Gas Transfer to Blood Flowing in Coiled Circular Tubes

The transfer of physiological gases to blood flowing laminarly in helically coiled permeable-walled tubes was investigated. It is demonstrated, experimentally, as well as theoretically, that helical coiling of such a tube leads to significant improvement in gas transfer rates because of induced secondary velocities. The gas transfer rate for this coiled tube geometry depends on the Reynolds number, the Schmidt number, and the ratio of helix to tube diameters, K*. For typical values of these parameters and a zero wall thickness, the gas transfer rate might be a hundred times faster than that for a comparable straight tube. This improvement may be masked by the tube wall, however, unless very thin walled tubing is used. In contrast to the results obtained for the straight tube geometry. It was shown that an oxygenator using coiled tubular membranes would be limited by the tube length required to eliminate carbon dioxide. This length is still much less than is needed in a straight tube oxygenator, however. The results of this investigation indicate that a membrane oxygenator utilizing coiled, tubular membranes is feasible.