Size scale effects on cavitating flows through microorifices entrenched in rectangular microchannels

Abstract

Cavitating flow of deionized water through various microorifices and microchannels has been investigated. Multifarious cavitating flow patterns, including incipient, choking and supercavitation have been detected. Effects of microorifice and microchannel size on cavitation have been discussed and results indicate the existence of strong size scale effects. Incipient and choking cavitation numbers are observed to increase with the area ratio between the microorifice and the microchannel while the orifice discharge coefficient plummets once cavitation activity erupts. Additionally, for a fixed microchannel width, the incipient and the choking cavitation numbers rise with the ratio between the hydraulic diameters of the microorifice and the microchannel. In addition, velocity and pressure effects on cavitation have been investigated for several microorifices and the observed trends have been compared with established macroscale results. Furthermore, the flow patterns encountered at choking and supercavitation are significantly influenced by the microorifice and microchannel size. Flow rate choking occurs irrespective of the inlet pressures and is a direct consequence of cavitation inside the microorifice. The predicted choked cavitation number is always higher than the experimental data. This discrepancy is suspected to be the result of exceedingly small residence time for nuclei growth and the ability of the liquid to withstand low pressures at such scales. Flow and cavitation hysteresis is observed but its effects are more pronounced for the smallest microorifice.