The heat transfer coefficient for hydrogen flowing over a sphere is to be determined by observing the temperature–time history of a sphere fabricated from pure copper. The sphere, which is 20 mm in diameter, is at 75°C before it is inserted into the gas stream having a temperature of 27°C. A thermocouple on the outer surface of the sphere indicates 55°C 97 s 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