2.19c. Benzene evaporation on the outside surface of a single cylinder.
Benzene is evaporating at the rate of 20 kg/hr over the surface of a porous 10-cm-diameter cylinder. Dry air at 325 K and 1 atm flows at right angle to the axis of the cylinder at a velocity of 2 m/s. The liquid is at a temperature of 315 K where it exerts a vapor 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 cm3/mol, Zc = 0.271 (Reid, et al., 1987).

Solution
Calculate the average properties of the film
From the Wilke-Lee equation
From the Lucas Method
From Eq. 2-45:
2.20b. Mass transfer in a packed bed.
Wilke and Hougan (Trans. AIChE, 41, 445, 1945) reported the mass transfer in beds of granular solids. Air was blown through a bed of porous celite pellets wetted with water, and by evaporating this water under adiabatic conditions, they reported gas-film coefficients for packed beds. In one run, the following data were reported:
effective particle diameter 5.71 mm
gas stream mass velocity 0.816 kg/m2-s
temperature at the surface 311 K
pressure 97.7 kPa
kG 4.415 ´ 10Ð3 kmol/m2-s-atm
With the assumption that the properties of the gas mixture are the same as those of air, calculate the gas-film mass-transfer coefficient using equation (2-55) and compare the result with the value reported by Wilke and Hougan.

Solution
From the Wilke-Lee equation
2.21b. Mass transfer and pressure drop in a packed bed.
Air at 373 K and 2 atm is passed through a bed 10-cm in diameter composed of iodine spheres 0.7-cm in diameter. The air flows at a rate of 2 m/s, based on the empty cross section of the bed. The porosity of the bed is 40%.
a) How much iodine will evaporate from a bed 0.1 m long? The vapor pressure of iodine at 373 K is 6 kPa.

Solution
From the Wilke-Lee equation:
b) Estimate the pressure drop through the bed.

Solution