Consider a house with a flat roof whose outer dimensions are 12 m × 12 m . and The outer walls of the house are 6 in high. The walls and the roof of the house are made of 20-cm-thick concrete ( k = 0.75 W/m .K ) . The temperatures of the inner and outer surfaces of the house are 15°C and 3°C, respectively. Accounting for the effects of the edges of adjoining surfaces. determine the rate of heat loss from the house through its walls and the roof. What is the error involved in ignoring the effects of the edges and corners and treating the roof as a 12 m × 12 m surface and the walls as 6 m × 12 m surfaces for simplicity?
Consider a house with a flat roof whose outer dimensions are 12 m × 12 m . and The outer walls of the house are 6 in high. The walls and the roof of the house are made of 20-cm-thick concrete ( k = 0.75 W/m .K ) . The temperatures of the inner and outer surfaces of the house are 15°C and 3°C, respectively. Accounting for the effects of the edges of adjoining surfaces. determine the rate of heat loss from the house through its walls and the roof. What is the error involved in ignoring the effects of the edges and corners and treating the roof as a 12 m × 12 m surface and the walls as 6 m × 12 m surfaces for simplicity?
Solution Summary: The author explains the Fourier Law of heat conduction and the heat transfer rate through the walls and roof of the house.
Consider a house with a flat roof whose outer dimensions are
12 m × 12 m
.
and The outer walls of the house are 6 in high. The walls and the roof of the house are made of 20-cm-thick concrete
(
k
=
0.75
W/m
.K
)
. The temperatures of the inner and outer surfaces of the house are 15°C and 3°C, respectively. Accounting for the effects of the edges of adjoining surfaces. determine the rate of heat loss from the house through its walls and the roof. What is the error involved in ignoring the effects of the edges and corners and treating the roof as a
12 m × 12 m
surface and the walls as
6 m × 12 m
surfaces for simplicity?
There are 3 people in a hemispherical house with an inner radius of 1.8 m, designed for short-term shelter. The walls of the house are made of 50 cm thick material with a heat transfer coefficient of 0.15 W / mK. The heat transfer coefficient of this house is 6 W / m2K on the inner surface and 15 W / m2K on the outer surface. The temperature of the floor where the house is located is considered to be constant at -5 ° C. Each person in the house generates 105 W of body heat. When the indoor air temperature of the house is measured as -3 ° C, calculate the outside temperature.
The inner and outer surfaces of a 0.3 cm thick 1.8 m x 2.5 m window glass in winter
are 20°C and 1°C, respectively. If the thermal conductivity of the glass is 0.8 W/m-K,
determine the amount of heat loss through the glass over a period of 4 h. What
would your answer be if the glass were 0.6 cm thick?
A flat wall is exposed to an environmental temperature of 38 oC. The wall is covered with a layer of insulation 2.5 cm thick whose thermal conductivity is 1.4 W/m oC, and the temperature of the wall on the inside of the insulation is 315 oC. The wall loses heat to the environment by convection. Compute the value of the convection heat-transfer coefficient that must be maintained on the outer surface of the insulation to ensure that the outer-surface temperature does not exceed 41oC.
Chapter 3 Solutions
Heat and Mass Transfer: Fundamentals and Applications
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