A4 cm diameter sphere of copper is initially at a temperature of 95 °c. it is placed in a very large water bath at time t- 0. the water bath is initially at a uniform temperature of 25 °c. the heat transfer coefficient is estimated to be 400 watts / (m2 °c). the specific heat of copper is 0.385 joule (gram °c) and its density is approximately 9 gram per cc. estimate the time at which the average temperature of the sphere will be 35 °c.

Along 8-cm diameter steam pipe whose external surface temperature is 900c connects two buildings. the pipe is exposed to ambient air at 70c with a wind speed of 50 km/hr blowing across the pipe. determine the heat loss from the pipe per unit length. (b) air at 500c enters a section of a rectangular duct (15 cm x 20 cm) at an average velocity of 7 m/s. if the walls of the duct are maintained at 100c. a) the length of the tube for an exit temperature of the air to be 40 0c. b)the rate of heat transfer from the air. c) the fan power needed to overcome the pressure drop in this section of the duct.