Comparison of different hollow fibre haemodialysis module configurations by a CFD multiscale approach

Abstract

Objectives The study aims to predict 3-D flow and solute concentrations fields both for blood and dialysate and overall performance parameters (such as dialysate pressure drop and clearance) for different hollow-fibre haemodialysis modules. Methods A multiscale approach was used. At small (unit cell)-scale, dialysate flow and mass transfer around straight cylindrical fibres arranged in regular lattices were simulated. At module-scale, hydraulic permeabilities and mass transfer coefficients derived from small-scale simulations were used to define two different porous media representative of blood and dialysate, sharing the same volume and exchanging solute. Simulations involved different module configurations, sharing the same membrane area but differing in geometry and inlet-outlet arrangement. Literature values of solute diffusive permeability for commercial PES membranes were used. Results and discussions For given blood and dialysate flow rates (300 and 450 mL/min, respectively), different module configurations yielded very different dialysate-side flow patterns and pressure drops, moderately different Sherwood numbers but similar values of the clearance. For urea, this ranged between 209 and 235 mL/min in most configurations, indicating that almost all the membrane area was active in most configurations. For a typical commercial geometry, the predicted clearances at different blood flow rates exhibited a satisfactory agreement with experimental measurements (maximum discrepancy ˂2%). Conclusions Using commercial membranes properties, dialysate-side mass transfer resistance is small compared with blood-side and membrane contributions. As membranes with higher diffusive permeability will be developed, the influence of dialysate-side resistance will become larger and an accurate prediction of the dialysate flow field will become more important.