Experimental Study of Mass Transfer from a Sphere in Pulsating Flow

Abstract

Mass transfer from a naphthalene sphere in a circular tube under steady and pulsating airflow at room temperature is investigated by measuring the loss in weight or the decrease in dimension of the body after a given time. Because of small mass-transfer rate, there is little difference between the results based on analyses with and without the resistance due to the rate of gas flow. Under the pulsating flow, however, the resistance is taken into consideration, because air and C10H8 gas may be mixed enough. Comparison of these results with theoretical ones reported previously gives the following semi-empirical expression: Sh=2+[(0.58)4+(O.38z0.4)4]1/4Sc1/3Re1/2p where, Sh=2rokf/D, z=(aω/U∞)3/2(a/ro)1/2, Sc=ν/D, Rep=2roU∞/ν (a: amplitude, D: diffusivity, kf: mass-transfer coefficient, ro: radius, U∞: free stream velocity, ν: kinematic viscosity, ω: angular frequency). As z=0, this expression agrees with the experimental one for steady flow mass-transfer, i.e., Sh=2+0.58Sc1/3Re1/2pThe experimental results for half naphthalene-coated sphere and of local mass-transfer show that the acceleration effect of pulsating flow on the mass transfer is remarkable in the dead-water region of the sphere, where the mass transfer is small under steady flow.Pressure and velocity in the pipe and around the sphere are measured by the use of a strain-gauge-type pressure transducer and a hot-wire anemometer, respectively, and the flow behavior is also examined.