Radiation-induced acoustic cavitation; apparatus and some results

Abstract

Equipment and techniques for acoustic cavitation w o~k are desc ribed . . The tes t liquid and its eontainer form part of a se lf· sustaining programmable oscIllator. EmphasIs IS laId on the treatme nt of the liquid necessa ry to yield re producible res ults after artificial nucl ea tion ,. especially b y ne utrons , a-recoi ls, and fi ss ion. With ne utrons , for instance, th e ca vitatIOn rate rI ses rapI~ly WIth acoustIc (negativ e) press ure, and at fix ed pressure is proportional to ne utron flux . The ca vItat~on events are ra~dom, and no ap prec ia bl e indu c t.ion or decay tim es are obse rve d. Each cav itatIOn anses from the actIOn of a s in"l e ne ut.ron (or a -recoil , or fi ss ion). The ca vit.atio n " thres ho ld " (rou ghly negative press ure below whi c l cavital ion is rare) is hi ghl y variab le fro m liquid to liquid. Thres holds at about room temperature for liquids irradi a t.ed with 10 MeV ne utrons ranged from 1 to 2 bars for n-pentane, e ther, and fre on 113 to ove r 50 ba rs for wate r.Key Words: Acoustic cavitati on, alph a-p artic le -in duced ca vitat.ion, ca vitation, cav itation nucl e us, cavitation thres hold, fission-induced cav itation, ne utron-indu ced cav ita ti on, radiationindu ced cav itation, thres hold .

Cavitation inception from bubble nuclei

“…Greenspan & Tschiegg [20] filtered away motes from distilled water and found that the tensile strength of water, measured by acoustic cavitation at 43 kHz, increased as the size of the motes became smaller, until at 0.2 mm a tensile strength of more than 200 bar could be sustained for seconds. Likewise, the tensile strength was increased when the gas content in the water was reduced, but when filtered to mote sizes smaller than 0.2 mm the gas content did not affect the tensile strength.…”

Reflections on cavitation nuclei in water

“…This may explain the very high tensile strength, its lack of dependency on particle size ͑when smaller than 0.2 m͒, as well as the lack of dependency on the gas content observed by Greenspan and Tschiegg. 12 The acoustic field they used to generate tensile stress has probably caused rectified diffusion of gas into small nano-voids, and this has made them grow over time, and has limited the duration of the high tensile strength. Significant contamination of the particle surfaces with amphiphilic surface-active substances is probably required for the tensile strength to reduce to that of skin-covered vapor bubbles of equivalent size.…”

“…Fluids 19, 072104 ͑2007͒ cleaned 7,10 or just distilled, and motes larger than 0.2 m are removed. 12 However, it is well known that clean surfaces contaminate very quickly when exposed to the environment, and generally surface-active molecules can be expected to form a skin around particles in water.…”

Cavitation Inception on Microparticles: A Self-Propelled Particle Accelerator

“…The discussion of their nature -stabilized spherical gas bubbles or surface nuclei on particles -has been ongoing. Though [3,5,8,9] point to the latter ones, the direct observation of cavity-particle separation has been missing until now. Further, the particle ejection suggests that accelerated particles may penetrate into nearby soft surfaces, e.g., biological tissue or cells during exposure to strong, focused sound fields.…”