MEASUREMENT OF SQUEEZE FLOW FIELD IN A BILEAFLET MECHANICAL HEART VALVE MODEL

Abstract

The squeeze flow (SQ) phenomenon occurs in the micronsized gap between the housing and the leaflet tip microsecs before the valve closing. Measurement on such micro-scale transient flow field with moving wall is extremely difficult, however it is of great importance in mechanical heart valve (MHV) cavitation potential. Applying microscope-aided Digital Particle Image Velocimetry (DPIV) technique, the SQ is measured in a 2D MHV model. In a 3:1 enlarged MHV transparent model, the MHV leaflet movement was driven by a physiological pressure based on the similarity laws. A microscope-aided DPIV was used to map the SQ flow field in the gap space with 50X magnification. A local seeding system was used to ensure appropriate tracer density. An optical triggering system with adjustable time delays was provided to synchronize the strobe with the leaflet rotating as it contacts the housing wall. Aqueous glycerin (37% by weight), seeded with 10 μm silver-coated hollow glass, was used as working fluid. At tip velocity of 0.3m/s, the observed maximum SQ velocity at the up-stream exit was two times high than that of the downstream exit. The transient SQ field was greatly affected by leaflet closing velocity and the geometry of the tip. The experimental results are used for CFD validation.