Hollow Fiber Membrane Bundle Research Articles

CFD ANALYSIS OF HYDRODYNAMIC CHARACTERISTICS OF A NOVEL PARACORPOREALPUMPING ARTIFICIAL LUNG

We are developing an Emergency Respiratory Support Lung (ERSL) to provide pulmonary assist for acute lung failure. A rotating hollow fiber membrane bundle actively mixes blood for efficient gas transfer and provides pumping ability required for its intended paracorporeal veno-venous operation. A CFD model was developed to support the design, and experimental testing of prototypes. Applicable equations were solved in 2D and 3D domains using FLUENT. Two different approaches were used; one utilized a porous media model and another was based on evaluation of flow around individual fibers. Both simulations showed that the rotating fiber bundle accelerates fluid entering the bundle, and the width of the acceleration zone does not exceed two fiber diameters. Simulation at 1500 rpm predicted that relative velocity inside the fiber bundle was five times greater than in stationary bundle and the ERSL was able to generate a pressure head increase across the device. CFD analysis showed that the area of maximum shear rate (200 s−1) for the stationary bundle case was in the outlet port vicinity; whereas the rotational case at 1500 rpm predicted a maximum shear rate of 3000 s−1at the housing's stationary walls. CFD predictions were compared to pressure measurements and dye injection flow visualization in order to validate the models. We obtained qualitative agreement between simulations and experiments. Optimization of inlet port geometry was performed to avoid stagnant zones and decrease probability of clotting. Evaluation of hemolysis using a CDF model will be performed for experimental ERSL prototype.

Analysis of heat and mass transfer phenomena in hollow fiber membranes used for evaporative cooling

This paper describes the potential use of hollow fiber membranes in evaporative cooling applications for space air-conditioning. Duct-mountable hollow fiber membrane bundles and arrays are utilized as contactors for the delivery of liquid water to an air stream in a heating, ventilating air-conditioning duct. A series of experimental and analytical parametric studies are presented to assess the heat and mass transfer phenomena in evaporative cooling with hollow fiber membranes. The focus of the studies was to compare experimentally determined heat and mass transfer coefficients to estimates obtained from literature, to determine the influence of membrane and operating parameters on achievable mass and heat flux and to assess the efficacy of using hollow fiber membranes for evaporative cooling. The results point to a proof for the concept and further indicate that reasonable numbers of fibers and membrane surface area can provide cooling effectiveness comparable to conventional evaporative cooling equipment.

EFFECT OF VESSEL COMPLIANCE ON THE IN-VITRO PERFORMANCE OF A PULSATING RESPIRATORY SUPPORT CATHETER

Intravena caval respiratory support (or membrane oxygenation) is a potential therapy for patients with acute respiratory insufficiency. A respiratory support catheter is being developed that consists of a bundle of hollow fiber membranes with a centrally positioned pulsating balloon to enhance gas exchange. This study examined the influence of vessel compliance on the gas exchange performance of the pulsating respirator, support catheter. Polyurethane elastic tubes were fabricated with compliance comparable to that measured in bovine vena cava specimens. The gas exchange performance of the respiratory catheter was studied in an in-vitro flow loop using either the model compliant tube or a rigid tube as a mock vena cava. Balloon pulsation enhanced gas exchange comparably in both rigid and model compliant vessels up to 120 bpm pulsation frequency. Above 120 bpm gas exchange increased with further pulsation in the rigid tube, but no additional increase in gas exchange was seen in the compliant tube. The differences above 120 bpm may reflect differences in the compliance of the elastic tube versus the natural vena cava.

Luminol/H2O2 chemiluminescence detector for the analysis of nitric oxide in exhaled breath.

