Overview of mass transfer enhancement factor determination for acidic and basic compounds absorption in water

International audienceAbsorption or gas-liquid mass transfer is a fundamental unit operation useful in many fields, particularly gas treatment (wet scrubbing). Absorption of basic or acidic compounds, even hydrophobic, in water can be achieved successfully due to the mass transfer enhancement linked to proton transfer reactions in the liquid film. The absorption rate takes this phenomenon into account through the enhancement factor E, which depends on many parameters: nature (irreversible or reversible), kinetics and stoichiometry of the reaction, reagents and products diffusion coefficients and concentrations. This article gives an overview of the enhancement factor determination for acidic and basic compounds transfer in water. Modeling is performed for three compounds of interest, hydrogen sulfide H2S, methyl mercaptan CH3SH and ammonia NH3, for different scenarii to assess the influence of the pH. The results demonstrate that recombination with HO- and protonation reactions are respectively the two preponderant reactions for respectively acidic and basic compounds. They enable to reach large values of the enhancement factor at appropriated pH and to reduce the mass transfer resistance in the liquid film. Furthermore, the simulations highlight that, in many cases, knowledge of the reaction kinetics is not necessary since the reaction can be considered as instantaneous compared to mass transfer

Effect of pH on the heat resistance of spores Comparison of two models

International audienceAll published models describing the effect of pH on the heat resistance of spores can be regarded either as a linear first degree equation or a linear second degree equation. This work aimed to compare both models from 3 sets of published data for , Clostridium sporogenes and Bacillus stearothermophilus respectively. The relative quality of fit of each model with respect to the other depends on the species, the strain and the heating temperature. Parameter estimation was more reliable for the second degree model than for of the simple first degree equation. However, in the case of acidic foodstuffs, predictions obtained from the second degree model are more sensitive toward errors of parameter values. The second degree model is better from the point of view of safety at most frequent ranges of pH of foods. Moreover, for Clostridium botulinum , the goodness of fit of this model is clearly higher than that of the first degree equation. If this observation is confirmed by further work, the second degree model in application of standard calculations of heat processes of foods would be preferred

Exploring classically chaotic potentials with a matter wave quantum probe

We study an experimental setup in which a quantum probe, provided by a quasi-monomode guided atom laser, interacts with a static localized attractive potential whose characteristic parameters are tunable. In this system, classical mechanics predicts a transition from a regular to a chaotic behavior as a result of the coupling between the longitudinal and transverse degrees of freedom. Our experimental results display a clear signature of this transition. On the basis of extensive numerical simulations, we discuss the quantum versus classical physics predictions in this context. This system opens new possibilities for investigating quantum scattering, provides a new testing ground for classical and quantum chaos and enables to revisit the quantum-classical correspondence

Relative humidity impact on aerosol parameters in a Paris suburban area

Measurements of relative humidity (RH) and aerosol parameters (scattering cross section, size distributions and chemical composition), performed in ambient atmospheric conditions, have been used to study the influence of relative humidity on aerosol properties. The data were acquired in a suburban area south of Paris, between 18 and 24 July 2000, in the framework of the 'Etude et Simulation de la Qualit&#233; de l'air en Ile-de-France' (ESQUIF) program. According to the origin of the air masses arriving over the Paris area, the aerosol hygroscopicity is more or less pronounced. The aerosol chemical composition data were used as input of a thermodynamic model to simulate the variation of the aerosol water mass content with ambient <i>RH</i> and to determine the main inorganic salt compounds. The coupling of observations and modelling reveals the presence of deliquescence processes with hysteresis phenomenon in the hygroscopic growth cycle. Based on the H&#228;nel model, parameterisations of the scattering cross section, the modal radius of the accumulation mode of the size distribution and the aerosol water mass content, as a function of increasing RH, have been assessed. For the first time, a crosscheck of these parameterisations has been performed and shows that the hygroscopic behaviour of the accumulation mode can be coherently characterized by combined optical, size distribution and chemical measurements

Absorption and biodegradation of toluene: Optimization of its initial concentration and the biodegradable non-aqueous phase liquid volume fraction

