Entropy generation at the onset of natural convection

Entropy generation in two-dimensional Rayleigh-Bénard convection at different Prandtl number (Pr) are investigated in the present paper by using the lattice Boltzmann Method. The major concern of the present paper is to explore the effects of Pr on the detailed information of local distributions of entropy generation in virtue of frictional and heat transfer irreversibility and the overall entropy generation in the whole flow field. The results of this work indicate that the significant viscous entropy generation rates (Su) gradually expand to bulk contributions of cavity with the increase of Pr, thermal entropy generation rates (S θ ) and total entropy generation rates (S) mainly concentrate in the steepest temperature gradient, the entropy generation in the flow is dominated by heat transfer irreversibility and for the same Rayleigh number, the amplitudes of Su, S θ and S decrease with increasing Pr. It is found that that the amplitudes of the horizontally averaged viscous entropy generation rates, thermal entropy generation rates and total entropy generation rates decrease with increasing Pr. The probability density functions of Su, S θ and S also indicate that a much thinner tail while the tails for large entropy generation values seem to fit the log-normal curve well with increasing Pr. The distribution and the departure from log-normality become robust with decreasing Pr.

Section: Entropy Generationmentioning

confidence: 99%

A Numerical Study on Entropy Generation in Two-Dimensional Rayleigh-Bénard Convection at Different Prandtl Number

Wei

Wang

Yue

2017

“…According to local thermodynamics of equilibrium with linear transport theory, the local volumetric entropy generation is given by [7]:…”

Section: Entropy Generationmentioning

confidence: 99%

“…Demirel and Kahraman [6] showed that irreversibility distributions are not continuous through the horizontal walls of a rectangular enclosure that it was differentially heated from its upper side. Magherbi et al [7] numerically studied entropy generation at the onset of natural convection in a square cavity. They showed that entropy generation depends on thermal Rayleigh number.…”

Section: Introductionmentioning

confidence: 99%

Entropy Generation at Natural Convection in an Inclined Rectangular Cavity

Bouabid

Magherbi

Hidouri

et al. 2011

Natural convection in an inclined rectangular cavity filled with air is numerically investigated. The cavity is heated and cooled along the active walls whereas the two other walls of the cavity are adiabatic. Entropy generation due to heat transfer and fluid friction has been determined in transient state for laminar natural convection by solving numerically: the continuity, momentum and energy equations, using a Control Volume Finite Element Method. The structure of the studied flows depends on four dimensionless parameters which are: the thermal Grashof number, the inclination angle, the irreversibility distribution ratio and the aspect ratio of the cavity. The obtained results show that entropy generation tends towards asymptotic values for lower thermal Grashof number values, whereas it takes an oscillative behavior for higher values of thermal Grashof number. Transient entropy generation increases towards a maximum value, then decreases asymptotically to a constant value that depends on aspect ratio of the enclosure. Entropy generation increases with the increase of thermal Grashof number, irreversibility distribution ratio and aspect ratio of the cavity. Bejan number is used to measure the predominance of either thermal or viscous irreversibility. At local level, irreversibility charts show that entropy generation is mainly localized on bottom corner of the left heated wall and upper corner of the right cooled wall.

“…To optimize the useful energy in such applications, many researchers have studied the entropy generation of natural convection in cavities. For example, Erbay et al [4,5] and Magherbi et al [6] studied the transient entropy generation of natural convection in square cavities with completely-or partially-heated left-side walls, respectively, and a completely cooled right-side wall. They have considered the effects of heat transfer irreversibility and fluid friction irreversibility on the entropy generation and had analyzed the transient behavior of the entropy generation in the studied cavity.…”

Section: Introductionmentioning

confidence: 99%

Numerical Investigation into Natural Convection and Entropy Generation in a Nanofluid-Filled U-Shaped Cavity

Cho

Yau

Chiu

et al. 2015

Abstract:This current work studies the heat transfer performance and entropy generation of natural convection in a nanofluid-filled U-shaped cavity. The flow behavior and heat transfer performance in the cavity are governed using the continuity equation, momentum equations, energy equation and Boussinesq approximation, and are solved numerically using the finite-volume method and SIMPLE C algorithm. The simulations examine the effects of the nanoparticle volume fraction, Rayleigh number and the geometry parameters of the U-shaped cavity on the mean Nusselt number and total entropy generation. It shows that the mean Nusselt number increases and the total entropy generation reduces as the volume fraction of nanoparticles increases. In addition, the results show that the mean Nusselt number and the total entropy generation are both increased as the Rayleigh number increases. Finally, it also shows that mean Nusselt number can be increased and the total entropy generation can be reduced by extending the length of the low temperature walls or widening the width of the low temperature walls.