CHEN 3005 Lecture Notes - Lecture 16: Heat Transfer
25 Dec 2014
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Start-up of flow and heat transfer v = 0 t = 0 v = 0 t is small we had to find that (penetration depth = boundary layer) for 2nd midterm similarly for startup of heat. Chen transport page 2 we know this isn"t correct we learned in lecture that. Simple answer: for startup, thermal and viscous boundary layer are separate, but at steady state, they"re coupled so eqns we used today only apply for startup vinfinity vinfinity, tinfinity viscous boundary layer. Chen transport page 3 thermal and viscous boundary layers aren"t necessarily the same but they influence each other, which is determined by pr. Pr just depends on material properties whereas re depends on whether it"s pipe flow, etcvelocity. For gases, pr ~ 0. 7 --> viscous diffusion and thermal diffusion are around same order of magnitude. Liquid: pr > 1 viscous diffusion is stronger than thermal diffusion --> have thicker viscous layer.
