Free decay of shape oscillations of bubbles acoustically trapped in water and sea water

Abstract

Asymptotic results for the free decay of shape oscillations of viscous liquid spheres have been extended to include higher-order terms in the ratios of the inner and outer viscous penetration lengths to the radius. The new expressions are shown to be important for studies in which the two fluids have dissimilar densities and viscosities such as air/liquid systems. The analysis also includes an expansion for the frequency of maximum response of driven oscillations. The calculations are supported by measurements of the small-amplitude quadrupole mode free decay of nearly spherical bubbles acoustically levitated in clean water. The bubble radii ranged from 400 μm to 1400 μm. The results are interpreted in light of the initial-value problem. The lack of excess damping suggests that the interface behaves ideally for times up to two hours after bubble injection. Measurements were also carried out on bubbles in 0.5 m NaCl solution and in sea water. Larger bubbles (radius > 800 μm) in clean water exhibit damping two to four times larger than predicted by theory. The transition from this anomalous damping to theoretical damping is a very abrupt function of radius. All observations were carried out with similar acoustic fields for counteracting buoyancy. The excess damping appears to be associated with some nonlinear response of the bubble.

Investigation of noninertial cavitation produced by an ultrasonic horn

“…The acoustic pressure and current were then measured as a function of time and high-speed video was also recorded simultaneously. This is a particularly useful technique for examining the individual modes when many are excited simultaneously, as the damping of each mode differs, 55 and therefore so do their decay times. Figure 4 shows the evolution in behavior of the signal obtained from a hydrophone placed in the cell in conjunction with measurement of the electrochemical signal from a 25 lm diameter Pt electrode.…”

Enhanced damping of capillary bridge oscillations using velocity feedback

“…Fluids 17, 032105 ͑2005͒ of shape oscillations of drops 8 and bubbles. 13 In the present situation, there is a small increase in the oscillation frequency during the decay associated with the term proportional to h in Eq. ͑B1͒.…”

“…The reason to delay the fitting by one period after the modulation burst is over, is to reduce any complications resulting from the early superposition of more rapidly decaying modes. 13,33,37,38 The fitting procedure is repeated again to yield the final values for 0 , ⌫, and h, and the final fit as shown in Fig. 4.…”

“…The dynamics of capillary wave modes have been studied for the case of isolated drops [7][8][9][10][11] and bubbles [12][13][14][15] as well as for liquids in contact with solid containers or supports. For liquids in contact with solid the primary geometries which have been investigated include pendant or sessile drops, [16][17][18] the brimful cylinder, 19,20 and capillary bridges.…”

“…For liquids in contact with solid the primary geometries which have been investigated include pendant or sessile drops, [16][17][18] the brimful cylinder, 19,20 and capillary bridges. [21][22][23][24][25][26] Damping measurements for capillary modes have been made on free drops, 7,8,10 bubbles, 13,14 and capillary bridges. 23,24 Earthbased damping measurements of pure capillary wave modes are usually performed for relatively small-scale systems, which means low-Q systems for which damping measurements are difficult.…”