The dialysis uid ow and solute removal performance of newly developed dialyzers and a downsized dialyzer were evaluated using a dimensionless correlation equation related to the mass transfer coef cient of the dialysate-side lm 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 uid ow for low molecular weight solutes. Hence, the recently developed dialyzers are based on new design concepts

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... ncorporating jackets or hollow bers that provide an evenly distributed ow. 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 d e is smaller in the APS-15DSplus than in the APS-15SA, while the other design speci cations are identical for these two devices. We measured vitamin B 12 clearance with the dialyzers operated at a blood-side ow rate Q B = 200 mL/min, dialysate-side ow rates Q D = 300-700 mL/min, and a net ltration rate Q F = 0 mL/min. We then calculated the overall mass transfer coef cient. Using this value, we derived the dimensionless correlation of the Sherwood number (Sh), which includes the dialysate-side lm mass transfer coef cient (k D ) and Reynolds number (Re D ). The exponent of Re D was approximately 0.5 for all the dialyzers. The newly developed dialyzers have various design features for improving dialysis uid ow. 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 k D on Re D . This nding is novel and is attributed to the similarity in the relationship between dialysate-side uid ow and dialysate-side lm mass transfer in the two devices. In both dialyzers, the jacket has a full baf e and short taper structure, and the wave design of the hollow ber membranes is identical. However, d e was smaller in APS-15DSplus. Thus, analogous design concept employing the dimensionless correlation can be adopted for downsizing a device.