http://bioprocesos.unq.edu.ar/Biopro%20II/Paper%20escalado.pdf

Bioreactor scale-up and oxygen transfer rate in microbial processes: An overview

Process and product models are commonly used for performing life-cycle assessments (LCAs) of the environmental impacts of materials and products through different stages of fabrication, use, and end-of-life options. In this article, we show that these models can be represented as process flow diagrams or as matrices of process interactions. In either representation, the inventory of environmental emissions and resources used is comparable, provided the process models are proportional in nature (any increase in product output produces a corresponding environmental burden). Matrix representations are advantageous if application cost, feedback flow, or speed of analysis is important. They are also useful in conjunction with comprehensive, general equilibrium models in which the system boundary of the problem (e.g., an LCA of a product) being analyzed is on the level of the national economy.

Economic Input–Output Models for Environmental Life-Cycle Assessment

▪ Abstract An overview of the near and far-field breakup and atomization of a liquid jet by a high speed annular gas jet is presented. The various regimes of liquid jet breakup are discussed in the parameter space of the liquid Reynolds number, the aerodynamic Weber number, and the ratio of the momentum fluxes between the gas and the liquid streams. Recent measurements of the gas-liquid interfacial instabilities are reviewed and used to analyze the underlying physical mechanisms involved in the primary breakup of the liquid jet. This process is shown to consist of the periodic stripping of liquid sheets, or ligaments, which subsequently break up into smaller lumps or drops. Models to predict the liquid shedding frequency, as well as the global parameters of the spray such as the liquid core length and spray spreading angle are discussed and compared with the experiments. The role of the secondary liquid breakup on the far-field atomization of the liquid jet is also considered, and an attempt is made to ap...

Liquid Jet Instability and Atomization in a Coaxial Gas Stream

Surfactants form a unique class of chemical compounds. This review provides an introduction to the nature and physical properties of surfactants, emphasizing their ability to radically alter surface and interfacial properties and to self-associate and solubilize themselves in micelles. These properties provide the means to apply surfactants in wettability modification, detergency, and the displacement of liquid phases through porous media on one hand, and to stabilize dispersions (including foams, froths and emulsions), or to destabilize dispersions (again including foams and emulsions) on the other hand. These in turn lead to a vast array of practical application areas which are illustrated in terms of mineral and petroleum processing, biological systems, health and personal care products, foods, and crop protection.

http://www.beauty-review.nl/wp-content/uploads/2014/06/Surfactants-and-their-applications.pdf

2 Surfactants and their applications

Bubble-size distributions and flow fields in bubble columns are calculated numerically. The population balance is simplified and reduced to a balance equation for the average bubble volume. Models developed predict the rate of bubble breakup and coalescence based on physical principles. The flow fields are numerically calculated for bubble columns with cylindrical cross sections using the Euler-Euler method. The newly derived balance equations for the average bubble volumes are implemented into a commercial CFD code. The solutions of the balance equation for high superficial gas velocities result mainly in two fractions: one for the fraction with small and the other for the fraction with large bubble diameters. Both are considered pseudocontinuous phases, in addition to the liquid phase. The calculated flow fields are characterized by several large-scale vortices. The local volume fractions of gas and liquid are locally inhomogeneous and highly time-dependent. The time-averaged flow field is axisymmetric and stationary. The calculated volume fractions, velocities, and bubble-size distributions agree well with existing and previously published experimental results for bubble columns up to 0.3 m in diameter.

Bubble‐Size distributions and flow fields in bubble columns

Design procedures for gas sparged contractors for both low and high viscosity liquids were developed to predict overall kLa. Bubble size close to the orifice, for moderately high gas rates, was found to increase at a rate proportional to one third power of gas rate and one tenth power of liquid viscosity. Bubble breakup phenomenon was shown to be related to liquid turbulence in the vessel rather than gas turbulence in the orifice. Procedures were developed through a simple liquid circulation model to obtain a criterion for the onset of bubble breakup. Results indicate that intense liquid mixing and high interfacial area can be achieved in low viscosity liquids by gas sparging alone. In high viscosity fluids, bubble breakup was not observed. The liquid circulation model predicts laminar flow at these experimental conditions over the complete range of gas rates observed.

The design of gas sparged devices for viscous liquid systems

Instances are cited in which the pressure gradient in an oil pipe line has been reduced by the injection of water into the pipeline. A general mathematical analysis is presented for two immiscible liquids flowing (1) in two layers between wide parallel plates, and (2) concentrically in a circular pipe. This will form a basis for the further study of oil-water systems. Equations are derived relating the volumetric flow rates and the viscosities of the liquids with the pressure gradient. The conditions for which minimum pressure gradients and minimum power requirements occur were determined and these minimum values have been compared with known values for a pipeline flowing full with only a single liquid. The factors by which the pressure gradient and power requirement can be reduced are very large. For example, for an oil of viscosity 1,000 cp. flowing concentrically with water, the reduction factor is approximately 500. The pressure gradient reduction factors reported in the literature are compared with those predicted by theory, and conclusions are drawn regarding the position of the water phase.

The effect of the less viscous liquid in the laminar flow of two immiscible liquids

The flow characteristics of the two-phase system —white mineral oil and water—were examined in a horizontal, smooth, one-inch pipe. Flow conditions were investigated over a range of input oil-water volume ratios from 0.1 to 10 at thirteen superficial water velocities ranging from 0.116 ft./sec. to 3.55 ft./sec. A theoretical analysis of the laminar flow of two immiscible liquids between wide parallel plates yielded a modified parallel plate friction factor based on the water properties and the superficial water velocity. It was evaluated for a number of input oil-water volume ratios and plotted against the superficial water velocity. The experimental pressure drop data that were obtained were correlated using a modified Fanning friction factor which was evaluated for the range of input ratios studied and correlated with the superfical water velocity. A flow pattern correlation was obtained for visually observed types of flow—bubble, stratified and mixed—and it was shown that these patterns occurred in laminar, transitional or turbulent conditions of flow. The theoretical analysis for flow between wide parallel plates was adapted to obtain hold-up relationships, and a plot of the hold-up ratio HR (the input divided by the in situ oil-water volume ratio) versus the input oil-water ratio was constructed. This plot indicated that in the laminar region of flow the hold-up was not dependent on the superficial water velocity but was only a function of liquid viscosity and input ratio. Experimental results for flow in the pipe conformed with this prediction while indicating that in the turbulent region superficial water velocity was also a factor.

T. W. F. Russell

Papers

The design of gas sparged devices for viscous liquid systems

The effect of the less viscous liquid in the laminar flow of two immiscible liquids

Horizontal pipeline flow of mixtures of oil and water

Bubble breakage in pipeline flow

Reactor Analysis and Process Synthesis for a Class of Complex Reactions