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In the present study, entropy generation in a non-axisymmetric steady-state incompressible viscous flow over a single rotating porous disk is investigated analytically. The dimensionless form of the local and total entropy generation caused by frictional and thermal effects are derived. The effects of the injection rate and Brinkman number on the entropy generation are revealed. It is found that there exists an optimal injection rate for each Brinkman number, which minimizes the total entropy generation. [ABSTRACT FROM AUTHOR]

In this paper, the work and performance of the premixed methane-air porous axisymmetrical burner have firstly been simulated numerically using the CFD tools. For this purpose the set of governing equations has been enriched by an additional energy equation in porous solid, and the chemical species transport has been extended onto the multi-step mechanism (GRI-2-11). This numerical model has been verified on the base of available benchmark experiments. Next, we have studied the local entropy generation problem taking into account not only classical contributions like viscous and turbulent dissipation but also, the porous combustion of gases. The results showed that the greatest portion of entropy generation in the porous medium burner is related to chemical reactions, followed by heat transfer, mass diffusion (mixing) and friction (viscous dissipation), respectively. According to the results, as the excess air ratio increases, the local entropy generation rate due to heat transfer and friction increases and the local entropy generation rate due to chemical reactions is decreased. Also, by increasing the volumetric heat transfer coefficient, the local entropy generation rate due to heat transfer decreases and the local entropy generation rate due to friction and chemical reactions increases. Also, the local entropy generation rate due to mixing does not show a significant change with the changing excess air ratio and volumetric heat transfer coefficient. [ABSTRACT FROM AUTHOR]

Entropy generation analysis for the Cu–water nanofluid flow through a heat exchanger tube equipped with perforated conical rings is numerically investigated. Frictional and thermal entropy generation rates are defined as functions of velocity and temperature gradients. Governing equations are solved by using finite volume method, and Reynolds number is in the range of 5000–15,000. The effects of geometrical and physical parameters such as Reynolds number, number of holes and nanoparticles volume fraction on the thermal and viscous entropy generation rates and Bejan number are investigated. The results indicate that the thermal irreversibility is dominant in most part of the tube. But it decreases with increasing the nanoparticle volume fraction. Frictional entropy generation reduces with increasing the number of holes from 4 to 10. This is because of stronger velocity gradient near the perforated holes. Bejan number decreases with augment of Reynolds number. [ABSTRACT FROM AUTHOR]

This paper employs large eddy simulation (LES) to investigate non-premixed flameless oxidation occurring in the IFRF furnace with varying fuel-injection angle. In order to model radiation and combustion using Open FOAM software, finite volume discrete ordinate model and partially stirred reactor are applied whereas the detailed mechanism GRI-2.11 is undertaken represent chemistry reactions. The obtained results are compared with the experimental measurements of Mancini's et al. After ensuring the accuracy of the LES method, the combustion characteristics are examined when using different fuel injection angles into the combustion chamber. The results explain using fuel injection with an angle into the combustion chamber, the net rate of reaction and entropy generation increases. [ABSTRACT FROM AUTHOR]

The objective of this work is to estimate the accuracy of a predicted velocity profile which can be gained from experimental results, in comparison with the exact ones by the methodology of entropy generation. The analysis is concerned with the entropy generation rate in hydrodynamic, steady, laminar, and incompressible flow for Newtonian fluids in the insulated channels of arbitrary cross section. The entropy generation can be calculated from two local and overall techniques. Adaptation of the results of these techniques depends on the used velocity profile. Results express that in experimental works, whatever the values of local and overall entropy generation rates are close to each other, the results are more accuracy. In order to extent the subject, different geometries have been investigated. Also, the influence of geometry on the entropy generation rate is studied, and the distribution of volumetric local entropy generation rate for the selected geometries is drawn. [ABSTRACT FROM AUTHOR]

In this paper, a new application is presented for a helical screw tape insert in a 3D tube. In this application, an eccentricity is created between the centrelines of helical screw tape and tube. Accordingly, the effects of this eccentricity on thermal-hydraulic performance and entropy generation are investigated numerically. A three-dimensional SSTk − ω turbulence model is applied to simulate this problem. All simulations are made for eight values of the eccentricity in the range of 0 to 3.5 and Reynolds numbers in the range of 5000 to 12,000. The calculated results showed that incorporating the helical screw tape near the tube wall (by increasing the eccentricity value) diverts the swirling flow from the core region towards the tube surface where high velocity flow impinges over the tube wall, hence extracting higher amount of thermal energy. Moreover, 42% and 237% increments are observed in the frictional and thermal entropy generations, respectively for an eccentricity in the range of 0 to 3.5. [ABSTRACT FROM AUTHOR]