The influence of the dialysate flow rate on hollow fiber hemodialyzer performance

The clearance characteristics of two sizes of hemodialyzers (0.9 m2 and 1.5 m2) from the same range of products have been studied over the dialysate flow range of 500-3,000 ml/min to establish the device's overall mass transfer resistance characteristics. The results obtained demonstrate a difference in the overall mass transfer resistance which is most marked at the commonly used dialysate flow rate of 500 ml/min. This difference suggests that the increase in size results in the introduction of flow imperfections which reduces the benefit that might be gained by the use of a larger surface area. Results established indicate a reduction in the overall mass transfer resistance with an increasing dialysate flow rate. This reduction is attributed to the presence of turbulence in the dialysate pathway at higher flow rates. The presence of such turbulence was confirmed by visual inspection of the dialyzer after the completion of the study when it was noted that the original well-ordered configuration present in a new dialyzer had been substantially disturbed. Correlation of the dialysate flow rate with overall mass transfer resistance by the use of a Wilson plots indicates a nonlinear relationship. This nonlinearity is attributed to a nonfully developed turbulent flow profile in the dialysate pathway.