In membrane oxygenators the primary resistance to gas transfer exists in the blood layer adjacent to the membrane. A number of techniques have already been tried to augment gas transfer by reducing the fluid side resistance. One attractive way to improve gas transfer is to induce laminar secondary flow in the coiled tube. The primary flow is along streamlines parallel to the tube axis; simultaneously secondary motion perpendicular to the primary flow is induced due to centrifugal and viscous forces. In other words a fluid particle has velocity component in planes normal to the tube axis. The applications of this technique to blood oxygenation were tried theoretically and experimentally, and it was shown that the secondary motion was able to significantly enhance gas transfer to blood compared with the transfer performance in straight tubes, although the flow resistance was concomitantly increased. The main drawback of helically coiled tubes is that the helical coil does not always provide a large packing density of tubings in order to minimize the total volume of an oxygenator. These requirements may be met by utilizing curved tubes tightly wound in woven patterns. Weaving patterns provide an efficient method of packing the tubes and basically consists of curved tubes with varying curvature periodically. The secondary flow is set up periodically along the tube length by reversing the curvature of the helix so that the direction of secondary motion is altered. This provides for a mixing effect by disturbing alternately established secondary flows and this can augment gas transfer to blood. Basic patterns of curved tubes with spatially varying curvature are the serpentine tube and a tube, which is shown in this article. Transfer augmentation was observed with these tubes. A fluid mechanical analysis for the flow in a serpentine tube has been published earlier. In this study the authors investigated the gas transfer performance to water and blood for curved tubes wound in 3 forms of weaving patterns, which provide for more freedom and flexibility to the configuration of tubings compared with the helical coils.
|Title of host publication||Transactions of the American Society for Artificial Organs|
|Number of pages||5|
|Publication status||Published - 1978|
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