High frequency oscillatory flow in micro channels

This paper deals with computational and experimental studies on the oscillatory flow at high frequencies up to 100 Hz performed with the Oscillating Drop and Bubble Analyzer (ODBA) setup based on the capillary pressure technique. The CFD results are validated considering pressure amplitude experimental data. The simulated results of phase shift between the generated oscillatory flow and the consequent pressure amplitudes show also good agreement with the experimental data. In absence of any compressibility and viscoelasticity effects and assumptions, a complex velocity field during oscillation is the main reason for the observation of a phase shift. The results of velocity profiles at the moment of maximum instant flow rate illustrate a transient of the regular parabolic laminar flow inside the tip at low frequencies to a complex flow profile at intermediate and high frequencies. For the moment of maximum pressure amplitude a complex shape with triple maximum/minimum velocity regions is observed. The evolution of the velocity profile shape depends significantly on the frequency and capillary tip size, however, not by the volume amplitude. The results are in good correlation with the concept of the hydrodynamic relaxation time, however, the presented approach reveals more details. The creation of a double parabolic-like flow inside the tip, which can be defined as fluid flow through much smaller tubes or channels is the main reason for observing a maximum pressure loss with a certain phase shift to the maximum instant liquid flow rate.