Some aspects of high-pressure phenomena of bubbles in liquids and liquid-solid suspensions

Some aspects of bubble dynamics and macroscopic hydrodynamic properties in high-pressure bubble columns and three-phase fluidization systems are discussed. Experimental results along with discrete-phase simulations of a single bubble rising in liquids and liquid-solid suspensions at high pressures are presented. A mechanistic model is described, which accounts for the initial size of bubble from a single orifice in liquid-solid suspensions. The mechanism for bubble breakup at high pressures is illustrated by considering bubble instability induced by internal gas circulation inside a bubble, and an analytical expression is obtained to quantify the maximum stable bubble size. Experimental examinations on the roles of bubbles of different sizes indicate the importance of large bubbles in dictating the macroscopic hydrodynamics of slurry bubble columns. Further, extensive studies are made of the key macroscopic hydrodynamic properties, including moving packed bed phenomena, flow regime transition, overall gas holdup, mean bubble size, and bubble size distribution. An empirical correlation is introduced which predicts the gas holdup in slurry bubble columns of different scales. A similarity rule is revealed for the overall hydrodynamics of high-pressure slurry bubble columns, which takes into account the operating conditions, the maximum stable bubble size, and the physical properties of the gas, liquid, and solids. The heat transfer characteristics under high pressures are also investigated. A consecutive film and surface renewal model is used to characterize the heat transfer mechanism. (C) 1999 Elsevier Science Ltd. All rights reserved.