Theoretical estimation of the temperature and pressure within collapsing acoustical bubbles

Abstract

Formation of highly reactive species such as OH, H, HO2 and H2O2 due to transient collapse of cavitation bubbles is the primary mechanism of sonochemical reaction. The crucial parameters influencing the formation of radicals are the temperature and pressure achieved in the bubble during the strong collapse. Experimental determinations estimated a temperature of about 5000 K and pressure of several hundreds of MPa within the collapsing bubble. In this theoretical investigation, computer simulations of chemical reactions occurring in an O2-bubble oscillating in water irradiated by an ultrasonic wave have been performed for diverse combinations of various parameters such as ultrasound frequency (20-1000 kHz), acoustic amplitude (up to 0.3 MPa), static pressure (0.03-0.3 MPa) and liquid temperature (283-333 K). The aim of this series of computations is to correlate the production of OH radicals to the temperature and pressure achieved in the bubble during the strong collapse. The employed model combines the dynamic of bubble collapse in acoustical field with the chemical kinetics of single bubble. The results of the numerical simulations revealed that the main oxidant created in an O2 bubble is OH radical. The computer simulations clearly showed the existence of an optimum bubble temperature of about 5200±200 K and pressure of about 250±20 MPa. The predicted value of the bubble temperature for the production of OH radicals is in excellent agreement with that furnished by the experiments. The existence of an optimum bubble temperature and pressure in collapsing bubbles results from the competitions between the reactions of production and those of consumption of OH radicals at high temperatures.

Spiral computed tomography evaluation of rabbit VX2 hepatic tumors treated with 20 kHz ultrasound and microbubbles

“…Ultimately, the energy carried by cavitation bubbles is released when the MBs collapse and sonication cavitation occurs and during the cavitation, the MBs undergo volumetric oscillations, thereby changing the local mechanical condition of the tissue (40). When MBs collapse, they can create shockwaves, increasing the local pressure by 100 atm and the local temperature by several thousands of degrees (41). Shockwaves can cause substantial cell damage and possible cell lysis nearby (42).…”

“…The formation of highly reactive species, including OH, H, HO 2 and H 2 O 2 , due to the transient collapse of cavitation bubbles is the primary mechanism of the sonochemical reaction (41), which can also damage the vessel wall.…”

Pengendalian Suhu Ultrasonikasi Pada Pelapisan Nanopartikel Magnet (Fe3O4) Dengan Kitosan

“…Pada proses penumbuhan-pemecahan gelembung tahap berikutnya, energi tinggi yang dihasilkan dapat digunakan untuk pembentukan radikal aktif baik pada kitosan maupun nanopartikel magnetik yang telah terlepas dari ikatan hidrogen dengan molekul air, dan memungkinkan terjadinya ikatan antara kedua bahan (Merouani et al 2014). Gambaran secara skematik dari proses reaksi yang terjadi ditampilkan pada Gambar 3.…”

“…Kenaikan viskositas pada larutan kitosan akan menyulitkan terbentuknya gelembung awal dan juga pertumbuhan gelembung (Jenkins dan Kiely 2012). Ukuran gelembung menjadi lebih kecil sehingga energi yang terlepas pada proses pemecahan juga rendah (Merouani et al 2014). Penjalaran gelembung juga akan lebih sulit pada medium dengan viskositas tinggi sehingga homogenisasi reaksi lebih lama tercapai.…”

Sonodynamic antimicrobial chemotherapy: First steps towards a sound approach for microbe inactivation

“…It has been estimated that on a nanosecond time scale the collapse of the microbubble can induce spikes of temperatures reaching 5000 K and pressures of 250 MPa. 36 In these "hot spots" confined to the vicinity of the microbubbles, the high liquid shear-forces, the shock waves, and the localized heating, promote sonochemical reactions (sonolysis), and light emission (sonoluminescence). 37 Two hypotheses were formulated to explain ROS generation from acoustic cavitation; one of them suggests that the high energy released by the collapsing microbubble promotes the sonolysis of water molecules and/or of the sensitiser molecules: the radicals formed can then react with oxygen, triggering the production of reactive oxygen species.…”