Identical Dependence of Dialysate-side Mass Transfer Coefficient on Reynolds Number Using Dimensionless Correlation Based on the Mass Transfer Model in Newly Developed Dialyzers and a Downsized Dialyzer

Makoto Fukuda , Koki Namekawa , Kiyotaka Sakai
Vol. 5 (2016) p. 118-123

The dialysis fluid flow and solute removal performance of newly developed dialyzers and a downsized dialyzer were evaluated using a dimensionless correlation equation related to the mass transfer coefficient of the dialysate-side film in a mass transfer model, which was used in quantitative analyses in our previous study. The solute removal performance is greatly dependent on the dialysis fluid flow for low molecular weight solutes. Hence, the recently developed dialyzers are based on new design concepts incorporating jackets or hollow fibers that provide an evenly distributed flow. The new dialyzers tested were APS-15SA, PES-15Sαeco, PN-140S, and NV-15U. APS-15DSplus was used as a downsized version of the APS-15SA. The dialysate-side equivalent diameter de is smaller in the APS-15DSplus than in the APS-15SA, while the other design specifications are identical for these two devices. We measured vitamin B12 clearance with the dialyzers operated at a blood-side flow rate QB = 200 mL/min, dialysate-side flow rates QD = 300–700 mL/min, and a net filtration rate QF = 0 mL/min. We then calculated the overall mass transfer coefficient. Using this value, we derived the dimensionless correlation of the Sherwood number (Sh), which includes the dialysate-side film mass transfer coefficient (kD) and Reynolds number (ReD). The exponent of ReD was approximately 0.5 for all the dialyzers. The newly developed dialyzers have various design features for improving dialysis fluid flow. Unlike previous devices, the various new designs result in a convergence of performance. A comparison of APS-15SA and the downsized APS-15DSplus showed similar dependence of kD on ReD. This finding is novel and is attributed to the similarity in the relationship between dialysate-side fluid flow and dialysate-side film mass transfer in the two devices. In both dialyzers, the jacket has a full baffle and short taper structure, and the wave design of the hollow fiber membranes is identical. However, de was smaller in APS-15DSplus. Thus, analogous design concept employing the dimensionless correlation can be adopted for downsizing a device.