A new instrument for the detection of nitric oxide has been developed and applied to the analysis of exhaled breath. The instrument is based on conversion of NO to NO2, using the oxidant chromium trioxide, followed by detection of chemiluminescence in the reaction of NO2 with an alkaline luminol/H2O2 solution. The presence of H2O2 is found to enhance the sensitivity of NO2 detection by a factor of approximately 20. A bundle of porous polypropylene hollow fiber membranes is used to bring the gaseous sample into contact with the luminol solution. Chemiluminescence occurring within the translucent hollow fibers is detected using a miniature photomultiplier tube. The limit of detection for NO is 0.3 ppbv for S/N = 3, and the 1/e response time is 2 s. A large interference resulting from the 4-6% CO2 concentration in exhaled breath is removed by use of an ascarite scrubber in the air stream. Breath measurements of NO were made using a sampling technique developed by Sensor Medics (Yorba Linda, CA) with simultaneous detection using the luminol/H2O2 and NO + O3 chemiluminescence techniques. The two instruments were found to be in excellent agreement. Nitric oxide levels were in the range 6.0-22.0 ppbv for healthy individuals and 40.0-80.0 ppbv for individuals with asthma or a respiratory infection. This new detector offers the advantages of compact size, low cost, and a simple configuration compared to NO detectors based on NO + O3 chemiluminescence.

High-Precision Conductometric Detector for the Measurement of Atmospheric Carbon Dioxide

A new, lightweight instrument has been developed for measuring atmospheric mixing ratios of the greenhouse gas carbon dioxide with high precision and accuracy. This modified total organic carbon analyzer uses a bundle of semipermeable hollow fiber membranes to continuously equilibrate CO2 in air with a recirculated stream of deionized water. Aqueous carbon dioxide hydrolyzes and dissociates to form the ions H3O+ and HCO3-, thereby increasing the conductivity. The bipolar pulsed method is used to measure the conductivity of the water before and after contact with air. Potential interferences that may also increase the conductivity, such as acids and bases, are removed at the inlet by bicarbonate and bisulfate scrubbers. The detector has been field tested and exhibits a 1/e response time of ∼30 s and precision (RSD) of 0.1%. Field results for measurements at altitudes in the range of 1700−3600 m MSL exhibited an average deviation of 0.16% from values obtained by flask sampling and laboratory measurement usi...

Is condensation the cause of plasma leakage in microporous hollow fiber membrane oxygenators

Extracorporeal membrane oxygenators are comprised of large bundles of microporous hollow fiber membranes (HFMs) across which oxygen and carbon dioxide are transferred to and from blood. Long term use of extracorporeal oxygenators is limited by plasma leakage through the pores of the HFM walls, requiring replacement of the oxygenator. Condensation of water vapor on the pore walls is thought to be a possible precursor to plasma leakage. To explore this mechanism, a simple theoretical analysis is used to examine the temperature of the gas flow through the HFMs. For conditions representative of two commercially available oxygenators, the analysis predicts that the gas heats up to the temperature of blood flow outside of the fibers after passing through less than 0.5% of the fiber lengths. Once the gas temperature and hence the fiber wall temperature equilibrates with the blood, condensation of water vapor is no longer possible. In vitro testing of microporous HFMs under gas flow rates and temperature conditions similar to those of extracorporeal oxygenators but with the fibers submerged in water is also presented. The fibers showed negligible degradation in carbon dioxide transfer over a four-day period. These results of both the theoretical and experimental analyses indicate that the condensation of water vapor within the pores of the HFMs is unlikely to be the cause of plasma leakage in clinically used extracorporeal oxygenators.

Recent progress in engineering the Pittsburgh intravenous membrane oxygenator.

The University of Pittsburgh intravenous membrane oxygenator (IMO) is undergoing additional engineering development and characterization. The focus of these efforts is an IMO device that can supply as much as one-half basal O2 consumption and CO2 elimination rates while residing within the inferior and superior vena cavae after peripheral venous insertion. The current IMO design consists of a bundle of hollow fiber membranes potted to manifolds at each end, with an intra-aortic type balloon integrally situated within the fiber bundle. Pulsation of the balloon using helium gas and a balloon pump console promotes fluid and fiber motion and enhances gas exchange. During the past year, more than 15 IMO prototypes have been fabricated and extensively bench tested to characterize O2 gas exchange capacity, balloon inflation/deflation over relevant frequency ranges, and the pneumatics of the sweep gas pathway through the device. The testing has led to several engineering changes, including redesign of the helium and sweep gas pathways within the IMO device. As a result, the maximum rate of balloon pulsation has increased substantially above the previous 70 bpm to 160 bpm, and the vacuum pressure required for sufficient sweep gas flow has been reduced. The recent IMO prototypes have demonstrated an O2 exchange capacity of as much as 90 ml/min/m2 in water, which appears within 70% of our design goal when extrapolated to scaled up devices in blood.