The Experts below are selected from a list of 273 Experts worldwide ranked by ideXlab platform
George Karaiskakis - One of the best experts on this subject based on the ideXlab platform.
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time distribution of adsorption entropy of gases on heterogeneous surfaces by Reversed Flow gas chromatography
Journal of Chromatography A, 2006Co-Authors: N A Katsanos, Athanasia Koliadima, Dimitrios Gavril, John Kapolos, N Bakaoukas, V C Loukopoulos, George KaraiskakisAbstract:The Reversed-Flow gas chromatography (RF-GC) technique has been applied to measure the adsorption entropy over time, when gaseous pentane is adsorbed on the surface of two solids (gamma-alumina and a silica supported rhodium catalyst) at 393.15 and 413.15K, respectively. Utilizing experimental chromatographic data, this novel methodology also permits the simultaneous measurement of the local adsorption energy, epsilon, local equilibrium adsorbed concentration, c(s)(*), and local adsorption isotherm, theta(p, T, epsilon) in a time resolved way. In contrast with other inverse gas chromatographic methods, which determine the standard entropy at zero surface coverage, the present method operates over a wide range of surface coverage taking into account not only the adsorbate-adsorbent interaction, but also the adsorbate-adsorbate interaction. One of the most interesting observations of the present work is the fact that the interaction of n-pentane is spontaneous on the Rh/SiO(2) catalyst for a very short time interval compared to that on gamma-Al(2)O(3). This can explain the different kinetic behavior of each particular gas-solid system, and it can be attributed to the fact that large amounts of n-C(5)H(12) are present on the active sites of the Rh/SiO(2) catalyst compared to those on gamma-Al(2)O(3), as the local equilibrium adsorbed concentration values, c(s)(*), indicate.
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Study of the mechanism of the interaction of vinyl chloride with water by Reversed-Flow gas chromatography
Journal of chromatography. A, 2001Co-Authors: Dimitrios Gavril, Khan Atta Rashid, George KaraiskakisAbstract:Abstract The investigation of the mechanism for the interaction of vinyl chloride (VC) with liquid foods is of great significance in food science. In the present work the model system VC–water was studied by using the relatively new technique of Reversed-Flow gas chromatography. Using suitable mathematical analysis the following physicochemical quantities were determined: (a) diffusion coefficients of VC into water, (b) overall mass transfer coefficients of VC in the water, and in the carrier gas nitrogen, (c) partition coefficients of VC between water and nitrogen, and (d) constants of Henry’s law for the adsorption of VC by water. From the variation of the above parameters with temperature, and the stirring rate of the water, useful conclusions concerning the mechanism for the VC–water interaction were extracted. The experimental results for the transfer of VC into the bulk water suggest (i) a mechanism consisted of a fast equilibrium step between the VC in the gas phase and in the interface, followed by a slow adsorption of VC into the bulk of water, which is the rate-determining step, when the water is quiescent, and (ii) a mechanism consisted of a slow diffusion of VC from the gas phase to the interface, which is the rate-determining step, followed by a fast equilibrium step between the VC in the interface and in the water bulk, when the water is stirred.
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Gas chromatographic study of interaction between vinyl chloride and poly(vinyl chloride)
Journal of Chromatography A, 1991Co-Authors: Athanasia Koliadima, P. Agathonos, George KaraiskakisAbstract:Abstract A Reversed-Flow gas chromatographic method for studying the interactions between vinyl chloride monomer (VCM)_and poly(vinyl chloride) (PVC) is described. The method permits the calculation of the VCM diffusion coefficient in the gas phase and the determination of the partition coefficient of VCM between PVC and the carrier gas (nitrogen). From the variation of the partition coefficients with temperature, differential thermodynamic parameters (enthalpy and entropy) of adsorption of VCM on PVC were calculated. These are discussed in comparison with the same parameters as determined by inverse gas chromatography.
Chen Yunlin - One of the best experts on this subject based on the ideXlab platform.
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Local overall gas–liquid mass transfer coefficient in a gas–liquid–solid Reversed Flow jet loop reactor
Chemical Engineering Journal, 2002Co-Authors: Wen Jianping, Na Ping, Huang Lin, Chen YunlinAbstract:Abstract Local overall gas–liquid mass transfer coefficients ( K L a ) of gas–liquid–solid three-phase Reversed Flow jet loop reactors have been experimentally investigated by means of a transient gassing-in method. Effects of liquid jet Flow rate, gas jet Flow rate, particle density, particle diameter, solid loading, nozzle diameter and axial position on local overall gas–liquid mass transfer coefficient profiles are discussed. It was observed that the local overall gas–liquid mass transfer coefficient profiles of the Reversed Flow jet loop reactor with a three-phase system increase with increase in gas jet Flow rates and liquid jet Flow rates and particle density and particle diameter, and with decrease in nozzle diameter and axial position. The presence of solids at low concentrations increases the local overall gas–liquid mass transfer coefficient profiles, and the optimum of adding solid loading for maximum profile of the local overall K L a was found to be 0.16×10 −3 m 3 corresponding to a solid volume fraction, ϵ S =2.5%.
