Direct visualization of diffusion convection phenomena at liquid solid interfaces by the use of a chemiluminescent...

A new method is developed for direct visualization of the local mass transfer at solid liquid interfaces. Peroxidase is immobilized by entrapment in a polyacrylamide gel coating the interior surface of a glass tube. The reaction of oxidation of luminol by H2O2 catalyzed by this enzyme involves light emission. Furthermore at low H2O2 concentration (less than or equal to 5. x 10(-5) M), this reaction is controlled by the diffusion of H2O2 from the bulk flow to the wall, as evidenced by the Re1/3 dependence of the light flux V measured in the laminar case. It is possible in these conditions to directly relate V as measured at each point of the wall, to the local properties of the flow : (i) a decrease of V is always observed when moving downstream from the input of the tube, but it is much more pronounced for laminar flows than for turbulent ones, as theoretically expected; (ii) the sensitivity of the method has been tested for evaluating the diffusion convection phenomena at the wall downstream from a stenosis. Furthermore the local hydrodynamic properties have been characterized by measuring through pulsed Doppler velocimetry the velocity of the moving liquid phase as a function of the position in the flow. The data obtained show the presence of a maximum of V in the vicinity of the reattachment point of the liquid streamlines at the wall. This constitutes the first experimental confirmation of calculations on diffusion convection phenomena downstream from stenoses. These first experiments show one the ability of the method to detect the local properties of the parietal mass transfer phenomena, as a function of the geometry of the wall and the hydrodynamic characteristics of the flow.