Letteratura scientifica selezionata sul tema "Voie Gac/Rsm"

Les composés organiques volatils (COV), sous-produits du métabolisme émis par l’ensemble desorganismes vivants, sont volatils en conditions environnementales en raison de leurs propriétés physicochimiques.Chez les bactéries, et notamment celles du genre Pseudomonas, les COV sontprincipalement étudiés pour leur capacité à inhiber des microorganismes phytopathogènes. Leur rôledans la communication, un mécanisme indispensable à la coordination des communautés bactérienneslors de la formation de biofilm, est rarement considéré.L'objectif des travaux menés est l'analyse les COVs produits par la souche Pseudomonas fluorescensMFE01 et leur impact sur sa communication. Les voies de communication de MFE01 sont peu connueset ne correspondent pas aux systèmes déjà décrits chez de nombreuses bactéries du genrePseudomonas. La caractérisation du bouquet de molécules émises par MFE01 met en évidence uneforte émission de 1-undécène. Un mutant du gène undA, codant l’enzyme de synthèse du 1-undécène,n’émet plus ce COV et a une capacité réduite à former des biofilms. L’exposition de ce mutant à du 1-undécène exogène restaure la formation de biofilm. Le 1-undécène serait donc une molécule decommunication intraspécifique chez P. fluorescens MFE01. Le gène undA semble être en opéron avecle gène rbdA, codant un senseur putatif. Nous formulons l’hypothèse que Rbda serait impliqué dans laperception du 1-undécène et que la transduction du signal s’effectuerait via la synthèse de di-guanosinemonophosphate cyclique, un messager secondaire connu pour induire la formation de biofilm.L’étude de la voie de régulation Gac/Rsm, connue pour gouverner le métabolisme et la communicationdes Pseudomonas, montre qu’elle module fortement la quantité et le profil de COV émis par MFE01.Cette voie pilote chez MFE01 l’émission de 1-undécène et l’inhibition aérienne du pathogène humainLegionella pneumophila ainsi que celle du phytopathogène Phytophtora infestans. L’expression du gènegacS, codant le senseur principal de la voie Gac/Rsm, serait activée par au moins un COV,potentiellement le 2-tridecanone et/ou le 2-undecanone
Volatile organic compounds (VOCs), by-products of metabolism emitted by all living organisms, arevolatile under environmental conditions due to their physicochemical properties. In bacteria, especiallythose of the genus Pseudomonas, VOCs are mainly studied for their ability to inhibit phytopathogenicmicroorganisms. Their role in communication, which is a crucial mechanism for coordinating bacterialcommunities during biofilm formation, is understudied.This research focuses on investigating VOCs emitted by the Pseudomonas fluorescens MFE01 strainand their implications in its communication. The uncharacterized communications pathways of MFE01are untypical and does not involve pathways already described in others Pseudomonas.Characterization of molecules the emitted by MFE01 reveals a huge emission of 1-undecene. A mutantlacking the undA gene, responsible for 1-undecene synthesis, no longer emits this VOC and exhibitsreduced biofilm formation capabilities. Exposure of this mutant to exogenous 1-undecene restoresbiofilm formation, Therefore, 1-undecene seems to be an intraspecific communication molecule in P.fluorescens MFE01. The undA gene seems to be in an operon with the rbdA gene, encoding a putativesensor. We hypothesize that Rbda is involved in 1-undecene perception with signal transduction likelyoccurring via the synthesis of cyclic di-guanosine monophosphate, a known secondary messenger thatinduces biofilm formation.Additionally, the study of the Gac/Rsm regulatory pathway, a critical regulator of metabolism andcommunication in Pseudomonas, demonstrates that it strongly modulates the quantity and profile ofVOCs emitted by MFE01. This pathway governs 1-undecene emission and the aerial inhibition of humanpathogen Legionella pneumophila and phytopathogen Phytophtora infestans by MFE01. At least oneVOC, possibly 2-tridecanone and/or 2-undecanone, may activate the expression of the gacS gene,which encodes the principal sensor of the Gac/Rsm pathway

