Combustion gases passing through a 3-cm-internal-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/m2k and the inner surface temperature of the tube is 110°c, determine (a) the tube length and (b) the rate of evaporation of water.