Cooling Load Density Optimization of an Irreversible Simple Brayton Refrigerator

2002 ◽  
Vol 09 (04) ◽  
pp. 325-337 ◽  
Author(s):  
Shengbing Zhou ◽  
Lingen Chen ◽  
Fengrui Sun ◽  
Chih Wu
Keyword(s):  
Heat Exchangers ◽  
Pressure Ratio ◽  
Design Parameters ◽  
Working Fluid ◽  
Cooling Load ◽  
Temperature Ratio ◽  
Cold Side ◽  
Optimum Pressure ◽  
Heat Conductance ◽  
Numerical Examples

The performance optimization of an irreversible simple Brayton refrigerator coupled to constant-temperature heat reservoirs is carried out by taking the cooling load density, i.e., the ratio of cooling load to the maximum specific volume in the cycle, as the optimization objective using finite-time thermodynamics (FTT) or entropy generation minimization (EGM) in this paper. The analytical formulae about the relations between cooling load density and pressure ratio, as well as between coefficient of performance (COP) 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 expander. The influences of the effectiveness of the heat exchangers, the temperature ratio of the reservoirs, and the efficiencies of the compressor and expander on the cooling load density versus COP are provided by numerical examples. The cooling load density optimization is performed by searching the optimum pressure ratio of the compressor, and searching the optimum distribution of heat conductance of the hot- and cold-side heat exchangers for the fixed total heat exchanger inventory. The influences of some design parameters, including the effectiveness of the heat exchangers between the working fluid and heat reservoirs, the efficiencies of compressor and expander, the temperature ratio of heat reservoirs, on the maximum cooling load density, the optimum heat conductance distribution and the optimum pressure ratio are provided by numerical examples. The refrigeration plant design with optimization leads to a smaller size including the compressor, expander, and the hot- and cold-side heat exchangers.

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.

Parametric Study and Optimization of an Irreversible Closed Intercooled Regenerative Brayton Cycle

2007 ◽  
Author(s):  
Brian Wolf ◽  
Shripad T. Revankar
Keyword(s):  
Total Pressure ◽  
Pressure Ratio ◽  
Working Fluid ◽  
Inlet Temperature ◽  
Variable Component ◽  
Brayton Cycle ◽  
Heat Reservoir ◽  
Temperature Ratio ◽  
Cold Side ◽  
Total Pressure Ratio

In this paper, entropy generation minimization techniques are used in the analysis of an irreversible closed intercooled regenerative Brayton cycle coupled to variable temperature heat reservoirs. First, dimensionless power and efficiency equations are derived for a base case (single stage) which replicates those obtained in recent literature. Second, equations are derived for a multi-stage Brayton cycle. The dimensionless power and efficiency equations are used to analyze the effects of total pressure ratio, intercooling pressure ratio, thermal capacity rates of the working fluid and heat reservoirs, and the component (regenerator, intercooler, hot and cold side heat exchangers) effectiveness. Using detailed numerical examples, the optimal power and efficiency corresponding to variable component effectiveness, compressor and turbine efficiencies, intercooling pressure ratio, total pressure ratio, pressure recovery coefficients, heat reservoir inlet temperature ratio, and the cooling fluid in the intercooler and the cold side heat reservoir inlet temperature ratio are analyzed.

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.

Effects of Several Major Irreversibilities on the Thermodynamic Performance of a Regenerative MHD Power Cycle

2005 ◽  
Vol 127 (2) ◽  
pp. 103-118 ◽  
Author(s):  
Jincan Chen ◽  
S. K. Tyagi ◽  
S. C. Kaushik ◽  
V. Tiwari ◽  
Chih Wu
Keyword(s):  
Power Output ◽  
Working Fluid ◽  
Temperature Ratio ◽  
Cold Side ◽  
Power Cycle ◽  
Thermodynamic Performance ◽  
Compressor Efficiency ◽  
Increasing Function ◽  
Optimum Relation ◽  
Cycle Temperature

