Criteria for jet cavitation and cavitation jet drilling

The research history of cavitation jets is reviewed, and a mechanism that explains cavitation, methods to measure when cavitation occurs and factors that affect cavitation are introduced. The rationality of the cavitation number, which is often used to predict cavitation, is discussed. The results show that cavitation cannot be predicted using the cavitation number. The problems with the Rayleigh equation in calculating the impulse pressure under an annihilation of a cavity for explaining that a cavitation jet having more power to break rocks than that of a common jet are analyzed. A new explanation is suggested: the rock surface pressure pulses due to density changes in the cavitation jet, which makes the cavitation jet more effective. Because the static pressure at the bottom of the well is extremely high and cavitation only occurs at the vapor pressure, the pressure in the nozzle must decrease from the static pressure to the vapor pressure. Reducing the pressure in the nozzle from the static pressure to the vapor pressure is extremely difficult, and thus, much work is still required before cavitation jet drilling can be used in a practical application. (C) 2014 Elsevier Ltd. All rights reserved.