thus reduce the fuel consumption and CO2 emission. However, the application of these approaches in small automotive power plants has been relatively less explored because of the inherent difficulties, such as the detrimental backpressure and higher complexity imposed by the additional devices. Therefore, research has been conducted, in which modifications were made to the traditional arrangement aiming to minimize the weaknesses. The turbocharger of the baseline series turbo-compounding was eliminated from the system so that the power turbine became the only heat recovery device on the exhaust side of the engine, and operated at a higher expansion ratio. The compressor was separated from the turbine shaft and mechanically connected to the engine via CVT. According to the results, the backpressure of the novel system is significantly reduced comparing with the series turbo-compounding model. The power output at lower engine speed was also promoted. For the pressurized Brayton bottoming cycle, rather than transferring the thermal energy from the exhaust to the working fluid, the exhaust gas was directly utilized as the working medium and was simply cooled by ambient coolant before the compressor. This arrangement, which is known as the inverted Brayton cycle was simpler to implement. Besides, it allowed the exhaust gasses to be expanded below the ambient pressure. Thereby, the primary cycle was less compromised by the bottoming cycle. The potential of recovering energy from the exhaust was increased as well. This paper analysed and optimized the parameters (including CVT ratio, turbine and compressor speed and the inlet pressure to the bottoming cycle) that are sensitive to the performance of the small vehicle engine equipped with inverted Brayton cycle and novel turbo-compounding system respectively. The performance evaluation was given in terms of brake power output and specific fuel consumption. Two working conditions, full and partial load (10 and 2 bar BMEP) were investigated. Evaluation of the transient performance was also carried out. Simulated results of these two designs were compared with each other as well as the performance from the corresponding baseline models. The system models in this paper were built in GT-Power which is a one dimension (1-D) engine simulation code. All the waste heat recovery systems were combined with a 2.0 litre gasoline engine.

A Study of Supercritical Carbon Dioxide Power Cycle for Concentrating Solar Power Applications Using an Isothermal Compressor

2018 ◽  
Vol 140 (7) ◽  
Author(s):  
Jin Young Heo ◽  
Jinsu Kwon ◽  
Jeong Ik Lee
Keyword(s):  
Carbon Dioxide ◽  
Supercritical Carbon Dioxide ◽  
Thermal Efficiency ◽  
Solar Power ◽  
Working Fluid ◽  
Brayton Cycle ◽  
Concentrating Solar Power ◽  
Power Cycle ◽  
Compressor Inlet ◽  
Supercritical Carbon

For the concentrating solar power (CSP) applications, the supercritical carbon dioxide (s-CO2) power cycle is beneficial in many aspects, including high cycle efficiencies, reduced component sizing, and potential for the dry cooling option. More research is involved in improving this technology to realize the s-CO2 cycle as a candidate to replace the conventional power conversion systems for CSP applications. In this study, an isothermal compressor, a turbomachine which undergoes the compression process at constant temperature to minimize compression work, is applied to the s-CO2 power cycle layout. To investigate the cycle performance changes of adopting the novel technology, a framework for defining the efficiency of the isothermal compressor is revised and suggested. This study demonstrates how the compression work for the isothermal compressor is reduced, up to 50%, compared to that of the conventional compressor under varying compressor inlet conditions. Furthermore, the simple recuperated and recompression Brayton cycle layouts using s-CO2 as a working fluid are evaluated for the CSP applications. Results show that for compressor inlet temperatures (CIT) near the critical point, the recompression Brayton cycle using an isothermal compressor has 0.2–1.0% point higher cycle thermal efficiency compared to its reference cycle. For higher CIT values, the recompression cycle using an isothermal compressor can perform above 50% in thermal efficiency for a wider range of CIT than the reference cycle. Adopting an isothermal compressor in the s-CO2 layout can imply larger heat exchange area for the compressor which requires further development.

Ecological Optimization of Generalized Irreversible Chemical Engines

2010 ◽  
Vol 8 (1) ◽  
Author(s):  
Lingen Chen ◽  
Dan Xia ◽  
Fengrui Sun
Keyword(s):  
Mass Transfer ◽  
Entropy Production ◽  
Production Rate ◽  
Power Output ◽  
Optimization Criterion ◽  
Ecological Function ◽  
Maximum Efficiency ◽  
Entropy Production Rate ◽  
Output Entropy ◽  
Ecological Optimization

Optimal ecological performance of generalized irreversible chemical engine cycles with both linear and diffusive mass transfer laws are derived by taking an ecological optimization criterion as the objective, which consists of maximizing a function representing the best compromise between the power output and the entropy production rate of the chemical engines. In this paper, the relations between the ecological function, power output, entropy production rate and the efficiency of a chemical engine cycle with irreversibilities of mass transfer, mass leakage and internal dissipation, in which the mass transfer, are derived. This paper also derives the maximum ecological function and the corresponding power output, entropy production rate and efficiency, the maximum power output and the corresponding ecological function, entropy production rate and efficiency, and the maximum efficiency and the corresponding ecological function, power output and entropy production rate. The results can provide some theoretical guidelines for the design of practical chemical engines.

scholarly journals Thermal performance analysis of organic flash cycle using R600A/R601A mixtures with internal heat exchanger

