Measurement of local mass-transfer coefficients by holographic interferometry

Double exposure holography as a tool for profilometric measurements on coated surfaces is described. The coating material is camphene, a transparent, crystalline substance of high vapour pressure at room temperature. The application of the technique to measurements of local mass-transfer coefficients under the condition of forced and free convection along a flat plate is shown. The results agree very well with the theoretically predicted values. The technique can also be used to analyze the flow field by means of the local mass transfer. As an example the longitudinal vortex instabilities were visualized and their influence on mass transfer was measured.