Hydrodynamics and mass transfer of slug flow in horizontal capillaries with different inner diameter (0.92 mm for hydrodynamics, 1.70 mm, 1.86 mm, and 2.53 mm for mass transfer) in water-air and glycerol-air (water-air-solid and glycerol-air-solid for mass transfer) systems were studied. Experimental data of bubble velocity and pressure drop was compared with values calculated by mathematical model of slug flow in capillaries proposed earlier. A simple equation to calculate the gas bubble velocity was obtained. The intensification of mass transfer in slug flow regime at the expense of the Taylor circulation was demonstrated experimentally. Semi-empirical formula for Sherwood number in a wide range of capillary number was obtained. (C) 2012 Elsevier Ltd. All rights reserved.