Hi all, I'm kind of stuck in my validation for Al2O3 water nanofluid. the correlations for Nusselt number from Pak and Choi; Xuan and Li and Maiga seem a bit strange for me to compare my numerical results. I have got the results under constant temperature where the average increment for heat transfer coefficient was around 25%. But from the literature it should be 5-10%. I'm not sure whether my numerical results are right?
I think Eulerian two-phase model in fluent over predicts the outlet temperature of pipe.
and another doubt: Is constant heat flux boundary condition not compatible with mixture model in fluent?
Any suggestions would be really helpful.
In simple terms for a constant property system the heat transfer coefficient is a function of gas velocity. For flow inside tubes the relationship is h = k1 x V^.8, for flow outside of tubes it is h = k2 x v^.5: this is, of course, a simplification but a reasonable approximation. k1 and k2 are constants for a given system v is the fluid velocity. Thus, a doubling of Re (or velocity) for flow outside a tube gives an increase of h of about 40%, or, inside of about 80%.
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