Investigation of Exergy Destruction Based on Avoidable and Unavoidable Concepts for Helical Coils

2010 ◽  
Author(s):  
Farid Bahiraee ◽  
Aidin Salehzadeh ◽  
Rahim Khoshbakhti Saray
Keyword(s):  
Reynolds Number ◽  
Forced Convection ◽  
Entropy Generation ◽  
Working Fluid ◽  
Inlet Temperature ◽  
Exergy Destruction ◽  
Minimum Entropy ◽  
Dean Number ◽  
Design Work ◽  
Minimum Entropy Generation

An inevitable problem challenges heat exchanger designers is that the heat transfer augmentation in a thermal system is always achieved at the expense of an increase in pressure loss. Thus, the optimal trade-off by choosing the most proper configuration and best flow condition has become the critical problem for design work. The brief survey on literature shows that optimal Reynolds number (i.e. the Reynolds number which corresponds to minimum entropy generation) of laminar forced convection in a helical tube, was specified based on minimum entropy generation. Therefore, the present study analyzes the thermodynamic potential of improvement for steady, laminar, fully developed, forced convection in a helical coiled tube subjected to uniform wall temperature based on the concept of avoidable and unavoidable exergy destruction. The influence of coil curvature ratio, dimensionless inlet temperature difference, dimensionless passage length of the coil, and fluid properties on avoidable exergy destruction have been investigated for water as working fluid. Results show considerable potential of thermodynamic optimization of helical coil tubes. Also, in the range of present study a relation for determining the amount of optimum Dean number is proposed.

scholarly journals Thermohydraulic Performance and Entropy Generation of a Triple-Pass Solar Air Heater with Three Inlets

Energies ◽  
2021 ◽  
Vol 14 (19) ◽  
pp. 6399
Author(s):  
Nguyen Minh Phu ◽  
Ngo Thien Tu ◽  
Nguyen Van Hap
Keyword(s):  
Reynolds Number ◽  
Air Temperature ◽  
Entropy Generation ◽  
Solar Air Heater ◽  
Minimum Entropy ◽  
Air Heater ◽  
The Third ◽  
Thermohydraulic Efficiency ◽  
The Difference ◽  
Minimum Entropy Generation

In this paper, a triple-pass solar air heater with three inlets is analytically investigated. The effects of airflow ratios of the second and third passes (ranging from 0 to 0.4), and the Reynolds number of the third pass (ranging from 8000 to 18,000) on the thermohydraulic efficiency and entropy generation are assessed. An absorber plate equipped with rectangular fins on both sides is used to enhance heat transfer. The air temperature change in the passes is represented by ordinary differential equations and solved by numerical integration. The results demonstrate that the effect of the third pass airflow ratio on the thermohydraulic efficiency and entropy generation is more significant than that of the second pass airflow ratio. The difference in air temperature through the collector shows an insignificant reduction, but the air pressure loss is only 50% compared with that of a traditional triple-pass solar air heater. Increasing the air flow ratios dramatically reduces entropy generation. Multi-objective optimization found a Reynolds number of 11,156 for both the airflow ratio of the second pass of 0.258 and airflow ratio of the third pass of 0.036 to be the an optimal value to achieve maximum thermohydraulic efficiency and minimum entropy generation.

Genetic Algorithm-Based Optimal Design of Plate Fins Following Minimum Entropy Generation Considerations

2005 ◽  
Vol 219 (8) ◽  
pp. 757-765 ◽  
Author(s):  
R. K. Jha ◽  
S Chakraborty
Keyword(s):  
Heat Transfer ◽  
Genetic Algorithm ◽  
Optimal Design ◽  
Forced Convection ◽  
Entropy Generation ◽  
Generation Rate ◽  
Entropy Generation Rate ◽  
Minimum Entropy ◽  
Minimum Entropy Generation ◽  
Continuous Plate

This paper deals with estimation of the optimal dimensions of arrays of plate fins cooled by forced convection. The optimization is achieved by minimizing the entropy generation rate using genetic algorithm-based evolutionary computing techniques. Results are presented for staggered plate fins configuration and continuous plate fins configuration. The effects of heat transfer and fluid friction on entropy generation rate are also reported.

