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 air flow 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 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 experimental expression:
Sh=2+ [ (0.58) ⁴+ (0.38z^0.4) ⁴] ^1/4Sc^1/3Re_p^1/2, where Sh=2γ₀k_f/D, z= (aω/U_∞) ^3/2 (a/γ₀) ^1/2, Sc=υ/D, Re_p=2γ₀U_∞/υ (a, amplitude; D, diffusivity; k_f, mass-transfer coefficient; γ₀, radius; U_∞, free stream velocity; υ, kinematic viscosity; ω, angular frequency). As z=0, this expression agrees with the experimental one for steady flow mass-transfer.
The experimental results of half sphere and 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.