Authors: C. Aubert, S. Colin and R. Caen
Affilation: Laboratoire de Genie Mecanique de Toulouse, France
Pages: 486 - 491
Keywords: microfluidics, slip flow, frequency behavior, micropump, fluidic diode
The aim of the paper is to contribute to the modeling of unsteady slip flows in rectangular microchannels with slowly varying cross-sections. A model is proposed for a microdiffuser submitted to sinusoidal pressure fluctuations at one of its ends. The role of the geometrical parameters is analyzed and the influence of slip at the walls is underlined. It is notably shown that the band past of the microdiffuser is underestimated, when slip at the walls is not taken into account. Then the model is used to test the diode effect of such a diffuser placed in a microchannel, submitted to sinusoidal pressure fluctuations at its inlet. Two layouts (A and B) are considered: the direction of the diffuser is such that section increases from inlet to outlet in layout A, and decreases in layout B. A gain is defined as the ratio of the outlet over inlet fluctuating pressure amplitudes. To characterize the transmission of pressure fluctuations, an efficiency E of tbe diode is introduced. This efficiency (defined as the ratio of the gain in layout A over tbe gain in layout B) is studied, as a function of the frequency. With a microdiffuser, E appears to be less than unity below a critical frequency. This denotes a diode effect reversed compared with the case of a diffuser with millimetric dimensions, for which E is less than unity beyond a critical frequency. An analysis of these results is presented. with the purpose of better understanding the behavior of micropumps which use diffuser/nozzle-type microdiodes, and can present a peak of the mean flow at a precise frequency (typically between 1 kHz and 10 kHz), sometimes followed (for higher frequencies) by an inversion of the mean flow direction. It is suggested that the direction of the mean flow, as well as this typical frequency, may be predicted by the previous model, assuming that the mean flow results from a change in the local mean pressure. This change could be due to the increase of pressure fluctuations, notably through non-linear convective terms in the momentum equation.
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