DEVELOPMENT OF SQUEEZE FLOW IN MECHANICAL HEART VALVE-A PARTICLE IMAGE VELOCIMETRY INVESTIGATION

Abstract

Background and Objectives: MHVcavitation has been widely investigated by capturing the formation and collapse of vaporous bubbles caused by sharp pressure drop. This momentarily pressure drop occurs when the valve occluder approaches the orifice wall. With the reducing flow channel between the occluder and the wall, fluid in-between tends to be squeezed out causing a high-speed flow. Limited experimental work has been into this squeeze flow phenomenon, which is likely to be the origin of cavitation. Methods: The experiment was carried out in pulsatile mock loop simulating physiological flow conditions. PIV was applied and an actual size transparent MHVmodel was used. To observe flow within a narrowing flow channel in the region of 0.1 to 0.5 mm, a microscope was incorporated into the PIV system.The system was time triggered by a mechanism to capture images when the occluder nearly closed. Results: Series of images of flow within the narrowing flow channel were captured. As the gap between the tip of the valve occluder and orifice wall becomes narrower, evidence of high speed jet flow becomes more apparent. When the gap narrowed down to around 0.1 mm, flow velocity of up to 3 m/s was noted with a corresponding high vorticity of 3800 is near the leading edge tip of the occluder. The sudden increase in high-speed jet flow is expected to be accompanied by a local pressure reduction. Conclusion: Squeeze flow arising from the closing of the occluder is evident from experimental findings. High jet flow can be detrimental due to the potential cavitation and momentarily high shear stress.