MASS TRANSFER IN LOW VELOCITY GAS STREAMS

Experimental studies of the mixing of coaxial streams of carbon dioxide and air at ambient temperature and atmospheric pres sure were made at Reynold numbers of cal, 4-inch galvanized iron pipe. Carbon dioxide was introduced into the center of an air stream free of moisture and carbon dioxide by means of an injection tube which extended the full length of a calming section 14 feet 4 inches long. Radial concentration profiles of carbon dioxide were measured at three positions downstream. Gas samples were withdrawn by a pitot type probe amd analyzed by a thermal conductivity cell. Velocity distributions were determined by means of a five-loop, circular hot-wire anemometer. Total diffusivities of carbon dioxide in air for the entire radius of the pipe were computed by a seminumerical method. The total diffusivities were found to vary significantly with position in the pipe and to be rather complicated functions of local flow conditions. An approximate analytical solution of the general mass transfer equations describing the system was employed to compute total diffusivity values representative of the over-all mass transfer process. This solution was derived assuming the total diffusivity and velocity to be independent of radial position. (auth)