Thickness of a liquid film adhering to a surface slowly withdrawn from the liquid

When a solid body is immersed in a bath of liquid and withdrawn, a film of the liquid adheres to the solid surface and gradually drains back into the bath when the motion ceases.The relationship existing between the average film thickness, the speed of withdrawal, and the kinematic viscosity of the liquid is the subject dealt with in this paper.According to the generally accepted theory the film thickness varies with the square root of the product of the speed and the kinematic viscosity.It was noticed that corrections based on this relationship and used in the calibration of a gas-measuring standard were not satisfactory.Therefore an experimental apparatus was designed to test the theory.Analysis of the data revealed that within the range of speeds used the theory does not correctly predict the film thickness, and an empiricaJ equation of the form t=k (vs)n was employed, in which t is the average film thickness, v is the kinematic viscosity of the liquid, s is the speed of withdrawal of the surface, k and n are quantities varying slightly with the liquid used.The approximate values of k and n found by experiment are 0.015 and 0.63, respectively.Nine liquids were tested, including mineral, vegetable, and animal oils, and synthetic organic compounds of oily nature.