Maximum Attainable Performance of Stirling Engines and Refrigerators

2003 ◽  
Vol 125 (5) ◽  
pp. 911-915 ◽  
Author(s):  
P. C. T. de Boer
Keyword(s):  
Power Output ◽  
Thermal Efficiency ◽  
Power Dissipation ◽  
Coefficient Of Performance ◽  
Cold Side ◽  
Stirling Engines ◽  
Compression And Expansion ◽  
Linearized Theory ◽  
Flow Through ◽  
Stirling Refrigerator

The flow through the regenerator of a Stirling engine is driven by differences of pressure in the compression and expansion spaces. These differences lead to power dissipation in the regenerator. Using linearized theory, it is shown that this dissipation severely limits the maximum attainable thermal efficiency and nondimensional power output. The maximum attainable values are independent of the value of the regenerator conductance. For optimized nondimensional power output, the thermal efficiency equals only half the Carnot value. The power dissipated in the regenerator is removed as part of the heat withdrawn at the regenerator’s cold side. Analogous results are presented for the Stirling refrigerator. At optimized nondimensional rate of refrigeration, its coefficient of performance is less than half the Carnot value.

Basic Limitations on the Performance of Stirling Engines

2003 ◽  
Author(s):  
P. C. T. de Boer
Keyword(s):  
Power Output ◽  
Thermal Efficiency ◽  
Essential Element ◽  
Void Volume ◽  
Pressure Gradients ◽  
Linear Temperature ◽  
Volume Increase ◽  
Stirling Engines ◽  
Linearized Theory ◽  
Net Power Output

The performance of Stirling engines is subject to limitations resulting from power dissipation in the regenerator. The dissipation is caused by pressure gradients in the regenerator to generate flow. Without this flow the power output would by zero. Hence the dissipation is an essential element of the operation of the engine. Using linearized theory, the equation for pressure in the regenerator is solved for the case of a linear temperature distribution. The regenerator is taken to be thermally perfect. All various are taken to be sinusoidal in time. Expressions are derived for the net power output and the thermal efficiency. The net power output is optimized under various constraints. The constraint yielding the best results is fixed piston amplitude in the compression chamber. Upper bounds on the dimensionless power output are found as function of regenerator void volume and regenerator temperature. These bounds are derived in the limit of zero frequency, and ae independent of the conductance of the regenerator. Both power output and thermal efficiency decrease decreases as frequency and regenerator void volume increase.

scholarly journals Power and Thermal Efficiency Optimization of an Irreversible Steady-Flow Lenoir Cycle

Entropy ◽  
2021 ◽  
Vol 23 (4) ◽  
pp. 425
Author(s):  
Ruibo Wang ◽  
Yanlin Ge ◽  
Lingen Chen ◽  
Huijun Feng ◽  
Zhixiang Wu
Keyword(s):  
Steady Flow ◽  
Power Output ◽  
Thermal Efficiency ◽  
Heat Exchangers ◽  
Cold Side ◽  
Heat Conductance ◽  
Efficiency Increase ◽  
Optimal Values ◽  
Internal Irreversibility ◽  
Conductance Distribution

Using finite time thermodynamic theory, an irreversible steady-flow Lenoir cycle model is established, and expressions of power output and thermal efficiency for the model are derived. Through numerical calculations, with the different fixed total heat conductances (UT) of two heat exchangers, the maximum powers (Pmax), the maximum thermal efficiencies (ηmax), and the corresponding optimal heat conductance distribution ratios (uLP(opt)) and (uLη(opt)) are obtained. The effects of the internal irreversibility are analyzed. The results show that, when the heat conductances of the hot- and cold-side heat exchangers are constants, the corresponding power output and thermal efficiency are constant values. When the heat source temperature ratio (τ) and the effectivenesses of the heat exchangers increase, the corresponding power output and thermal efficiency increase. When the heat conductance distributions are the optimal values, the characteristic relationships of P-uL and η-uL are parabolic-like ones. When UT is given, with the increase in τ, the Pmax, ηmax, uLP(opt), and uLη(opt) increase. When τ is given, with the increase in UT, Pmax and ηmax increase, while uLP(opt) and uLη(opt) decrease.

scholarly journals Performance Analysis and Optimization for Irreversible Combined Carnot Heat Engine Working with Ideal Quantum Gases

