Consider two long, slender rods of the same diameter but different materials. One end of each rod is attached to a base surface maintained at 100 ° C, while the surfaces of the rods are exposed to ambient air at 20 ° C . By traversing the length of each rod with a thermocouple, it was observed that the temperatures of the rods were equal at the positions x A = 0.15 m and x B = 0.075 m, where x is measured from the base surface. If the thermal conductivity of rod A is known to be k A = 70 W/m ⋅ K , determine the value of k B for rod B.
Consider two long, slender rods of the same diameter but different materials. One end of each rod is attached to a base surface maintained at 100 ° C, while the surfaces of the rods are exposed to ambient air at 20 ° C . By traversing the length of each rod with a thermocouple, it was observed that the temperatures of the rods were equal at the positions x A = 0.15 m and x B = 0.075 m, where x is measured from the base surface. If the thermal conductivity of rod A is known to be k A = 70 W/m ⋅ K , determine the value of k B for rod B.
Solution Summary: The author explains the value of thermal conductivity k B for rod B. The temperature of the base surface is 100 o C.
Consider two long, slender rods of the same diameter but different materials. One end of each rod is attached to a base surface maintained at
100
°
C,
while the surfaces of the rods are exposed to ambient air at
20
°
C
.
By traversing the length of each rod with a thermocouple, it was observed that the temperatures of the rods were equal at the positions
x
A
=
0.15
m
and
x
B
=
0.075
m,
where x is measured from the base surface. If the thermal conductivity of rod A is known to be
k
A
=
70
W/m
⋅
K
,
determine the value of
k
B
for rod B.
In many manufacturing plants, individuals are often working around high temperature surfaces.
Exposed hot surfaces that are potential for thermal burns on human skin tissue are considered to
be hazards in the workplace. Metallic surface of temperature above 70°C is considered
extremely high temperature in the context of thermal burn, where skin tissue damage can occur
instantaneously upon contact with the hot surface.. Consider an AISI 1010 carbon steel strip (p =
7832 kg/m3) of 2 mm thick and 3 cm wide that is conveyed into a chamber to be cooled at a
constant speed of 1 m/s. The steel strip enters the cooling chamber at 597 C. Determine the
amount of heat rate that needed to be removed so that the steel strip exits the chamber at 47°C
to avoid instantaneous themal burn upon accidental contact with skin tissue. Discuss how the
conveyance speed can affect the neat rate needed to be removed from the steel strip in the
cooling chamber.
FIGURE P1-25
Cooling chamber
Steel strip
Im/s
=47°C…
3. Consider a 3 m high rectangular enclosure consisting of two
surfaces separated by a 0.1 m air gap at 1 atm. If the surface
temperatures across the air gap are 30 °C and -10 °C,
determine the ratio of the heat transfer rate for the
horizontal orientation (with hotter surface at the bottom)
to that for vertical orientation. [1.66]
0.1 m
3 m
Air
-10°C
-10°C
30°C
Air
30°℃
>
3m
Required information
Consider an electrically heated brick house (k = 0.40 Btu/h-ft-°F) whose walls are 9 ft high and 1 ft thick. Two
of the walls of the house are 50 ft long and the others are 35 ft long. The house is maintained at 70°F at all
times while the temperature of the outdoors varles. On a certain day, the temperature of the Inner surface of
the walls is measured to be at 64°F while the average temperature of the outer surface is observed to
remain at 45°F during the day for 10 h and at 35°F at night for 14 h.
35 ft
50 ft
9 ft
Determine the amount of heat lost from the house that day. (You must provide an answer before moving on to the next part.)
The amount of heat lost from the house that day is [ 18526 Btu.
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