Air at 52°C, 101.3 kPa, and 10 percent relative humidity enters a 5-cm-diameter tube with an average velocity of 5 m/s. The tube inner surface is wetted uniformly with water, whose vapor pressure at 52°C is 13.6 kPa. While the temperature and pressure of air remain constant, the partial pressure of vapor in the outlet air is increased to 10 kPa. Determine

(a) The average mass transfer coefficient in m/s,

(b) The log-mean driving force for mass transfer in molar concentration units,

(c) The water evaporation rate in kg/h, and (d) the length of the tube.