Vapour cavitation in very confined spaces for Newtonian and non Newtonian fluids

Experiments were conducted in very confined spaces comprised between a rotating cylinder and a stationary flat plate, with a minimum gap down to 5 microns, using water and a 600 ppm aqueous solution of Polyox WSR 301. The conditions for cavitation occurrence as well as the morphology of the developed cavities were determined. In the case of water, onset of cavitation is in the form of isolated spots randomly distributed along a cylinder generatrix. If the local pressure is further reduced, spots increase in size to form larger cavities, become less random and, finally, form a string of cavities whose length, in the direction of the flow, is larger than the width. As compared to the solvent, the polymer solution delays cavitation inception, decreases the length of developed cavities, and eliminates the interstitial film between successive cavities. These effects can be related to the strong elongational flow prevailing in the confined space and the viscoelastic characteristics of the polymer solution. From...