Nonlinear behavior of a microbubble under ultrasound was investigated with consideration of heat transfer inside bubble and through the bubble wall. The polytropic relation which has been used for the process of volume change of ideal gases cannot properly treat the heat transfer involving the oscillating bubble under ultrasound. In this study, the heat transfer related to the motion of the bubble under ultrasound, which is affected by heat transfer across the bubble wall crucially was investigated by a set of solutions of the Navier-Stokes equations for the gas inside the bubble and an analytical treatment of the Navier-Stokes equations for the liquid adjacent to the bubble wall. The entropy generation due to finite heat transfer, which induces the lost work during bubble evolution, reduces the collapsing process, and affects the nonlinear behavior of bubble considerably.

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