Abstract
Studies of the mass transfer mechanisms which occur when carbon dioxide is absorbed into flowing water films in an inclined cell are described. The amount of gas absorbed is small and therefore requires a highly sensitive detection apparatus. For this purpose a new modified Michelson interferometer was constructed which enabled direct concentration readings to be obtained. Gas concentrations in the liquid were also obtained by titration. The experimental work was mainly confined to angles of inclination less than 5°. Hydrodynamic results showing increased flow rates at the sides of the inclined cell, due to meniscus effects, are presented. Hydrodynamic "end effects" at the liquid exit from the cell, which cause increases in the absorption rate, have been successfully minimised by the design of the apparatus and the experimental technique employed. The take up of gas, concentrations and concentration profiles have been obtained relative to the gas-liquid contact time, from both experimental and theoretical considerations. It has been shown that there is an appreciable surface resistance to the absorption process. The applicability of certain theoretical equations to the results has been studied. It has been demonstrated, for angles of inclination less than 3°, that convective disturbances (in the form of microflows, eddies or perturbations) are present. This causes an increased transport of solute from the liquid surface than can occur by molecular diffusion alone. Beyond 3° eddies or disturbances are present due to hydrodynamic instabilities eventually leading to "observable" wave formation. The effect of waves on the concentration profile, and the amount of gas absorbed, has been considered. Experimental results have also been obtained for desorption of gases from horizontal stagnant water pools, using a simultaneous birefringent interferometric and pressure transducer technique. The systems investigated were carbon dioxide-water, acetylene-water, ammonia-water, sulphur dioxide-water and acetone-water. The amount of gas desorbed, concentrations, concentration profiles and surface resistance were obtained relative to the desorption times from experiment; A theoretical analysis has been made. The effect of pool depth and pool area on the desorption of acetone from water were investigated (for pool depths between 0.3 mm and 25 mm; pool areas between 2.2 cm[2] and 17 cm[2]). The desorption study was performed in order to assist the interpretation of results obtained from the flowing liquid cell. This was mainly in connection with the nature of the surface resistance and convective disturbances encountered during absorption into thin liquid films.