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NusseltNumber overprediction COnjugateheat transfer

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Old   June 27, 2017, 15:47
Default NusseltNumber overprediction COnjugateheat transfer
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Manu Chakkingal
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Hello all


I have a bottom heated top cooled cavity with conducting packed bed of sphere in side. The Rayleigh number based on box height is 10^8. I am comparing my numerical results with the experimental data.
What do I compare

Nusselt_expriment is determined from the power input required to maintain constant bottom wall temperature

h=power/(Area *(Th-Tc))
Nu_exp=h*L/kf

where Th,Tc are hot and cold wall temperatures, Kf =fluid conductivity.

It is compared with Nusselt number obtained from simulations calculated as
Nu_sim= sngrad(T)*L/(Th-Tc)
The Nusselt number so calculated is equivalent to assuming the fluid with conductivity 1. In order to compare it with the experiments
Nu_f_sim =Nu_sim*1/kf .

When I compare Nu_exp and Nu_f_sim,the Nu_f_sim is almost off (high) from experiments by 50%.

Could some one suggest possible reasons for such over prediction.

(Note: No turbulence models are used.The flow is fully resolved. The flow at the chosen Ra is assumed to be laminar. Behaviour is same for even fine grids.).
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Manu

Last edited by manuc; June 28, 2017 at 08:54.
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