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III. An aluminum plate 4 mm thick is mounted in a horizontal position, and its bottom surface is well insulated. A special, thin coating is applied to the top surfacesuch that it absorbed 90% of any incident solar radiation, while having an emissivity of 0.20. The density ? and specific heat C of aluminum are known to be 2,700kg/m3 and 900 J/kg.oK, respectively. Consider conditions for which the plate is at a temperature of 25oC and its top surface is suddenly exposed to ambient air at T? =20oC and to solar radiation that provides an incident flux of 1,000 W/m2. The convection heat transfer coefficient between the surface and the air is h = 25 W/m2.oK.Stefan-Boltzmann constant: ? = 5.67?10-8 W/m2.oK4.

1) The initial rate of change of the plate temperature is ____________

2) Neglect heat loss by radiation, the steady state temperature of the plate is ____________

3) Include heat loss by radiation, the steady state temperature of the plate is ____________

4) Neglect heat loss by radiation,
the time it takes for the plate to reach 40oC is ____________

IV. One surface of a 10-mm-thick wall of stainless steel (k = 15 W/m.oK) is maintained at 90oC by condensing steam, while the opposite surface is exposed to an airstream for which T? = 20oC and h = 25 W/m2.oK.

Neglect radiation, the temperature of the surface adjoining the air is _______________

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