Local thermal non-equilibrium conjugate forced convection and entropy generation in an aircraft cabin with air channel partially filled porous insulation

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Oktay Çiçek ◽  
A. Cihat Baytaş
Keyword(s):  
Thermal Conductivity ◽  
Reynolds Number ◽  
Forced Convection ◽  
Cross Section ◽  
Entropy Generation ◽  
Channel Wall ◽  
Darcy Number ◽  
Content Type ◽  
Exit Cross Section ◽  
Air Channel

Purpose The purpose of this study is to numerically investigate heat transfer and entropy generation between airframe and cabin-cargo departments in an aircraft. The conjugate forced convection and entropy generation in a cylindrical cavity within air channel partly filled with porous insulation material as simplified geometry for airframe and cabin-cargo departments are considered under local thermal non-equilibrium condition. Design/methodology/approach The non-dimensional governing equations for fluid and porous media discretized by finite volume method are solved using the SIMPLE algorithm with pressure and velocity correction. Findings The effects of the following parameters on the problem are investigated; Reynolds number, Darcy number, the size of inlet and exit cross-section, thermal conductivity ratio for solid and fluid phases, angle between the vertical symmetry axis and the end of channel wall exit and the gap between adiabatic channel wall and horizontal adiabatic wall separating cabin and cargo sections. Originality/value This paper can provide a basic perspective and framework for thermal design between the fuselage and cabin-cargo sections. The minimum total entropy generation number is calculated for various Reynolds numbers and thermal conductivity ratios. It is observed that the channel wall temperature increases for high Reynolds number, low Darcy number, narrower exit cross-section and wider the gap between channel wall and horizontal.

The Role of Fin Geometry in Heat Sink Performance

2006 ◽  
Vol 128 (4) ◽  
pp. 324-330 ◽  
Author(s):  
W. A. Khan ◽  
J. R. Culham ◽  
M. M. Yovanovich
Keyword(s):  
Reynolds Number ◽  
Aspect Ratio ◽  
Entropy Generation ◽  
Heat Sink ◽  
Control Volume ◽  
Generation Rate ◽  
Heat Transfer Fluid ◽  
Entropy Generation Rate ◽  
Minimum Entropy ◽  
Axis Ratio

The following study will examine the effect on overall thermal/fluid performance associated with different fin geometries, including, rectangular plate fins as well as square, circular, and elliptical pin fins. The use of entropy generation minimization, EGM, allows the combined effect of thermal resistance and pressure drop to be assessed through the simultaneous interaction with the heat sink. A general dimensionless expression for the entropy generation rate is obtained by considering a control volume around the pin fin including base plate and applying the conservations equations for mass and energy with the entropy balance. The formulation for the dimensionless entropy generation rate is developed in terms of dimensionless variables, including the aspect ratio, Reynolds number, Nusselt number, and the drag coefficient. Selected fin geometries are examined for the heat transfer, fluid friction, and the minimum entropy generation rate corresponding to different parameters including axis ratio, aspect ratio, and Reynolds number. The results clearly indicate that the preferred fin profile is very dependent on these parameters.

Second-Law Analysis on Wavy Plate Fin-and-Tube Heat Exchangers

1998 ◽  
Vol 120 (3) ◽  
pp. 797-800 ◽  
Author(s):  
W. W. Lin ◽  
D. J. Lee
Keyword(s):  
Entropy Generation ◽  
Operating Conditions ◽  
Generation Rate ◽  
Entropy Generation Rate ◽  
Second Law ◽  
Spanwise Direction ◽  
Minimum Entropy ◽  
Tube Heat Exchanger ◽  
Second Law Analysis ◽  
Minimum Entropy Generation

Second-law analysis on the herringbone wavy plate fin-and-tube heat exchanger was conducted on the basis of correlations of Nusselt number and friction factor proposed by Kim et al. (1997), from which the entropy generation rate was evaluated. Optimum Reynolds number and minimum entropy generation rate were found over different operating conditions. At a fixed heat duty, the in-line layout with a large tube spacing along streamwise direction was recommended. Furthermore, within the valid range of Kim et al.’s correlation, effects of the fin spacing and the tube spacing along spanwise direction on the second-law performance are insignificant.

