Mass transfer in turbulent pulsating flows

This thesis reports on the effects of imposed flow oscillations on the mass transfer coefficient and the mass transfer intensity in a turbulent flow.The equations for the turbulent fluctuations in the velocity and concentration fields and the equations for the mean and oscillating components of the phase averaged concentration field are derived and presented. From examining these equations, one can determine which terms would cause changes in the time averaged velocity and concentration fields and which terms would cause oscillations in the phase averaged velocity and concentration fields.Experiments were performed in a two inch diameter horizontal pipe. A reciprocating piston pump imposed the pulsations in the mean flow rate. Mass transfer coefficients were measured electrochemically. A platinum plated brass section served as a cathode to measure the average mass transfer coefficient and to insure a fully developed concentration boundary layer. Platinum electrodes, insulated from the cathode, were embedded in the cathode to measure the phase averaged mass transfer coefficient and the fluctuations in the phase averaged mass transfer coefficient. Numerical methods were developed to solve the phase averaged mass balance equation by modeling the phase averaged Reynolds transport with an eddy diffusivity model.The following results were obtained in this study: The imposed flow oscillations have no effect upon the time averaged mass transfer coefficient or the time averaged mass transfer intensity. The imposed oscillations in the velocity field cause oscillations in the phase averaged mass transfer coefficient and the phase averaged mass transfer intensity. The oscillations in the streamwise velocity fluctuations cause oscillations in the normal velocity fluctuations which cause oscillations in the phase averaged mass transfer coefficient and the phase averaged mass transfer intensity. The pseudo steady state and relaxation eddy diffusivity models provide good agreement with the experimental data at low frequencies of pulsation. However, at high frequencies of pulsation, there is an interaction between the imposed pulsations and the turbulence that is not included in these models. A modified eddy diffusivity model in which the eddy diffusivity is a function of $\omega\sp{+2}$ provided good agreement with the experimental results at all frequencies that were studied.U of I OnlyETDs are only available to UIUC Users without author permissio