Katsuine Tabei

Study of Cavitation Light Emission Generated by a Waterhammer

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.© 2003 ASME

Study of Properties of Ar Micro Arc Plasma Jets for Fine Cutting with Synthetic Spectra Method.

Based upon a collisional and radiative process theory, and synthetic spectra for argon plasmas, the experimental method for spatial properties of Ar plasma jets was presented, and applied to diagnostics for micro Ar plasma jets for fine cutting. A plasma torch had a nozzle of 0.7 mm in diameter and a discharge length of 2 to 10 mm, and was operated with an arc current of 10 to 30 A. Data from a CCD image processor and Mach-Zehnder interferometer were dealt with an Abel transformation to obtain true spacial profiles of electron density and temperature, and heavy particle temperature. Electron temperature in the main flow was found to be about 12 000 to 13 500 K, electron density of an order of 1016 cm-3, both increasing with an arc current. It was also found that heavy particle temperature was significantly lower than electron temperature in the nozzle exit region and increased to coincide with electron temperature downstream. Experimental relation of electron temperature and density could be approximated well by that calculated from steady-state collisional and radiative processes.

Visualization of Weakly Luminous Region of the Cavitation in a Circular Orifice Flow

Light-emitting region of cavitation bubble flows generated behind an orifce in a circular pipe has been visualized by optical methods. Xenon gas wsa dissolved in clear water for enhancement of weak emission from cavitation, and its effect on the luminous properties of the flows was investigated. Spacial emission profiles and shadowgraph images of clear water and water-xenon cavitation were obtained by photon counting and and ordinary photographic methods, and compared with each other. It was found that the emission property of the water-xenon cavitation was very similar to that of clear water, and the photographic method was directly apoplicable for the orifice cavitation flow under the enhanced condition.

Temperature measurements of atmospheric Ar plasma freejets by means of the Moire-Schlieren and spectroscopic methods.

The atmospheric Ar plasma freejets, generated by an electric arc discharge, are visualized and measured by the Moire-Schlieren method to obtain the details of their high temperature fields. Electron temperatures and electron number densities are also deduced from a combined method of the absolute intensity measurements of Ar spectral lines and the collisional-radiative process theory. From the experiments performed under the conditions of arc currents of 100-200 A and nozzle diameters of 3-4 mm, the following are found : (i) The gas temperatures are 1000-5000 K and the electron temperatures are about 8500 K. (ii) The distributions of gas temperature for the conditions show a similar form. (iii) The freejets are thermally in nonequilibrium, though the plasmas are fairly dense.