Bundle Of Hollow Fibers Research Articles

INVESTIGATIONS OF DISTRIBUTIONS OF O2 AND CO2 CONCENTRATION IN A BLOOD LAYER AND GAS TRANSFER PERFORMANCE OF A PARTIAL OXYGENATOR MODEL WITH COMPUTATIONAL FLUID DYNAMICS (CFD)

It is difficult to predict the gas transfer performance in oxygenators theoretically. Because there have not been a method which could calculate nonlinear blood-gas reactions and dealt blood and gas layer simultaneously. We have been trying to calculate blood-gas transfer with a CFD method involving nonlinear hemoglobin-gas reactions. In this study, we analyzed distribution of gaseous concentrations and gas transfer performance of a partial oxygenator model. Referenced whole oxy-genator has a rectangular formed hollow fiber bundle. Partial oxygenator model had a part of blood flow section and the same length of primary blood flow direction (30 mm) of whole oxygenator's fiber bundle, and was made of a blood layer, gas layers and staggered cylindrical hollow fibers (225 μm outer diameter). Our method adopted O2 and CO2 reaction models derived on nonlinear relationship equations for source terms in mass transfer equations between each concentration and reaction source. In a result, a state of nonlinear distributions could be observed under Reynolds number=3.9. If a blood flow section of this model converted into that of whole oxygenator in condition of uniform blood flow, 0, and CO, transfer rates were 71.1 mL/min and 80.0 mL/min, respectively at 1 UL/min gas flow, and 71.1 mL/min and 83.7 mL/min, respectively at 3 L/min gas flow in case of 1 L/min blood flow. This calculated results showed an enough performance with reality.

Design progress of the ultracompact integrated heart lung assist device--part 1: effect of vaned diffusers on gas-transfer performances.

The integrated heart lung assist device (IHLAD) has been developed to overcome the problems of currently available extracorporeal membrane oxygenation devices. The integrated structure of a centrifugal blood pump and cylindrical bundle of polyolefin hollow-fibers has allowed a remarkably compact size for the device. This study deals with the design change of the IHLAD that added to the vaned diffuser between the impeller of the centrifugal pump and the hollow-fiber bundle with a view to enhancing the gas-transfer performance. Ex vivo gas-transfer performance tests were carried out, as well as hydrodynamic characteristics and hemolysis test using fresh goat blood. The oxygen transfer rate was generally improved, and the carbon dioxide removal rate was slightly improved. Intolerable amount of hemolysis (index of hemolysis= 0.177) was caused by the IHLAD, which must be resolved by improving the design in the future.

Investigation into the behaviour of hollow glass fibre bundles under compressive loading

Abstract In this study the behaviour of small epoxy resin-bonded hollow glass fibre (HGF) tows, in a range of fibre hollow fractions and external diameters, was investigated under axial compressive loading. The relative magnitudes of compression strength for HGF tows and nominally identical bundles of solid fibres of the same external diameter (D) were measured. The interactions between fibres in a micro-tow replicated the conditions found in unidirectional composite materials. A significant degree of scatter in compression strengths were observed. However, experimental and calculated compression strengths for the range of specimens tested show a strong dependence on fibre geometry. Large fibre D and fibre hollow fraction (K2) appears to give higher experimental strength values relative to the equivalent solid fibre specimens. Conversely, strength values calculated using actual glass cross-sectional area indicate that smaller D, high K2 fibres should offer the best compressive performance. It would appear from these findings that the arrangement of the fibres within the bundle (i.e. alignment, spacing, etc.) rather than the individual fibre property has an overriding effect on subsequent compression performance.

Designing Blood Oxygenators

Extracorporeal blood oxygenators are used to provide cardiopulmonary support during open heart surgery. In the study reported here, mass transfer correlations were determined for commercially available blood oxygenators. Two configurations used commercially, flow outside and across bundles of hollow fibers and flow in thin channels between parallel flat sheet membranes, were investigated. Water and glycerol/water mixtures were used as a substitute for blood. Diffusion of oxygen into and out of these solutions was studied. For flow across bundles of hollow fibers, the mass transfer correlations derived here are in agreement with analogous correlations for crossflow heat exchangers. However, for flow in thin channels, the rate of mass transfer is often less than predicted from theory. This compromised mass transfer can be explained by considering slight variations in the thickness of the blood flow channels. The mass transfer correlations developed here could be used to design better blood oxygenators.

