Q2: Conducted Heat A concrete wall and a wood wall both conduct heat from your w

Question

Q2: Conducted Heat A concrete wall and a wood wall both conduct heat from your warm horse barn to the Hoosier outdoors in winter. Each wall is 3.0m x 2.0m in area and the conductivity is as per the table up above. The temperature is (-21C) outside and (+15C) inside the barn. The concrete wall is 0.91m thick and the wood wall is 0.053m thick. How much thermal power (Watt) is being lost through each wall? Thermal conductivity k Material (%). L Wood Concrete 0.15 1.1 /kA (Remember that if you tell me "but you didn't provide the time" I'll have to whack you with a dead fish; maybe a trout this time?) Q3: Radiant heat The solar constant (the power of incoming sunlight per intercepted area) is 1361 W/m2 of PROJECTED area (circle). Assuming that the earth reflects 31% of this solar energy back into space and that the earth acts as a blackbody in the infrared (-1) with the emitting area of a sphere, calculate the average radiating temperature ofthe earth. Q=7"At Remember: =5.67E-8 wrn2K4) and Ricarth)-6371km-637 1000-m infrared emissions (out) Sun solar radiationEa (in)

Explanation / Answer

given A = 3*2 = 6 m^2
kw = 0.15 W/mC
kc = 1.1 W/mC
To = -21 C
Ti = 15 C
tc = 0.91 m
tw = 0.053 m
heat lost through wooden wall, Qw = kw*A*(Ti - To)/t
Qw = 0.15*6(15 + 21)/0.053 = 611.32 W

heat lost through concrete wall
Qc = kc*A*(Ti - To)/tc
Qc = 1.1*6(15 + 21)/0.91 = 261.098 W

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