Abstract:Multibubble sonoluminescence (MBSL) is the emission of light from imploding cavitation bubbles in dense ensembles or clouds. We demonstrate a technique of high-speed recording that allows imaging of bubble oscillations and motion together with emitted light flashes in a nonstationary multibubble environment. Hereby a definite experimental identification of light emitting individual bubbles, as well as details of their collapse dynamics can be obtained. For the extremely bright MBSL of acoustic cavitation in xe… Show more
“…It has also been shown that the lack of buoyancy enhances the energy concentration at the final stage of the bubble collapse [20], even for bubbles that are highly spherical and generally assumed not to be subject to deformation by gravity (maximum bubble radius R 0 ∼ 40 µm at atmospheric pressure). Bubbles collapsing with pronounced microjets in multibubble fields have been shown to emit less light (or none) compared to the spherically collapsing bubbles [21].…”
Presented here are observations that demonstrate how the deformation of millimetric cavitation bubbles by a uniform pressure gradient quenches single collapse luminescence. Our innovative measurement system captures a broad luminescence spectrum (wavelength range 300-900 nm) from the individual collapses of laser-induced bubbles in water. By varying the bubble size, driving pressure and the perceived gravity level aboard parabolic flights, we probed the limit from aspherical to highly spherical bubble collapses. Luminescence was detected for bubbles of maximum radii within the previously uncovered range R 0 = 1.5-6 mm for laser-induced bubbles. The relative luminescence energy was found to rapidly decrease as a function of bubble asymmetry quantified by the anisotropy parameter ζ, which is the dimensionless equivalent of the Kelvin impulse. As established previously, ζ also dictates the characteristic parameters of bubble-driven microjets.The threshold of ζ beyond which no luminescence is observed in our experiment closely coincides with the threshold where the microjets visibly pierce the bubble and drive a vapor-jet during the rebound. The individual fitted blackbody temperatures range between T lum = 7000 and 11500 K but do not show any clear trend as a function of ζ. Time-resolved measurements using a highspeed photodetector disclose multiple luminescence events at each bubble collapse. The averaged full width at half maximum of the pulse is found to scale with R 0 and to range between 10-20 ns.
“…It has also been shown that the lack of buoyancy enhances the energy concentration at the final stage of the bubble collapse [20], even for bubbles that are highly spherical and generally assumed not to be subject to deformation by gravity (maximum bubble radius R 0 ∼ 40 µm at atmospheric pressure). Bubbles collapsing with pronounced microjets in multibubble fields have been shown to emit less light (or none) compared to the spherically collapsing bubbles [21].…”
Presented here are observations that demonstrate how the deformation of millimetric cavitation bubbles by a uniform pressure gradient quenches single collapse luminescence. Our innovative measurement system captures a broad luminescence spectrum (wavelength range 300-900 nm) from the individual collapses of laser-induced bubbles in water. By varying the bubble size, driving pressure and the perceived gravity level aboard parabolic flights, we probed the limit from aspherical to highly spherical bubble collapses. Luminescence was detected for bubbles of maximum radii within the previously uncovered range R 0 = 1.5-6 mm for laser-induced bubbles. The relative luminescence energy was found to rapidly decrease as a function of bubble asymmetry quantified by the anisotropy parameter ζ, which is the dimensionless equivalent of the Kelvin impulse. As established previously, ζ also dictates the characteristic parameters of bubble-driven microjets.The threshold of ζ beyond which no luminescence is observed in our experiment closely coincides with the threshold where the microjets visibly pierce the bubble and drive a vapor-jet during the rebound. The individual fitted blackbody temperatures range between T lum = 7000 and 11500 K but do not show any clear trend as a function of ζ. Time-resolved measurements using a highspeed photodetector disclose multiple luminescence events at each bubble collapse. The averaged full width at half maximum of the pulse is found to scale with R 0 and to range between 10-20 ns.
“…a) Blasenfeld, Bildbreite 2 mm. b) Kollision zweier leuchtender Blasen (von oben nach unten); Bildhöhe 300 µm, Bildabstand 200 µs (nach , American Physical Society 2017).…”
Section: Blasendynamik In Blasenwolkenunclassified
“…Immerhin gelang es unserer Gruppe in Göttingen kürzlich, bei der besonders hellen Vielblasen‐Sonolumineszenz von Xenon in konzentrierter Phosphorsäure mit einer sehr empfindlichen Hochgeschwindigkeitskamera, die Blitze und die Blasen gleichzeitig aufzunehmen (Abbildung ) . Dies bedeutet einen Fortschritt, denn wir können in den Blasenwolken eine Vielzahl von nichtsphärischen Blasenformen ausmachen, unter denen dennoch ein extrem heller Blitz entsteht.…”
Section: Blasendynamik In Blasenwolkenunclassified
Zusammenfassung
Ultraschall kann in Flüssigkeiten Lichtblitze erzeugen. Diese Sonolumineszenz stammt aus implodierenden Kavitationsblasen. Das Gas in kollabierenden Blasen kann sich dabei so stark erwärmen, dass kurzzeitig ein Plasma mit blitzartiger Lichtemission auftritt. Aus dem optischen Spektrum des Leuchtens schließt man auf die physikalischen Vorgänge bei der extremen Kompression des Blaseninneren. Dabei zeigen Wolken aus Blasen und isolierte Einzelblasen, die in akustischen Stehwellen gefangen sind, unterschiedliche Eigenschaften. Isolierte Einzelblasen haben eher eine symmetrische Kugelgestalt als die sich gegenseitig beeinflussenden Wolkenblasen. Neuere Arbeiten untersuchen, wie sich im Detail Blasenbewegungen und asymmetrische Implosionen auf die Sonolumineszenz auswirken.
“…It has also been experimentally shown that the secondary Bjerknes force favors the formation of bubble clusters instead of dendritic filament branches which alters the sonoluminescence intensity [49]. Thus, the study of multibubble dynamics may benefit sonochemical engineering applications where quenching of sonoluminescence is frequently encountered [29,50,51]. Moreover, the coupling between the individual bubbles in a collapsing bubble cloud may play an important role in the generation of shock waves and broadband cavitation noise [52][53][54][55].…”
Most of the current applications of acoustic cavitation use bubble clusters that exhibit multibubble dynamics. This necessitates a complete understanding of the mutual nonlinear coupling between individual bubbles. In this study, strong nonlinear coupling is investigated in bubble pairs which is the simplest case of a bubble-cluster. This leads to the derivation of a more comprehensive set of coupled Keller-Miksis equations (KMEs) that contain nonlinear coupling terms of higher order. The governing KMEs take into account the convective contribution that stems from the Navier-Stokes equation. The system of KMEs is numerically solved for acoustically excited bubble pairs. It is shown that the higher order corrections are important in the estimation of secondary Bjerknes force for closely spaced bubbles. Further, asymmetricity is witnessed in both magnitude and sign reversal of the secondary Bjerknes force in weak, regular, and strong acoustic fields. The obtained results are examined in the light of published scientific literature. It is expected that the findings reported in this paper may have implications in industries where there is a requirement to have a control on cavitation and its effects.
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