scholarly journals Power, Efficiency, Power Density and Ecological Function Optimization for an Irreversible Modified Closed Variable-Temperature Reservoir Regenerative Brayton Cycle with One Isothermal Heating Process

Energies ◽  
2020 ◽  
Vol 13 (19) ◽  
pp. 5133 ◽  
Author(s):  
Lingen Chen ◽  
Chenqi Tang ◽  
Huijun Feng ◽  
Yanlin Ge
Keyword(s):  
Power Density ◽  
Heat Exchangers ◽  
Variable Temperature ◽  
Pressure Ratio ◽  
Ecological Function ◽  
Function Optimization ◽  
Cycle Performance ◽  
Heating Process ◽  
Brayton Cycle ◽  
Isothermal Heating

One or more isothermal heating process was introduced to modify single and regenerative Brayton cycles by some scholars, which effectively improved the thermal efficiency and significantly reduced the emissions. To analyze and optimize the performance of this type of Brayton cycle, a regenerative modified Brayton cycle with an isothermal heating process is established in this paper based on finite time thermodynamics. The isothermal pressure drop ratio is variable. The irreversibilities of the compressor, turbine and all heat exchangers are considered in the cycle, and the heat reservoirs are variable-temperature ones. The function expressions of four performance indexes; that is, dimensionless power output, thermal efficiency, dimensionless power density and dimensionless ecological function are obtained. With the dimensionless power density as the optimization objective, the heat conductance distributions among all heat exchangers and the thermal capacitance rate matching among the working fluid and heat reservoir are optimized. Based on the NSGA-II algorithm, the cycle’s double-, triple- and quadruple-objective optimization are conducted with the total pressure ratio and the heat conductance distributions among heat exchangers as design variables. The optimal value is chosen from the Pareto frontier by applying the LINMAP, TOPSIS and Shannon entropy methods. The results show that when the pressure ratio in the compressor is less than 12.0, it is beneficial to add the regenerator to improve the cycle performance; when the pressure ratio is greater than 12.0, adding the regenerator will reduce the cycle performance. For single-objective optimization, the four performance indexes could be maximized under the optimal pressure ratios, respectively. When the pressure ratio is greater than 9.2, the cycle is simplified to a closed irreversible simple modified Brayton cycle with one isothermal heating process and coupled to variable-temperature heat reservoirs. Therefore, when the regenerator is used, the range of pressure ratio is limited, and a suitable pressure ratio should be selected. The triple objective (dimensionless power output, dimensionless power density and dimensionless ecological function) optimization’ deviation index gained by LINMAP or TOPSIS method is the smallest. The optimization results gained in this paper could offer some new pointers for the regenerative Brayton cycles’ optimal designs.

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 of an irreversible closed variable-temperature heat reservoir brayton cycle under maximum power density and maximum power conditions

2005 ◽  
Vol 219 (7) ◽  
pp. 559-565 ◽  
Author(s):  
L Chen ◽  
J Zheng ◽  
F Sun ◽  
C Wu
Keyword(s):  
Power Density ◽  
Heat Exchangers ◽  
Variable Temperature ◽  
Thermal Capacity ◽  
Maximum Power ◽  
Working Fluid ◽  
Brayton Cycle ◽  
Maximum Power Density ◽  
Temperature Ratio ◽  
Temperature Heat

The power density is taken as an objective for performance analysis of an irreversible closed Brayton cycle coupled to variable-temperature heat reservoirs. The analytical formulas about the relationship between power density and working fluid temperature ratio (pressure ratio) are derived with the heat resistance losses in the hot- and cold-side heat exchangers, the irreversible compression and expansion losses in the compressor and turbine, and the effect of the finite thermal capacity rate of the heat reservoirs. The obtained results are compared with those results obtained by using the maximum power criterion. The influences of some design parameters, including the temperature ratio of the heat reservoirs, the effectivenesses of the heat exchangers between the working fluid and the heat reservoirs, and the efficiencies of the compressor and the turbine, on the maximum power density are provided by numerical examples, and the advantages and disadvantages of maximum power density design are analysed. The power plant design with maximum power density leads to a higher efficiency and smaller size. When the heat transfers between the working fluid and the heat reservoirs are carried out ideally and the thermal capacity rates of the heat reservoirs are infinite, the results of this article become similar to those obtained in the recent literature.