This communication presents the thermodynamic analysis along with a detailed parametric study of an irreversible regenerative MHD power cycle. The power output is adopted as the objective function and optimized with respect to the cycle temperature ratio for a typical set of operating parameters. The power output is found to be an increasing function of the effectiveness and the heat capacitance rates on the hot- and cold-side reservoirs, the regenerative effectiveness, and the compressor and generator efficiencies, while it is found to be a decreasing function of the working fluid heat capacitance rates and the Mach number. The effects of the cold-side effectiveness and heat capacitance rate are found to be more than those of the other side effectiveness and heat capacitance rates on the performance of the cycle. The effect of the compressor efficiency is found to be more than that of the generator efficiency on the power output while it is reverse in the case of thermal efficiency. It is also found that there is an optimum relation among the various heat capacitance rates at which the cycle attains the maximum performance.

scholarly journals Design of a Semiclosed Cycle Gas Turbine With Carbon Dioxide-Argon as Working Fluid

1997 ◽  
Author(s):  
Inaki Ulizar ◽  
Pericles Pilidis
Keyword(s):  
Carbon Dioxide ◽  
Gas Turbine ◽  
Pressure Ratio ◽  
Air Separation ◽  
Working Fluid ◽  
Optimum Pressure ◽  
Low Efficiency ◽  
Nozzle Guide ◽  
Main Engine ◽  
No Emissions

The main performance features of a semiclosed cycle gas turbine with carbon dioxide-argon working fluid are described here. This machine is designed to employ coal synthetic gas fuel and to produce no emissions. The present paper outlines three tasks carried out. Firstly the selection of main engine variables, mainly pressure and temperature ratios. Then a sizing exercise is carried out where many details of its physical appearance are outlined. Finally the off-design performance of the engine is predicted. This two spool gas turbine is purpose built for the working fluid, so its physical characteristics reflect this requirement. The cycle is designed with a turbine entry temperature of 1650 K and the optimum pressure ratio is found to be around 60. Two major alternatives are examined, the simple and the precooled cycle. A large amount of nitrogen is produced by the air separation plant associated with this gas turbine and the coal gasifier. An investigation has been made on how to use this nitrogen to improve the performance of the engine by precooling the compressor, cooling the turbine nozzle guide vanes and using it to cool the delivery of the low pressure compressor. The efficiencies of the whole plant have been computed, taking into account the energy requirements of the gasifier and the need to dispose of the excess carbon dioxide. Hence the overall efficiencies indicated here are of the order of 40 percent. This is a low efficiency by current standards, but the fuel employed is coal and no emissions are produced.

Optimization of an Oxyfuel Combined Cycle Regarding Performance and Complexity Level

2013 ◽  
Author(s):  
Adrian Dahlquist ◽  
Magnus Genrup ◽  
Mats Sjoedin ◽  
Klas Jonshagen
Keyword(s):  
Gas Turbine ◽  
Flue Gas ◽  
State Of The Art ◽  
Pressure Ratio ◽  
Combined Cycle ◽  
Design Parameters ◽  
Inlet Temperature ◽  
Optimum Pressure ◽  
Compressor Inlet ◽  
Cooling Model

The aim of this paper is to establish and motivate the design parameters of a 125 MW Oxyfuel Combined Cycle (OCC) also referred to as the Semi-Closed Oxyfuel-Combusted Combined Cycle (SCOC-CC). This paper proposes a compatible OCC that does not include any unconventional features, beyond what is state-of-the-art in gas turbine technology today. Such features could challenge the feasibility to bring the concept to the market in a reasonable time. The OCC requires a higher pressure ratio compared to a conventional combined cycle in order to achieve exhaust conditions that fit the design of the bottoming cycle. However, a high gas turbine pressure ratio increases the complexity of the machine and must be weighted against the gain in efficiency. The OCC gas turbine is modeled using a cooling model which keeps the metal temperature of all cooled turbine stages constant while seeking the optimum pressure ratio. As the cycle is semi-closed the compressor inlet temperature is a design parameter: it is shown that there is an efficiency optimum clearly in the range of what is normally achievable. As the gas properties of the OCC flue gas differ from the conventional plant, the effects of this on the HRSG design are explored.