THE EFFECTS OF A VANED DIFFUSER PROFILE ON THE PERFORMANCE OF AN INTEGRATED HEART-LUNG ASSIST DEVICE

The integrated heart-lung assist device (IHLAD) has a composite structure of a centrifugal pump and a cylindrically located hollow fiber bundle to realize quick setting-up and improved mobility. Implementation of a vaned diffuser between the centrifugal pump and the hollow-fiber unit remarkably enhanced the gas-exchange efficiency. In this study, the optimum profile of the vaned diffuser was investigated especially to reduce the blood damage. A visualization using high-speed video was applied to identify flow phenomena having close relationships with hemolysis. Periodic alternating flow known as rotating stall was observed, which could augment hemolysis by the increased chances for blood cells to pass through the intensive flow area such as diffuser tips. To reduce rotating stall, vane number was reduced from 7 to 5. The effect of vane profile modification was evaluated by hemolysis testings at 5 L/min against the pressure head of 300 mmHg. The amount of hemolysis in the form of NIH was 0.177 for 7 vanes and 0.040 for 5 vanes. The attempt to reduce rotating stall was also carried out by changing the gap between the impeller and the diffuser vanes. Hemolysis testings were performed to compare the test rigs having several gap clearances (0.5, 1,2,3 mm). The gap size of 2 mm indicated the lowest NIH value of 0.007 while the current 3 mm showed NIH of 0.009. In conclusion, the performance of IHLAD in terms of hemolysis could be successfully improved by optimization of flow passages of the vaned diffuser.

617 流体力学解析手法の人工臓器設計への応用

This paper describes a computational fluid dynamics technique for artificial lung designing. A suitable artificial lung for extracorporeal circulation must offer low resistance and adequate gas exchange. These requirements are largely a function of device geometry, particularly as it relates to fuluid dynamics. To analyze flow behavior, computational fluid dynamics software (STAR-LT : CD Adapco Japan) was used to calcutate flow velocity and pressure drop in the artificial lung models. The inner part (Hollow fiber bundle) of the model was defined as porous medium, which acts like a sponge. Such modeling is highly useful as part of the process of developing artificial lung.

A novel theoretical model for mass transfer of hollow fiber hemodialyzers

A novel theoretical model for mass transfer of hollow fiber bundles in hemodialyzers is presented. In the model, a hemodialyzer is considered as a porous zone which is composed of two non-interpenetrating porous flow zones. Firstly, the dialysate side (shell side) is thought as a porous medium zone. Then by solidifying the dialysate flow zone and the occupied zone by hollow fiber membrane, the rest zone of hemodialyzer (i.e. blood side or lumen side) is considered as a porous medium zone too. Finally, the interface of the two flow zones is the fiber membrane through which mass transfer is performed. The dialysate and blood flows are all described by Navier-Stokes equations with Darcy momentum source terms. Kedem-Katchalsky equations as other source terms are added into Navier-Stokes equations to simulate the permeating flux through the membrane. All equations must be coupled together in the process of computing. The model is validated by the experimental data in literature. The simulative results show that the predicted clearances agree well with the experimental data, and the model in this paper is better than other models for the forecast of clearance.

Lead removal from drinking water - development and validation of point-of-use treatment devices

Two lead removal water filters were developed to lower lead levels in drinking water below 10 μg.L-1 in order to meet the new regulation given by the European Directive 98-83, applicable in December 2013. An appropriate adsorbent was selected through a stringent research program among a wide range of media, and is composed of a synthetic zeolite and an activated carbon. Two prototypes were developed: the first is a faucet-mounted filter which contains a fixed bed of the adsorbent and a hollow fiber bundle, while the second is an under-sink cartridge made of a porous extruded block of carbon and adsorbent. Both are able to treat at least 1,000 litres of any water containing on average 100 to 150 μg Pb.L-1, by lowering the lead concentration below 10 μg.L-1. Once their safety considerations were addressed by an independent laboratory according to the French Ministry of Health recommendations, 20 prototypes were installed at consumers' taps in northeastern France. Their performance in terms of lead removal, HPC control and bad taste and odor reduction was followed for 6 months. This field testing program resulted in the validation of both prototypes which meet the new French Ministry of Health recommendations and assures that the filtered water is fully ED 98-83 compliant. Their commercialization will be launched first in France in middle 2002.