Entropy ◽  
2021 ◽  
Vol 23 (5) ◽  
pp. 536
Author(s):  
Lingen Chen ◽  
Zewei Meng ◽  
Yanlin Ge ◽  
Feng Wu
Keyword(s):  
Power Output ◽  
Thermal Efficiency ◽  
Combined Cycle ◽  
Quantum Gases ◽  
Carnot Cycle ◽  
Leakage Loss ◽  
Optimal Power ◽  
Heat Leakage ◽  
Working Medium ◽  
Ideal Quantum

An irreversible combined Carnot cycle model using ideal quantum gases as a working medium was studied by using finite-time thermodynamics. The combined cycle consisted of two Carnot sub-cycles in a cascade mode. Considering thermal resistance, internal irreversibility, and heat leakage losses, the power output and thermal efficiency of the irreversible combined Carnot cycle were derived by utilizing the quantum gas state equation. The temperature effect of the working medium on power output and thermal efficiency is analyzed by numerical method, the optimal relationship between power output and thermal efficiency is solved by the Euler-Lagrange equation, and the effects of different working mediums on the optimal power and thermal efficiency performance are also focused. The results show that there is a set of working medium temperatures that makes the power output of the combined cycle be maximum. When there is no heat leakage loss in the combined cycle, all the characteristic curves of optimal power versus thermal efficiency are parabolic-like ones, and the internal irreversibility makes both power output and efficiency decrease. When there is heat leakage loss in the combined cycle, all the characteristic curves of optimal power versus thermal efficiency are loop-shaped ones, and the heat leakage loss only affects the thermal efficiency of the combined Carnot cycle. Comparing the power output of combined heat engines with four types of working mediums, the two-stage combined Carnot cycle using ideal Fermi-Bose gas as working medium obtains the highest power output.

Heat Compensation in Buildings Using Thermoelectric Windows: An Energy Efficient Window Technology

2008 ◽  
Author(s):  
Rhys-Sheffer Birthwright ◽  
Achille Messac ◽  
Timothy Harren-Lewis ◽  
Sirisha Rangavajhala
Keyword(s):  
Energy Efficient ◽  
Coefficient Of Performance ◽  
Building Structures ◽  
Practical Applications ◽  
Current Input ◽  
Flow Through ◽  
Conventional Systems ◽  
Window Design ◽  
Absorption Power ◽  
Do So

In this paper, we explore the design of thermoelectric (TE) windows for applications in building structures. Thermoelectric windows are equipped with TE units in the window frame to provide a heat absorption power, given a direct current input. We explore the design performance of the TE window to compensate for its own heat gains. While existing energy efficient windows have made advances towards reducing the heat transfer through them, they still depend on the building’s heating, ventilation and air-conditioning (HVAC) system to compensate for their heat gains. Our research explores the design of a window that can actively compensate for the passive heat flow through the window panes, and to do so with a better coefficient of performance (COP) than conventional HVAC systems. We also optimize the TE window design, and present results of the potential performance for practical applications in the building structure. For the geographic locations considered (Hawaii and Miami), the results are promising. Interestingly, the proposed TE window design actively compensates for the conduction heat gains with a COP greater than three, while that of conventional systems is typically less than three.

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.

Effect of Ethanol-Air Equivalence Ratio on Performance of an Endoreversible Otto Engine

2011 ◽  
Vol 110-116 ◽  
pp. 273-277
Author(s):  
Rahim Ebrahim ◽  
Mahmoud Reza Tadayon ◽  
Farshad Tahmasebi Gandomkari ◽  
Kamyar Mahbobian
Keyword(s):  
Performance Evaluation ◽  
Compression Ratio ◽  
Power Output ◽  
Thermal Efficiency ◽  
Equivalence Ratio ◽  
Maximum Power ◽  
Otto Cycle ◽  
World Community ◽  
Maximum Power Output ◽  
The World

Today, the world community is looking for fuel efficient and environmentally viable alternatives for many of the traditional energy conversion approaches. This development has further worked to increase the technical focus on conventional cycles for making them more optimum in terms of performance. Hence, the objective of this paper is to study the effect of ethanol-air equivalence ratio on the power output and the indicated thermal efficiency of an air standard Otto cycle. Optimization of the cycle has been performed for power output as well as for thermal efficiency with respect to compression ratio. The results show that the maximum power output, the optimal compression ratio corresponding to maximum power output point, the optimal compression ratio corresponding to maximum thermal efficiency point and the working range of the cycle first increase and then decrease as the equivalence ratio increases. The result obtained herein provides a guide to the performance evaluation and improvement for practical Otto engines.

