Hydrodynamics and mass transfer in bubble column: Influence of liquid phase surface tension

According to literature, few experiments are performed in organic solvents which are mostly used in commercial gas–liquid reactors. However, it is commonly accepted that data obtained in aqueous solution allow to predict the surface tension effects, and to model the behaviour of organic solvents. In this work, we examine the validity of this approximation. In this objective, the flows observed in two pure media having similar viscosity but different surface tension—respectively, water (reference) and cyclohexane (solvent)—are successively compared at two scales: in a bubble column and in bubble plumes. In bubble plumes, as expected, the mean bubble size is smaller in the medium having the smallest surface tension (cyclohexane), but for this medium the destabilisation of flow is observed to occur at smaller gas velocity, due to break-up and coalescence phenomena. In bubble column, these phenomena induce the bubbling transition regime at lower gas velocity, whatever the operating conditions for liquid phase: batch or continuous. Consequently, when the two media are used at similar gas superficial velocity, but in different hydrodynamic regimes, greater gas hold-up and smaller bubble diameter can be observed in water; the interfacial area is then not always higher in cyclohexane. This result differs from the behaviour observed in the literature for aqueous solutions. The analysis of bubble plumes in aqueous solutions of butanol shows that this difference is due to a fundamental difference in coalescent behaviour between pure solvents and aqueous mixtures: the surface tension effect is less important in pure liquid than in aqueous solutions, because of the specific behaviour of surfactants. It is then still difficult to predict a priori the bubbling regime or the flow characteristics for a given medium, and all the more to choose an appropriate liquid as a model for industrial solvents

Axial and Radial Investigation of Hydrodynamics in a Bubble Column;Influence of Fluids Flow Rates and Sparger Type

A detailed investigation of local hydrodynamics in a pilot plant bubble column has been performed using various techniques, exploring both axial and radial variations of the gas hold-up, bubble average diameter and frequency, surface area. A wide range of operating conditions has been explored up to large gas and liquid flow rates, with two sparger types. Two main complementary techniques were used: a quasi local measurement of gas hold-up via series of differential pressure sensors to get the axial variation and a double optic probe giving radial variations of gad hold-up, bubble average size and frequency and surface area. According to axial evolutions, three zones, where radial evolutions have been detailed,have been separated: at the bottom the gas injection zone, the large central region or column bulk and the disengagement zone at the column top. It was found that significant axial and radial variations of the two phase flow characteristics do exist even in the so called homogeneous regime. The normalized profiles of bubble frequency appear sparger and gas velocity independent contrary to bubble diameter, gas hold-up and interfacial area normalized profiles. In any case bubbles are larger in the sparger zone than elsewhere. The main result of this work is the very strong effect of liquid flow on bubble column hydrodynamics at low gas flow rate. First the flow regime map observed in batch mode is dramatically modified with a drastic reduction of the homogeneous regime region, up to a complete heterogeneous regime in the working conditions (uG> 0.02 m/s). On the contrary, liquid flow has limited effects at very high gas flow rates. A large data bank is provided to be used for example in detailed comparison with CFD calculations

Local Identity in Food Packaging Design Case Study : Samut Songkhram Province

Abstract    “Small and Micro Community Enterprise” (SMCE) has been the major factor to drive the economy of Thai communities. Nowadays, Thai SMCE lacks valid and appropriate directions, by focusing mainly on business procedures in order to struggle in the competitive free-capitalism export market as to the globalization stream. Thus, the directions of packaging design of Thai community products have now been influenced by international conditions. The identity and uniqueness, therefore, are inevitably swept away by the globalized society. The aims of this research are 1) to study the way of geometric art composition on packaging in order to create the image and reflect both characteristics and origins of community food products in Samut Songkhram province and 2) to seek for the way to apply the identity of the community onto the food products’ packaging, which is used for retail trade, transportation, and sale promotion, making it usable and cost-effective.    Researching process to create a local identity for food packaging design in Thailand started from valid and appropriate directions, by defining “SMCE” with a new paradigm aiming to create an integrated balanced system for the strength and the sustainability of communities. This study divides the economic advantage factors of communities into three categories, including 1) non-monetary capital, 2)knowledge, and 3) community marketing. The Sufficiency Economy philosophy is used as the framework in this study, and a guideline for applying the philosophy to the community products for highest productivity.    A study shows that the local food products can be coded by that 3 variables factors, separating the smaller group of the local food products into 6 criteria, which are 1) Types of raw materials 2) Opportunities to replace the raw materials 3) Processing 4) Familiarity of products 5) Reputation of brands and 6) Product’s life cycle, which divide the local food products to the total of 64 codes to be used as the basis of design guidelines to make it suitable for the available market within the market in and outside the community as well as the export markets. This research will not include necessary food consumed in everyday life.    The guidelines of local identity design principle for food packaging are analyzed through a table matrix from the variable factors of community economic advantages with 4 basic marketing functions of packaging 1) Communications and identification 2) Reflection of brand image 3) Accessibility to target market and 4) Sale promotion, which can make the total of 32 principles for local food packaging design, which can make use of the design analysis to create a layout of questionnaire for finding the real need of target group by 8 principles and 32 groups of local food product suitable for distribution in a particular season, and 2 groups of local product have a good opportunity to be sold in a market outside community or export market, then the design principles that define the guidelines to be applied for all types of local food product in community.Keywords: Local identity, Food packaging design, Community enterpris

