Molecular Tagging Velocimetry (MTV) has been applied to quantify velocity fields associated with convective phenomena which occur during solidification in aqueous ammonium chloride solution (NH4Cl-H2O), a popular transparent low-temperature analog of metal alloys.
A phosphorescent line pattern was “written” into the melt to quantify one component of the velocity field within a plume and in the fluid surrounding the plume. These results represent the first quantitative, continuous field measurements of velocity for such studies. The data compare well with the magnitude of the maximum plume velocities estimated in the literature using particle tracking methods. Asymmetric and symmetric plume velocity profiles were quantified. Velocity fields associated with downward flowing sheaths of fluid surrounding the plume were quantified. Although the shape of the velocity profile measured using MTV compares reasonably well with that predicted by an analytical model proposed in the literature, significant differences were detected. The extension of the MTV method using a tagged plane, rather than a tagged line of phosphorescent fluid, for qualitative 3-D dynamic, visualization is described. This realization of the MTV method has the potential for revealing the basic three-dimensional structure of the velocity field.
The results presented here demonstrate that it is feasible to apply MTV as an advanced diagnostic measurement method to further improve our knowledge of convective phenomena which occur during solidification.