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 107CP
Consider steady one-dimensional heat conduction in a plane wall in which the thermal conductivity varies linearly. The error involved in heat transfer calculations by assuming constant thermal conductivity at the average temperature is (a) non, (b) small, or (c) significant.
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HEAT TRANSFER
(a) Determine the thermal conductivity of an insulating material given the following data: steel pipe with 0.1025 m inner diameter and 0.1150 m outer diameter, insulation thickness 3 cm, heat flow per meter is 150 W/m, steel thermal conductivity 55 W/m-°C, and overall temperature difference of 72.2°C. If the temperature of the steam inside the pipe is 128°C, (b) find the outside temperature of the insulating material.
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
Electric current flows in a 10 mm diameter conductor device with a length of 1 m. A rod with a surface temperature of 222 ° C is placed in an environment with a temperature of 25 ° C, and it is desired to be coated with a heat transfer coefficient of 1.4 W / mK. According to the heat transfer coefficient between the surface and the environment, 122 W / m2K; a) When the subject is covered with a thickness of 6 mm, will the water quenching from the rod decrease compared to w w w? Explain why it decreases or not. b) How much is the heat loss reduced in% when the bar is covered with a height of 55 mm?
Chapter 2 Solutions
Heat and Mass Transfer: Fundamentals and Applications
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