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 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.

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.

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.

“Entransy,” and Its Lack of Content in Physics

2014 ◽  
Vol 136 (5) ◽  
Author(s):  
Adrian Bejan
Keyword(s):  
Heat Transfer ◽  
Thermal Resistance ◽  
Entropy Generation ◽  
Solid Body ◽  
Thermodynamic Temperature ◽  
Entransy Dissipation ◽  
Minimum Entropy ◽  
Constructal Law ◽  
Minimum Entropy Generation ◽  
False Claim

Here, I show that “entransy” has no meaning in physics, because, at bottom, it rests on the false claim that in order to transfer heat to a solid body of thermodynamic temperature T, the heat transfer must be proportional to T. Entransy “dissipation” is a number proportional to well known measures of irreversibility such as entropy generation and lost exergy (destroyed available work). Furthermore, the “principle of entransy dissipation minimization” adds nothing to existing work based on minimum entropy generation, minimum thermal resistance, and constructal law. The broader trend illustrated by the entransy hoax is that it is becoming easy to take an existing idea, change the keywords, and publish it as new.

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