2020 ◽  
pp. 296-296
Author(s):  
Guidong Huang ◽  
Songyuan Zhang ◽  
Zhong Ge ◽  
Zhiyong Xie ◽  
Zhipeng Yuan ◽  
...  
Keyword(s):  
Heat Exchanger ◽  
Power Output ◽  
Thermal Efficiency ◽  
Electricity Generation ◽  
Internal Heat ◽  
Working Fluid ◽  
Cycle System ◽  
Internal Heat Exchanger ◽  
Generation Costs ◽  
Net Power Output

In this study, the thermal performance of an internal heat exchanger-organic flash cycle system driven by geothermal water was investigated.R600a/R601a mixtures were selected as the working fluid. The effects of the mole fraction of mixtures on the heat absorption capacity of the heater, the temperature rise of cold working fluid in the internal heat exchanger, net power output, thermal efficiency, and electricity generation costs were analyzed. The net power outputs, electricity generation costs, and thermal efficiency of the internal heat exchanger-organic flash cycle and simple organic flash cycle systems were compared. Results showed that the system using theR600a/R601a mixtures (0.7/0.3mole fraction) has the largest net power output, which increased the net power output by 3.68% and 42.23% over the R601a and R600a systems, respectively. WhentheR600a mole fraction was 0.4, the electricity generation costs reduction of the internal heat exchanger-organic flash cycle system was the largest (1.77% compared with the simple organic flash cycle system).The internal heat exchanger can increase the thermal efficiency of organic flash cycle, but the net power output does not necessarily increase.

scholarly journals Comparison of single and double stage regenerative organic rankine cycle for medium grade heat source through energy and exergy estimation

2019 ◽  
Vol 8 (2) ◽  
pp. 141 ◽  
Author(s):  
Ghalya Pikra ◽  
Nur Rohmah
Keyword(s):  
Heat Source ◽  
Flow Rate ◽  
Power Output ◽  
Thermal Efficiency ◽  
Organic Rankine Cycle ◽  
Rankine Cycle ◽  
Exergy Efficiency ◽  
Working Fluid ◽  
Energy And Exergy ◽  
Net Power Output

Regenerative organic Rankine cycle (RORC) can be used to improve organic Rankine cycle (ORC) performance. This paper presents a comparison of a single (SSRORC) and double stage regenerative organic Rankine cycle (DSRORC) using a medium grade heat source. Performance for each system is estimated using the law of thermodynamics I and II through energy and exergy balance. Solar thermal is used as the heat source using therminol 55 as a working fluid, and R141b is used as the organic working fluid. The initial data for the analysis are heat source with 200°C of temperature, and 100 L/min of volume flow rate. Analysis begins by calculating energy input to determine organic working fluid mass flow rate, and continued by calculating energy loss, turbine power and pump power consumption to determine net power output and thermal efficiency. Exergy analysis begins by calculating exergy input to determine exergy efficiency. Exergy loss, exergy destruction at the turbine, pump and feed heater is calculated to complete the calculation. Energy estimation result shows that DSRORC determines better net power output and thermal efficiency for 7.9% than SSRORC, as well as exergy estimation, DSRORC determines higher exergy efficiency for 7.69%. ©2019. CBIORE-IJRED. All rights reserved

Brayton Cycle Optimization

1997 ◽  
Author(s):  
Sushanta K. Mitra ◽  
Achintya Mukhopadhaya
Keyword(s):  
Heat Transfer ◽  
Transfer Process ◽  
Power Output ◽  
Practical Importance ◽  
Heat Transfer Process ◽  
Working Fluid ◽  
Operating Parameters ◽  
Inlet Temperature ◽  
Brayton Cycle ◽  
The Ideal

The Brayton Cycle is the ideal cycle for simple gas turbine applications. The heat transfer process in such a cycle is of practical importance as far as power output is considered. The present work focusses on the power output from an ideally reversible Brayton cycle and criteria for optimum power based on its operating parameters like the specific heat of hot and cold fluids, working fluid and heater inlet temperature is discussed here.

scholarly journals Power Optimization of a Modified Closed Binary Brayton Cycle with Two Isothermal Heating Processes and Coupled to Variable-Temperature Reservoirs

Energies ◽  
2020 ◽  
Vol 13 (12) ◽  
pp. 3212 ◽  
Author(s):  
Chenqi Tang ◽  
Lingen Chen ◽  
Huijun Feng ◽  
Wenhua Wang ◽  
Yanlin Ge
Keyword(s):  
Combustion Chamber ◽  
Power Output ◽  
Variable Temperature ◽  
Working Fluid ◽  
Inlet Temperature ◽  
Brayton Cycle ◽  
Isothermal Heating ◽  
Cycle Model ◽  
Thermal Capacitance ◽  
Topping Cycle

A modified closed binary Brayton cycle model with variable isothermal pressure drop ratios is established by using finite time thermodynamics in this paper. A topping cycle, a bottoming cycle, two isothermal heating processes and variable-temperature reservoirs are included in the new model. The topping cycle is composed of a compressor, a regular combustion chamber, a converging combustion chamber, a turbine and a precooler. The bottoming cycle is composed of a compressor, an ordinary regenerator, an isothermal regenerator, a turbine and a precooler. The heat conductance distributions among the six heat exchangers are optimized with dimensionless power output as optimization objective. The results show that the double maximum dimensionless power output increases first and then tends to be unchanged while the inlet temperature ratios of the regular combustion chamber and the converging combustion chamber increase. There also exist optimal thermal capacitance rate matchings among the working fluid and heat reservoirs, leading to the optimal maximum dimensionless power output.

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