Mass Transfer Characteristics of Haemofiltration Modules-Experiments and Modeling.

Alexandra Moschona,Anastasios J Karabelas,Margaritis Kostoglou

doi:10.3390/membranes12010062

Alexandra Moschona, Anastasios J Karabelas + Show 1 more

Open Access

https://doi.org/10.3390/membranes12010062

Copy DOI

Abstract

Reliable mathematical models are important tools for design/optimization of haemo-filtration modules. For a specific module, such a model requires knowledge of fluid- mechanical and mass transfer parameters, which have to be determined through experimental data representative of the usual countercurrent operation. Attempting to determine all these parameters, through measured/external flow-rates and pressures, combined with the inherent inaccuracies of pressure measurements, creates an ill-posed problem (as recently shown). The novel systematic methodology followed herein, demonstrated for Newtonian fluids, involves specially designed experiments, allowing first the independent reliable determination of fluid-mechanical parameters. In this paper, the method is further developed, to determine the complete mass transfer module-characteristics; i.e., the mass transfer problem is modelled/solved, employing the already fully-described flow field. Furthermore, the model is validated using new/detailed experimental data on concentration profiles of a typical solute (urea) in counter-current flow. A single intrinsic-parameter value (i.e., the unknown effective solute-diffusivity in the membrane) satisfactorily fits all data. Significant insights are also obtained regarding the relative contributions of convective and diffusive mass-transfer. This study completes the method for reliable module simulation in Newtonian-liquid flow and provides the basis for extension to plasma/blood haemofiltration, where account should be also taken of oncotic-pressure and membrane-fouling effects.

Highlights

IntroductionHaemofiltration in its various modes (i.e., haemodialysis, haemodiafiltration, expanded haemodialysis, etc.), employing hollow fiber (HF) ultrafiltration membrane modules, is a complicated process, which involves mass transfer of relatively small toxic molecules through the membranes, from a non-Newtonian fluid of significant oncotic pressure (i.e., blood) to a counter-currently flowing Newtonian liquid (dialysate)
Haemofiltration in its various modes, employing hollow fiber (HF) ultrafiltration membrane modules, is a complicated process, which involves mass transfer of relatively small toxic molecules through the membranes, from a non-Newtonian fluid of significant oncotic pressure to a counter-currently flowing Newtonian liquid
Despite the very significant progress made in the field of haemofiltration, during the past two decades, on membrane material properties [3] and introduction of novel operating protocols (e.g., [4,5]), serious gaps exist in our knowledge of the HF-module performance as a function of the imposed flow rates at bloodand dialysate-side [6]

Summary

Introduction

Haemofiltration in its various modes (i.e., haemodialysis, haemodiafiltration, expanded haemodialysis, etc.), employing hollow fiber (HF) ultrafiltration membrane modules, is a complicated process, which involves mass transfer of relatively small toxic molecules through the membranes, from a non-Newtonian fluid of significant oncotic pressure (i.e., blood) to a counter-currently flowing Newtonian liquid (dialysate). This process is characterized by significant spatial variability of all process parameters across the module, since the composition of both fluids tends to vary because of (a) liquid trans-membrane flow and (b) diffusive and convective type of species transfer through the HF membranes. Comprehensive and reliable fluid-mechanical modeling/simulation of this flow-field, based on first principles, is almost impossible at present

Results

Discussion

Conclusion