Multiphase Flow Vertical Aerated Column with Superhydrophobic Internals using X-ray Computed Tomography and Wire Mesh Sensors

Bubbly flow in bubble column reactors promotes mixing necessary for many chemical processes. We show that if superhydrophobic-coated material is introduced into a bubble column, there can be a substantial difference in gas holdup and earlier initiation of churn-turbulent flow which can alter larger-scale mixing without a need to change the superficial gas velocity. Additionally, pressurized water reactors operate in a single-phase flow. Localized nucleation sites arise to promote convectional heat transfer to the bulk liquid. During an event of flow loss or any condition that can result in bulk liquid temperatures exceeding saturation temperatures, bubbles will form more frequently, creating a boiling casualty. If a superhydrophobic-coated material is introduced into a fuel cell assembly, the vapor bubbles will show an affinity to the air layer in these coatings and therefore escape faster from the flow regime, resulting in a larger margin to reach Critical Heat Flux. As the flow becomes optically opaque at few percent gas phase volume fraction, we utilize two dual plane wire mesh sensors to obtain velocity profiles and bubble size distributions, in addition to the traditional pressure and level-based gas holdup measurements to calculate average phase fraction. A custom build photon-counting dual energy threshold X-ray computed tomography system is employed to get a higher resolution view of the time average phase fraction non-intrusively. We report satisfactory agreement between these gas holdup measurement techniques with differences arising for understood reasons, and use the insight thus yielded to discuss the effect of superhydrophobic surfaces on bubble column flow dynamics.