VAPOR 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 dow n to 5 microns, using water and a 600 ppm aqueous solution of Polyox W SR 301. The conditions for cavitation occurrence as well as the morpho logy of the developed cavities were determined. In the case of water, onset of cavitation is in the form of isolated spots randomly distribu ted along a cylinder generatrix. If the local pressure is further redu ced, spots increase in size to form larger cavities, become less rando m and, finally, form a string of cavities whose length, in the directi on 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 s uccessive cavities. These effects can be related to the strong elongat ional flow prevailing in the confined space and the viscoelastic chara cteristics of the polymer solution. From a comparison of the Newtonian and non Newtonian inception cavitation numbers, the elongational visc osity of the polymer solution is estimated. (C) 1996 American Institut e of Physics.