HeatTransfer-I-Section-5

# Below we see the eect of bi for steady condions

This preview shows page 1. Sign up to view the full content.

This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: rise to situa/ons where the internal thermal gradient € is small. 4 Transient Conduc/on •  When this occurs, temperature is nearly uniform throughout the wall at any instant of /me. Below, we see the eﬀect of Bi for steady condi/ons. Conduction L / kA hL Bi = = = < 0.1 Convection 1 / hA k € 5 Transient Conduc/on •  Lumped Analysis: consider a body ini/ally at some temperature Ti which is greater than the temperature of a large thermal reservoir at Too. 6 Transient Conduc/on •  The body is suddenly immersed in this large reservoir and will cool. If we assume that it cools isothermally, i.e. at any instant we only have T(t), then we write: ˙ ˙ ˙ E stored = E in − E out or dT ρc pV = − hA(T ( t ) − T∞ ) dt •  For convenience introduce θ = T ­Too. Rearranging and integra/ng gives: € t dθ ∫ θ = − ∫ dt θi 0 or ρc pV θ i t= ln hA θ ρc pV...
View Full Document

## This document was uploaded on 02/14/2014 for the course ENGR 6901a at Memorial University.

Ask a homework question - tutors are online