Heat Transfer

$5\mathrm{.}9$ The heat transfer coefficient for hydrogen flowing over a sphere is to be determined by observing the tem$-$perature$-$time history of a sphere fabricated from pure copper. The sphere, which is $20$ mm in diameter, is at $75C$ before it is inserted into the gas stream having a temperature of $27C.$ A thermocouple on the outer surface of the sphere indicates $55C97s$ after the sphere is inserted into the hydrogen. Assume and then justify that the sphere behaves as a spacewise isothermal object and calculate the heat transfer coefficient.

Use density of $8953k\frac{g}{m^3}$ and specific heat of $385\frac{J}{k}g$ K