Optimum Criteria on the Important Parameters of an Irreversible Otto Heat Engine With the Temperature-Dependent Heat Capacities of the Working Fluid

2007 ◽  
Vol 129 (4) ◽  
pp. 348-354 ◽  
Author(s):  
Yingru Zhao ◽  
Bihong Lin ◽  
Jincan Chen
Keyword(s):  
Compression Ratio ◽  
Relevant Literature ◽  
Heat Engine ◽  
Heat Capacities ◽  
Working Fluid ◽  
Cylinder Wall ◽  
Work Output ◽  
Heat Leak ◽  
Temperature Dependent ◽  
Compression And Expansion

An irreversible cycle model of the Otto heat engine is established, in which the temperature-dependent heat capacities of the working fluid, the irreversibilities resulting from the nonisentropic compression and expansion processes, and heat leak losses through the cylinder wall are taken into account. The adiabatic equation of ideal gases with the temperature-dependent heat capacity is strictly deduced without using the additional approximation condition in the relevant literature and used to analyze the performance of the Otto heat engine. Expressions for the work output and efficiency of the cycle are derived by introducing the compression ratio of two isochoric processes. The performance characteristic curves of the Otto heat engine are presented for a set of given parameters. The optimum criteria of some important parameters such as the work output, efficiency, compression ratio, and temperatures of the working fluid are given. Moreover, the influence of the compression and expansion efficiencies, the variable heat capacities, the heat leak, and other parameters on the performance of the cycle is discussed in detail. The results obtained are novel and general, from which some relevant conclusions in literature may be directly derived. This work may provide a significant guidance for the performance improvement and optimal design of the Otto heat engine.

scholarly journals Action and Entropy in Heat Engines: An Action Revision of the Carnot Cycle

Entropy ◽  
2021 ◽  
Vol 23 (7) ◽  
pp. 860
Author(s):  
Ivan R. Kennedy ◽  
Migdat Hodzic
Keyword(s):  
Heat Engine ◽  
Working Fluid ◽  
Field Energy ◽  
Carnot Cycle ◽  
Gibbs Potential ◽  
Atmospheric Gases ◽  
Temperature Dependent ◽  
Expansion Phase ◽  
Heat Engines ◽  
The Difference

Despite the remarkable success of Carnot’s heat engine cycle in founding the discipline of thermodynamics two centuries ago, false viewpoints of his use of the caloric theory in the cycle linger, limiting his legacy. An action revision of the Carnot cycle can correct this, showing that the heat flow powering external mechanical work is compensated internally with configurational changes in the thermodynamic or Gibbs potential of the working fluid, differing in each stage of the cycle quantified by Carnot as caloric. Action (@) is a property of state having the same physical dimensions as angular momentum (mrv = mr2ω). However, this property is scalar rather than vectorial, including a dimensionless phase angle (@ = mr2ωδφ). We have recently confirmed with atmospheric gases that their entropy is a logarithmic function of the relative vibrational, rotational, and translational action ratios with Planck’s quantum of action ħ. The Carnot principle shows that the maximum rate of work (puissance motrice) possible from the reversible cycle is controlled by the difference in temperature of the hot source and the cold sink: the colder the better. This temperature difference between the source and the sink also controls the isothermal variations of the Gibbs potential of the working fluid, which Carnot identified as reversible temperature-dependent but unequal caloric exchanges. Importantly, the engine’s inertia ensures that heat from work performed adiabatically in the expansion phase is all restored to the working fluid during the adiabatic recompression, less the net work performed. This allows both the energy and the thermodynamic potential to return to the same values at the beginning of each cycle, which is a point strongly emphasized by Carnot. Our action revision equates Carnot’s calorique, or the non-sensible heat later described by Clausius as ‘work-heat’, exclusively to negative Gibbs energy (−G) or quantum field energy. This action field complements the sensible energy or vis-viva heat as molecular kinetic motion, and its recognition should have significance for designing more efficient heat engines or better understanding of the heat engine powering the Earth’s climates.

