A flat silicon wafer 15 cm in diameter (surface area 176.7 cm²) is removed from an annealing furnace and laid flat-side down onto a flat insulating surface. It is then allowed to cool down to room temperature,which is maintained at a constant 20°C (293 K). Initially the silicon wafer is at 1020°C. The heat-transfer coefficient for the air over the exposed flat surface of the silicon wafer is 20 W/m²· K. What is the heat-transfer rate, in Watts, from the wafer surface to the surrounding air after 330 seconds? 

Thermophysical properties of silicon at the temperature range of interest are:

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Material Thermal Heat Bulk Density Conductivity Capacity J/kg · K kg/m³ W/m· K Polycrystalline 30 760 2300 silicon ~1000°C