Hydrodynamic cavitation in microsystems. II. Simulations and optical observations

Abstract

International audienceNumerical calculations in the single liquid phase and optical observations in the two-phase cavitating flow regime have been performed on microdiaphragms and microventuris fed with deionized water. Simulations have confirmed the influence of the shape of the shrinkage upon the contraction of the jet, and so on the localisation of possible cavitating area downstream. Observations of cavitating flow patterns through hybrid silicon-pyrex microdevices have been performed either via a laser excitation with a pulse duration of 6 ns, or with the help of a high-speed camera. Recorded snapshots and movies are presented. Concerning microdiaphragms, it is confirmed that very high shear rates downstream the diaphragms are the cause of bubbly flows. Concerning microventuris, a gaseous cavity forms on a boundary downstream the throat. As a consequence of a microsystem instability, the cavity displays a high frequency pulsation. Low values Strouhal numbers are associated to such a sheet cavitation. Moreover, when the intensity of the cavitating flow is reduced, there is a mismatch between the frequency of the pulsation of the cavity and the frequency of shedded clouds downstream the channel. That may be the consequence of viscous effects limiting the impingement of a re-entrant liquid jet on the attached cavity

Hydrodynamic cavitation of binary liquid mixtures in laminar and turbulent flow regimes

“…Water exhibits inception of cavitation at r values similar to those of isopropanol. However, the transition occurs at Re values around 2100, and it has been stated that local turbulent vortices downstream the diaphragm are likely to trigger the transition [8,9].…”

“…In the present paper, we shall only recall the main parameters useful for the understanding of the experiment. Detailed calculations and technical informations about the micromachining of the devices can be found in the papers of Medrano et al [8,9]. Hydrodynamic cavitation in microsystems is the consequence of Bernoulli law.…”

“…In the recent past years, our team has scrutinized the cavitation flow regime of water through several microdiaphragms and microventuris, and has recorded high speed camera movies [8,9]. With the help of these devices exhibiting a cavitating flow regime at flow rates below 1 L/h, it has been established that the transition from a single liquid phase to a two -phase flow is triggered by vortices in the recirculating area downstream the shrinkage of microdiaphragms.…”

Luminescence Based Measurements in Micro Cavitating Flow

“…These kind of channels have been used extensively by our team [8][9][10] and others [11][12][13][14]. Channel geometries most used are micro diaphragms (figure 1b) and micro Venturis.…”

Hydrodynamic Cavitation through “Labs on a Chip”: From Fundamentals to Applications

“…Microventuris give way to pocket cavitation: a vapour pocket is linked to the throat and develop on one side of the diffuser downstream [9]. Microdiaphragms give way to shear cavitation: the liquid jet emerging from the constriction shears a residual liquid pocket, inducing vortices from where bubbles clouds can grow up.…”