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

Design and implementation of a multi-octave-band audio camera for realtime diagnosis

Noise pollution investigation takes advantage of two common methods of diagnosis: measurement using a Sound Level Meter and acoustical imaging. The former enables a detailed analysis of the surrounding noise spectrum whereas the latter is rather used for source localization. Both approaches complete each other, and merging them into a unique system, working in realtime, would offer new possibilities of dynamic diagnosis. This paper describes the design of a complete system for this purpose: imaging in realtime the acoustic field at different octave bands, with a convenient device. The acoustic field is sampled in time and space using an array of MEMS microphones. This recent technology enables a compact and fully digital design of the system. However, performing realtime imaging with resource-intensive algorithm on a large amount of measured data confronts with a technical challenge. This is overcome by executing the whole process on a Graphic Processing Unit, which has recently become an attractive device for parallel computing

L’Allier face à la métropolisation

La métropolisation est un processus de sélection des territoires, à travers la concentration des hommes et des activités dans les villes les plus importantes et les plus dynamiques. Dans ce contexte, on peut s’interroger sur la place des territoires apparemment en marge. Le département de l’Allier (en Auvergne) fournit un bon exemple des dynamiques dans des espaces métropolisés par des centres extérieurs mais offrant néanmoins des formes d’intégration.Metropolization is a selective process of human and economic concentration in the most dynamic cities. In this context, what is the situation of territories occupying a so-called marginal position? The department of Allier (Auvergne, France) offers a good example of sociospatial dynamics in a metropolized space, depending on external urban centres but also opposing certain features of integration

Plasmon scattering approach to energy exchange and high frequency noise in nu=2 quantum Hall edge channels

Inter-edge channel interactions in the quantum Hall regime at filling factor nu= 2 are analyzed within a plasmon scattering formalism. We derive analytical expressions for energy redistribution amongst edge channels and for high frequency noise, which are shown to fully characterize the low energy plasmon scattering. In the strong interaction limit, the predictions for energy redistribution are compared with recent experimental data and found to reproduce most of the observed features. Quantitative agreement can be achieved by assuming 25 % of the injected energy is lost towards other degrees of freedom, possibly the additional gapless excitations predicted for smooth edge potentials.Comment: 4 pages, 4 figure

Cardiometabolic Risk Factors and Associated Features in 5th Grade Schoolchildren in Ouagadougou, Burkina Faso (West Africa)

The onset of cardiometabolic risk factors in childhood may be tracked into adulthood. However, little is known about such risk factors particularly in African schoolchildren. We conducted in Ouagadougou the capital city of Burkina Faso (West Africa) a cross-sectional study in 5th grade pupils of 12 schools (4 private and 8 public of which 2 were periurban). Weight, height, and blood pressure (BP) were measured and fasting serum lipids and glycaemia were determined. Sample mean age was 11.8 ±1.4 y (207 children, 51% girls). Mean total cholesterol (TC), LDL-C, HDL-C and triglycerides were 133.9, 83.5, 45.1 and 67.1 mg/dl, respectively; glycaemia stood at 87.9 ±7.1 mg/dl. Systolic (SBP) and Diastolic Blood Pressure (DBP) were 103.2 and 62.3 mmHg respectively. The main risk factor was low HDL-C (19.3%) followed by high TC and LDL-C (11.6% each). Elevated SBP and DBP were 9.7% and 4.3%, respectively. Being a girl was independently associated with increased serum lipids including HDL-C paradoxically. BMI was independently associated with increased BP. While attending a private school was independently associated (p<0.01) with higher HDL-C and lower TG and DBP, attending urban (vs periurban) school and higher age were independently associated with lower HDL-C. A sizeable proportion of children exhibited cardiometabolic risk factors and therefore, preventive measures would appear timely in low income country schoolchildren, and not only strategies targeting malnutrition

Color Correction in the Framework of Color Logarithmic Image Processing

International audienceThe Logarithmic Image Processing (LIP) approach is a mathematical framework developed for the representation and processing of images valued in a bounded intensity range. The LIP theory is physically and psychophysically well justified since it is consistent with several laws of human brightness perception and with the multiplicative image formation model. In this paper, the so-called Color Logarithmic Image Processing (CoLIP) framework is introduced. This novel framework expands the LIP theory to color images in the context of the human color visual perception. Color images are represented by their color tone functions that can be combined by means of basic operations, addition, scalar multiplication and subtraction, opening new pathways for color image processing. In order to highlight the CoLIP relevance with color constancy, a color correction method based on the subtraction is proposed and tested on CoLIP approach and Logarithmic hUe eXtension (LUX) approach, also based on the LIP theory, on differently illuminated images: underwater images with a blue illuminant, and indoor images with yellow illuminant