Ice slurry is being transported in a pipe ( k = 15 W/m .K, D i =2 .5 cm, D o =3 cm and L= 5 m) and with an iliner surface temperature of 0°C. The ambient condition surrounding the pipe has a temperature of 20°C, a convection heat transfer coefficient of 10 V1in2K, and a dew point of 10°C. If the outer surface temperature of the pipe drops below the dew point. condensation can occur on the surface. Since this pipe is located in a vicinity of high-voltage devices, water droplets from the condensation can create an electrical hazard. To prevent an electrical accident, the pipe surface needs to be insulated. Detennine the insulation thickness for the pipe using a material with k = 0 .95W/m .K to prevent the outer surface temperature from dropping below the dew point.
Ice slurry is being transported in a pipe ( k = 15 W/m .K, D i =2 .5 cm, D o =3 cm and L= 5 m) and with an iliner surface temperature of 0°C. The ambient condition surrounding the pipe has a temperature of 20°C, a convection heat transfer coefficient of 10 V1in2K, and a dew point of 10°C. If the outer surface temperature of the pipe drops below the dew point. condensation can occur on the surface. Since this pipe is located in a vicinity of high-voltage devices, water droplets from the condensation can create an electrical hazard. To prevent an electrical accident, the pipe surface needs to be insulated. Detennine the insulation thickness for the pipe using a material with k = 0 .95W/m .K to prevent the outer surface temperature from dropping below the dew point.
Solution Summary: The author explains how to calculate the rate of heat transfers from side to side the wall.
Ice slurry is being transported in a pipe
(
k
=
15
W/m
.K,
D
i
=2
.5 cm, D
o
=3 cm and L= 5 m)
and with an iliner surface temperature of 0°C. The ambient condition surrounding the pipe has a temperature of 20°C, a convection heat transfer coefficient of 10 V1in2K, and a dew point of 10°C. If the outer surface temperature of the pipe drops below the dew point. condensation can occur on the surface. Since this pipe is located in a vicinity of high-voltage devices, water droplets from the condensation can create an electrical hazard. To prevent an electrical accident, the pipe surface needs to be insulated. Detennine the insulation thickness for the pipe using a material with
k = 0
.95W/m
.K
to prevent the outer surface temperature from dropping below the dew point.
= 0.243 W/m K) while the bottom surface is exposed to a hot steam at 100°C with a convection hea
6-22 The top surface of a metal plate (kplate = 237 W/m-K) is being cooled by air (kair
transfer coefficient of 30 W/m2-K. If the bottom surface temperature of the plate is 80°C, determine the temperature gradient in the air and the temperature gradient in the plate at the top surface
of the plate.
FIGURE P6-22
Air, hi To
T2
Solid plate
TI
Hot steam, hteam. Tool
(b)
A transistor with a height of 0.4 cm and a diameter of 0.6 cm is mounted on a circuit board
as shown in Figure 3. The transistor is cooled by air flowing over it with an average heat
transfer coefficient of 30 W/m².K. If the air temperature is 55°C and the transistor case
temperature is not to exceed 70°C, determine the amount of power this transistor can
dissipate safely. Disregard any heat transfer from the transistor base.
Air
55°C
Power
transistor 0.6 cm
T, ≤ 70°C
-0.4 c
0.4 cm-
Figure 3
A solid plate, with a thickness of 15 cm and a thermal conductivity of 80 W/m-K, is being cooled
at the upper surface by air. The air temperature is 10°C, while the temperatures at the upper and
lower surfaces of the plate are 50 and 60°C, respectively. Determine the convection heat transfer
coefficient of air at the upper surface and discuss whether the value is reasonable or not for force
convection of air.
Air, T. = 10°C
T1 = 50°C
T2 = 60°C
L = 15 cm
Chapter 3 Solutions
Heat and Mass Transfer: Fundamentals and Applications
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