The current study shows computational and experimental analysis of multiphase flows (gas-liquid two-phase flow) in channels with sudden area change. Four test sections used for sudden contraction and expansion of area in experiments and computational analysis. These are 0.5–0.375, 0.5–0.315, 0.5–0.19, 0.5–0.14, inversely true for expansion channels. Liquid Flow rates ranging from 0.005 kg/s to 0.03 kg/s employed, while gas flow rates ranging from 0.00049 kg/s to 0.029 kg/s implemented. First, single-phase flow consists of only water, and second two-phase Nitrogen-Water mixture flow analyzed experimentally and computationally. For Single-phase flow, two mathematical models used for comparison: the two transport equations k-epsilon turbulence model (K-Epsilon), and the five transport equations Reynolds stress turbulence interaction model (RSM). A Eulerian-Eulerian multiphase approach and the RSM mathematical model developed for two-phase gas-liquid flows based on current experimental data. As area changes, the pressure drop observed, which is directly proportional to the Reynolds number. The computational analysis can show precise prediction and a good agreement with experimental data when area ratio and pressure differences are smaller for laminar and turbulent flows in circular geometries. During two-phase flows, the pressure drop generated shows reasonable dependence on void fraction parameter, regardless of numerical analysis and experimental analysis.

In order to investigate the seismic vibration effect on two-phase flow structure, experiments were performed for upwards bubbly flow in an annulus channel with and without externally-induced vibration. The inner and outer diameters of the annulus are 19.1 mm and 38.1 mm respectively, and the total height of the test section is 2.32 m. To simulate seismic vibrations, the test section is attached to an eccentric cam vibration module with an eccentricity of 9.5 mm. The eccentric cam rotation speed can reach up to 210 rpm. Local two-phase flow parameters were measured along radial direction within the annulus gap using miniaturized four-sensor conductivity probe at axial location of z/Dh = 77. The semi-instantaneous local parameters at different vibration angles were analyzed by tracing the quasi-sinusoidal acceleration signal under vibration conditions. The results showed that the seismic vibration can significantly affect the local parameters in bubbly flow regime. Void fraction can increase by 10% compared with non-vibration condition. During the vibration cycle, the void fraction also changed greatly, especially in the near wall region. The interfacial area concentration (IAC) and Sauter mean diameter displayed the same behavior as the respective void fraction profiles.

The effect of an internal turbulent bubbly flow on vibrations of a channel wall is investigated in this paper both experimentally and theoretically. Vibrations of an isolated channel wall and associated wall pressure fluctuations are measured using several accelerometers and pressure transducers along streamwise direction under various gas void fractions and characteristic bubble diameters. A waveguide theory based mathematical model, i.e. a solution to the 3D Helmholtz Equation in an infinite long channel, and the physical properties of bubbles is developed to predict the spectral frequencies of the vibration and the wall pressure fluctuation, the corresponding attenuation coefficients of spectral peak and propagated phase speeds. Results show that compared with the same flow without bubbles, the presence of bubbles substantially enhances the power spectral density of the channel wall vibrations and pressure wall fluctuations in the 250–1200 Hz by up to 27 dB and 26 dB, respectively, and increases their overall rms values by up to 14.1 times and 12.7 times, respectively. In the lower frequency range than the resonant frequency of individual bubble, i.e. 250–1200 Hz range, both vibrations and spectral frequencies increase substantially with increasing void fraction and slightly with increasing bubble diameter. The origin for enhanced vibrations and wall pressure fluctuations is demonstrated to be the excitation of the streamwise propagated acoustic pressure waves, which are created by the initial energy generated during bubble formations. The measured magnitudes and trends of the frequency of the spectral peaks, their attenuation coefficients and phase velocities are well predicated by the model. All the three variables decrease as the void fraction or bubble diameter increase. But the effect of void fraction is much stronger than that of bubble diameter. For the same void fraction and bubble diameter, the peaks at higher spectral frequencies decay faster.

