Press Room - Using STAR-CD for kidney analysis

Using STAR-CD for kidney analysis

Baxter Healthcare is a global company which through its subsidiaries, provides critical therapies for people with life threatening illnesses. Baxter’s Bioscience, Medication Delivery, and Renal products and services are used to treat patients with some of the most challenging medical conditions such as cancer, hemophilia, immune deficiencies, infectious diseases, kidney disorders, and trauma.

We have been using the STAR-CD code at Baxter for the past seven years. The code has primarily been used to help engineers understand flow phenomena in various devices. The application of STAR-CD has included feasibility studies, design validations, parametric studies, device optimization and problem solving for various products. For one of the most recent projects, STAR-CD was used to assist in the design of a dialyzer, a device that helps patients with end-stage kidney failure.

The dialyzer is also known as an artificial kidney. It consists of thousands of porous, hollow fibers arranged in a bundle and housed in a cylindrical tube. During the hemodialysis procedure, blood from the patient is pumped into the interiors of the fibers at one end while the dialysate solution flows around the outside of the fibers. Urea and other waste products are transferred from the blood to the dialysate through the phenomena of diffusion and ultrafiltration. The clean blood exiting at the other end of the fiber bundle is then returned to the patient.

The efficiency of the mass transfer and the device performance depend, in part, on the evenness of the flow distribution. A significant cause of poor performance is “dialysate flow shunting” in which significant amounts of dialysate flows around the fiber bundle rather than between the fibers within the bundle.

The STAR-CD code was first used to investigate both blood and dialysate flow distributions for existing devices. The numerical results were then used to guide the design engineers towards improving device configurations for both the fiber bundles and the blood inlet and outlet headers. The new designs were analyzed numerically to confirm the uniformity of flow distribution. Finally, prototype models were built and flow tested. A flow visualization study was performed and it was found that the flow patterns were in accord qualitatively with the numerical predictions. The efficiency of the dialyzer was measured and found to be acceptable.

The design and testing time of the new dialyzer was substantially reduced compared to previous similar devices. In conclusion, this particular project proved STAR-CD to be a useful tool at Baxter.

Figs 1a (Blood flow) & 1b: California Polytechnic State University (Dialysate flow): STAR-CD predicted blood and dialysate pressure contours for a generic dialyzer

Fig 2: STAR-CD predictions for the velocity magnitude contours (top-view) for a dialyzer blood inlet header. Blood flow rate = 500 ml/min. (a) h=0.15”, (b) h=0.1”, (c) h=0.05”, (d) h=0.01”, h is the distance above the potting surface