Designing Microporous Hollow Fibre Blood Oxygenators

Extracorporeal blood oxygenators are used to oxygenate the blood during open-heart surgery. Today the vast majority of these blood oxygenators use hydrophobic microporous hollow fibre membranes to separate the blood and gas phases. Oxygen diffuses from the gas phase through the gas-filled membrane pores into the blood. Oxygen in the blood plasma binds to haemoglobin present in the red blood cells. Consequently the rate of oxygen transfer is enhanced compared to the oxygenation of water where the oxygen does not react in the liquid phase. Here mass transfer and friction factor correlations developed for nonreactive Newtonian and non-Newtonian fluids are used to predict results for blood. Characteristic parameters such as the Reynolds and Schmidt numbers and the friction factor have been modified to account for the shear-thinning behaviour of blood. A mass transfer enhancement factor has been developed based on film theory which accounts for the reaction between oxygen and haemoglobin. These equations may be used to predict the performance of a blood oxygenator based on results for simple systems such as the oxygenation of water. Consequently in the initial stages of new blood oxygenator designs, experiments may be conducted using water rather than blood to save time and money.