Many naturally occurring and industrial processes involve turbulent flows that contain particles such as bubbles or drops dispersed in a fluid. In these cases, the dispersed phase can exchange mass and heat with the surrounding fluid in a way that depends on details of the turbulent flow. This award will support experiments to understand the role of mass and heat transfer on large-scale statistics of turbulent flows. The challenge is to relate microscopic mass transfer on the scale of individual bubbles or drops to macroscopic mixing and mass transport. A vertical water tunnel will be used to study bubbles that can be held stationary and imaged to determine the concentration field of tracers that are exchanged between the bubbles and surrounding fluid. The rate of mass exchange will be correlated with parameters that describe the turbulence intensity and characteristics of the dispersed phase. An LED illumination system will be used to quantify temperature profiles in turbulent flow, which provides insight into large-scale mixing efficient of vapor bubbles. This system will also be used to study the concentrations of particles of various shapes to analyze mixing in turbulent flow. The results of these studies will be broadly relevant to such applications as evaporating sprays, rain droplets in clouds, air bubbles in fermentation reactors, and multiphase chemical reactors. The research team will prepare demonstrations of multiphase flows for K-12 student groups participating in programs at Penn State and for the Central Pennsylvania Festival of the Arts.
A vertical tunnel facility will be used to study mass transfer in particle-laden turbulent flows. An opposing mean flow balances the buoyancy drive rise or settling of particles, which allows the particles to remain in a field of view for imaging. The facility allows the mean flow and the turbulence Reynolds number to be adjusted independently. A combination of imaging methods will be used to measure the three-dimensional Lagrangian trajectories of dispersed particles, statistics of the surrounding flow, and the concentration field of mass exchanged between the two phases by interfacial transfer. Experiments will be conducted to identify the relevant parameters for turbulent multiphase flow with interfacial transfer. Flows containing bubbles and other particles with inertia will be examined to determine if inertial particles enhance mass transfer and mixing. The possibility of two-way couplings between interfacial momentum transfer and mass transfer will be investigated. The role of interfacial mass transfer on breakup and coalescence of bubbles will be determined.
