Benzene evaporation on the outside surface of a single cylinder

Benzene is evaporating at 20 kg/h over the surface of a porous 10-cm-diameter cylinder. Dry air at 325 K and 1 atm flow at a right angle to the cylinder's axis at a velocity of 2 m/s. The liquid is at a temperature of 315 K and exerts a vapour pressure of 26.7 kPa. Estimate the length of the cylinder. For benzene, Tc = 562.2 K, Pc = 48.9 bar, M = 78, Vc = 259 cm^3/mol, and Zc = 0.271 Answer: 1.74 m