MEASUREMENT OF LIQUID FILM THICKNESS ON THE SURFACE OF A PARTIALLY IMMERSED VERTICAL ROTATING DISK USING A GAMMA CAMERA

The liquid film thickness on the surface of a partially immersed vertical rotating disk was determined using a gamma camera imaging system to measure the amount and spatial distribution of a dissolved 99m-Technetium pertechnetate radionuclide tracer. The method allows simultaneous measurement of film thickness in individual regions having a projected surface area of less than 1 cm(2) and distributed over the entire exposed surface of the disk. Measurement accuracy is limited only by counting statistics, and for these studies was better than +/- 4% of the absolute film thickness. Experiments were conducted with a 31.5 em diameter aluminum disk rotating from 18 to 99 revolutions per minute; seven aqueous solutions of glycerol and polyvinylpyrrolidone (PVP) within the viscosity range 1 to 19.7 cp were used. The average film thickness varied between 0.045 and 0.45 mm, and was a function of solution viscosity and disk angular velocity. Local film thickness was dependent on both radial and angular position, and varied from 0.5 to 3.0 times the average thickness. This variation may be important to the characterization of mass transfer when diffusion through the film is a rate limiting step.