Churn K. Poh

Effect of Flow Baffles on the Dialysate Flow Distribution of Hollow-Fiber Hemodialyzers: A Nonintrusive Experimental Study Using MRI

We used an innovative, nonintrusive MRI technique called the two-dimensional (2D) Phase-Contrast (2DPC) velocity-imaging technique to investigate the effect of flow baffles on the dialysate-side flow distribution in two different hollow-fiber hemodialyzers (A and B); each with flow rates between 200 and 1000 mL/min (3.33 x 10(-6) and 1.67 x 10(-5) m3/s). Our experimental results show that (1) the dialysate-side flow distribution was nonuniform with channeling flow occurred at the peripheral cross section of these hollow-fiber hemodialyzers, and (2) the existing designs of flow baffles failed to promote uniform dialysate-side flow distribution for all flow rates studies.

The use of magnetic resonance imaging to measure the local ultrafiltration rate in hemodialyzers

Abstract Hemodialyzers used for renal dialysis rely upon ultrafiltration to eliminate middle molecular-weight uremic solutes. It is valuable to measure the ultrafiltration rate locally to better understand dialyzer operation and to ensure there is no backfiltration of potential pyrogens into the patient’s blood stream. We used a magnetic resonance flow imaging method to measure the local variation of the ultrafiltration rate along the length of a SYNTRA·160 hemodialyzer. The technique uses magnetic resonance fourier velocity imaging (MRFVI) to determine the percentage of flow in different velocity ranges. From these velocity profiles we estimate the maximum flow velocity in the lumen of the dialyzer fibers. Assuming laminar flow with a parabolic flow profile we estimated the variation in the total volume flow rate at each location where images are made. The local ultrafiltration rate declined uniformly over the length of the dialyzer, and the total rate is in agreement with independent measurements of ultrafiltration rate using pure water.

A Numerical and Experimental Study of Mass Transfer in the Artificial Kidney

To develop a more efficient and optimal artificial kidney, many experimental approaches have been used to study mass transfer inside, outside, and cross hollow fiber membranes with different kinds of membranes, solutes, and flow rates as parameters. However, these experimental approaches are expensive and time consuming. Numerical calculation and computer simulation is an effective way to study mass transfer in the artificial kidney, which can save substantial time and reduce experimental cost. This paper presents a new model to simulate mass transfer in artificial kidney by coupling together shell-side, lumen-side, and transmembrane flows. Darcys equations were employed to simulate shell-side flow, Navier-Stokes equations were employed to simulate lumen-side flow, and Kedem-Katchalsky equations were used to compute transmembrane flow. Numerical results agreed well with experimental results within 10% error. Numerical results showed the nonuniform distribution of flow and solute concentration in shell-side flow due to the entry/exit effect and Darcy permeability. In the shell side, the axial velocity in the periphery is higher than that in the center. This numerical model presented a clear insight view of mass transfer in an artificial kidney and may be used to help design an optimal artificial kidney and its operation conditions to improve hemodialysis.

Nonintrusive characterization of fluid transport phenomena in hollow-fiber membrane modules using MRI: An innovative experimental approach

ABSTRACT A nonintrusive experimental tool is useful for a better physical understanding of fluid transport phenomena in hollow-fiber membrane modules and as test cases for validating, improving, or developing numerical models. In this chapter, we introduced two innovative, nonintrusive flow-imaging techniques using magnetic resonance imaging (MRI) for characterizing fluid transport phenomena in hollow-fiber membrane modules. These flow-imaging techniques are called the 2-D Phase-Contrast (2DPC) and 2-D Fourier-Transform (2DFT) techniques. The principles, validation, advantages, limitations, and some examples of experimental results are presented. We used the 2DPC technique to study the spatial flow distribution and the 2DFT technique to characterize the flow profile and quantify the local ultrafiltration rates in hollow-fiber artificial kidneys (also known as hemodialyzers). These flow-imaging techniques are equally applicable to other hollow-fiber membrane modules.