Mass transfer in bubble column for industrial conditions—effects of organic medium, gas and liquid flowrates and column design

Most of available gas–liquid mass transfer data in bubble column have been obtained in aqueous media and in liquid batch conditions, contrary to industrial chemical reactor conditions. This work provides new data more relevant for industrial conditions, including comparison of water and organic media, effects of large liquid and gas velocities, perforated plates and sparger hole diameter. The usual dynamic O2 methods for mass transfer investigation were not convenient in this work (cyclohexane, liquid circulation). Steadystate mass transfer of CO2 in an absorption–desorption loop has been quantified by IR spectrometry. Using a simple RTD characterization, mass transfer efficiency and kLa have been calculated in a wide range of experimental conditions. Due to large column height and gas velocity, mass transfer efficiency is high, ranging between 40% and 90%. kLa values stand between 0.015 and 0.050 s−1 and depend mainly on superficial gas velocity. No significant effects of column design and media have been shown. At last, using both global and local hydrodynamics data, mass transfer connection with hydrodynamics has been investigated through kLa/G and kLa/a

On the reliability of an optical fibre probe in bubble column under industrial relevant operating conditions

When bubble columns are operated under industrial relevant conditions (high gas and liquid flow rates, large bubbles and vortices,. . .), local data, and especially bubble size values, are difficult to obtain. However, such data are essential for the comprehension of two-phase flow phenomena in order to design or to improve industrial installations. When high gas flow rates and organic liquids are used, intrusive optic probes are considered. This work investigates different ways to derive reliable local information on gas phase from double optic probe raw data. As far as possible, these results have been compared with global data, easier to measure in such conditions. Local gas hold-up, eG, and bubble frequency, fB, are easily obtained, but bubble velocity and bubble diameter determination is not obvious. For a better reliability, the final treatment that is proposed for velocity and size estimation is based on mean values only: the bubble velocity is considered as the most probable velocity ~v issued from raw signals inter-correlation function and the mean Sauter diameter is calculated through dSM ¼ 3~veG 2f B

Application of the double optic probe technique to distorted tumbling bubbles in aqueous or organic liquid

The optic probe technique is widely used to investigate bubble reactors. To derive values of bubble local velocities and bubble local sizes, a specific signal treatment is usually applied under severe assumptions for bubble path and shape. However, in most industrial reactors, bubble motion is chaotic and no common shape can be assumed. In this work, the reliability of the signal treatment associated with the optic probe technique is examined for distorted and tumbling bubbles. A double-tip optic probe is settled in a glass tank and the rise of bubbles is filmed simultaneously. Several trains of bubbles are studied, interactions between bubbles being gradually increased. Referring to image analysis, several ways to derive mean bubble velocities from optic probe data have been compared. Crenels from front tipand rear tipra w signals are associated and individual bubble velocities are derived. Nevertheless, complete velocity distributions are difficult to obtain, as they depend on the choice of the time within which the bubble is searched on the second tip. Using a simpler approach it is shown that the most probable velocity, calculated through the raw signals inter-correlation, is a correct estimation of the average bubble velocity. Concerning bubble size, bubble chord distributions show too high values due to bubble distortion and deviation. A simplified estimation of bubble mean Sauter diameter, using the most reliable measurements only (i.e., local gas hold-up, local mean bubbling frequency, and most probable bubble velocity), was tested for highly distorted bubbles; this method was validated both in water and cyclohexane

Refractory compounds abatement by adsorption and oxidative catalytic regeneration on activated carbon Experimental and modelling of competitive adsorption

Experimental and modelling of competitive adsorptio

Adsorption of aqueous organic mixtures on activated carbon: experiments and modelling of competitive adsorption

Experiments and modelling of competitive adsorptio