Industrial & Engineering Chemistry Research, Vol.51, No.50, 16495-16504, 2012
Hydrodynamics of Gas-Liquid Cocurrent Flows in Micropacked Beds-Wall Visualization Study
An inverted microscopy technique was implemented to scrutinize the wall-region hydrodynamics of gas-liquid cocurrent flows in micropacked beds. Digital image analysis enabled characterization of two contiguous flow regimes, hysteresis, and transition thereof. Low- and high-interaction regimes featuring, respectively, slow and rapid displacements of gas-liquid boundary were identified. The onset of regime changeover was delineated by distinguishing the fluctuating behavior in time of characteristic lengths extracted from the areas occupied by gas and liquid in the field of view. A Charpentier and Favier flow regime map demarcating low and high interaction regimes in conventional macroscale trickle beds was elaborated for the sake of comparison of micropacked bed transitions for three different gas liquid systems (air-water, argon-water, and argon-sucrose solution). The flow regime map suggests that micropacked bed transition occurs at considerably lower L/G values. Manifestation of hysteresis in micropacked beds was apprehended via pressure drop measurements and wetting fraction determination both in imbibition and drainage modes. In agreement with macroscale packed bed observations, the drainage branch revealed a larger pressure drop and wetting fraction compared with the imbibition branch for the same set of bed and fluid flow rates.