M.Sc Thesis


M.Sc StudentHadar Raz
SubjectNumerical Modeling of a Squeeze Film Levitated Micro-Valve
DepartmentDepartment of Mechanical Engineering
Supervisor Full Professors Bucher Izhak
Full Thesis textFull thesis text - English Version


Abstract

Micro-Valves are being used today as very accurate, fast responding and affordable means to control compressible flow flux, even at extremely small flow rates, for demanding applications such as drug delivery and lab-on-chip. When the valve is in closed state and high pressure gradients are present, a small undesirable leak flow can develop across the valve. A new, Micro Electro Mechanical Structure (MEMS) dynamic system is proposed, which inherently minimizes the leak flow. The dynamics of this system play several roles; Vertical vibrations are created in order to reduce the friction between the moving part (rotor, shutter) and the static base (stator containing a hole), and horizontal vibrations control the flow-rate. The vertical vibrations create a squeeze film effect between the base and the shutter such that friction is eliminated and thus the flow-rate can be accurately controlled without hysteresis. By controlling the horizontal movement of the shutter, the amount of gas or fluid that passes between the shutter and the opening (hole) can be controlled. At rest, the valve covers the hole and is designed in such a way that the pressure gradient is directly applied on the valve, enhancing the closure force. We start by studying analytically the squeeze-film phenomena, and then numerically solving the flow regime, assuming the structure is free-free. Next we couple the compressible fluid to the elastic structure (the valve) using a simple and innovative coupling procedure, and solve the two fields numerically, using two dimensional finite difference scheme for the fluid and three dimensional finite elements for the structure. When the system is excited, energy transfer occurs between the squeeze-film and the elastic modes of the structure, thus reducing the film’s ability to carry load. We show that the squeeze-film is able to lift the valve, and that the application in MEMS is possible. We then study an elastic valve on elastic supports, and show the complex dynamics involved.