Power Density Analysis for a Regenerated Closed Brayton Cycle

2001 ◽  
Vol 08 (04) ◽  
pp. 377-391 ◽  
Author(s):  
Lingen Chen ◽  
Junlin Zheng ◽  
Fengrui Sun ◽  
Chih Wu
Keyword(s):  
Power Density ◽  
Heat Exchangers ◽  
Pressure Ratio ◽  
Maximum Power ◽  
Design Parameters ◽  
Working Fluid ◽  
Brayton Cycle ◽  
Maximum Power Density ◽  
Recovery Coefficient ◽  
Advantages And Disadvantages

In this paper, the power density, defined as the ratio of power output to the maximum specific volume in the cycle, is set as the objective for performance analysis of an irreversible, regenerated and closed Brayton cycle coupled to constant-temperature heat reservoirs from the viewpoint of finite time thermodynamics (FTT) or entropy generation minimization (EGM). The analytical formulae about the relations between power density and pressure ratio are derived with the heat resistance losses in the hot- and cold-side heat exchangers and the regenerator, the irreversible compression and expansion losses in the compressor and turbine, and the pressure loss in the pipe. The results obtained are compared with those obtained by using the maximum power criterion. The influences of some design parameters, including the effectiveness of the regenerator, the temperature ratio of heat reservoirs, the effectivenesses of heat exchangers between working fluid and heat reservoirs, the efficiencies of the compressor and the turbine, and the pressure recovery coefficient, on the maximum power density are illustrated by numerical examples, and advantages and disadvantages of maximum power density design are analyzed. When heat transfers between working fluid and heat reservoirs are carried out ideally, the results of this paper coincide with those obtained in recent literature.

Power Density Optimization for an Irreversible Closed Brayton Cycle

2001 ◽  
Vol 08 (03) ◽  
pp. 241-260 ◽  
Author(s):  
Lingen Chen ◽  
Junlin Zheng ◽  
Fengrui Sun ◽  
Chih Wu
Keyword(s):  
Power Density ◽  
Heat Exchangers ◽  
Pressure Ratio ◽  
Maximum Power ◽  
Brayton Cycle ◽  
Maximum Power Density ◽  
Cold Side ◽  
Heat Conductance ◽  
Optimum Heat ◽  
Conductance Distribution

In this paper, the power density, defined as the ratio of power output to the maximum specific volume in the cycle, is taken as objective for performance optimization of an irreversible closed Brayton cycle coupled to constant-temperature heat reservoirs in the viewpoint of finite time thermodynamics (FTT) or entropy generation minimization (EGM). The analytical formulas about the relations between power density and pressure ratio are derived with the heat resistance losses in the hot- and cold-side heat exchangers and the irreversible compression and expansion losses in the compressor and turbine. The maximum power density optimization is performed by searching the optimum heat conductance distribution corresponding to the optimum power density of the hot- and cold- side heat exchangers for the fixed heat exchanger inventory. The influence of some design parameters on the optimum heat conductance distribution, the maximum power density, and the optimum pressure ratio corresponding to the maximum power density are provided. The power plant design with optimization leads to a higher efficiency and smaller size including the compressor, turbine, and the hot- and cold-side heat exchangers.

Second Law Efficiency of an Intercooled-Reheated-Regenerative-Brayton Cycle With Variable Temperature Heat Reservoirs

2012 ◽  
Author(s):  
Vishal Anand ◽  
Krishna Nelanti ◽  
Kamlesh G. Gujar
Keyword(s):  
Gas Turbine ◽  
Variable Temperature ◽  
Pressure Ratio ◽  
Working Fluid ◽  
Thermodynamic Efficiency ◽  
Second Law ◽  
Brayton Cycle ◽  
Cooling Fluid ◽  
Turbine Engine ◽  
Temperature Heat

