Proceedings of PSFVIP-4 June 3-5, 2003, Chamonix, France. F4076 Copyright 2003 by PSFVIP-4 1 Investigations of micro jet flows in Micro Electro-Mechanical Systems (MEMS) J.-R. Frutos 1 , Y. Bailly 2,3 , L. Girardot 2 , M. De Labachelerie 1,3 , F. Guermeur 2 1 Laboratoire de Physique et Métrologie des Oscillateurs (LPMO), Besançon, France. 2 Centre de Recherche sur les Ecoulements Surfaces et Transferts (CREST), UMR CNRS 6000, Belfort, France. 3 Institut des Microtechniques Franche-Comté, Besançon, France. KEYWORDS : Main subject(s): Micro fluidic, Fluid: aerodynamics, Visualization method(s): Laser Doppler Velocimetry, Hot Wire Anemometry Other keywords: Microsystems,MEMS. ABSTRACT : Several micro actuators for flow control were realized at IMFC/LPMO but fluidic performances (flow rate, exit air jet velocity) were weaker than expected [1, 2]. Therefore, we propose to focus our interest in estimating pressure discrepancies in micro fluidic systems (air supply pipes, cavities and exit orifices) and here we particularly focused on pressure losses through exit orifices considering 2 different section shapes : rectangular micro slots (section s= 50 x 1000 μm 2 , thickness of the strip t= 20 μm) and axis symmetrical micro holes (diameter d= 350 μm and 500 μm, t= 500 μm) for an inlet pressure range from 0 to 300 mbar. Speed values obtained for continuous jets with sub millimetric hot wire anemometer and with LDV show differences with classical fluid models and computational fluid dynamics (CFD) specially for the shortest distances downstream the exit orifice. 1. Introduction During recent years, micro fluidic systems have been an area of increasing interest in the field of Micro Electro-Mechanical Systems (MEMS). Potential applications are very numerous and cover many activities including medicine (micro-analysis), pharmaceutics (drugs delivery) to automobile or aeronautic industry (air flow control for instance)[3,4,5]. In this latter domain, some research try to develop micro actuators able to locally disturb the boundary layer by introducing pulsed micro jet. Schematically, such devices are composed of a cavity and an orifice closed by a micro-actuator alternately (fig. 1).