A PHOTOGRAPHIC STUDY OF THE FORMATION OF VORTEX RINGS AND BUBBLE ENTRAINMENT FOLLOWING THE IMPACT OF WATER DROPS UPON WATER POOLS

Recent research on nucleate boiling implicates bubble entrainment by drops as a source of bubble nuclei. A search for the mechanism for such entrainment revealed evidence that drop-formed vortex rings have the potential for such entrainment but only superficial observations could be found. This study was begun to study the cause of the entrainment and attempt to resolve different hypotheses which account for the formation of drop-formed vortex rings.;A new hypothesis for the formation of drop-formed vortex rings is tested. It is shown that bubbles appear during the destruction of an air film present between the striking drop and the pool surface. Similarities and differences are noted between vortex rings formed by drops and those generated by bursts of flow from a tube. Drops with a prolate shape on impact were found to give the most penetrating vortex rings contrary to recent literature.;A criterion is presented for determining whether on impact a drop causes a splash or immediately coalesces. The smaller the drop, the higher the impact velocity required to cause a splash.;Bubble entrainment caused by drop-formed vortex rings was studied by using high speed photography with special emphasis on close-up photography to obtain an enlarged image. Many photographs showing details of the transition from drop to vortex ring are presented. Dyed water drops with diameters ranging between .49 and 4.4 mm were used.