Mass transfer process analysis near phase boundary with combined PIV -PLIF method, a single -camera single -laser approach

A detailed characterization of interfacial mass transfer phenomena is of great importance in providing further insight into the fundamental physics of interfacial dynamics, and in developing improved engineering models for various environmental and industrial applications. Despite extensive efforts of experimental and theoretical investigations, there remain several fundamental issues yet to be clarified, mainly due to the lack of detailed dynamical information around the interface, and more challengingly, within the “interface” of finite physical dimension. Consequently, extensive data with sufficient spatial and temporal resolution is still much needed. A combined PIV-PLIF system for synchronous velocity and concentration measurement has been developed and implemented. The single-camera single-laser system, when employed for a two-fluid mass transfer system, greatly reduces the complexity of system design and configuration, as it involves fewer optical components and much simpler control circuitry. Using a fluorescent dye (Rhodamine 6G) as a passive tracer soluble in a water-butanol system, temporal and spatial concentration distributions in both phases are measured around the established phase boundary, under both quiescent and agitated cases. Measurements in the quiescent case, which corresponds to a Fickian diffusive process in either phase, clearly show that an interfacial area of finite thickness is present, and that concentration profiles along the bulk transfer direction possess an apparent positive gradient along the aqueous side, indicating an interfacial mass transfer resistance. Furthermore, data in the agitated case reveals such a concentration profile “abnormality”, however to a much weaker extent. Using partition coefficients and diffusivities derived from the measurements, a one-dimensional, analytic model is examined based on the Crank solution. Numerical solutions using finite differencing scheme are also carried out. Results show reasonable agreement outside of the interfacial area for either model, however the proper modeling of the unique concentration profile associated with the interfacial mass transfer resistance, remains a challenging issue