The photographic and electrical conductivity methods to measure the structure of two phase flow, especially bubble size, bubble frequency, local gas hold-up and, for the latter, the bubble velocity are described.

Bubble column bioreactors

Gas-liquid direct-contact evaporators are characterized by the bubbling of a superheated gas through the solution to be concentrated. In other words, they are nonisothermal bubble columns. Despite their simplicity of construction, these units exhibit rather complex hydrodynamics and, similar to what occurs to isothermal bubble columns, the design of such units still poses a problem. The present paper reviews the literature regarding this kind of equipment, addressing both experimental studies and modeling efforts. The covered issues include classic and potential applications, bubbling regimes, gas holdup and bubble size distributions, as well as mathematical models proposed for simulating the unit. Additionally, pertinent literature on isothermal bubble columns is also discussed. Recommendations are made for future research.

Gas‐Liquid Direct‐Contact Evaporation: A Review

: This review focuses on the hydrodynamic and mass transfer characteristics of various three-phase, gaslift fluidized bioreactors. The factors affecting the mixing and volumetric mass transfer coefficient (kLa), such as liquid properties, solid particle properties, liquid circulation velocity, superficial gas velocity, bioreactor geometry, are reviewed and discussed. Measurement methods, modeling and empirical correlations are reviewed and compared. To the authors' knowledge, there is no 'generalized' correlation to calculate the volumetric mass transfer coefficient, instead, only 'type-specific' correlations are available in the literature. This is due to the difficulty in modeling the gaslift bioreactor, caused by the variation in geometry, fluid dynamics, and phase interactions. The most important design parameters reported in the literature are: gas hold-up, liquid circulation velocity, 'true' superficial gas velocity, mixing, shear rate, aeration rate and volumetric mass transfer coefficient,...

Hydrodynamic and mass transfer characteristics of three-phase gaslift bioreactor systems.

Direct-contact evaporation in the homogeneous and heterogeneous bubbling regimes. Part I: experimental analysis

Bubble columns with and without solid suspensions have been used widely as chemical reactors and bioreactors.This paper summarizes research on the design parameters of bubble columns with and without solid suspensions, and introduces new trends in research activities such as applications of computational fluid dynamics and of newly developed experimental techniques to bubble columns, and research on high pressure bubble columns.

Design Parameters of Bubble Column Reactors with and without Solid Suspensions

The average diameter, d, of bubbles generated from a porous plate in pure liquid and in aqueous solutions of inorganic electrolyte were measured at various gas flow rates by taking photographs of bubbles the size of which was controlled by bubble coalescence on and above the plate. For the extreme case when coalescence occurred at the maximum rate such as in water and in pure organic liquid, the empirical equations for d based on previous data and those from this experiment are proposed. The addition of inorganic electrolyte to water reduced the coalescence and thus simultaneously reduced d. The average bubble diameter in the aqueous solutions is well correlated to the experimental conditions with an empirical equation including the non-dimensional group proposed by Marrucci and also corresponding to the controlling factor of the bubble coalescence.

Bubbles generated from porous plate in pure liquid and in aqueous solutions of inorganic electrolytes

The average diameter of bubbles generated from the porous plate in aqueous solution of organic substance and in a mixture of polar organic liquid and non-polar liquid were measured at various gas flow rates by taking photographs of bubbles. An addition of organic substance to water or to an organic liquid of opposite polarity reduces the degree of bubble coalescence on and above the plate, and hence the bubble size. As the degree of bubble coalescence and hence the degree of reduction of bubble size depends on da/dc1 of the solution and the diffusivity of the solute, an empirical equation for average bubble diameter is introduced, taking the above two properties into consideration.

Takashi Hayashi

Papers

Bubbles generated from porous plate in pure liquid and in aqueous solutions of inorganic electrolytes

Bubbles generated from porous plate in organic solutions and aqueous solutions of organic substances