Hydrodynamic cavitation in microsystems. I. Experiments with deionized water and nanofluids

Abstract

International audienceAn experimental study of hydrodynamic cavitation downstream microdiaphragms and microventuris is presented. Deionized water and nanofluids have been characterized within silicon-Pyrex micromachined devices with hydraulic diameters ranging from 51 μm to 104 μm. The input pressure could reach up to 10 bars, and the flow rate was below 1 liter per hour. The output pressure of the devices was fixed at values ranging from 0.3 bar to 2 bars, so that it was possible to study the evolution of the cavitation number as a function of the Reynolds number in the orifice of the diaphragms or in the throat of the venturis. A delay on the onset of cavitation has been recorded for all the devices when they are fed with deionized water, because of the metastability of the liquid and because of the lack of roughness of the walls. For the first time, hydrodynamic cavitation of nanofluids (nanoparticles dispersed into the liquid) has been considered. The presence of nano-aggregates in the liquid does not exhibit any noticeable effect on the cavitation threshold through the venturis. However, such a presence has a strong influence on the cavitation onset in microdiaphragms: above a critical volume solid concentration of ≈10−5, the metastability is broken and the nanofluids behave as tap water filled up with large nuclei. These microdevices, where a low amount of fluid is required to reach cavitating flows, appear to be useful tools in order to study cavitating phenomena in localized area with specific fluids

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

“…With microdiaphragms or microventuris considered here, 0.3 L/h < Q cav < 1 L/h with pressure drops below 8 bar. Metastable effects have been observed with pure deionized water as the working fluid, because the smooth walls of the micromachined devices prohibit the contribution of the nuclei [7]. Once the two-phase cavitating flow has started, there is a small drop of the flow rate together with a low but audible crackle due to the collapse of the bubbles.…”

“…Microdiaphragms and microventuris were the only geometries considered up to now to perform hydrodynamic cavitation "on a chip" [2,3,7]. We have recently developed a new geometry, so-called microstep profile, which will be presented in Section 3.…”

“…The design of the sizes of the channels and of their related constriction is monitored by considerations taking into account a balance between the pressure losses due to the shrinkage and the dynamic pressure drop 1=2qu 2 0 , where q is the density of the liquid and u 0 the average velocity in the constriction (the dynamic pressure upstream and downstream the constriction is negligible in front of 1=2qu 2 0 ). Detailed calculations [7] demonstrate that in microdiaphragms and microventuris, the width w of the constriction must be shorter than the height H of the grooved channel. The vertical walls of the channels must be performed by a so-called Deep-Reactive Ion Etching (D-RIE) process.…”

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

“…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.…”

“…The most spectacular effect was the possible delay to the inception of cavitation, due to the metastability of deionized water and to the lack of roughness of the walls. We could then for the first time study hydrodynamic cavitation of nanofluids [8]. The presence of dilute nanoaggregates in the liquid did not give way to noticeable effects on the flow regimes through the venturis.…”