Heat Transfer Questions & Answers  




It's better to use $\rho_\infty$ to distinguish between laminar and turbulent flow. This is because what triggers the turbulence are disturbances happening on the edge of the boundary layer (where $\rho=\rho_\infty$). This has little to do with the density midway through the boundary layer. Thus you should also use $\rho_\infty$, not $\rho_f$, to determine whether $5 \cdot 10^5 < {\rm Re}_x < 10^7$ because the lower limit of this Reynolds number range is related to laminar to turbulence transition. This applies also to other correlations for external flow over flat plates. But for external flow around cylinders and spheres and for natural convection, the Reynolds/Rayleigh number ranges are not related to laminartoturbulence transition. Thus, for these correlations, use $\rho_f$ not $\rho_\infty$. 1 point bonus.




There is no mistake in the answers provided. You're missing out on an important aspect of radiation heat transfer. You should think about this more.




Good question. You can use the free stream values. Pr and $c_p$ don't change too much with temperature so it won't make much of a difference.




I am not sure what you mean by the point at which separation occurs. Separation of what? Why would this dissipate the heat? I don't understand. Rephrase your question better. Please write one question per post. I deleted the others.



$\pi$ 