Light flashes and shocks from a cavitating flow

The nature of the light emitted from the cavitating flow of tap water through a Venturi tube has been studied. The light is emitted as flashes of duration less than 5 μsec and its spectrum lies between 400 and 700 nm with a maximum intensity at 470 nm. Shock waves were detected by miniature pressure transducers implanted in the wall of the tube: a shock is associated with every light flash, and the intensity of light along the tube correlates with that of the shocks. The temperature attained within most of the collapsing cavities in plain tap water appears to be too low to produce detectable light flashes although these cavities give out shocks similar to those from hotter cavities. However, the emission of light from all cavities is much enhanced by the addition of carbon disulphide to the water although it seems that this solute does not nucleate the water. This effect was compared with that of adding carbon disulphide to ultrasonically induced cavitation in water at 25 and 500 kc/s. Differences in the light emission from flow induced and ultrasonically induced cavitation are attributed to the different growth and collapse characteristics of the cavities. The analysis of the enhanced light flashes is a useful technique in studying the physical effects of a cavitating flow.