Cavitation light emission generated by a waterhammer is investigated experimentally and theoretically for water containing a small amount of rare gas (xenon and argon). In the experiment, the water is forced to flow upwards in an evacuated vertical circular tube by the rapid opening of a ball valve that is connected to the liquid reservoir. The liquid vaporizes until the flow reaches the top end of the tube, and many minute cavitation bubbles are generated in the liquid. When the water column collides with the end of the closed pipe, a waterhammer with a pressure of over 1 MPa is generated in the multi-phase liquid, and it progresses toward the reverse direction. In such a process, the cavitation bubble collapses, and emits an instantaneous flash of light. Physical quantities such as the propagation velocity of the pressure waves and the cavitation emission intensity are measured. In addition, the momentary patterns of the bubbly flow and the light emission are also visualized by using an image intensifier and a stroboscope. The theory is constituted for the multi-phase flow of the waterhammer, in which the Keller and Miksis’ equation for the collapse of a bubble includes the effect of the ionization reaction of rare gas in the bubble. From the study, the following features are shown: Light emission occurs only at the front of the shock wave of the waterhammer. The position of light emission moves exactly at the same speed as the propagation speed of the pressure wave. Changes of pressure and emission intensity in the waterhammer are both strongly dependent on a void fraction. The ratio of emission intensity for water dissolved with argon and water dissolved with xenon is nearly 1:5.

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