The characteristics of two-phase flow in a vertical pipe are investigated to gain a better understanding of vibration excitation mechanisms. An analytical model for two-phase flow in a pipe was developed by Sim et al. (2005), based on a power law for the distributions of flow parameters across the pipe diameter, such as gas velocity, liquid velocity and void fraction. An experimental study was undertaken to verify the model. The unsteady momentum flux impinging on a ‘turning tee’ (or a ‘circular plate’) has been measured at the exit of the pipe, using a force sensor. From the measured data, especially for slug flow, the predominant frequency and the RMS value of the unsteady momentum flux have been evaluated. It is found that the analytical method, given by Sim et al. for slug flow, can be used to predict the momentum flux.

A new, compact Fourier Transform Michelson interferometer (FTUVS) with an unapodized spectral resolution of 0.07 cm-1 has been developed for field and laboratory measurements of trace gas-phase species in the UV through visible region (200-800 nm). The instrument uses a flex pivot swing carriage mechanism driven by a voice coil actuator with a maximum translation of 5 cm. Essentially frictionless motion is achieved with high mirror velocity stability (rms velocity error less than 0.01%). Residual alighment errors are corrected dynamically to 0.1 μrad using a servo-controlled piezoelectric mirror tilt mechanism. The mirror moves at a constant velocity controlled by a commercial HP Laser Positioning System servo-axis driver which uses a 2.1 MHz Zeeman split, linearly polarized two-frequency He-Ne laser. The Doppoer shifted beam from the arm with the moving mirror is compared to the laser reference frequency for measurement and control of the mirror velocity.

In order to clarify the microscopic flow structure, the ultrasonic Doppler method was applied to the measurement of two-phase bubbly flow in vertical pipe (i.d.50mm). Liquid flow structure might strongly be influenced by the characteristic of the injected bubbles, i.e. bubbles’ size and void fraction. In this study, a bubble generator was newly designed with the purpose to control the bubble size and void fraction, independent of liquid main-flow rate. The experiment was performed at z/d = 66 from the bubble generator. Liquid flow rates were of the Reynolds numbers ranging from Rem = 3700 to 6200. The gas flow rate was constant at JG = 0.00348(m/s) at the measurement position. By analyzing the bubbles’ picture, it was confirmed that bubble size distribution and average bubble size were almost constant if the liquid flow rate were changed. The ultrasonic Doppler method has the capability of measuring the instantaneous velocity profiles of both phases at the same time. By processing the data based on pattern recognition, the recorded data can be classified to several groups. Using this method, the authors have tried to measure the bubbly flow in rectangular channel. In the present study, the application of this method to bubbly flow in circular pipe was satisfactory to obtain the liquid velocity distribution in bubbly flow and surrounding bubbles. From these results, it was clarified that velocity profile in bubbly flow in circular pipe has a maximum value near the pipe wall. Furthermore, velocity profiles around the bubble are influenced by leading bubbles.

The turbulent structure of flow field with microbubbles which is generated by electrolysis in a horizontal water channel is investigated at Reynolds number Rem = 24000 (based on the channel height). Firstly, Shadow Image Technique (SIT) is applied to investigate the relation between the shape and the velocity of microbubbles. The experiments have been carried out at the current value 100mA, 200mA, 300mA. The amount of gas generated by electrolysis per unit time is estimated 1.89–5.67 mm3/s. The void fraction is 0.95 × 10−5 – 2.93 × 10−4 %. The mode of the equivalent diameter is 5–10 μm regardless of the condition of the current value. In contrast the mean of the equivalent diameter increases with the increasing of the current value. The mean streamwise velocity of microbubbles increases with the current value. Secondly, Particle Image Velocimetry (PIV) is applied to investigate the turbulent structure in a microbubble channel flow. The experiments have been carried out at the current value 250mA, 300mA. The streamwise mean velocity decreases with the increasing of the current value. The velocity normal from the wall increases by microbubbles. The turbulent intensity with microbubble is bigger than that without microbubble. The Reynolds shear stress with microbubble, however, is smaller than that without microbubble. The decreasing of contribution to the friction coefficient of the turbulent component is calculated about 6.4 % using FIK identify at a low void fraction 2.93 × 10−4 %. The increasing of the frequency of inner interaction and outer interaction causes the decreasing of Reynolds shear stress is clarified by quadrant analysis.

