The roof of a car in a parking lot absorbs a solar radiant flux of 900 W/m2, while the underside is perfectly insulated. The convection coefficient between the roof and the ambient air is 20 W/m2-K.
(i) Neglecting radiation exchange with the surroundings, calculate the temperature of the roof under steady-state conditions if the ambient air temperature is 25 ℃.
(ii) For the same ambient air temperature, calculate the temperature of the roof if its surface emissivity is 0.7
Answers
The roof of a car in a parking lot absorbs a solar radiant flux of 800 \mathrm{W} / \mathrm{m}^{2}, and the underside is perfectly insulated. The convection coefficient between the roof and the ambient air is 12 \mathrm{W} / \mathrm{m}^{2} \cdot \mathrm{K}. (a) Neglecting radiation exchange with the surroundings, calculate the temperature of the roof under steady-state conditions if the ambient air temperature is 20^{\circ} \mathrm{C}20
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C. (b) For the same ambient air temperature, calculate the temperature of the roof if its surface emissivity is 0.8. (c) The convection coefficient depends on airflow conditions over the roof, increasing with increasing air speed. Compute and plot the roof temperature as a function of h for 2 \leq h \leq 200 \mathrm{W} / \mathrm{m}^{2} \cdot \mathrm{K}.