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.

scholarly journals Efficiency Reduction in Stirling Engines Resulting from Sinusoidal Motion

Energies ◽  
2018 ◽  
Vol 11 (11) ◽  
pp. 2887 ◽  
Author(s):  
Salvatore Ranieri ◽  
Gilberto Prado ◽  
Brendan MacDonald
Keyword(s):  
Thermal Efficiency ◽  
Thermal Power ◽  
Heat Sources ◽  
Sinusoidal Motion ◽  
Wide Range ◽  
Stirling Engines ◽  
Isothermal Analysis ◽  
The Impact ◽  
Alpha Type ◽  
The Ideal

Stirling engines have a high potential to produce renewable energy due to their ability to use a wide range of sustainable heat sources, such as concentrated solar thermal power and biomass, and also due to their high theoretical efficiencies. They have not yet achieved widespread use and commercial Stirling engines have had reduced efficiencies compared to their ideal values. In this work we show that a substantial amount of the reduction in efficiency is due to the operation of Stirling engines using sinusoidal motion and quantify this reduction. A discrete model was developed to perform an isothermal analysis of a 100cc alpha-type Stirling engine with a 90 ∘ phase angle offset, to demonstrate the impact of sinusoidal motion on the net work and thermal efficiency in comparison to the ideal cycle. For the specific engine analyzed, the maximum thermal efficiency of the sinusoidal cycle was found to have a limit of 34.4%, which is a reduction of 27.1% from Carnot efficiency. The net work of the sinusoidal cycle was found to be 65.9% of the net work from the ideal cycle. The model was adapted to analyze beta and gamma-type Stirling configurations, and the analysis revealed similar reductions due to sinusoidal motion.

Flow Insulation Characteristics of Combined Two Cordierite Alumina Porous Plates with Free Space

2017 ◽  
Vol 889 ◽  
pp. 275-281
Author(s):  
Preecha Khantikomol ◽  
Maitree Polsongkram
Keyword(s):  
Fluid Flow ◽  
Air Temperature ◽  
Thermal Efficiency ◽  
Free Space ◽  
Porous Plate ◽  
Temperature Drop ◽  
Fluid Temperature ◽  
Air Flow Rate ◽  
Efficiency Increase ◽  
Flow Through

Flow insulator is the material which having fluid flow through itself resulting to the fluid temperature difference between the upstream and downstream regions. The flow insulation characteristics of combined two cordierite alumina (Cr-Al) porous plates with 2 mm free space was investigated experimentally. The results indicated the air temperature drop across the flow insulator and the thermal efficiency increase with the inlet air temperature and decrease with increasing air flow rate. The higher PPI porous plate placing upstream layer resulted in increasing the thermal efficiency of the flow insulator significantly.

Improved µ-Scale Turbine Expander for Energy Recovery

2010 ◽  
Author(s):  
Marcus Keding ◽  
Piotr Dudzinski ◽  
Alexander Reissner ◽  
Stefan Hummel ◽  
Martin Tajmar
Keyword(s):  
High Pressure ◽  
Power Output ◽  
Energy Recovery ◽  
Turbine Blades ◽  
Low Pressure ◽  
Heat Pumps ◽  
Coefficient Of Performance ◽  
Work Recovery ◽  
Micro Power ◽  
Pressure Part

Micro power converters for energy recovery are increasingly important for a number of future applications. The Austrian Institute of Technology (AIT) is presently developing an innovative μ-scale turbine expander for work recovery in transcritical CO2 heat pumps. The main drawback of a lower COP (coefficient of performance) of transcritical CO2 heat pumps compared to conventional heat pump systems can be compensated by utilizing the pressure difference between the high pressure and low pressure part of the pump for work recovery. Work recovery can be realized by substituting the expansion valve between the high and low pressure side by a Pelton turbine with specific two phase flow turbine blades. In order to increase the power output, the generator was integrated into the turbine to reduce the friction losses and hence increase the overall efficiency. An important aspect is that the generator is directly connected with the high pressure part of the turbine. One part of the project is the optimization of the turbine geometry via simulation tools. The paper will give an overview about our microturbine development as well as a comparison of the power output of each turbine generation. Furthermore the present paper discusses a concept that utilizes our microturbine together with a micro combustion module that enables a micro power generator with very high power-to-weight ratios based on green fuels.

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