The effects of temperature-dependent specific heats of the working fluid on the performance of a Dual cycle with heat loss and friction

2011 ◽  
Author(s):  
Jiann-Chang Lin ◽  
Shuhn-Shyurng Hou ◽  
Shu-Jhang Li
Keyword(s):  
Heat Loss ◽  
Working Fluid ◽  
Temperature Dependent ◽  
Specific Heats ◽  
Dual Cycle ◽  
Effects Of Temperature

Effects of Heat Transfer and Friction on the Performance of a Miller Cycle Diesel Engine with Considerations of Variable Specific Heats of the Working Fluid

2013 ◽  
Vol 311 ◽  
pp. 211-216
Author(s):  
Jiann Chang Lin ◽  
Shuhn Shyurng Hou
Keyword(s):  
Heat Transfer ◽  
Diesel Engine ◽  
Power Output ◽  
Thermal Efficiency ◽  
Friction Loss ◽  
Working Fluid ◽  
Miller Cycle ◽  
Temperature Dependent ◽  
Specific Heats ◽  
Negative Effect

The objective of this study is to analyze the effects of friction and heat transfer with considerations of variable specific heats of working fluid on the performance of a Miller cycle Diesel engine. The variations in power output and thermal efficiency with compression ratio, and the relations between the power output and the thermal efficiency of the Miller cycle Diesel engine are presented. The results show that the power output as well as the efficiency where maximum power output occurs will decrease with the increase of heat loss. The temperature-dependent specific heats of working fluid have a significant influence on the performance. The power output and the working range of the Miller cycle Diesel engine increase with the increase of specific heats of working fluid, while, the efficiency decreases with the increase of specific heats of working fluid. The influence of the parameter b related to the friction loss has a negative effect on the performance. Therefore, the power output and efficiency of the cycle decrease with increasing b. Note that the effects of heat transfer with considerations of variable specific heats of working fluid and friction loss on the performance are significant and should be considered in practice cycle analysis.

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.

scholarly journals Numerical study of flow patterns and heat transfer in mini twisted oval tubes

2015 ◽  
Vol 26 (12) ◽  
pp. 1550140 ◽  
Author(s):  
Amin Ebrahimi ◽  
Ehsan Roohi
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Performance ◽  
Numerical Study ◽  
Critical Role ◽  
Reynolds Numbers ◽  
Flow Patterns ◽  
Working Fluid ◽  
Transfer Performance ◽  
Temperature Dependent ◽  
Overall Performance

Flow patterns and heat transfer inside mini twisted oval tubes (TOTs) heated by constant-temperature walls are numerically investigated. Different configurations of tubes are simulated using water as the working fluid with temperature-dependent thermo-physical properties at Reynolds numbers ranging between 500 and 1100. After validating the numerical method with the published correlations and available experimental results, the performance of TOTs is compared to a smooth circular tube. The overall performance of TOTs is evaluated by investigating the thermal-hydraulic performance and the results are analyzed in terms of the field synergy principle and entropy generation. Enhanced heat transfer performance for TOTs is observed at the expense of a higher pressure drop. Additionally, the secondary flow generated by the tube-wall twist is concluded to play a critical role in the augmentation of convective heat transfer, and consequently, better heat transfer performance. It is also observed that the improvement of synergy between velocity and temperature gradient and lower irreversibility cause heat transfer enhancement for TOTs.

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