Heat and Mass Transfer: Fundamentals and Applications
5th Edition
ISBN: 9780073398181
Author: Yunus A. Cengel Dr., Afshin J. Ghajar
Publisher: McGraw-Hill Education
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Chapter 2, Problem 158P
Consider a large plane wall of thicness L, thermal conductivity k, and surface area A. The left surface of the wall is exposed to the ambient air at
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1-D, steady-state conduction with uniform internal energy generation occurs in a plane wall with
a thickness of 50 mm and a constant thermal conductivity of 5 W/m/K. The temperature
distribution has the form T = a + bx + cx² °C. The surface at x=0 has a temperature of To =
120 °C and experiences convection with a fluid for which T..
surface at x= 50 mm is well insulated (no heat transfer). Find:
(a) The volumetric energy generation rate q. (15)
(b) Determine the coefficients a, b, and c.
20 °C and h 500 W/m² K. The
To:
= 120°C
T = 20°C
h = 500 W/m².K
111
Fluid
T(x)-
=
q, k = 5 W/m.K
L = 50 mm
Q1: Consider one-dimensional conduction in a plane composite wall (1m x Im) as shown in the figure
below. The outer surfaces are exposed to a fluid at 25°C and a convection heat transfer coefficient of
1000 W/m2.K. The middle wall B experiences uniform heat generation dB, while there is no generation
in walls A and C. The temperatures at the interfaces are T1=261°C and T2=211°C. Assuming negligible
contact resistance at the interfaces:
A) Determine the outside surface temperature of walls A and C?
B) Compute the value of q;?
T2
T h
25
241
A
B
-2LB Lc
.03
Ta
kA = 25 W/m-K
kc = 50 W/m-K
LA = 30 mm
Lg = 30 mm
Lc = 20 mm
%3D
An industrial wall is constructed of 20 cm thick fireclay of thermal conductivity 1W/m 0C. This is covered on the outer surface with a 3 cm layer of insulating material of thermal conductivity 0.075 W/m0C. The innermost surface is at 940 0C and the outermost surface is at 40 0C . The steady state of heat transfer is occurring through the wall. So what is the rate of heat transfer rate that is occurring through the wall? What is the temp of the interface of these walls?
Chapter 2 Solutions
Heat and Mass Transfer: Fundamentals and Applications
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