| Blood pumps suitable for use as a heart assist or replacement devices have significant clinical applications. Rotary blood pumps frequently use volutes as a discharge system, because they can result in a significant pressure recovery. However, a volute can also cause radial forces and disturb flow patterns off the design operating point. Unfortunately, an effective volute analysis method for blood pump applications has not yet been demonstrated. Moreover, no literature is available on the effects of volute sizing parameters upon the volute performance in blood pump applications.; In this work, a series of volute housings were designed using Pro/Engineer and prototyped using stereolithography. An experimental loop was set up to measure the volute pressure distribution, with which the volute efficiency and impeller radial force were evaluated.; Important volute sizing parameters were identified and investigated. Results showed that the most critical parameters for volute efficiency are volute throat area and volute outlet to inlet area ratio, secondary to which is the Radius to Centroid. It appears that volute cross-sectional shape and area variance are of little significance to volute efficiency. The measured impeller radial force is maximum at shut off region and decreases with increasing flow rate to a non-zero minimum at the best efficiency point. Radial force of a blood pump with a volute casing is a function of rotational speed, impeller radius; impeller overall width, Radius to Centroid and flow capacity. Impeller radial force seems to be independent of volute cross-sectional shape and area variance.; A commercial Computational Fluid Dynamics (CFD) code-CFX was employed to explore some volute fluid mechanics that is unobtainable experimentally. A flow visualization technique based on tracer method was used to obtain flow pattern data in volutes, and aided in validating the CFD work. Both flow visualization and CFD simulation showed that flow patterns are well behaved for properly sized volutes, away from extremely high or low flow. At or below design flow, the conventional assumption is valid that impeller channel flow is uniformly distributed. However, CFD simulation result seems to favor the non-uniform impeller channel flow distribution at very high flowrate.; As a result of this study, semi-empirical equations to better predict volute efficiency and impeller radial force were developed. Some guidelines were proposed to design high performance blood pump volutes that minimize pump size and maximize efficiency without severe penalties with respect to the bearing loads, blood cell damage or risk of thrombosis. |
