Abstract
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 (Sθ) 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, Sθ 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, Sθ 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.
Highlights
Natural convection heat transfer is widely applied in some important processes in engineering such as thermal storage, environmental comfort, grain drying, electronic cooling and other areas [1,2]
The process efficiency loss in all real processes can be closely related with the friction, mass transference, thermal gradients, chemical reactions, etc
This indicates the entropy generation in the flow is dominated by heat transfer irreversibility
Summary
Natural convection heat transfer is widely applied in some important processes in engineering such as thermal storage, environmental comfort, grain drying, electronic cooling and other areas [1,2]. A systematic investigation of the dependence of the efficiency loss on the Prandtl number is worth performing. The process efficiency loss in all real processes can be closely related with the friction, mass transference, thermal gradients, chemical reactions, etc. Previous studies of entropy had emphasized potential advantages to evaluation of loss in engineering applications [13,14,19,20,21,22]
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