Three-phase contactor with distributed U-shaped bundles of hollow-fibers for pertraction

Pertraction of dimethylcyclopropanecarboxylic acid (DMCCA) and phenol in a new hollow-fiber (HF) contactor of three liquid phases with distributed U-shaped bundles of microporous HF was studied. Trioctylamine (TOA), Hostarex A327 and Cyanex 471X have been used as carriers. The performance of this contactor is similar to other HF contactors. Its advantage is that both bundles of fibers can elongate without deformation of fibers and maldistribution of fibers in the bundles. Pulsation of the membrane phase increases the transport rate by 35–61% and it reaches a plateau value at the pulsation velocity of about 1.1 mm s −1. With increasing velocity of the feed in the fiber lumen the value of the overall mass-transfer coefficient increases, but soon a steady value is approached at the velocity of about 5.5 cm s −1. The diffusion resistances in a series model do not describe the pertraction of DMCCA well. The suggested new diffusion-reaction model, considering the resistance based on the kinetics of the stripping reaction, fits experimental data well. Not only the rate of the acid–carrier complex decomposition, but also that of the DMCCA dimer decomposition have to be considered. The estimated values of the apparent reaction rate constant were for the membrane with TOA 1.91×10 −6 m s −1 and for pure n-alkanes 5.78×10 −6 m s −1. The kinetic resistance on the stripping interface represents 20–60% of the overall mass-transfer resistance and its value is comparable to the diffusion resistance of the both walls.

Mass and momentum transfer in commercial blood oxygenators

In modern blood oxygenators, microporous membranes (flat sheet or hollow fibre) are used to separate the blood and gas phases. Blood flows on one side of the membrane while gas (usually oxygen or air) flows on the other side. Since the membranes used are hydrophobic (e.g., polypropylene, Teflon), the pores are gas filled resulting in a negligible membrane mass transfer resistance. The major resistance to gas transfer is due to the blood side mass transfer boundary layer. In this study mass transfer and friction factor correlations for commercially available hollow fibre and flat sheet blood oxygenators have been determined experimentally. Water was used as a substitute for blood. The diffusion of oxygen into and out of water has been studied. Two different flow configurations used commercially have been investigated: flow outside and across woven hollow fibre bundles and flow in thin channels. The results for flow across bundles of woven hollow fibres may be compared to analogous results for flow in cross flow heat exchangers. The results obtained here can be used to further optimize the design of blood oxygenators.

Mass and momentum transfer in hollow fibre blood oxygenators

Mass transfer and friction factor correlations for microporous hollow fibre blood oxygenators (BOs) have been determined experimentally. Water and glycerol water solutions were used as a substitute for blood. The diffusion of oxygen into and out of water and glycerol water solutions has been studied. The liquid stream flowed outside and across bundles of woven hollow fibres while the gas stream flowed inside the fibres. In previous studies, it has been assumed that the Sherwood number varies with the one-third power of the Schmidt number. By conducting experiments using various glycerol water mixtures the kinematic viscosity of the liquid and the diffusivity of oxygen in the liquid phase have been varied. The results obtained here experimentally confirm the dependence of the Sherwood number on the Schmidt number raised to the one-third power. The experimental mass transfer and friction factor results for hollow fibre BOs are compared to the j factor analysis presented by Chilton and Colburn. These results may be used to further optimize the design of BOs.

Mass and momentum transfer in blood oxygenators

Mass transfer and friction factor correlations for commercially available hollow fibre and flat sheet blood oxygenators have been determined experimentally. Water was used as a substitute for blood. The diffusion of oxygen into and out of water has been studied. Three different flow configurations have been investigated: flow inside hollow fibres, flow outside and across woven hollow fibre bundles and flow in thin channels. For flow inside the fibres, the results obtained are in close agreement with analogous theoretical correlations. The results for flow across bundles of woven hollow fibres may be compared to analogous results for flow in cross flow heat exchangers. For flow in thin channels, the results obtained here are in agreement with the analogous theoretical heat transfer correlation developed by Lévêque. However, at Graetz numbers less than 10, the results deviate from the predictions of Lévêque. This deviation cannot be predicted by extensions to the Lévêque solution or from the more rigorous analysis by Graetz. However it is possible to predict the observed deviation by considering slight polydispersity in the thickness of the thin liquid flow channels.

