Numerical Analysis of Blood Flow in the Clearance Regions of a Continuous Flow Artificial Heart Pump *Jay Anderson, *Houston G. Wood, *Paul E. Allaire, and †Don B. Olsen *Mechanical & Aerospace Engineering, University of Virginia, Charlottesville, Virginia; and †Artificial Heart Laboratory, University of Utah, Salt Lake City, Utah, U.S.A. Abstract: The CFVAD3 is the third prototype of a con- tinuous flow ventricular assist device being developed for implantation in humans. The pump consists of a fully shrouded 4-blade impeller supported by magnetic bear- ings. On either side of this suspended rotating impeller is a small clearance region through which the blood flows. The spacing and geometry of these clearance regions are very important to the successful operation of this blood pump. Computational fluid dynamics (CFD) solutions for this flow were obtained using TascFlow, a software pack- age available from AEA Technology, U.K. Flow in these clearance regions was studied parametrically by varying the size of the clearance, the blood flow rate into the pump, and the rotational speed of the pump. The numeri- cal solutions yield the direction and magnitude of the flow and the dynamic pressure. Experimentally measured pump flow rates are compared to the numerical study. The results of the study provide guidance for improving pump efficiency. It is determined that current clearances can be significantly reduced to improve pump efficiency without negative impacts. Key Words: Computational fluid dy- namics—Heart pump—Hemolysis—Thrombosis. Due to the short supply of donor hearts for trans- plants, the need and demand for artificial heart pumps has been well documented (1). The technol- ogy for artificial heart pumps has evolved from pul- satile pumps that mimic the natural beating of the heart to continuous flow rotary blood pumps. These rotary blood pumps fall into 2 categories: centrifugal and axial. Each of these types has advantages and disadvantages. The axial flow pumps tend to be smaller in size, but experience with these pumps has shown a tendency to thrombi formation around the bearings that are lubricated by the blood (2–4). The centrifugal pumps are somewhat larger but more en- ergy efficient than axial pumps. However, centrifu- gal pumps are now being developed that are small enough to be implanted into small humans. Conven- tional centrifugal pumps also rely on mechanical bearings lubricated by blood (5) and have a similar propensity to produce thrombi as the axial pumps. The focus of the present work deals with a cen- trifugal pump that utilizes magnetic bearings that significantly reduce the likelihood of producing thrombi. The centrifugal pump under consideration is the CF3, the third version of a series of continuous flow left ventricular assist devices. Centrifugal flow pumps have a long history with excellent books available that provide guidance for the design of pumps for specific purposes (6,7). However, the very small dimensions required for an implantable pump are outside the domain of experience provided in these books. This shortage of design information can be filled using the methodologies of fluid dynamics such as computational fluid dynamics (CFD), experi- mental measurements of the flow field, and flow vi- sualization. All of these design sources were used to develop the CF3 and are being used to develop the next ver- sion, CF4, which will be significantly smaller. The overall dimensions of the CF3 are a height of 41.6 mm (1.637 inches) and a diameter of 118.7 mm (4.67 inches) The design goals for the CF4 are a height of 36.0 mm(1.4 inches) and a diameter of 66.0 mm (2.6 inches). Received December 1999. Presented in part at the 7th Congress of the International So- ciety for Rotary Blood Pumps, held August 26–27, 1999, in Tokyo, Japan. Address correspondence and reprint requests to Dr. Houston G. Wood, Mechanical & Aerospace Engineering, University of Virginia, Thornton Hall, Charlottesville, VA 22903, U.S.A. E-mail: hwood@virginia.edu Artificial Organs 24(6):492–500, Blackwell Science, Inc. © 2000 International Society for Artificial Organs 492