In a blood oxygenator, the blood spends approximately 2 s passing through the device. Estimate a minimum value for hm, the mass transfer coefficient characterizing oxygen transport from the plasma to the inside of a red blood cell (RBC), such that the RBCs are completely (i.e. >99%) oxygenated before leaving the oxygenator (100% oxygenated refers to the maximum oxygen loading the cells can achieve in this oxygenator if the RBCs were left in the oxygenator for a very long time). You may assume that the RBCs entering the device are 50% oxygenated. Let the volume of each RBC be 98 µm3 and its surface area be 130 µm2. The diffusion coefficient of oxygen both in plasma and inside of the cell can be taken as 2 × 10−5 cm2/s.

A porous block attached to an air line emits tiny air bubbles (of diameter 0.15 mm, 21% oxygen) at the bottom of a fish tank filled with water at 25 °C. The absolute pressure in the bubbles at the bottom of the tank is 1.07 × 106 g/cm per s2 when they are released. They reach their terminal upward velocity almost instantly, since they enter the tank at nearly this velocity. Find the rate of oxygen transfer from one of these bubbles to the water. You may neglect the concentration of oxygen already in the water. The diffusion coefficient of oxygen in water is 2 × 10−5 cm2/s.