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Heat Transfer Phenomena //

A stainless steel ball (diameter D = 25 cm, = 8055 kg/m3, Cp= 480 J/(kg K)) that initially is at 300C is exposed to an air flow at 1 atm and 25C that moves with 3 m/s.

(a) Determine the heat transfer coefficient at the initial conditions.

(b) Estimate how long it will take for the steel ball to cool down to 200C. The properties of air at 25C and 300 are given in figure attached

Table 1: Properties of air Temperature Density Thermal Viscosity (C) (kg/m) Conductivity (kg/(ms)) (W/(K m)) 25 1.184 0.02551 1.849 x 10-5 300 0.6158 0.04418 2.934 x 10 Prandtl number ( 0.7296 0.6935 5 Air Steel ball 300C TE=25C u=3 m/s