Performance improvements of the recuperated gas turbine cycle using absorption inlet cooling and evaporative aftercooling

2002 ◽  
Vol 216 (4) ◽  
pp. 295-306 ◽  
Author(s):  
A. M. Bassily
Keyword(s):  
Gas Turbine ◽  
Parametric Study ◽  
Cooling System ◽  
Pressure Ratio ◽  
Inlet Temperature ◽  
Temperature Ratio ◽  
Optimum Pressure ◽  
Performance Improvements ◽  
Gas Turbine Cycle ◽  
The Impact

An absorption inlet cooling system is introduced into the recuperated gas turbine cycle. The exhaust gases of the cycle are used to run the system. Five different layouts of the recuperated gas turbine cycle are presented. These include the effects of absorption inlet cooling, evaporative inlet cooling and evaporative cooling of compressor discharge (evaporative aftercooling), and the combined effect of absorption inlet cooling and evaporative aftercooling. A parametric study of the effect of pressure ratio, ambient temperature and relative humidity on the performance of all cycles is carried out. The results indicate that absorption inlet cooling could increase the efficiency of the recuperated cycle by up to 4 per cent, compared with 2.2 per cent for evaporative inlet cooling. Absorption inlet cooling with evaporative aftercooling could increase the optimum per efficiency of the recuperated cycle by up to 5 per cent and its maximum power by up to 65 per cent. Evaporative aftercooling reduces the impact of inlet cooling. Another parametric study of the effect of the turbine compressor inlet temperature ratio on the optimum pressure ratios indicated that cycles with evaporative aftercooling have higher optimum pressure ratios, which could be a function of the inlet temperature ratio and air temperature at the compressor outlet.

Cooling Load Density Analysis and Optimization for an Endoreversible Air Refrigerator

2001 ◽  
Vol 08 (02) ◽  
pp. 147-155 ◽  
Author(s):  
Shengbing Zhou ◽  
Lingen Chen ◽  
Fengrui Sun ◽  
Chih Wu
Keyword(s):  
Heat Exchanger ◽  
Performance Analysis ◽  
Specific Volume ◽  
Pressure Ratio ◽  
Cooling Load ◽  
Numerical Examples ◽  
Density Analysis

The performance analysis and optimization of an endoreversible air refrigerator is carried out by taking the cooling load density, which is defined as the ratio of cooling load to the maximum specific volume in the cycle, as the optimization objective in this paper. The results obtained are different from those with the cooling load objective. Numerical examples show the effects of pressure ratio and allocation of heat exchanger inventory on the cooling load density of the refrigerator.

Efficiency Optimizations of an Irreversible Brayton Heat Engine

1998 ◽  
Vol 120 (2) ◽  
pp. 143-148 ◽  
Author(s):  
C.-Y. Cheng ◽  
C.-K. Chen
Keyword(s):  
Heat Transfer ◽  
Thermal Efficiency ◽  
Heat Exchangers ◽  
Heat Engine ◽  
Thermal Conductance ◽  
Working Fluid ◽  
Reservoir Temperature ◽  
Temperature Ratio ◽  
Conductance Ratio ◽  
Internal Irreversibility

A steady-flow approach for finite-time thermodynamics is used to calculate the maximum thermal efficiency, its corresponding power output, adiabatic temperature ratio, and thermal-conductance ratio of heat transfer equipment of a closed Brayton heat engine. The physical model considers three types of irreversibilities: finite thermal conductance between the working fluid and the reservoirs, heat leaks between the reservoirs, and internal irreversibility inside the closed Brayton heat engine. The effects of heat leaks, hot-cold reservoir temperature ratios, turbine and compressor isentropic efficiencies, and total conductances of heat exchangers on the maximum thermal efficiency and its corresponding parameters are studied. The optimum conductance ratio could be found to effectively use the heat transfer equipment, and this ratio is increased as the component efficiencies and total conductances of heat exchangers are increased, and always less than or equal to 0.5.

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