Session: 01-02: Micro/Nanofluidics and Lab-On-A-Chip

Paper Number: 130919

130919 - A New Strategy for Numerical Analysis of Non-Harmonic Acoustic Streaming 

Abstract: 

Acoustic streaming stands out as a potent acoustofluidic technique that has revolutionized the way we manipulate fluids and particles. This manipulation is achieved without direct contact, which is particularly beneficial in applications where contamination and sterility are concerns. Traditional acoustic streaming methods have depended on harmonic pressure waves. These waves are generated by the mechanical vibration of piezoelectric transducers. Yet, the inherent physical nature of these transducers does not lend itself well to the scale required by cutting-edge microfluidics applications. The bulky nature of the transducers and their mechanical vibration requirements present a significant challenge when we aim to miniaturize devices for advanced applications.

However, the landscape of microfluidics has been significantly altered with the advent of laser streaming. This new technique leverages the laser-induced photo-thermo-acoustic effect to induce microscale flow entirely through light-driven processes. With laser streaming, the need for mechanical transducers is completely obviated, allowing for a much greater degree of miniaturization and integration into microfluidic devices. This represents a paradigm shift in the field, enabling more complex and varied applications, from medical diagnostics to materials synthesis.

Despite its considerable potential, laser streaming introduces complex new phenomena that challenge our fundamental understanding. The interaction of the fluid medium with the non-harmonic acoustic waves generated by pulsed lasers is intricate and not well understood. This complexity arises because the prevailing analysis used for harmonic acoustic streaming is no longer applicable. The harmonic perturbation analysis relies on the concept of time-averaged second-order velocity fields, but this concept breaks down in the presence of non-harmonic fields. Such fields cannot be characterized by time averages of instantaneous quantities, rendering traditional analytical methods inadequate.

With the inapplicability of these methods, direct numerical simulation (DNS) has become the only tool capable of resolving the millisecond-scale flow field driven by the nanosecond laser pulses. Although DNS offers a detailed resolution, it is computationally expensive and often requires significant computational power, which can be a limitation for many research facilities.

The current work introduces a novel hybrid approach that synergistically combines perturbation theory and DNS, aiming to model laser streaming flows more efficiently. Our strategy unfolds in a sequential three-step process. Initially, the laser's non-harmonic impact on the fluid's boundary is analyzed using Fourier series expansion. This decomposition process allows the complex motion to be viewed as a spectrum of independent harmonic waves. With these constituent frequencies defined, we then apply perturbation methods to derive first-order solutions for each harmonic component. This process also yields the time-averaged streaming force term for each frequency. Lastly, we sum the effects of these forces across the spectrum to input as a singular force into the second-order momentum equations. This summation is vital for constructing the steady-state laser streaming field.

Validating this model through comparison with experimental data, we find strong congruence. Such congruence not only reaffirms the viability of the new approach but also underscores its potential utility in understanding and exploring a range of non-conventional acoustic streaming phenomena. This work, therefore, is a significant step forward, providing a robust framework for both interpreting the complex physics of laser streaming and potentially broadening the application of acoustofluidic principles in microscale devices.

Presenting Author: Dong Liu University of Houston

Presenting Author Biography: Dr. Dong Liu is a Professor and the Director of Graduate Studies in the Department of Mechanical Engineering at the University of Houston (UH). He received his B.S. and M.S. from Tsinghua University, China, and his Ph.D. from Purdue University. He joined UH in 2007. He is currently the Associate Editor of ASME Journal of Thermal Science and Engineering Applications and previously served as the Chair of ASME K-9 Committee on Nanoscale Thermal Transport Processes. His research interests include micro/nanofluidics, phase change heat transfer, boiling and two-phase flow and light-matter interactions.

Authors:

Dong Liu University of Houston
Runjia Li University of Houston
Jiming Bao University of Houston