A 1 .0 m × 1 .5 m double-pane window consists of two 4-mm-thick layers of glass ( k = 0 .78 W/m .K) and that are separated by a 5-mm air gap ( k a i r = 0 .025 W/m .K) . and The heat flow through the air gap is assumed to be by conduction. The inside and outside air temperatures are 20°C and -20°C, respectively, and the inside and outside heat transfer coefficients are 40 and 20 W/m 2 ⋅K. Determine (a) the daily rate of heat loss through the window in steady operation and (b) the temperature difference across the largest thermal resistance.
A 1 .0 m × 1 .5 m double-pane window consists of two 4-mm-thick layers of glass ( k = 0 .78 W/m .K) and that are separated by a 5-mm air gap ( k a i r = 0 .025 W/m .K) . and The heat flow through the air gap is assumed to be by conduction. The inside and outside air temperatures are 20°C and -20°C, respectively, and the inside and outside heat transfer coefficients are 40 and 20 W/m 2 ⋅K. Determine (a) the daily rate of heat loss through the window in steady operation and (b) the temperature difference across the largest thermal resistance.
Solution Summary: The author explains the rate of heat loss per day through the window. The conductive thermal resistance of the glass 1 is determined as R_1=
A 1
.0 m
×
1
.5 m
double-pane window consists of two 4-mm-thick layers of glass
(
k
= 0
.78 W/m
.K)
and that are separated by a 5-mm air gap
(
k
a
i
r
= 0
.025 W/m
.K)
.
and The heat flow through the air gap is assumed to be by conduction. The inside and outside air temperatures are 20°C and -20°C, respectively, and the inside and outside heat transfer coefficients are
40 and 20 W/m2 ⋅K. Determine (a) the daily rate of heat loss through the window in steady operation and (b) the temperature difference across the largest thermal resistance.
A 5-mm-diameter spherical ball at 50 oC is covered by a 1-mm-thick plastic insulation (k=0.13 W/m.oC). The ball is exposed to a medium at 15 oC, with a combined convection and radiation heat transfer coefficient of 20 W/m2.oC. Determine if the plastic insulation on the ball will help or hurt heat transfer from the ball.
A long stainless-steel (AISI 316) steam pipe, with an inside diameter of 6.00 cm and an outside diameter of 8.00 cm, is covered with a layer of asbestos insulation (k = 0.150 W/m-K) 1.00 cm thick, which in turn is covered with foam insulation (k = 0.044 W/m-K) 6.00 cm thick. The inside surface temperature of the stainless-steel steam pipe is measured to be 250.0°C, while the outside surface of the foam is exposed to convection, T_inf = 25.0°C, h_inf = 15.0 W/m^2-K.
• Draw and label a sketch of this system. Include dimensions, known temperatures, etc.
• Draw and completely label the corresponding 1-D steady-state conduction resistor diagram.
• Determine the heat transfer rate through the pipe per unit length.
• Calculate the temperature at the asbestos/foam interface.
Because you forgot to let the pipes drip during a freezing night, a section of an outdoor pipe is now frozen. The frozen section is L = 1 m long and the inner pipe diameter is D = 1.8 cm. During the day, the pipe is exposed to the cold air, the Sun, and the radiating surroundings. The cold air temperature is T∞ = -10°C, and has convection heat transfer coefficient h = 20 W/m2·K. The Sun provides solar irradiance of Gsun = 1350 W/m2. The steel pipe surface has absorptivity α = 0.6 and emissivity ε= 0.1. The surroundings, such as vegetation, houses, ground, etc. can be assumed to be blackbody held at Tsur = 280 K. A) Using the energy conservation system illustrated below, establish an equation that describes the stored energy in the section of frozen water (Est). B) Determine the amount of time needed to melt the ice in the pipe. Ice has density ρ= 920 kg/m3, and latent heat of fusion hsf = 334 kJ/kg. The ice is Tw = 0°C. Ignore conduction through the pipe walls – assume the pipe…
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