Solar heating of a house is much more efficientif there is a way to store the thermal energy collected during theday to warm the house at night. Suppose one solar-heated homeutilizes a concrete slab of area 12 m2and 25 cm thick. (a) If thedensity of concrete is 2400 kg>m3, what is the mass of the slab?(b) The slab is exposed to sunlight and absorbs energy at a rate of1.4 * 107J>h for 10 h. If it begins the day at 22 °C and has a specificheat of 750 J>1kg # K2, what is its temperature at sunset? (c) Modelthe concrete slab as being surrounded on both sides (contact area24 m2) with a 2.0-m-thick layer of air in contact with a surface thatis 5.0 °C cooler than the concrete. At sunset, what is the rate atwhich the concrete loses thermal energy by conduction throughthe air layer? (d) Model the concrete slab as having a surface areaof 24 m2and surrounded by an environment 5.0 °C cooler thanthe concrete. If its emissivity is 0.94, what is the rate at which theconcrete loses thermal energy by radiation at sunset?
Solar heating of a house is much more efficient
if there is a way to store the thermal energy collected during the
day to warm the house at night. Suppose one solar-heated home
utilizes a concrete slab of area 12 m2
and 25 cm thick. (a) If the
density of concrete is 2400 kg>m3, what is the mass of the slab?
(b) The slab is exposed to sunlight and absorbs energy at a rate of
1.4 * 107
J>h for 10 h. If it begins the day at 22 °C and has a specific
heat of 750 J>1kg # K2, what is its temperature at sunset? (c) Model
the concrete slab as being surrounded on both sides (contact area
24 m2
) with a 2.0-m-thick layer of air in contact with a surface that
is 5.0 °C cooler than the concrete. At sunset, what is the rate at
which the concrete loses thermal energy by conduction through
the air layer? (d) Model the concrete slab as having a surface area
of 24 m2
and surrounded by an environment 5.0 °C cooler than
the concrete. If its emissivity is 0.94, what is the rate at which the
concrete loses thermal energy by radiation at sunset?
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