Benzene vapor in an air stream is adsorbed in a fixed bed of 4 x 6 mesh silica gel packed to an external void fraction of 0.5. The bed is 2 feet in inside diameter and the air flow rate is 25 lb/min (benzene-free basis). At a location in the bed where the pressure is 1 atm, the temperature is 70°F, and the bulk mole fraction of benzene is 0.005, estimate the external, gas-to-particle mass-transfer and heat-transfer coefficients.