The gas turbine engine works on the principle of the Brayton Cycle. One of the ways to improve the efficiency of the gas turbine is to make changes in the Brayton Cycle. In the present study, Brayton Cycle with intercooling, reheating and regeneration with variable temperature heat reservoirs is considered. Instead of the usual thermodynamic efficiency, the Second law efficiency, defined on the basis of lost work, has been taken as a parameter to study the deviation of the irreversible Brayton Cycle from the ideal cycle. The Second law efficiency of the Brayton Cycle has been found as a function of reheat and intercooling pressure ratios, total pressure ratio, intercooler, regenerator and reheater effectiveness, hot and cold side heat exchanger effectiveness, turbine and compressor efficiency and heating capacities of the heating fluid, the cooling fluid and the working fluid (air). The variation of the Second law efficiency with all these parameters has been presented. From the results, it can be seen that the Second law efficiency first increases and then decreases with increase in intercooling pressure ratio and increases with increase in reheating pressure ratio. The results show that the Second law efficiency is a very good indicator of the amount of irreversibility of the cycle.

Modelling, Analyses and Optimization for Exergy Performance of an Irreversible Intercooled Regenerated Brayton CHP Plant: Part 1 — Thermodynamic Modelling and Parametric Analyses

2017 ◽  
Author(s):  
Lingen Chen ◽  
Bo Yang ◽  
Huijun Feng ◽  
Zemin Ding
Keyword(s):  
Heat Exchangers ◽  
Variable Temperature ◽  
Pressure Ratio ◽  
Exergy Efficiency ◽  
Heat Reservoir ◽  
Output Rate ◽  
Rate Versus ◽  
Optimum Heat ◽  
Set Up ◽  
Parametric Analyses

A variable-temperature heat reservoir irreversible intercooling regenerated Brayton combined heat and power (CHP) plant model is set up in this paper. The model considers the heat transfer losses in all the heat exchangers, the working substance pressure drop loss in the piping, and the expansion and compression losses in turbine and compressor. Exergy output rate and exergy efficiency are considered as the research targets, and their analytical formulae are obtained. The optimal performances are gotten by optimizing the intercooled pressure ratio and total pressure ratio. The influences of some important parameters on the performances are studied in detail. Besides, the relation of exergy output rate versus exergy efficiency is investigated, and the curve is loop-shaped one. The results indicate that optimum heat capacity rate matching between the heat reservoir and working substance, and optimum heat consumer required temperature exist respectively, which generate double-maximal exergy output rate and double-maximal exergy efficiency, respectively. The heat conductance allocation optimization of all the heat exchangers will be carried out in Part 2 of this paper.

Simple Recuperated s-CO2 Cycle Revisited: Optimization of Operating Parameters for Maximum Cycle Efficiency

2019 ◽  
Author(s):  
Anchit Dutta ◽  
Adhip Gupta ◽  
Sharath Sathish ◽  
Aman Bandooni ◽  
Pramod Kumar
Keyword(s):  
Design Of Experiments ◽  
Design Space ◽  
Pressure Ratio ◽  
Cycle Performance ◽  
Maximum Temperature ◽  
Brayton Cycle ◽  
High Side ◽  
Side Pressure ◽  
Cycle Efficiency ◽  
The Impact

Abstract The paper presents modeling and Design of Experiments (DOE) analysis for a simple recuperated s-CO2 closed loop Brayton cycle operating at a maximum temperature of 600°C and a compressor inlet temperature of 45°C. The analysis highlights the impact of isentropic efficiencies of the turbine and compressor, decoupled in this case, on other equipment such as recuperator, gas cooler and heater, all of which have a bearing on the overall performance of the s-CO2 Brayton cycle. A MATLAB program coupled with REFPROP is used to perform the thermodynamic analysis of the cycle. A design space exploration with a Design of Experiments (DOE) study is undertaken using I-sight™ (multi-objective optimization software), which is coupled with the MATLAB code. The outcome of the DOE study provides the optimal pressure ratios and high side pressures for maximum cycle efficiency in the design space. By varying pressure ratios along with a floating high side pressure, the analysis reveals that the cycle performance exhibits a peak around a pressure ratio of 2.5, with cycle efficiency being the objective function. A further interesting outcome of the DOE study reveals that the isentropic efficiencies of the compressor and turbine have a strong influence not only on the overall cycle efficiency, but also the optimum pressure ratio as well as the threshold pressures (low as well as high side pressure). An important outcome of this exercise shows that the isentropic efficiency of the turbine has a much greater impact on the overall cycle performance as compared to that of the compressor.

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