Combustion gases passing through a 3-cminternal-diameter circular tube are used to vaporize waste water at atmospheric pressure. Hot gases enter the tube at 115 kPa and 250°C at a mean velocity of 5 m/s, and leave at 150°C. If the average heat transfer coefficient is 120 W/m²∙K and the inner surface temperature of the tube is 110°C, determine

(a) The tube length

(b) The rate of evaporation of water.