A MEMS-Based Micro Heat Engine With Integrated Thermal Switch

2006 ◽  
Author(s):  
L. W. Weiss ◽  
J. H. Cho ◽  
D. J. Morris ◽  
D. F. Bahr ◽  
C. D. Richards ◽  
...  
Keyword(s):  
Silicon Nitride ◽  
Heat Engine ◽  
Working Fluid ◽  
Operating Pressure ◽  
Work Output ◽  
Silicon Membrane ◽  
Thermal Switch ◽  
Silicon Nitride Membrane ◽  
Micro Heat Engine ◽  
Membrane Deflection

This work details the effect of top membrane compliance on the performance of a MEMS based micro-heat engine and integrated thermal switch at operating speeds of 20, 40, and 100Hz and heat inputs of up to 60mJ per cycle. The engine consists of two flexible membranes encapsulating a volume of saturated working fluid. A thermal switch is used to intermittently reject heat from the engine to a constant temperature cooling sink. Mechanical work output is measured based on the engine's top membrane deflection and internal operating pressure. Three top membranes are considered; a 2micron thick silicon membrane, a 300nm thick silicon-nitride membrane, and a 3micron thick corrugated silicon membrane. The engine is shown to produce 1.0mW of mechanical power when operated at 100Hz.

scholarly journals Maximum work output of multistage continuous Carnot heat engine system with finite reservoirs of thermal capacity and radiation between heat source and working fluid

2010 ◽  
Vol 14 (1) ◽  
pp. 1-9 ◽  
Author(s):  
Jun Li ◽  
Lingen Chen ◽  
Fengrui Sun
Keyword(s):  
Heat Transfer ◽  
Heat Source ◽  
Heat Sink ◽  
Heat Engine ◽  
Thermal Capacity ◽  
Working Fluid ◽  
Work Output ◽  
Maximum Work ◽  
Engine System ◽  
Maximum Work Output

Optimal temperature profile for maximum work output of multistage continuous Carnot heat engine system with two reservoirs of finite thermal capacity is determined. The heat transfer between heat source and the working fluid obeys radiation law and the heat transfer between heat sink and the working fluid obeys linear law. The solution is obtained by using optimal control theory and pseudo-Newtonian heat transfer model. It is shown that the temperature of driven fluid monotonically decreases with respect to flow velocity and process duration. The maximum work is obtained. The obtained results are compared with those obtained with infinite low temperature heat sink.

Effect of Heat Transfer Law on the Ecological Optimization of a Generalized Irreversible Carnot Engine

2005 ◽  
Vol 12 (03) ◽  
pp. 249-260 ◽  
Author(s):  
Xiaoqin Zhu ◽  
Lingen Chen ◽  
Fengrui Sun ◽  
Chih Wu
Keyword(s):  
Heat Transfer ◽  
Heat Engine ◽  
Optimization Criterion ◽  
Working Fluid ◽  
Entropy Production Rate ◽  
Heat Leak ◽  
Ecological Performance ◽  
Heat Leakage ◽  
Internal Irreversibility ◽  
Ecological Optimization

The optimal ecological performance of a irreversible Carnot engine with the losses of heat-resistance, heat leak and internal irreversibility, in which the transfer between the working fluid and the heat reservoirs obeys a generalized heat transfer law Q ∝ ∆(Tn), is derived by taking an ecological optimization criterion as the objective, which consists of maximizing a function representing the best compromise between the power and entropy production rate of the heat engine. Some special examples are discusses. A numerical example is given to show the effects of heat transfer law, heat leakage and internal irreversibility on the optimal performance of the generalized irreversible heat engine. The results can provide some theoretical guidance for the designs of practical engine.

Optimal Configuration and Performance of Heat Engines with Heat Leak and Finite Heat Capacity

2002 ◽  
Vol 09 (01) ◽  
pp. 85-96 ◽  
Author(s):  
Lingen Chen ◽  
Shengbing Zhou ◽  
Fengrui Sun ◽  
Chih Wu
Keyword(s):  
Heat Capacity ◽  
High Temperature ◽  
Low Temperature ◽  
Heat Engine ◽  
Optimal Configuration ◽  
Working Fluid ◽  
Heat Leak ◽  
Heat Engines ◽  
And Performance ◽  
Maximum Work Output

The optimal configuration of a class of two-heat-reservoir heat engine cycles in which the maximum work output can be obtained under a given cycle time is determined with the considerations of heat leak, finite heat capacity high-temperature source and infinite heat capacity low-temperature heat sink. The heat engine cycles considered in this paper include: (1) infinite low- and high-temperature reservoirs without heat leak, (2) infinite low- and high-temperature reservoirs with heat leak, (3) finite high-temperature source and infinite low-temperature sink without heat leak, and (4) finite high-temperature source and infinite low-temperature sink with heat leak. It is assumed that the heat transfer between the working fluid and the reservoirs obeys Newton's law. It is shown that the existence of heat leak doesn't affect the configuration of a cycle with an infinite high-temperature source. The finite heat capacity of a high temperature source without heat leak makes the cycle a generalized Carnot heat engine cycle. There exists a great difference of the cycle configurations for the finite high-temperature source with heat leak and the former three cases. Moreover, the relations between the optimal power output and the efficiency of the former three configurations are derived, and they show that the heat leak affects the power versus efficiency characteristics of the heat engine cycles.

