Liquid jet response to internal modulated ultrasonic radiation pressure and stimulated drop production

Abstract

Experimental evidence shows that a liquid jet in air is an acoustic waveguide having a cutoff frequency inversely proportional to the jet diameter. Ultrasound applied to the jet supply liquid can propagate within the jet when the acoustic frequency is near to or above the cutoff frequency. Modulated radiation pressure is used to stimulate large amplitude deformations and the breakup of the jet into drops. The jet response to the modulated internal ultrasonic radiation pressure was monitored along the jet using (a) an optical extinction method and (b) images captured by a video camera. The jet profile oscillates at the frequency of the radiation pressure modulation and where the response is small, the amplitude was found to increase in proportion to the square of the acoustic pressure amplitude as previously demonstrated for oscillating drops [P.L. Marston and R.E. Apfel, J. Acoust. Soc. Am. 67, 27-37 (1980)]. Small amplitude deformations initially grow approximately exponentially with axial distance along the jet. Though aspects of the perturbation growth can be approximated from Rayleigh's analysis of the capillary instability, some detailed features of the observed jet response to modulated ultrasound are unexplained neglecting the effects of gravity.

Liquid-Column Sustainment Driven by Acoustic Wave Guiding

“…Such a geometry, however, makes the stabilization process very sensitive to the details of the actual acoustic field surrounding the liquid column and, more importantly, breaks its axial symmetry [11]. On the other hand, very recently, bulk [16] and surface [17] acoustic waves have been shown to be able to trigger interface destabilization leading to jetting, whereas amplitude modulated leaky waves propagating along liquid jets have been used to control jet breakup [18]. In this Letter, we experimentally demonstrate that acoustic wave guiding by the liquid column itself, which preserves its axial symmetry, can be efficiently used to stabilize it.…”

An activated fluid stream – New techniques for cold water cleaning

“…In addition, in the following experiments an electrochemically enhanced UAS (e 2 UAS) approach will be adopted. Here, as well as producing significant acoustic fields (through the device design [33,34] and materials used), a bubble swarm [28] will be electrochemically generated in the system and the cleaning ability investigated on a particular fluorescent marker material. Figure 2 shows the approach adopted with particular reference to the timing of the electrochemical and acoustic stimuli applied to the system.…”

Node formation mechanisms in acoustofluidic capillary bridges

“…This is a further obstacle to forming a resonance in the fluid since sound must pass multiple times between the side-walls to form a resonance. The cut-off dimension for wave propagation in a fluid is in the region of half a wavelength, this was calculated and shown experimentally in reference [49] where at 1 MHz the minimum cut-off diameter for axisymmetric acoustic propagation in a cylindrical water jet is 1.1 mm. Experiments in microchannels have also shown [50] that, significant wave attenuation occurs in channels less than a half wavelength high.…”