FLOW AND MASS TRANSFER IN DRIVEN CAVITIES WITH A FREE SURFACE (DEVOLATILIZATION, ABSORPTION GAS, POLYMER PROCESSING).

摘要

This dissertation is concerned with the flow of viscous liquids contained in an open cavity in which the flow is driven by a moving wall. It also deals with the problem of mass transfer between a gas and a liquid contained in a driven cavity.; The creeping flow equations for a Newtonian liquid inside a driven cavity were solved analytically for infinitely deep cavities when the interface is planar. Solutions for cavities having finite aspect ratios were obtained numerically using a finite differences technique. The theoretical predictions were compared with the results of experimental studies of the flow structure in a box-cylinder system which consisted of a stationary box partially filled with a viscous liquid set in motion by means of a rotating cylinder. Photographic techniques were used to measure the interfacial velocity profile and the position of the center of the principal vortex for values of the Reynolds number in the range 1 (LESSTHEQ) Re (LESSTHEQ) 50.; The air entrainment at the dynamic contact line was experimentally studied in the box-cylinder system using liquids with viscosities in the range 0.01-100 Pa(.)sec. Two regimes of air intake were found depending on the viscosity of the liquid, but the critical speed for air entrainment was found to be independent of the dimensions and orientation of the cavity. The critical conditions for the onset of the process were correlated in terms of the Capillary number, a dimensionless physical properties group and a modified Reynolds number over a range of values for the Capillary number 0.5 (LESSTHEQ) Ca (LESSTHEQ) 100.; The transient absorption of a gas by a viscous liquid was studied in an enclosed box-cylinder system. Simple penetration theory models were developed for the mass transfer in the recirculating pool and in the film coated on the surface of the rotating cylinder. Preliminary experimental results for the rate of absorption of carbon dioxide by glycerol-water solutions are presented for values of the Peclet number in the range 10('7) (LESSTHEQ) Pe (LESSTHEQ) 10('8).