Effects of Bubble Size and Gas Density on the Shock-induced Collapse of Nanoscale Cavitation Bubble
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ORIGINAL RESEARCH
Effects of Bubble Size and Gas Density on the Shock‑induced Collapse of Nanoscale Cavitation Bubble Yuan‑Ting Wu1,2 · Ashfaq Adnan1 Received: 4 February 2020 / Revised: 14 May 2020 / Accepted: 25 June 2020 © Korean Multi-Scale Mechanics (KMSM) 2020
Abstract In this paper, we studied the nature of shockwave induced cavitation bubble collapse using molecular dynamics (MD) simulation. A major objective of this study is to determine how the variation of nanoscale bubble size and entrapped gas density affects the bubble dynamics. It is known that cavitation bubble collapse/implosion is a robust dynamic event that occurs when the potential energy of the acting pressure performs work in a rapid and violent manner. Usually, the energy converges into a significantly smaller region compared to the original cavitation bubble. While the mechanisms of cavitation have been studied for more than a century, recently, it has received renewed interests due to its connection with biomedical applications and traumatic brain injury (TBI). One of the common causes of TBI is blast-induced shock exposure. A shockwave, as a moving discontinuity of pressure, can lead to the formation and collapse of cavitation bubble and produce an impactful jet stream. The jet stream may cause a localized mechanical/thermal damage to the structures that come on its path. We have considered two different bubble sizes (10 and 20 nm). We found that different gas densities inside the cavitation bubble largely change the intensity of the aftermath. We also found the peak temperature during the collapse is linked to the bubble size but unrelated with the peak pressure. Keywords Cavitation · Shock · Bubble dynamics · Molecular simulation
Introduction Cavitation bubble is defined as a bubble in liquid formed by pressures below the vapor pressure (pvp) of the liquid. Anytime when the pressure raises above pvp, the cavitation bubble shrinks, or collapses, and disappears [1–3]. Since the trapped water vapors (or any gas molecules) inside the cavitation bubble compress significantly as it shrinks, during bubble collapse the pressurized gas molecules rapidly expand and deliver a significant amount of kinetic energy to the nearby surrounding liquid. The dynamic event raises the temperature, velocity and pressure in the liquid near the collapsing center, and often leads to the formation of
* Ashfaq Adnan [email protected] 1
Mechanical and Aerospace Engineering, University of Texas at Arlington (UTA), Texas 76019, USA
Department of Neural and Behavioral Sciences, College of Medicine, Penn State University (PSU), Hershey, PA, USA
2
a secondary shock outward and causes damage to the surrounding [4–10]. To determine how a shock interacts with a cavitation bubble and the surrounding liquid, a time-ratio should be obtained by comparing (1) the time scale of complete collapsing of the cavitation bubble and (2) the time scale of shock front passing by the bubble. Through this comparison, one can determine whether a shock will lead to a symmetric or
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