3-68 A 5-m-wide, 4-m-high, and 40-m-long kiln used to cure concrete pipes is made of 20-cm-thick concrete walls and ceiling (k = 0.9 W/m-K). The kiln is maintained at 40°C by injecting hot steam into it. The two ends of the kiln, 4 m x 5 m in size, are made of a 3-mm-thick sheet metal covered with 2-cm-thick Styrofoam (k = 0.033 W/m K). The convection heat transfer coefficients on the inner and the outer surfaces of the kiln are 3000 W/m2-K and 25 W/m2-K, respectively. Disregarding any heat loss through the floor, determine the rate of heat loss from the kiln when the ambient air is at -4°C. FIGURE P3-68 Tout-4°C 40 m Tin=40°C 4 m 20 cm 5 m

Question
3-68 A 5-m-wide, 4-m-high, and 40-m-long kiln used to cure concrete pipes is made of 20-cm-thick concrete walls and ceiling (k = 0.9 W/m-K). The kiln is maintained at 40°C by injecting hot steam into it.
The two ends of the kiln, 4 m x 5 m in size, are made of a 3-mm-thick sheet metal covered with 2-cm-thick Styrofoam (k = 0.033 W/m K). The convection heat transfer coefficients on the inner and the outer
surfaces of the kiln are 3000 W/m2-K and 25 W/m2-K, respectively. Disregarding any heat loss through the floor, determine the rate of heat loss from the kiln when the ambient air is at -4°C.
FIGURE P3-68
Tout-4°C
40 m
Tin=40°C
4 m
20 cm
5 m
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Transcribed Image Text

3-68 A 5-m-wide, 4-m-high, and 40-m-long kiln used to cure concrete pipes is made of 20-cm-thick concrete walls and ceiling (k = 0.9 W/m-K). The kiln is maintained at 40°C by injecting hot steam into it. The two ends of the kiln, 4 m x 5 m in size, are made of a 3-mm-thick sheet metal covered with 2-cm-thick Styrofoam (k = 0.033 W/m K). The convection heat transfer coefficients on the inner and the outer surfaces of the kiln are 3000 W/m2-K and 25 W/m2-K, respectively. Disregarding any heat loss through the floor, determine the rate of heat loss from the kiln when the ambient air is at -4°C. FIGURE P3-68 Tout-4°C 40 m Tin=40°C 4 m 20 cm 5 m