Modeling and experimental study of microfiltration using a composite module

Microfiltration is usually conducted in either a dead-end or a cross-flow filtration mode, with a bundle of hollow fibers or a sheet of membrane as the filtration medium. This paper reports a development of microfiltration using a membrane screen-hollow fiber composite module involving both dead-end and cross-flow filtrations together. In the composite module, a cylindrical membrane screen of larger pores is installed outside a bundle of hollow fibers of smaller pores, and the suspension to be treated is passed through the membrane screen for pre-treatment before it is further treated through the hollow fibers. The membrane screen is operated in a cross-flow filtration mode whereas the hollow fibers are in a dead-end filtration mode. A simplified analysis was conducted for the prediction of permeation flux through the membrane screen-hollow fiber composite module, and the modular performance was evaluated through microfiltration experiments with kaolin suspensions. It was found that the addition of the membrane screen in the composite module largely improved microfiltration performance, and the theoretical model developed in the simplified analysis could be adequately fitted to the experimental permeation fluxes through the composite module under various operation conditions.

Mass transfer in blood oxygenators using blood analogue fluids.

Mass transfer correlations for hollow fiber blood oxygenators have been determined experimentally using Newtonian and non-Newtonian blood analogue fluids. The Newtonian fluids consisted of deionized water and glycerol/water mixtures. The non-Newtonian fluids were prepared by adding small amounts of xanthan gum to the Newtonian blood analogue fluids. The rheological behavior of the non-Newtonian blood analogue fluids was modeled using the power law. The diffusion of oxygen into and out of the Newtonian and non-Newtonian blood analogue fluids has been studied. The liquid stream flowed outside and across bundles of woven hollow fibers, while the gas stream flowed inside the fibers.

Mufiltration of polydispersed suspension by a membrane screen/hollow-fiber composite module

Membrane and hollow-fiber technologies have widely been used in pure water production, and are increasingly used in conventional water and wastewater treatment for solid—liquid separation. A major challenge to these applications is to prevent or reduce particle fouling so that the membrane or hollow-fiber modules can be operated at a higher permeation flux and over a longer period of time. In this study, a membrane screen/hollow-fiber composite module has been developed for the mufiltration of polydispersed suspensions. The module combines a cylindrical membrane of larger pores as a screen and a bundle of hollow fibers of smaller pores for polishing treatment. Both cross-flow and dead-end filtrations occur in the same module. Experiments were conducted at various concentrations with kaolin particles of size ranging from 0.5 μm to 10 μm. The results showed that the membrane screen effectively removed larger particles from the permeating flow and reduced solid loading to the hollow fibers. As a result, the composite module generated considerably higher permeation flux, as compared to a similar hollow-fiber module without the membrane screen. It was found that larger particle deposition was more significantly affected by the cross flow, and initially deposited particles contributed greater specific resistance to the permeating flow.

Nylon screen incorporated into hollow fiber microfiltration system for wastewater treatment

Low permeate flux due to clogging is the major challenge of hollow fiber microfiltration systems in wastewater treatment because of the high content of suspended solids. In this research, a new crossflow microfiltration module to overcome this problem was studied. The module consisted of a housing, a cylindrical membrane and a bundle of hollow fibers. The nominal pore size of the cylindrical membrane was 5 μm and that of the hollow fibers was 0.1 μm. The cylindrical membrane worked as a screen for pretreatment to remove those particles larger than its pore size and therefore to reduce the solid loading to the hollow fibers. Extensive experiments were conducted under various transmembrane pressures, influent concentrations, and crossflow velocities with polydispersed suspensions prepared with ISO Test Particles of size ranging from less than 0.5 μm to 10 μm. The quantity and quality of the filtrate were monitored over time. The results have shown that the cylindrical membrane worked effectively in reducing solid fouling, and therefore increasing permeate production for the hollow fiber microfiltration system.

