Suppose that the 10 cm thick concrete wall of a commercial building measures 30 mby 4 m. The energy impinging on the surface is 700 Wm-2. Under these conditionsthe external air temperature is 25ºC, and the internal and external surfacetemperatures of the concrete wall are 17ºC and 40ºC, respectively.(a) State and briefly describe the three heat transfer mechanisms.[30%](b) Calculate the net amount of thermal energy radiated by the wall.[40%](c) State your assumptions and briefly discuss their effect on the relativesizes of the heat transfer mechanisms.[30%]Data for Question A3.Heat transfer coefficient of air at 25ºC = 5 Wm-2K-1Thermal conductivity of concrete = 1.2 Wm-1K-1Emissivity of concrete = 0.85Stefan’s constant = 5.7 x 10-8 Wm-2K-4
Suppose that the 10 cm thick concrete wall of a commercial building measures 30 m
by 4 m. The energy impinging on the surface is 700 Wm-2. Under these conditions
the external air temperature is 25ºC, and the internal and external surface
temperatures of the concrete wall are 17ºC and 40ºC, respectively.
(a) State and briefly describe the three heat transfer
[30%]
(b) Calculate the net amount of thermal energy radiated by the wall.
[40%]
(c) State your assumptions and briefly discuss their effect on the relative
sizes of the heat transfer mechanisms.
[30%]
Data for Question A3.
Heat transfer coefficient of air at 25ºC = 5 Wm-2K-1
Thermal conductivity of concrete = 1.2 Wm-1K-1
Emissivity of concrete = 0.85
Stefan’s constant = 5.7 x 10-8 Wm-2K-4
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