Example Calculation, Small Bi Case Cooling of a Copper Sphere in Air

1 Example Calculation, Small Bi Case Cooling of a Copper Sphere in Air 

A copper sphere 1 cm in diameter initially at 100°C is cooled in a stream of air at 20°C, flowing at 5 m s 1. Estimate the time taken for the sphere to reach 25°C. 

From Table 2 for forced convection to a sphere under these conditions, 

Bi is small and so the thermal resistance of the air him dominates the overall heat transfer process. 

13 Estimate Time. Rearranging Equation (28) and solving for time t when T = 25°C 

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