APPLICATION OF CFD IN THE DESIGNING OF A MEMBRANE OXYGENATOR

A CFD (Computational Fluid Dynamics) model was developed to simulate flow in a membrane oxygenator. The hollow fiber bundles were treated as a porous medium. This study demonstrated that the numerical model could accurately predict the distributions of flow velocity, pressure, shear stresses, temperature, and oxygen concentration in the device. The numerical model is a powerful tool for the designing of a membrane oxygenator.

MODELING OF DIALYSATE FLOW IN AN ARTIFICIAL KIDNEY

Modeling and computer simulation of dialysate flow in an artificial kidney is more difficult than that of blood flow because of non-uniformity and complexity of the dialysate flow. In the present study, a porous media approach was used to model dialysate flow. Coupling of Darcy's law (diaysate flow), Navier-Stokes equation (blood flow), and Kedem-Katchalsky equation (permeating flux through membrane) allowed simulation of mass transfer under different blood/dialysate flow conditions. A novel experimental method to measure the Darcy permeability of the CT190 (Baxter) hollow fiber bundles was also used. The Darcy permability coefficients in radial and axial directions were measured to be Kn= 4.16±10−11m2, and Kzz=1.29±10−9m2, respectively. Determination of dialysate-side velocity profile revealed a non-uniform flow distribution, with the peripheral region having a 5% higher velocity than the central region. Dialysate-side solute concentration distribution also was not uniform due to the asymmetry of shell configuration and flow. Numerical results were corroborated by experiments in which local urea clearance was measured in different annular regions of CT190 dialyzers (see Huang et al, this meeting). In conclusion, a porous media model based on Darcy's law accurately simulates dialysate flow. This approach may be useful in optimizing dialyzer mass transfer.

Blood Flow around Hollow Fibers

In an artificial lung, blood is oxygenated and flows around a bundle of hollow fibers while gas flows inside the fiber. The objective of this study is to understand the hydrodynamics of three different fiber banks (inline square IS, staggered square SS and equilateral triangle ET) and to investigate the influence of both a Newtonian and non-Newtonian Casson viscosity model on the flow field. A two-dimensional finite element model for permanent, isothermal, laminar blood flow perpendicular to hollow fibers is used. All fibers are assumed identical, straight and parallel. Porosity ranges from 0.4 to 0.6 and Reynolds number varies from 1 to 60. For a given Re, ET generates less resistance than SS, the latter being comparable with IS. A lower porosity increases resistance. Non-Newtonian viscosity affects velocity patterns only at low Re (<0.5) and higher porosity (>0.5). Resistance at low Re is significantly elevated in the fiber banks due to an overall increase in viscosity. This model makes it possible to study the influence of geometry and viscosity on hydrodynamics in fiber banks and may aid in the optimization of hollow fiber artificial lung design.

Modification of butterfat by selective hydrolysis and interesterification by lipase: Process and product characterization

AbstractButterfat was chemically modified via combined hydrolysis and interesterification, catalyzed by a commercial lipase immobilized onto a bundle of hydrophobic hollow fibers. The main goal of this research effort was to engineer butterfat with improved nutritional properties by taking advantage of the sn‐1,3 specificity and fatty acid specificity of a lipase in hydrolysis and ester interchange reactions, and concomitantly decrease its level of long‐chain saturated fatty acid residues (viz., lauric, myristic, and palmitic acids) and change its melting properties. All reactions were carried out at 40°C in a solvent‐free system under controlled water activity, and their extent was monitored via chromatographic assays for free fatty acids, esterified fatty acid moieties, and triacylglycerols; the thermal behavior of the modified butterfat was also assessed via calorimetry. Lipase‐modified butterfat possesses a wider melting temperature range than regular butterfat. The total saturated triacylglycerols decreased by 2.2%, whereas triacylglycerols with 28–46 acyl carbons (which contained two or three lauric, myristic, or palmitic acid moieties) decreased by 13%. The total monoene triacylglycerols increased by 5.4%, whereas polyene triacylglycerols decreased by 2.9%. The triacylglycerols of interesterified butterfat had ca. 10.9% less lauric, 10.7% less myristic, and 13.6% less palmitic acid residues than those of the original butterfat.