scholarly journals Action and Entropy in Heat Engines: An Action Revision of the Carnot Cycle

2021 ◽  
Author(s):  
Ivan Robert Kennedy ◽  
Migdat Hodzic
Keyword(s):  
Heat Engine ◽  
Working Fluid ◽  
Field Energy ◽  
Carnot Cycle ◽  
Gibbs Potential ◽  
Atmospheric Gases ◽  
Temperature Dependent ◽  
Expansion Phase ◽  
Heat Engines ◽  
The Difference

Despite the remarkable success of Carnot’s heat engine cycle in founding the discipline of thermodynamics two centuries ago, false viewpoints of his use of the caloric theory in the cycle still linger, limiting his legacy. An action revision of the Carnot cycle can correct this, showing that the heat flow powering external mechanical work is compensated internally with configurational changes in the thermodynamic or Gibbs potential of the working fluid, differing in each stage of the cycle quantified by Carnot as caloric. Action (@) is a property of state having the same physical dimensions as angular momentum (mrv=mr2ω). However, this property is scalar rather than vectorial, including a dimensionless phase angle (@=mr2ωδφ). We have recently confirmed with atmospheric gases that their entropy is a logarithmic function of the relative vibrational, rotational and translational action ratios with Planck’s quantum of action ħ. The Carnot principle shows that the maximum rate of work (puissance motrice) possible from the reversible cycle is controlled by the difference in temperature of the hot source and the cold sink, the colder the better. This temperature difference between the source and the sink also controls the isothermal variations of the Gibbs potential of the working fluid, that Carnot identified as reversible temperature-dependent but unequal exchanges in caloric. Importantly, the engine’s inertia ensures that heat from work performed adiabatically in the expansion phase is all restored to the working fluid during the adiabatic recompression, less the net work performed. This allows both the energy and the thermodynamic potential to return to the same values at the beginning of each cycle, a point strongly emphasized by Carnot. Our action revision equates Carnot’s calorique, or the non-sensible heat later described by Clausius as ‘work-heat’ exclusively to negative Gibbs energy (-G) or quantum field energy. This action field complements the sensible energy or vis-viva heat as molecular kinetic motion and its recognition should have significance for designing more efficient heat engines or better understanding of the heat engine powering the Earth’s climates.

A Compendium of Methods for Determining the Exergy Balance Terms Applied to Reciprocating Internal Combustion Engines

2021 ◽  
pp. 1-39
Author(s):  
Bibhuti B. Sahoo ◽  
Maryom Dabi ◽  
Ujjwal K. Saha
Keyword(s):  
Internal Combustion Engines ◽  
Internal Combustion ◽  
Evaluation Methods ◽  
Cylinder Wall ◽  
Exhaust Gas ◽  
Work Output ◽  
Heating Value ◽  
Dead State ◽  
Ic Engines ◽  
Exergy Balance

Abstract Exergy analysis of the reciprocating internal combustion (IC) engines is studied by estimating various input and output energy transfer parameters concerning a dead state reference. Exergy terms such as fuel input, work output, cooling, and exhaust gas are measured and are set into the exergy balance equation to determine the amount of loss or destruction. Exergy destructions are found in many forms such as combustion (entropy generation), cylinder wall, friction, mixing, blow-by, and others. These exergy terms have been estimated by considering various factors such as engine type, fuel type, environmental condition, and others. In this article, the different methods employed in estimating these exergy terms have been reviewed. It attempts to make a compendium of these evaluation methods and segregates them under individual exergy terms with necessary descriptions. The fuel input measurement is mostly based on Gibb's free energy and the lower heating value, whereas its higher heating value is used during the fuel exergy calculation on a molar basis. The work output of the engines is estimated either from the crankshaft or by analyzing the cylinder pressure and volume. The exergy transfer with cooling medium and exhaust gas depends on the temperature of gas. The maximum achievable engine performance is quantified by estimating the exergy efficiency. This piece of study will not only provide a plenty of information on exergy evaluation methods of IC engines but will also allow the future researchers to adopt the appropriate one.

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