Probing Luminescence from Conical Bubble Collapse
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Probing Luminescence from Conical Bubble Collapse M. Navarrete1, C. Sánchez2, F. A. Godínez1, R. Valdés 1, E. Mejía3, M. Villagrán2 1 Instituto de Ingeniería, 2Lab. de Fotofísica, CCADET,3 Lab. de Fotónica de Microondas, CCADET; Universidad Nacional Autónoma de México, Av. Universidad 3000, C. P. 04510, D. F. México, [email protected]
ABSTRACT A summary of experimental findings on the luminescence from conical bubble collapse, CBL is presented. Spatial, temporal, and spectral features of luminescence were investigated. In the experimental runs, two inert gases (Ar, Xe) and 1,2-Propanediol, PD, as work liquid were used. Single and multiple light emission events were recorded. Results show that there is a spectral evolution inside each pulse and through the whole experimental sequence. The average spectra consist of a broad continuum background, on which line emissions of OHº, CN, Na+, K+, and Swan lines are superimposed. An increase in continuum intensity from 300 to 860 nm was observed. The molecular and atomic lines as well as the continuum emission arise from different chemical pathways that take place during the bubble compression. Pathways come from the degradation of the liquid due to the repetition of the compression process, resulting in changes of the thermo-chemical conditions inside the cavity, such that each collapse was different. This becomes evident, by using low gas pressures, in which the luminescence was spatially and temporally non uniform. On the other hand if Xe instead of Ar is used the intensity of the luminescence increased one order of magnitude. These findings indicate that several components are presents in the bubble, besides the residual air and inert gas, vapor and liquid droplets, and within the latest water vapor, inert gas and alkali solutions are dissolved. INTRODUCTION Luminescence can also be a consequence of the cavitation phenomenon; fundamentally there are four basic types of cavitation according to how it is generated: a) acoustic cavitation: pressure variations by acoustic waves, single, SL [1-2], multibubble, MBSL [3], mechanoluminescence [4]; b) hydrodynamic cavitation: pressure changes by pipeline geometry such as Venturi tube [5], the tube arrest [6], the hammer system [7], and conical bubble cavitation [8-14]; c) optical cavitation: light burst or spark discharge through the liquid [15-16, 20] and finally; d) rupturing a liquid by elementary particles [17]. Under appropriate conditions, regardless of the method in which the cavitation is produced, on the latter stages of the collapse, the bubble emits a light pulse. The intensity, width and the spectrum of this light [SL or SBSL] have been used to look inside the bubble or bubbles during the collapse for determining intracavity temperatures and pressures. Through these studies extraordinary conditions inside the bubble have been calculated (temperatures up to 20,000 K; pressures of several thousand bar; and heating and cooling rates > 1012 Ks-1) [18-19]. According to these and with the purpose of to up-scaling the
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