The wall of an oven used to cure plastic parts is ofthickness L = 0.05 m and is exposed to large surroundings and air at its outer surface. The air and the surroundings are at 300 K. (a) If the temperature of the outer surface is 400 Kand its convection coefficient and emissivity are h = 20 W/m 2 ⋅ K and ∈ = 0.8 , respectively, what is the temperature of the inner surface if the wall has a thermal conductivity of k = 0.7 W/m 2 ⋅ K ? (b) Consider conditions for which the temperature of the inner surface is maintained at 600 K. while the air and large surroundings to which the outer surface is exposed are maintained at 300 K. Explore the effects of variations in k , h , and ∈ on (i) the temperature of the outer surface, (ii) the heat flux through the wall, and (iii) the heat fluxes associated with convection and radiation heat transfer from the outer surface. Specifically, compute and plot the foregoing dependent variables for parametric variations about base line conditions of k = 10 W/m 2 ⋅ K, h = 20 W/m 2 ⋅ K , and ∈ = 0.5 . The suggested ranges of the independent variables are 0.1 ≤ k ≤ 400 W/m ⋅ K, 2 ≤ h ≤ 200 W/m 2 ⋅ K , and 0 .05 ≤ ∈ ≤ 1 . Discuss the physical implications of your results. Under what conditions will the temperature of the outer surface he less than 45°C, which is a reasonable upper limit to avoid burn injuries if contact is made?
The wall of an oven used to cure plastic parts is ofthickness L = 0.05 m and is exposed to large surroundings and air at its outer surface. The air and the surroundings are at 300 K. (a) If the temperature of the outer surface is 400 Kand its convection coefficient and emissivity are h = 20 W/m 2 ⋅ K and ∈ = 0.8 , respectively, what is the temperature of the inner surface if the wall has a thermal conductivity of k = 0.7 W/m 2 ⋅ K ? (b) Consider conditions for which the temperature of the inner surface is maintained at 600 K. while the air and large surroundings to which the outer surface is exposed are maintained at 300 K. Explore the effects of variations in k , h , and ∈ on (i) the temperature of the outer surface, (ii) the heat flux through the wall, and (iii) the heat fluxes associated with convection and radiation heat transfer from the outer surface. Specifically, compute and plot the foregoing dependent variables for parametric variations about base line conditions of k = 10 W/m 2 ⋅ K, h = 20 W/m 2 ⋅ K , and ∈ = 0.5 . The suggested ranges of the independent variables are 0.1 ≤ k ≤ 400 W/m ⋅ K, 2 ≤ h ≤ 200 W/m 2 ⋅ K , and 0 .05 ≤ ∈ ≤ 1 . Discuss the physical implications of your results. Under what conditions will the temperature of the outer surface he less than 45°C, which is a reasonable upper limit to avoid burn injuries if contact is made?
Solution Summary: The author explains the thermal conductivity of the wall.
The wall of an oven used to cure plastic parts is ofthickness
L
=
0.05
m
and is exposed to large surroundings and air at its outer surface. The air and the surroundings are at 300 K. (a) If the temperature of the outer surface is 400 Kand its convection coefficient and emissivity are
h
=
20
W/m
2
⋅
K
and
∈
=
0.8
,
respectively, what is the temperature of the inner surface if the wall has a thermal conductivity of
k
=
0.7
W/m
2
⋅
K
? (b) Consider conditions for which the temperature of the inner surface is maintained at 600 K. while the air and large surroundings to which the outer surface is exposed are maintained at 300 K. Explore the effects of variations in k, h, and
∈
on (i) the temperature of the outer surface, (ii) the heat flux through the wall, and (iii) the heat fluxes associated with convection and radiation heat transfer from the outer surface. Specifically, compute and plot the foregoing dependent variables for parametric variations about base line conditions of
k
=
10
W/m
2
⋅
K,
h
=
20
W/m
2
⋅
K
,
and
∈
=
0.5
. The suggested ranges of the independent variables are
0.1
≤
k
≤
400
W/m
⋅
K,
2
≤
h
≤
200
W/m
2
⋅
K
, and
0
.05
≤
∈
≤
1
. Discuss the physical implications of your results. Under what conditions will the temperature of the outer surface he less than 45°C, which is a reasonable upper limit to avoid burn injuries if contact is made?
The temperature of a cylindrical tank containing liquid nitrogen is -10 ° C. Tank diameter is 16 cm. The amount of heat lost by convection and radiation from the tank to the environment is 65.5 W / m. Calculate the temperature of the environment where the tank is located: h = 4.35 W / m2K, ∈ = 1.
You are cooling the door to a large heat-treating oven, which is 3.50 m tall by 1.30 m wide, with a large fan blowing air at 25.0°C over the outside of the door. The convection coefficient associated with this cooling process is h = 57.0 W/(m2-K). The outside surface temperature of the door is 58.0°C. Find the heat transfer rate q, in units of Watts, associated with this cooling process.
A pipe 30 m long with an outer diameter of 75 mm is used to deliver steam at a rate of 2000 kg / hour. The vapor pressure is 198.53 kPa entering the pipe with a quality of 98%. The pipe needs to be insulated with a thermal conductivity of 0.2 W / (m K) so that the quality of the steam will only slightly decrease to 95%. The outer surface temperature of the insulation is assumed to be 25 ° C. Ignore resistance conductive of the pipe material and it is assumed that there is no pressure drop in the pipe.
a. Determine the enthalpy of incoming vapor = AnswerkJ / kg.
b. Determine the enthalpy of steam coming out = AnswerkJ / kg.
c. Determine the vapor heat change / loss along the flow = Answerwatt.
d. Specify the minimum required insulation thickness = Answercm.
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