Accurate prediction of the interfacial area concentration is essential to successful development of the interfacial transfer terms in the two-fluid model. Mechanistic modeling of the interfacial area concentration entirely relies on accurate local flow measurements over extensive flow conditions and channel geometries. From this point of view, accurate measurements of flow parameters such as void fraction, interfacial area concentration, gas velocity, bubble Sauter mean diameter, and bubble number density were performed by the image processing method at five axial locations in vertical upward bubbly flows using a 1.02 mm-diameter pipe. The frictional pressure loss was also measured by a differential pressure cell. In the experiment, the superficial liquid velocity and the void fraction ranged from 1.02 m/s to 4.89 m/s and from 0.980% to 24.6%, respectively. The obtained data give near complete information on the time-averaged local hydrodynamic parameters of two-phase flow. These data can be used for the development of reliable constitutive relations which reflect the true transfer mechanisms in two-phase flow. As the first step to understand the flow characteristics in mini-channels, the applicability of the existing drift-flux model, interfacial area correlation, and frictional pressure correlation was examined by the data obtained in the mini-channel.

Abstract Artificial lift of oil by electric submersible pumps (ESP) is often complicated by free gas in production. Free gas content in production leads to ESP performance degradation in rate and head. Gas slip in the ESP impeller is one of the reasons of ESP performance degradation. Thus, the goal of the work is to determine the gas slip coefficient i.e. liquid holdup in the ESP impeller. It is known that a gas-liquid mixture (GLM) flow characterized by a slippage effect. Gas slippage relative to the liquid determines the GLM structure (bubble, dispersed-bubble, slug, stratified or annular), as well as the difference between the GLM densities calculated by liquid holdup or liquid volume content. Special stand was designed and created to determine the liquid holdup at the Department of Oil Fields Development and Operation of Gubkin University. Liquid holdup in the impeller of the ESP was measured by the method of cutting off the flow. This paper shows the results of experimental studies of liquid holdup and gas slip velocity in the ESP impeller (ESP5-50) at a rotational speed n = 2997 rpm, at an absolute intake pressure Pin = 0.4 MPa. The dependence of the liquid holdup on liquid volume content (i.e. the dependence of the gas void fraction on gas volume fraction) was determined for the model GLM "water-air", "water-surfactant-air" with different foaming capacity. The degradation of the ESP characteristics, boundaries of surging and gas locking limits are determined taking into account liquid holdup. The dependence of gas holdup was experimentally obtained over the entire range of ESP operation (from 0.5∙Qopt to Qmax). A comparison of the obtained correlation with existing models is presented too. A new correlation for predicting liquid holdup in the ESP impeller for the low-rate wells operation is obtained. A new approach to determining the liquid holdup and consequently gas slip velocity in the ESP impeller is proposed.

Dresser Waukesha’s 275GL engine family released in 2009 consists of a 214 liter (13,048 in3) 12 cylinder, and a 285 liter (17,398 in3) 16 cylinder engine derived from Waukesha’s ATGL family. These 1000 RPM engines are typically used in mechanical drive applications for natural gas compression at 2500 to 3300 kWb (3400–4500 bhp). Through market analysis and voice of customer (VOC) interviews, it was determined that lower Oxides of Nitrogen (NOx) output is essential for future engine sales in North America. Meeting this requirement with a minimal impact to fuel efficiency, fuel tolerance, turndown range, and altitude capability were also desired. To meet the lower NOx requirement, combustion was improved using Computational Fluid Dynamics (CFD) modeling and Design of Experiments (DoE) tools. To assure the low NOx emissions were maintained throughout the desired operating regime, an NOx sensor based air/fuel ratio control system was developed. This new NOx control capability is an enhancement to the Dresser Waukesha ESM™ engine control system. The result is an engine family that consistently meets stringent 0.5 g/bhp-hr NOx levels while maintaining fuel efficiency, fuel tolerance, and turndown range. Reduced combustion pressure in the 275GL Low NOx engine has also allowed a power increase over the original 275GL engine. This paper will discuss the testing and results of this development.