Case of Motionless Air at Room Temperature in Laminar Mode

1 Case of Motionless Air at Room Temperature in Laminar Mode 

This is the case of a square rubber of side 12 cm and 1 cm thick initially at 160°C immersed in motionless air at 20°C, in a vertical position. 

There is a free convection, and following Section 2.3.2, we have to evaluate the Niisselt number through the Grashof and Prandtl numbers. There is the following  

the boundary condition 2.27 at the rubber-air interface becomes  

The equations of heat transfer in the rubber thickness and next to the surface are  

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