tailieunhanh - Mass Transfer in Multiphase Systems and its Applications Part 11

Tham khảo tài liệu 'mass transfer in multiphase systems and its applications part 11', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 18 New Approaches for Theoretical Estimation of Mass Transfer Parameters in Both Gas-Liquid and Slurry Bubble Columns Stoyan NEDELTCHEV and Adrian SCHUMPE Institute of Technical Chemistry TU Braunschweig Germany 1. Introduction Bubble columns with and without suspended solids have been used widely as chemical reactors bioreactors and equipment for waste water treatment. The key design parameters in bubble columns are gas holdup gas-liquid interfacial area volumetric liquid-phase mass transfer coefficient gas and liquid axial dispersion coefficients Despite the large amount of studies devoted to hydrodynamics and mass transfer in bubble columns these topics are still far from being exhausted. One of the essential reasons for hitherto unsuccessful modeling of hydrodynamics and mass transfer in bubble columns is the unfeasibility of a unified approach to different types of liquids. A diverse approach is thus advisable to different groups of gas-liquid systems according to the nature of liquid phase used pure liquids aqueous or non-aqueous solutions of organic or inorganic substances non-Newtonian fluids and their solutions and according to the extent of bubble coalescence in the respective classes of liquids. It is also necessary to distinguish consistently between the individual regimes of bubbling pertinent to a given gas-liquid system and to conditions of the reactor performance. The mechanism of mass transfer is quite complicated. Except for the standard air-water system no hydrodynamic or mass transfer characteristics of bubble beds can be reliably predicted or correlated at the present time. Both the interfacial area a and the volumetric liquid-phase mass transfer coefficient kLa are considered the most important design parameters and bubble columns exhibit improved values of these parameters Wilkinson et al. 1992 . For the design of a bubble column as a reactor accurate data about bubble size distribution and hydrodynamics in bubble columns mechanism of bubble