A commercial hollow fiber blood oxygenation laboratory experiment was used to introduce lower level engineering students to mass balances in a two-phase system. Using measured values of concentration and flow rate, students calculated the rate of mass transfer from the gas phase and into the liquid phase, and compared the two values to determine whether the mass balance closed. Students also investigated the effect of the liquid and gas flow rates on the mass transfer rate. Learning outcomes were assessed in a pre-post comparison study. The group that performed the experiment had significantly higher post-test scores and higher average normalized gain than the comparison group; the effect of the intervention (Cohen's d) was 2.06. Further, the students who performed the experiment demonstrated a better ability to incorporate engineering principles into the design of a heart lung machine in a semester-long project, relative to the comparison group.