Search results for " Porous media."
showing 7 items of 17 documents
A parametric CFD study of hollow fiber membrane modules for hemodialysis
2022
Hemodialysis is a membrane-based process in which solute transport from the patient’s blood to a rinsing solution (dialysate) occurs by diffusion and ultrafiltration. Devices used in hemodialysis are cylindrical modules filled with hollow-fiber membranes which allow the removal of toxic substances and metabolic wastes from the blood, but inhibit the passage of proteins and cells to the dialysate. A predictive porous-media model of hemodialysis was developed and validated against experimental data. Unlike previous literature models, it requires only basic membrane properties (hydraulic and diffusive permeabilities and reflection coefficients) instead of relying on empirically adjusted global…
A porous media CFD model for the simulation of hemodialysis in hollow fiber membrane modules
2022
A computational model was developed to predict the performance of hollow fiber membrane hemodialyzers. Blood and dialysate were modelled as fluids flowing through two interpenetrating porous media. Concerning hydrodynamics, experimental Darcy permeabilities measured for commercial hemodialyzers were used for both compartments. Concerning mass transfer, both diffusion and ultrafiltration were simulated. On the blood side theoretical Sherwood numbers for parallel flow in pipes were adopted. On the dialysate side Sherwood numbers were derived from CFD predictions for regular hexagonal fiber bundles. Solute concentrations on the two sides were alternatively computed in an iterative way and were…
Performance Comparison of Alternative Hollow-Fiber Modules for Hemodialysis by Means of a CFD-Based Model
2022
Commercial hemodialyzers are hollow-fiber cylindrical modules with dimensions and inlet–outlet configurations dictated mostly by practice. However, alternative configurations are possible, and one may ask how they would behave in terms of performance. In principle, it would be possible to depart from the standard counter-flow design, while still keeping high clearance values, thanks to the increase in the shell-side Sherwood number (Sh) due to the cross-flow. To elucidate these aspects, a previously developed computational model was used in which blood and dialysate are treated as flowing through two interpenetrating porous media. Measured Darcy permeabilities and mass transfer coefficients…
Comparison of different hollow fibre haemodialysis module configurations by a CFD multiscale approach
2021
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 mod…
Nuclear Magnetic Resonance for Cultural Heritage
2007
Abstract Nuclear magnetic resonance (NMR) portable devices are now being used for nondestructive in situ analysis of water content, pore space structure and protective treatment performance in porous media in the field of cultural heritage. It is a standard procedure to invert T 1 and T 2 relaxation data of fully water-saturated samples to get “pore size” distributions, but the use of T 2 requires great caution. It is well known that dephasing effects due to water molecule diffusion in a magnetic field gradient can affect transverse relaxation data, even if the smallest experimentally available half echo time τ is used in Carr–Purcell–Meiboom–Gill experiments. When a portable single-sided N…
Water capillary absorption in porous media in different wettability conditions studied by Quantitative MRI and X-ray CT
2007
X-ray computed tomography (CT) and magnetic resonance imaging (MRI) have been successfully applied to study both the capillary properties of several samples of Lecce stone and the performances of treatments used for protection and conservation of historical stone artifacts. The presence of water inside the sample may be visualized by both MRI and X-ray CT. For the treated samples, the different dynamics of water absorption gives indirectly the efficacy of the polymer in the rock.
Model of hydrocarbons transport through the porous ground media
2014
Dispersion model of hydrocarbons transport in porous media has been presented. Mathematical description of this process allows to estimate whether the menace of ground waters can occur as a result of hydrocarbons transport through the soil. The convection term in the mass transport equation is taken into account due to the higher velocity of propagation in vertical direction. Additionally, introduction to the balance equation the biosorption link allows to take into account microorganisms influence on impurities concentration, especially on heavy oils derived compounds. To verify the theoretical model series of the experiment in the soil filter has been carried out.