Minimum entropy generation for isothermal endothermic/exothermic reactor networks

AIChE Journal ◽  
2014 ◽  
Vol 61 (1) ◽  
pp. 103-117 ◽  
Author(s):  
Paul G. Ghougassian ◽  
Vasilios Manousiouthakis
Keyword(s):  
Entropy Generation ◽  
Minimum Entropy ◽  
Reactor Networks ◽  
Minimum Entropy Generation

scholarly journals Optimal Design of Nanoparticle Enhanced Phan-Thien–Tanner Flow of a Viscoelastic Fluid in a Microchannel

Entropy ◽  
2018 ◽  
Vol 20 (12) ◽  
pp. 895
Author(s):  
Mohammad Abdollahzadeh Jamalabadi
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Entropy Generation ◽  
Volume Fraction ◽  
Circular Cross Section ◽  
Major Influence ◽  
Parameter Study ◽  
Bejan Number ◽  
Total Entropy ◽  
Minimum Entropy

The excellent thermal characteristics of nanoparticles have increased their application in the field of heat transfer. In this paper, a thermophysical and geometrical parameter study is performed to minimize the total entropy generation of the viscoelastic flow of nanofluid. Entropy generation with respect to volume fraction (<0.04), the Reynolds number (20,000–100,000), and the diameter of the microchannel (20–20,000 μm) with the circular cross-section under constant flux are calculated. As is shown, most of the entropy generation owes to heat transfer and by increasing the diameter of the channel, the Bejan number increases. The contribution of heat entropy generation in the microchannel is very poor and the major influence of entropy generation is attributable to friction. The maximum quantity of in-channel entropy generation happens in nanofluids with TiO2, CuO, Cu, and Ag nanoparticles, in turn, despite the fact in the microchannel this behavior is inverted, the minimum entropy generation occurs in nanofluids with CuO, Cu, Ag, and TiO2 nanoparticles, in turn. In the channel and microchannel for all nanofluids except water-TiO2, increasing the volume fraction of nanoparticles decreases entropy generation. In the channel and microchannel the total entropy generation increases by augmentation the Reynolds number.

Forced Convection Laminar Pulsating Flow in a 90-deg Bifurcation

2020 ◽  
Vol 13 (3) ◽  
Author(s):  
Fatih Selimefendigil ◽  
Hakan F. Öztop ◽  
Jay M. Khodadadi
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Forced Convection ◽  
Pulsating Flow ◽  
Working Fluid ◽  
Constant Wall Temperature ◽  
Numerical Work ◽  
Average Value ◽  
Number Variation ◽  
Volume Method

Abstract Numerical investigation of laminar forced convection of pulsating flow in a 90-deg bifurcation was performed with the finite volume method. The inlet velocity varies sinusoidally with time while constant wall temperature is utilized. The working fluid is air with constant properties and the numerical work is conducted for a range of the Reynolds numbers (100–2000), dividing flowrates (0.3–0.7) and Strouhal numbers (0.1–10). It is observed that the amplitudes of oscillating heat transfer are damped as the value of the Strouhal number increases. The average value of Nu number rises for higher Reynolds number and the dividing flowrate for the downstream wall of the y-channel branch. As the value of the dividing flowrate increases from 0.3 to 0.7, heat transfer is less effective in the vicinity of the branch at the Reynolds number of 500. The effects of the Reynolds number on the average Nu number variation is more pronounced for the y-branch wall for different values of dividing flowrates. Resonant type behavior of average Nu number is obtained for the y-branch channel for diving flowrates of 0.3 and 0.5.

Convective Heat Transfer Enhancement in Solar Receivers Using Minimum Entropy Generation Optimization

2011 ◽  
Author(s):  
Qi Li ◽  
Xigang Yuan ◽  
Pierre Neveu ◽  
Gilles Flamant
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Convective Heat ◽  
Entropy Generation ◽  
Minimum Entropy ◽  
Transfer Enhancement ◽  
Optimal Velocity ◽  
Minimum Entropy Generation ◽  
Convective Heat Transfer Enhancement

Convective heat transfer enhancement can significantly improve the thermal efficiency in the conversion, utilization, recovery and storage of energy (in particular solar thermal). Modifying velocity field is the most direct approach to enhance convective heat transfer. However, in most cases the optimal velocity field is unknown and difficult to find even for an experienced researcher. In this paper, a predictive optimization methodology in convective heat transfer enhancement based on minimum entropy generation (MEG) principle was developed. A set of Euler’s equations were derived by the variation calculus to the Lagrange function established by governing equations, specific constraints and objective functional—total entropy generation rate. The solution of these equations resulted in the optimal velocity fields, leading to the minimum entropy generation. To validate and demonstrate the future application of this methodology to solar absorbers used to convert concentrated solar energy, the steady laminar convection heat transfer process in a two-dimensional channel with fixed heat flux boundaries was optimized for given total viscous dissipations. The numerical simulation results showed that lower value of maximum wall temperature was obtained by MEG optimization, which means cheaper and safer materials. The present work indicated that the new methodology could be a good guide in convective heat transfer enhancement design work, especially in CSP receivers.

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