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 4, Problem 171P
Consider a 7.6-cm-diameter cylindrical lamb meat chunk 1030 kWm3,
(a) 136 min
(b) 21.2 min
(c) 13.6 min
(d) 11.0 min
(e) 8.5 min
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An egg with mean diameter of 40 mm and initially at 20 °C is placed in a boiling
water for (4min) and found to be boiled to consumers taste. For how long
should a similar egg for same consumer be boiled when taken from a
refrigerator at 5 °C.
Take the following properties for egg:
k = 10 W/m. °C
, p= 1200 kJ / kg. °C
C = 2 kJ / kg . °C,
and the heat transfer coefficient (h = 100 W/m?. °C)
An ordinary egg can be approximated as a 5.5-cm-diameter sphere whose thermal conductivity of roughly
k = 0.6-
W
mk
overall density of p = 1000; and heat capacity of C₂ = 3000-
kg
m²
The egg is initially at a uniform temperature of T₂ = 10°C and is dropped into boiling water at T..
= 90°C
W
- determine how long it will take for the egg to
m²K
Taking the convective heat transfer coefficient to be h
reach T = 70°C.
In solving the problem, please follow the steps below.
For the Lump Model
In solving this problem, please use the lump model method (ignoring the requirement of small Biot
number and discuss the outcomes,
1.
2. Compute the characteristic length Lc
Compute the volume and surface area of the sphere (as the egg model)
Vol
As
3. Compute the diffusivity α =
= 10-
k
p Cp
=
J
kgk
Compute non-dimensional excessive temperature 0
=
h Lc
k
4. Compute the Biot number using the characteristic length found above Bi
=
T-Too
5.
Ti-Too
6.
Calculate the Fourier number from the equation =…
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sheet No.3.pdf
Homework 01-03 -2021
one-dimensional heat transfer and disregarding radiation, determine the
rate of heat transfer through the wall.
Q4/ Steam at Te1-320°C flows in a cast iron pipe (k=80W/m.°C) whose
inner and outer diameters are D =5cm, and D=5.5cm, respectively. The
pipe is covered with 3 cm thick glass wool insulation with
k=0.05W/m.°C. Heat is lost to the surroundings at T02=5°C_by natural
convection and radiation, with a combined heat transfer coefficient to be
h,=18W/m.C. Taking the heat transfer coefficient inside the pipe to be
h,=60W/m.C, determine the rate of heat loss from the steam per unit
length of the pipe. Also determine the temperature drops across the pipe
shell and the insulation.
05/ Determine the overall heat transfer coefficient U based on the outer
surface of a D=2.5cm, and D=3.34 cm steel pipe (k=54.0W/m.°C) for
the following conditions: inside and outside heat transfer coefficients are
1200W/m."C. and 2000W/m."C…
Chapter 4 Solutions
Heat and Mass Transfer: Fundamentals and Applications
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