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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Textbook Question
Chapter 2, Problem 29P
Consider a medium in which the heat conduction equation is given in its simplest form as
- Is heat transfer steady or transient?
- Is heat transfer one- two-, or three-dimensional?
- Is there heat generation in the medium?
- Is the thermal conductivity of the medium constant or variable?
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Students have asked these similar questions
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
Consider steady-state conditions for one-dimensional conduction in a plane wall having a thermal conductivity k = 40 W/m-K and a
thickness L= 0.35 m, with no internal heat generation.
Case
1
Determine the heat flux, in kW/m2, and the unknown quantity for each case.
2
3
4
5
i 68
i -40
T₁ (°C)
50
-30
70
T₁
i 126
T₂(°C)
-20
-10
40
L
30
-T₂
i
dT/dx(k/m)
-200
i 57.142
160
-80
200
i
i
i
8
q (kW/m²)
-2.285
-6.4
i 3.2
i -8
The temperature distribution across a wall 0.3 m thick at a certain instant of time is T(x) = a+ b+cx?, where T is
in degrees Celsius and x is in meters, a = 200°C,b = -200°, and c =
conductivity of 1 W /m · K.
30°C/m² . The wall has a thermal
(a) On a unit surface area basis, determine the rate of heat transfer into and out of the wall and the rate of change of
energy stored by the wall.
(b) If the cold surface is exposed to a fluid at 100°C, what is the convection coefficient?
k=1W/m•k
T(x) =200-200x + 30x²
200°C-
ĖST
142.7°C
q"out
| Fluid
Too = 100°C,h
9"in
|L-0.3m
Chapter 2 Solutions
Heat and Mass Transfer: Fundamentals and Applications
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