Multibubble Sonoluminescence Intensity Dependence On Liquid Temperature At DiErent Ultrasound Intensities
Páginas: 10 (2438 palabras)
Publicado: 19 de octubre de 2011
Ultrasonics Sonochemistry 9 (2002) 103±106
www.elsevier.com/locate/ultsonch
Multibubble sonoluminescence intensity dependence on liquid temperature at dierent ultrasound intensities
N.V. Dezhkunov *
Belarusian State University of Informatics and Radioelectronics, P. Brovka St. 6, 220027 Minsk, Belarus Received 12 June 2000; accepted 25 June 2001
Abstract It is shown that the in¯uenceof liquid temperature on the sonoluminescence (SL) intensity is dierent depending on the ultrasound intensity. At the ultrasound intensities not much higher than the cavitation appearance threshold the SL intensity increases with the temperature. At the ultrasound intensities considerably exceeding the cavitation threshold the SL intensity decreases with an increase of the temperature. Atintermediate ultrasound intensities the SL intensity temperature dependence is extreme: the cavitation activity at ®rst increases with temperature, reaches a maximum and then decreases. Continuous and pulsed modes of irradiation at frequencies 880 and 21.9 kHz were used in experiments. Ó 2002 Published by Elsevier Science B.V.
Keywords: Ultrasound; Sonoluminescence; Temperature dependence
1.Introduction The cavitation nature of the high-power ultrasound eect on the majority of physico-chemical processes in liquids is not doubted at present. The intensity of this impact, i.e. the cavitation activity, is determined by the concentration of cavitation bubbles in a cavitation zone and by their eciency of conversion the ultrasound energy into shock waves, thermal energy and others. Variation ofthe liquid temperature is one of the simplest methods for modifying the activity of the cavitation. A change in the temperature entails a change in a number of parameters exerting a strong in¯uence on the sizes of cavitation nuclei, density of bubbles and their size distribution in the cavitation ®eld and on the dynamics of the cavitation bubbles. However, the available data [1±10] on thetemperature dependence of the cavitation activity (evaluated, for instance, by the sonoluminescence (SL) intensity or by the yield of the sonochemical reactions) are contradictory. Thus, in Refs. [1,2] the data obtained are indicative of the increase of the SL intensity with an increase of the temperature. In Refs. [3±5] the authors report about maximum in the SL output as a function of the tem*perature. The majority of investigators [6±10] point to the decrease of the SL intensity with the increase of the temperature. According to the data of Refs. [11,12] the intensity of light emission by a single levitating bubble decreases by increasing the temperature. In the present work it is shown that the possible reason of the above dierences lies in the fact that the temperature dependence of theSL intensity is dierent at dierent ultrasound intensities.
2. Experimental The experimental chamber is a stainless steel cylinder with a diameter of 75 mm and a height of 120 mm, the same shape as in Ref. [13]. The dissolved gas is air. A focusing 40 mm diameter piezoceramic transducer with a resonance frequency of 880 or 21.9 kHz transducer with a horn, 15 mm in diameter at the radiatingsurface is mounted at the cell bottom. The set-up allows the operation in continuous or in pulsed sound ®elds. The hydrophone is placed in the chamber in such a way that its sensitive piezoceramic unit (diameter of 2.7 mm and thickness of 0.2 mm) is at a distance of 30 mm above the centre of the focal spot of the 880 KHz transducer. The central region of the chamber is viewed through a 2.5 cmdiameter lightguide by the photomultiplier whose
Tel.: +375-172-398635; fax: +375-172-310914. E-mail address: dnv@bsuir.edu.by (N.V. Dezhkunov).
1350-4177/02/$ - see front matter Ó 2002 Published by Elsevier Science B.V. PII: S 1 3 5 0 - 4 1 7 7 ( 0 1 ) 0 0 1 1 6 - X
104
N.V. Dezhkunov / Ultrasonics Sonochemistry 9 (2002) 103±106
output is indicated by L. In the precavitation conditions...
www.elsevier.com/locate/ultsonch
Multibubble sonoluminescence intensity dependence on liquid temperature at dierent ultrasound intensities
N.V. Dezhkunov *
Belarusian State University of Informatics and Radioelectronics, P. Brovka St. 6, 220027 Minsk, Belarus Received 12 June 2000; accepted 25 June 2001
Abstract It is shown that the in¯uenceof liquid temperature on the sonoluminescence (SL) intensity is dierent depending on the ultrasound intensity. At the ultrasound intensities not much higher than the cavitation appearance threshold the SL intensity increases with the temperature. At the ultrasound intensities considerably exceeding the cavitation threshold the SL intensity decreases with an increase of the temperature. Atintermediate ultrasound intensities the SL intensity temperature dependence is extreme: the cavitation activity at ®rst increases with temperature, reaches a maximum and then decreases. Continuous and pulsed modes of irradiation at frequencies 880 and 21.9 kHz were used in experiments. Ó 2002 Published by Elsevier Science B.V.
Keywords: Ultrasound; Sonoluminescence; Temperature dependence
1.Introduction The cavitation nature of the high-power ultrasound eect on the majority of physico-chemical processes in liquids is not doubted at present. The intensity of this impact, i.e. the cavitation activity, is determined by the concentration of cavitation bubbles in a cavitation zone and by their eciency of conversion the ultrasound energy into shock waves, thermal energy and others. Variation ofthe liquid temperature is one of the simplest methods for modifying the activity of the cavitation. A change in the temperature entails a change in a number of parameters exerting a strong in¯uence on the sizes of cavitation nuclei, density of bubbles and their size distribution in the cavitation ®eld and on the dynamics of the cavitation bubbles. However, the available data [1±10] on thetemperature dependence of the cavitation activity (evaluated, for instance, by the sonoluminescence (SL) intensity or by the yield of the sonochemical reactions) are contradictory. Thus, in Refs. [1,2] the data obtained are indicative of the increase of the SL intensity with an increase of the temperature. In Refs. [3±5] the authors report about maximum in the SL output as a function of the tem*perature. The majority of investigators [6±10] point to the decrease of the SL intensity with the increase of the temperature. According to the data of Refs. [11,12] the intensity of light emission by a single levitating bubble decreases by increasing the temperature. In the present work it is shown that the possible reason of the above dierences lies in the fact that the temperature dependence of theSL intensity is dierent at dierent ultrasound intensities.
2. Experimental The experimental chamber is a stainless steel cylinder with a diameter of 75 mm and a height of 120 mm, the same shape as in Ref. [13]. The dissolved gas is air. A focusing 40 mm diameter piezoceramic transducer with a resonance frequency of 880 or 21.9 kHz transducer with a horn, 15 mm in diameter at the radiatingsurface is mounted at the cell bottom. The set-up allows the operation in continuous or in pulsed sound ®elds. The hydrophone is placed in the chamber in such a way that its sensitive piezoceramic unit (diameter of 2.7 mm and thickness of 0.2 mm) is at a distance of 30 mm above the centre of the focal spot of the 880 KHz transducer. The central region of the chamber is viewed through a 2.5 cmdiameter lightguide by the photomultiplier whose
Tel.: +375-172-398635; fax: +375-172-310914. E-mail address: dnv@bsuir.edu.by (N.V. Dezhkunov).
1350-4177/02/$ - see front matter Ó 2002 Published by Elsevier Science B.V. PII: S 1 3 5 0 - 4 1 7 7 ( 0 1 ) 0 0 1 1 6 - X
104
N.V. Dezhkunov / Ultrasonics Sonochemistry 9 (2002) 103±106
output is indicated by L. In the precavitation conditions...
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