Fluorescence aids flow measurement

Fluorescence aids flow measurement

Frank Johnson, a research assistant at Northwestern University (Chicago, IL), is using ImagePro Plus from Media Cybernetics (Silver Spring, MD) to study flow patterns formed by thin liquid films flowing down an inclined plate. The difficulty in acquiring experimental data for this type of research is measuring the depth of a fluid without disturbing flow patterns.

To address this, Johnson mixes water and glycerin with dye that causes the fluid to fluoresce when exposed to ultraviolet (UV) light. The intensity of the fluorescent light emitted from the fluid is proportional to the depth of the fluid. Image Pro Plus determines the fluid depth in the image by converting gray-scale values of the image to fluid depth values using a calibration curve. The calibration curve was determined from a curve fit of gray-scale readings for known volumes of fluid contained in a calibration dish.

Lighting nonuniformity causes areas along the sides of the image to appear darker than at center, even though fluid depths are equal. Johnson corrects this nonuniformity using the background calibration feature of ImagePro.