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1

Entropy analysis of third-grade MHD convection flows from a horizontal cylinder with slip

Madhavi K., Prasad V. R., Gaffar S. A., Venkatadri K.

Archive of Mechanical Engineering

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2018

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Vol. LXV, nr 3

417--440

EN

In thermos ﬂuid dynamics, free convection ﬂows external to diﬀerent geometries, such as cylinders, ellipses, spheres, curved walls, wavy plates, cones, etc., play major role in various industrial and process engineering systems. The thermal buoyancy force associated with natural convection ﬂows can play a critical role in determining skin friction and heat transfer rates at the boundary. In thermal engineering, natural convection ﬂows from cylindrical bodies has gained exceptional interest. In this article, we mathematically evaluate an entropy analysis of magnetohydrodynamic third-grade convection ﬂows from permeable cylinder considering velocity and thermal slip effects. The resulting non-linear coupled partial diﬀerential conservation equations with associated boundary conditions are solved with an eﬃcient unconditionally stable implicit ﬁnite diﬀerence Keller-Box technique. The impacts of momentum and heat transport coeﬃcients, entropy generation and Bejan number are computed for several values of non-dimensional parameters arising in the ﬂow equations. Streamlines are plotted to analyze the heat transport process in a two-dimensional domain. Furthermore, the deviations of the ﬂow variables are compared with those computed for a Newtonian ﬂuid and this has important implications in industrial thermal material processing operations, aviation technology, diﬀerent enterprises, energy systems and thermal enhancement of industrial ﬂow processes.

2

Entropy generation and thermodynamic analysis of solar air heaters with artificial roughness on absorber plate

Prasad R. K., Sahu M. K.

Archives of Thermodynamics

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2017

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Vol. 38, no. 3

23--48

EN

This paper presents mathematical modelling and numerical analysis to evaluate entropy generation analysis (EGA) by considering pressure drop and second law efficiency based on thermodynamics for forced convection heat transfer in rectangular duct of a solar air heater with wire as artificial roughness in the form of arc shape geometry on the absorber plate. The investigation includes evaluations of entropy generation, entropy generation number, Bejan number and irreversibilities of roughened as well as smooth absorber plate solar air heaters to compare the relative performances. Furthermore, effects of various roughness parameters and operating parameters on entropy generation have also been investigated. Entropy generation and irreversibilities (exergy destroyed) has its minimum value at relative roughness height of 0.0422 and relative angle of attack of 0.33, which leads to the maximum exergetic efficiency. Entropy generation and exergy based analyses can be adopted for the evaluation of the overall performance of solar air heaters.

3

Wpływ parametrów procesu na optymalne warunki pracy nośników katalizatorów stosowanych w procesach selektywnego utleniania i dopalania węglowodorów

Krajewski W., Kalinowski K., Najzarek Z.

Archiwum Gospodarki Odpadami i Ochrony Środowiska

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2012

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Vol. 14, nr 2

51-61

PL

Podano charakterystyki cieplno–przepływowe dla 11 nośników katalizatora. Dla tych nośników wyznaczono optymalne wartości liczb Bejana, przy których stosunek liczb Nusselta do bezwymiarowej szybkości generacji entropii osiąga wartość maksymalną. Te liczby wyznaczono zmieniając kolejno długość złoża, ciśnienie na wylocie ze złoża, temperaturę wlotowa powietrza na złoże i temperaturę ścianki. Podano korelacje na optymalne liczby Bejana w zależności od parametrów procesu. Przedstawiono również takie korelacje na optymalne liczby Reynoldsa oraz wartości maksymalne stosunku liczb Nusselta do bezwymiarowej szybkości generacji entropii.

EN

Heat-flow characteristics for the eleven catalyst carriers are presented. Within these carriers, optimal values of Bejan number were determined for which the maximal ratio of Nusselt number to the dimensionless entropy generation rate attained its maximum. These number values were determined under sequential changing of the bed length, the bed outlet pressure, the air temperature at the bed inlet, and the wall temperature. Correlations are given for the optimal Bejan number, depending on these process parameters. Such correlations are also presented for the optimal Reynolds number, as well as for the maximal ratio of Nusselt number to the dimensionless entropy generation rate.