International audienceDi (2-EthylHexyl) Phthalate (DEHP) was selected as a biodegradable organic solvent to be implemented in a two-phase partitioning bioreactor (TPPB) dedicated to remove a model hydrophobic volatile organic compound (VOC), toluene. In a first step, the absorption capacity of toluene in the selected organic solvent was examined according to the partition coefficients H. In a second step, toluene biodegradation in DEHP by non-acclimated activated sludge was carried out for different volume fractions of DEHP in water and five different toluene concentrations (4.3, 43, 106, 212 and 430 mg l−1). Toluene showed high affinity for DEHP with H = 0.99 Pa m3 mole−1. Both toluene and DEHP were completely consumed for 4.3 mg l−1 (initial toluene concentration) and a volume ratio of 0.1% DEHP in water. For an initial toluene concentration of 106 mg l−1 and a volume ratio of 0.1%, total toluene consumption and 87% DEHP degradation yield were obtained after seven days of incubation

Transport of Atom Packets in a Train of Ioffe-Pritchard Traps

We demonstrate transport and evaporative cooling of several atomic clouds in a chain of magnetic Ioffe-Pritchard traps moving at a low speed ($<1$~m/s). The trapping scheme relies on the use of a magnetic guide for transverse confinement and of magnets fixed on a conveyor belt for longitudinal trapping. This experiment introduces a new approach for parallelizing the production of Bose-Einstein condensates as well as for the realization of a continuous atom laser

Study of different membrane spargers used in waste water treatment : characterisation and performance

In urban waste water treatment, a novel gas sparger based on flexible rubber membrane has been used for the last ten years. The objective of this present work is to compare two flexible membranes (the new membrane and the old membrane provided by ONDEO-DEGREMONT group) used in waste water treatment. For this purpose, the different membrane properties (hole diameter, pressure drop, critical pressure, deflection at the centerline and elasticity) have been characterized. The bubble generation at the membranes with a single orifice and with four orifices have been studied and their performances have been compared in terms of interfacial area and power consumption. From the experimental and theoretical approach, the new membrane is less elastic (or more rigid) than the old membrane. The bubble diameters generated from the new membrane remain constant with the gas velocity through the orifice, whereas they increase logarithmically for the old membrane. The inverse behaviours are observed in terms of the bubble formation frequency. Moreover, the bubbles generated from the new membrane have significantly larger sizes and lower formation frequencies than those obtained with the old one. From these results, it can be noted that the new membrane has a behaviour comparable to a rigid orifice. No coalescence phenomenon at the bubble formation is observed from the new and the old membranes with four orifices. The interfacial area and the power consumption are evaluated and show slight differences between the interfacial area provided by the old and the new membranes for one value of power consumption

Fast transport of Bose-Einstein condensates

We propose an inverse method to accelerate without final excitation the adiabatic transport of a Bose Einstein condensate. The method, applicable to arbitrary potential traps, is based on a partial extension of the Lewis-Riesenfeld invariants, and provides transport protocols that satisfy exactly the no-excitation conditions without constraints or approximations. This inverse method is complemented by optimizing the trap trajectory with respect to different physical criteria and by studying the effect of noise

A quasi-monomode guided atom-laser from an all-optical Bose-Einstein condensate

We report the achievement of an optically guided and quasi-monomode atom laser, in all spin projection states ($m_F =$ -1, 0 and $+1$) of F=1 in Rubidium 87. The atom laser source is a Bose-Einstein condensate (BEC) in a crossed dipole trap, purified to any one spin projection state by a spin-distillation process applied during the evaporation to BEC. The atom laser is outcoupled by an inhomogenous magnetic field, applied along the waveguide axis. The mean excitation number in the transverse modes is $= 0.65 \pm 0.05$ for $m_F = 0$ and $= 0.8 \pm 0.3$ for the low field seeker $m_F = -1$

From multimode to monomode guided atom lasers: an entropic analysis

We have experimentally demonstrated a high level of control of the mode populations of guided atom lasers (GALs) by showing that the entropy per particle of an optically GAL, and the one of the trapped Bose Einstein condensate (BEC) from which it has been produced are the same. The BEC is prepared in a crossed beam optical dipole trap. We have achieved isentropic outcoupling for both magnetic and optical schemes. We can prepare GAL in a nearly pure monomode regime (85 % in the ground state). Furthermore, optical outcoupling enables the production of spinor guided atom lasers and opens the possibility to tailor their polarization