scholarly journals Nonlinear Models of Thermo-Viscoelastic Materials

Materials ◽  
2021 ◽  
Vol 14 (24) ◽  
pp. 7617
Author(s):  
Claudio Giorgi ◽  
Angelo Morro
Keyword(s):  
Entropy Production ◽  
Nonlinear Models ◽  
General Scheme ◽  
Second Law Of Thermodynamics ◽  
Second Law ◽  
Viscoelastic Materials ◽  
Constitutive Function ◽  
Plastic Materials ◽  
Special Cases ◽  
Strain Stress

The paper develops a general scheme for viscoelastic materials, where the constitutive properties are described by means of measures of strain, stress, heat flux, and their time derivatives. The constitutive functions are required to be consistent with the second law of thermodynamics. Indeed, a new view is associated with the second law: the non-negative expression of the entropy production is set equal to a further constitutive function. The introduction of the entropy production as a constitutive function allows for a much wider range of models. Within this range, a scheme to obtain nonlinear models of thermo-viscoelastic materials subject to large deformations is established. Notably, the Kelvin–Voigt, Maxwell, Burgers, and Oldroyd-B viscoelastic models, along with the Maxwell–Cattaneo heat conduction, are obtained as special cases. The scheme allows also for modelling the visco-plastic materials, such as the Prandtl–Reuss work-hardening function and the Bingham–Norton fluid.

scholarly journals Beating Carnot efficiency with periodically driven chiral conductors

2021 ◽  
Author(s):  
sungguen ryu ◽  
Rosa Lopez ◽  
L Serra ◽  
David Sanchez
Keyword(s):  
Entropy Production ◽  
Second Law Of Thermodynamics ◽  
Second Law ◽  
Fundamental Limits ◽  
Periodically Driven ◽  
Power Injection ◽  
Recent Developments ◽  
Proper Definition ◽  
Excitation Processes ◽  
Absence Of Power

Abstract Classically, the power generated by an ideal thermal machine cannot be larger than the Carnot limit. This profound result is rooted in the second law of thermodynamics. A hot question is whether this bound is still valid for microengines operating far from equilibrium. Here, we demonstrate that a quantum chiral conductor driven by AC voltage can indeed work with efficiencies much larger than the Carnot bound. The system also extracts work from common temperature baths, violating Kelvin-Planck statement. Nonetheless, with the proper definition, entropy production is always positive and the second law is preserved. The crucial ingredients to obtain efficiencies beyond the Carnot limit are: i) irreversible entropy production by the photoassisted excitation processes due to the AC field and ii) absence of power injection thanks to chirality. Our results are relevant in view of recent developments that use small conductors to test the fundamental limits of thermodynamic engines.

A Micro Combined Heat and Power Thermodynamic Analysis and Optimization

2010 ◽  
Author(s):  
Ali Gholizadeh ◽  
M. B. Shafii ◽  
M. H. Saidi
Keyword(s):  
Combustion Chamber ◽  
Entropy Production ◽  
Thermodynamic Analysis ◽  
Second Law Of Thermodynamics ◽  
Combined Heat And Power ◽  
Second Law ◽  
Entropy Production Rate ◽  
Prime Mover ◽  
Operation Condition ◽  
Laws Of Thermodynamics

In modeling and designing micro combined heat and power cycle most important point is recognition of how the cycle operates based on the first and second laws of thermodynamics simultaneously. Analyzing data obtained from thermodynamic analysis employed to optimize MCHP cycle. The data obtained from prime mover optimization has been used for basic stimulus cycle. Assumptions considered for prime mover optimization has been improved, for example in making optimum operation condition by using genetic algorithms constant pressure combustion chamber was considered. The exact value of downstream and upstream pressure changes in the combustion chamber reaction has been obtained. After extraction of the appropriate relationship for the primary stimulus cycle, data required for the overall cycle analysis identified, By using these data optimum total cycle efficiency and constructing the first and second laws of thermodynamics has been calculated for it. After reviewing Thermodynamic governing relations in each cycle and using the optimum values that the prime mover has been optimized with, other cycles have been optimized. In best performance condition of cycle, electrical efficiency was 41 percent and the overall efficiency of the cycle was 88 percent, respectively. After using the second law of thermodynamics mathematical model Second law of thermodynamics efficiency and entropy production rate was estimated. Second law of thermodynamics yield best performance against the 45.14 percent and the rate of entropy production in this case equal to 0.099 kW/K respectively.

COMMENT ON "EXPERIMENTAL DEMONSTRATION OF VIOLATIONS OF THE SECOND LAW OF THERMODYNAMICS FOR SMALL SYSTEMS AND SHORT TIME SCALES"

2005 ◽  
Vol 05 (02) ◽  
pp. C23-C24
Author(s):  
THEO M. NIEUWENHUIZEN ◽  
ARMEN E. ALLAHVERDYAN
Keyword(s):  
Entropy Production ◽  
Time Scales ◽  
Second Law Of Thermodynamics ◽  
Individual Particle ◽  
Second Law ◽  
Colloidal System ◽  
Experimental Demonstration ◽  
Particle Trajectories ◽  
Small Systems ◽  
Short Time

In a recent paper Wang et al. [1] report for a colloidal system the entropy production in individual particle trajectories. Some of the trajectories have a negative production, and this is claimed to violate the second law. We stressed that the second law only demands the entropy production averaged over all trajectories to be positive, and this is the case for the data of Wang et al.

Optimization of turbojet engine cycle with dual-purpose PSO algorithm

2019 ◽  
Vol 20 (6) ◽  
pp. 604 ◽  
Author(s):  
M.R. Ahadi Nasab ◽  
M.A. Ehyaei
Keyword(s):  
Entropy Production ◽  
Pressure Ratio ◽  
Second Law Of Thermodynamics ◽  
Pso Algorithm ◽  
Optimization Method ◽  
Exergy Efficiency ◽  
Second Law ◽  
Turbine Efficiency ◽  
Turbojet Engine ◽  
Compressor Pressure Ratio

In this article, the J85-GE-21 turbojet engine for an altitude of 1000–8000 m, with the speed of 200 m/s and at 10, 20, and 40 °C, was provided, and then, based on the objective functions, the above system was optimized using particle swarm optimization method. For the purpose of optimization, the Mach number, compressor efficiency, turbine efficiency, nozzle efficiency, and compressor pressure ratio were assumed to be in the range of 0.6–1.4, 0.8–0.95, 0.8–0.95, 0.8–0.95, and 7–10, respectively. The highest exergy efficiency of 73.1% for different components of the engine at sea level and speed of 200 m/s belonged to the diffuser. Second and third to it were nozzle and combustion chamber with 68.6 and 51.5%, respectively. The lowest exergy efficiency of 4% belonged to the compressor, and the second to it was the afterburner with 11.6%. Also, the values of entropy production and efficiency of the second law of thermodynamics were 1176.99 and 479 K/W, respectively, prior to optimization, which were respectively changed to 1129 and 51.4 K/W postoptimization. Obviously, the entropy production is reduced, while the efficiency of the second law of thermodynamics is increased.

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