1-1 If 3 kW is conducted through a section of insulating material 0.6 m2 in cross section and 2.5 cm thick and the thermal conductivity may be taken as 0.2 W/m - °C, compute the temperature difference across the material.

Elements Of Electromagnetics
7th Edition
ISBN:9780190698614
Author:Sadiku, Matthew N. O.
Publisher:Sadiku, Matthew N. O.
ChapterMA: Math Assessment
Section: Chapter Questions
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0.20
.l 12:42
景令60
...
KB/s
laung mateilais, (C) nquius, (u) gases:
9. Suppose a person stated that heat cannot be transferred in a vacuum. How do you
respond?
10. Review any standard text on thermodynamics and define: (a) heat, (b) internal energy,
(c) work, (d) enthalpy.
11. Define and discuss ge.
LIST OF WORKED EXAMPLES
1-1 Conduction through copper plate
1-2 Convection calculation
1-3 Multimode heat transfer
1-4 Heat source and convection
1-5 Radiation heat transfer
1-6 Total heat loss by convection and radiation
PROBLEMS
1-1 If 3 kW is conducted through a section of insulating material 0.6 m2 in cross section
and 2.5 cm thick and the thermal conductivity may be taken as 0.2 W/m - °C, compute
the temperature difference across the material.
1-2 A temperature difference of 85°C is impressed across a fiberglass layer of 13 cm
thickness. The thermal conductivity of the fiberglass is 0.035 W/m - °C. Compute the
heat transferred through the material per hour per unit area.
1-3 A truncated cone 30 cm high is constructed of aluminum. The diameter at the top is
7.5 cm, and the diameter
at 93°C; the upper surface, at 540°C. The other surface is insulated. Assuming one-
t the bottom is 12.5 cm. The lower surface is maintained
dimensional heat flow, what is the rate of heat transfer in watts?
he temperatures on the faces of a plane wall 15 cm thick are 375 and 85°C. The wall
is constructed of a special glass with the following properties: k=0.78 W/m - °C,
p=2700 kg/m³, cp=0.84 kJ/kg - °C. What is the heat flow through the wall at
steady-state conditions?
1-5 Acertain superinsulation material having a thermal conductivity of 2 x 10-4 W/m - °C
is used to insulate a tank
liquid nitrogen that is maintained at –196°C; 199 kJ is
required to vaporize each kilogram mass of nitrogen at this temperature. Assuming
that the tank is a sphere having an inner diameter (ID) of 0.52 m, estimate the amount
of nitrogen vaporized per day for an insulation thickness of 2.5 cm and an ambient
temperature
of 21°C. Assume that the outer temperature of the insulation is 21°C.
1-6 Rank the following materials in order of (a) transient response and (b) steady-state
conduction. Taking the material with the highest rank, give the other materials as
a percentage of the maximum: aluminum, copper, silver, iron, lead, chrome steel
(18% Cr, 8% Ni), magnesium. What do you conclude from this ranking?
1-7 A 50-cm-diameter pipeline in the Arctic carries hot oil at 30°C and is exposed to a
surrounding temperature of -20°C. A special powder insulation 5 cm thick surrounds
Problems
the pipe and has a thermal conductivity of 7 mW/m - °C. The convection heat-trans
coefficient on the outside of the pipe is 9 W/m² . °C. Estimate the energy loss fr
the pipe per me
1-8 Some people nigh46 of 758 out the top of your
weather becaus
validity of this statement.
1-9 A 5-cm layer of loosely packed asbestos is placed between
200°C. Calculate the heat transfer across the layer.
of length.
be sure to put on a
le in e
t on
at 100
1-10 A certain insulation has a thermal conductivity of 10 W/m . °C What thicknes
||
II
Transcribed Image Text:0.20 .l 12:42 景令60 ... KB/s laung mateilais, (C) nquius, (u) gases: 9. Suppose a person stated that heat cannot be transferred in a vacuum. How do you respond? 10. Review any standard text on thermodynamics and define: (a) heat, (b) internal energy, (c) work, (d) enthalpy. 11. Define and discuss ge. LIST OF WORKED EXAMPLES 1-1 Conduction through copper plate 1-2 Convection calculation 1-3 Multimode heat transfer 1-4 Heat source and convection 1-5 Radiation heat transfer 1-6 Total heat loss by convection and radiation PROBLEMS 1-1 If 3 kW is conducted through a section of insulating material 0.6 m2 in cross section and 2.5 cm thick and the thermal conductivity may be taken as 0.2 W/m - °C, compute the temperature difference across the material. 1-2 A temperature difference of 85°C is impressed across a fiberglass layer of 13 cm thickness. The thermal conductivity of the fiberglass is 0.035 W/m - °C. Compute the heat transferred through the material per hour per unit area. 1-3 A truncated cone 30 cm high is constructed of aluminum. The diameter at the top is 7.5 cm, and the diameter at 93°C; the upper surface, at 540°C. The other surface is insulated. Assuming one- t the bottom is 12.5 cm. The lower surface is maintained dimensional heat flow, what is the rate of heat transfer in watts? he temperatures on the faces of a plane wall 15 cm thick are 375 and 85°C. The wall is constructed of a special glass with the following properties: k=0.78 W/m - °C, p=2700 kg/m³, cp=0.84 kJ/kg - °C. What is the heat flow through the wall at steady-state conditions? 1-5 Acertain superinsulation material having a thermal conductivity of 2 x 10-4 W/m - °C is used to insulate a tank liquid nitrogen that is maintained at –196°C; 199 kJ is required to vaporize each kilogram mass of nitrogen at this temperature. Assuming that the tank is a sphere having an inner diameter (ID) of 0.52 m, estimate the amount of nitrogen vaporized per day for an insulation thickness of 2.5 cm and an ambient temperature of 21°C. Assume that the outer temperature of the insulation is 21°C. 1-6 Rank the following materials in order of (a) transient response and (b) steady-state conduction. Taking the material with the highest rank, give the other materials as a percentage of the maximum: aluminum, copper, silver, iron, lead, chrome steel (18% Cr, 8% Ni), magnesium. What do you conclude from this ranking? 1-7 A 50-cm-diameter pipeline in the Arctic carries hot oil at 30°C and is exposed to a surrounding temperature of -20°C. A special powder insulation 5 cm thick surrounds Problems the pipe and has a thermal conductivity of 7 mW/m - °C. The convection heat-trans coefficient on the outside of the pipe is 9 W/m² . °C. Estimate the energy loss fr the pipe per me 1-8 Some people nigh46 of 758 out the top of your weather becaus validity of this statement. 1-9 A 5-cm layer of loosely packed asbestos is placed between 200°C. Calculate the heat transfer across the layer. of length. be sure to put on a le in e t on at 100 1-10 A certain insulation has a thermal conductivity of 10 W/m . °C What thicknes || II
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