In a gas-fired boiler, water is being boiled at 120°C by
hot air flowing through a 5-m-long, 5-cm-diameter tube submerged
in water. Hot air enters the tube at 1 atm and 300°C at
a mean velocity of 7 m/s, and leaves at 150°C. If the surface
temperature of the tube is 120°C, determine the average convection
heat transfer coefficient of the air and the rate of water
evaporation, in kg/h.