Choked cavitation in micro-orifices: An experimental study

• New data for choked cavitation in micro-orifices.
• Cavitation number independent of pressure and velocity effects.
• Cavitation number increases with micro-orifice diameter and thickness.
• Micro-orifices less susceptible to choked cavitation than macro-orifices.

Choked cavitation was experimentally investigated with three circular micro-orifices with diameters of 150 μm and 300 μm and thicknesses of 1.04 mm, 1.06 mm and 1.93 mm. Water was used as the test fluid, and experiments were carried out with upstream pressures in the range of 5.1–13.5 MPa. The cavitation number at the inception and cessation of choked cavitation was found to increase with increasing the micro-orifice diameter and thickness. This suggests that micro-orifices could be characterized by very small choked cavitation numbers and therefore might be less susceptible to choking than their macro-scale counterparts. The cavitation number at the inception and cessation of choked cavitation was independent of the upstream pressure, downstream pressure, average flow velocity and orifice Reynolds number. At choking, the ratio of the upstream pressure to the downstream pressure is constant for a given micro-orifice, while during choked flow the mass flow rate through the micro-orifice is proportional to the square root of the upstream pressure.