Question

An aluminum alloy (2024) plate, heated to a uniform temperature of 227°C, is allowed to cool while vertically suspended in a room where the ambient air and surroundings are at 27°C. The plate is 0.3 m square with a thickness of 15 mm. a) calculate the rate of heat transfer from the plate to the surrounding air. b) Develop an expression for the time rate of change of the plate temperature, assuming the temperature to be uni form at any time. b) Determine the initial rate of cooling (K/s) when the plate temperature is 227°C. d) Justify the uniform plate temperature assumption. DATA The Stefan-Boltzmann constant σ-5.67 10" W/(m2K4 ) Physical Properties of air k-0.0388 w/m.K Pr-0.69 v 26.41 106 m2/s Physical Properties of aluminum ρ-2770 kg/m3 .K K-186 W/m. K , c-983 J/kg.K

Answer 1

O Assume emissivity of plate 2s ssume emissivity t OU clT at ud 6x38:3Mãç 26.41 x 8 1.308x,o 1+/014-92V 2. is satisfied (6.25+3.86 )「e: ols 4 186