HW #3 /Tutorial # 3 WRF Chapter 17; WWWR Chapter 18 ID Chapter 5 Tutorial # 3 WWWR #18.12 (additional data: h = 6W/m 2 -K); WRF#17.1; WWWR#18.4; WRF#17.10 ; WRF# To be discussed during the week 1-5 Feb., By either volunteer or class list. Homework # 3 (Self practice) WRF #17.9; WRF# ID # 5.6, 5.9.

Unsteady-State Conduction

Transient Conduction Analysis

Spherical metallic specimen, initially at uniform temperature, T 0 Energy balance requires

Large value of Bi Indicates that the conductive resistance controls There is more capacity for heat to leave the surface by convection than to reach it by conduction Small value of Bi Internal resistance is negligibly small More capacity to transfer heat by conduction than by convection

Example 1 (WWWR Page 266) A long copper wire, 0.635cm in diameter, is exposed to an air stream at a temperature of 310K. After 30 s, the average temperature of the wire increased from 280K to 297K. Using this information, estimate the average surface conductance, h.

Example 1

Heating a Body Under Conditions of Negligible Surface Resistance

BC (1) -> C 1 =0 BC (2) ->  = n  /L F o =  t/(L/2) 2 IC -> Fourier expansion of Y o (x) …..> Equation (18-12) Engineering Mathematics: PDE BC(1) BC(2) IC V/A = (WHL)/(2WH)=L/2 x

Detailed Derivation for Equations 18-12, Courtesy by all CN5 students, presented by Lim Zhi Hua,

Detailed Derivation for Equations 18-12, Courtesy by all CN5 students, presented by Lim Zhi Hua,

Example 2

Heating a Body with Finite Surface and Internal Resistance

Heat Transfer to a Semi-Infinite Wall

Temperature-Time Charts for Simple Geometric Shapes

Example 3

or Figure F.4

Example 4

WWWR 18-12; WWWR (a) x =0 WWWR (b) -k dT/dx = h x =0 WWWR 18-21

Courtesy contribution by ChBE Year Representative, 2006.