ON CAVITATION IN THIN LIQUID LAYERS

A new apparatus is described, which allows events occurring within a t hin liquid layer while being dynamically loaded in tension to be viewe d. Experiments were carried out with water layers of initial thickness of ca. 100 mu m and ca. 10 mu m. With the 100 mu m layers, the observ ed mechanism was that of cavities' nucleation and growth. A model is p roposed for the mechanism of cavity inception and growth which is base d on comparison between the rate of gas ejection into the cavities and the rate of total volume increase. Using the experimental results, th is model enables calculation of the 'evaporation constant'. Once the n umber density of cavities is fixed, and they begin to grow, a simple m odel of liquid volume conservation can be applied to describe the cavi ties' growth. The disintegration of the cavities' structure seems to b e caused by air flow from the rim of the layer towards its centre. Wit h the 10 mu m layers, the yield mechanisms are different and resemble, to some degree, the brittle fracture of solids. The yielding of the l iquid occurs within a few microseconds, and later time effects are cau sed by surface tension acting on the already separated parts of the li quid.