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Solid–liquid mass transfer in a gas–liquid–solid three-phase Reversed Flow jet loop reactor
Chemical Engineering Journal, 2000Co-Authors: Wen Jianping, Huang Lin, Zhu Yong, Li Chao, Chen YunlinAbstract:Abstract Solid–liquid mass transfer in gas–liquid–solid three-phase Reversed Flow jet loop reactors was experimentally investigated by means of an electrochemical method, and the effects of liquid jet Flow rate, gas jet Flow rate, particle size, particle density and nozzle diameter on the solid–liquid mass transfer coefficient were evaluated. The solid–liquid mass transfer coefficients in gas–liquid–solid three-phase Reversed Flow jet loop reactors are higher than those in the corresponding liquid–solid two-phase Reversed Flow jet loop reactors. A generalized correlation is developed which more accurately and conveniently predicts solid–liquid mass transfer in gas–liquid–solid three-phase Reversed Flow jet loop reactors.
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Local overall volumetric gas–liquid mass transfer coefficients in gas–liquid–solid Reversed Flow jet loop bioreactor with a non-Newtonian fluid
Biochemical engineering journal, 2000Co-Authors: Wen Jianping, Na Ping, Huang Lin, Chen YunlinAbstract:The local overall volumetric gas-liquid mass transfer coefficients at the specified point in a gas-liquid-solid three-phase Reversed Flow jet loop bioreactor (JLB) with a non-Newtonian fluid was experimentally investigated by a transient gassing-in method. The effects of liquid jet Flow rate, gas jet Flow rate, particle density, particle diameter, solids loading, nozzle diameter and CMC concentration on the local overall volumetric gas-liquid mass transfer coefficient (K(L)a) profiles were discussed. It was observed that local overall K(L)a profiles in the three-phase Reversed Flow JLB with non-Newtonian fluid increased with the increase of gas jet Flow rate, liquid jet Flow rate, particle density and particle diameter, but decreased with the increase of the nozzle diameter and CMC concentration. The presence of solids at a low concentration increased the local overall K(L)a profiles, and the optimum of solids loading for a maximum profile of the local overall K(L)a was found to be 0.18x10(-3)m(3) corresponding to a solids volume fraction, varepsilon(S)=2.8%.
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LOCAL OVERALL GAS–LIQUID VOLUMETRIC MASS TRANSFER COEFFICIENTS IN A GAS–LIQUID TWO-PHASE Reversed Flow JET LOOP REACTOR
Chemical Engineering Communications, 2000Co-Authors: Wen Jianping, Huang Lin, Tian Gang, Chen YunlinAbstract:Local overall gas-liquid volumetric mass transfer coefficient profiles at the specified point were experimentally investigated in a gas–liquid two-phase Reversed Flow jet loop reactor with Newtonian and non-Newtonian systems. It was observed that the local overall gas-liquid volumetric mass transfer coefficient profiles of this reactor with Newtonian and non-Newtonian systems increase with increase in gas jet Flow rates and liquid jet Flow rates, and with decrease in nozzle diameter and CMC concentration.
B W Van Oudheusden - One of the best experts on this subject based on the ideXlab platform.
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unsteady aspects of an incident shock wave turbulent boundary layer interaction
Journal of Fluid Mechanics, 2009Co-Authors: R A Humble, Fulvio Scarano, B W Van OudheusdenAbstract:An incident shock wave/turbulent boundary layer interaction at Mach 2.1 is investigated using particle image velocimetry in combination with data processing using the proper orthogonal decomposition, to obtain an instantaneous and statistical description of the unsteady Flow organization. The global structure of the interaction is observed to vary considerably in time. Although Reversed Flow is often measured instantaneously, on average no Reversed Flow is observed. On an instantaneous basis, the interaction exhibits a multi-layered structure, characterized by a relatively highvelocity outer region and low-velocity inner region. Discrete vortical structures are prevalent along their interface, which create an intermittent fluid exchange as they propagate downstream. A statistical analysis suggests that the instantaneous fullness of the incoming boundary layer velocity profile is (weakly) correlated with the size of the separation bubble and position of the reflected shock wave. The eigenmodes show an energetic association between velocity fluctuations within the incoming boundary layer, separated Flow region and across the reflected shock wave, and portray subspace features that represent the phenomenology observed within the instantaneous realizations.
R A Humble - One of the best experts on this subject based on the ideXlab platform.
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unsteady aspects of an incident shock wave turbulent boundary layer interaction
Journal of Fluid Mechanics, 2009Co-Authors: R A Humble, Fulvio Scarano, B W Van OudheusdenAbstract:An incident shock wave/turbulent boundary layer interaction at Mach 2.1 is investigated using particle image velocimetry in combination with data processing using the proper orthogonal decomposition, to obtain an instantaneous and statistical description of the unsteady Flow organization. The global structure of the interaction is observed to vary considerably in time. Although Reversed Flow is often measured instantaneously, on average no Reversed Flow is observed. On an instantaneous basis, the interaction exhibits a multi-layered structure, characterized by a relatively highvelocity outer region and low-velocity inner region. Discrete vortical structures are prevalent along their interface, which create an intermittent fluid exchange as they propagate downstream. A statistical analysis suggests that the instantaneous fullness of the incoming boundary layer velocity profile is (weakly) correlated with the size of the separation bubble and position of the reflected shock wave. The eigenmodes show an energetic association between velocity fluctuations within the incoming boundary layer, separated Flow region and across the reflected shock wave, and portray subspace features that represent the phenomenology observed within the instantaneous realizations.
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particle image velocimetry measurements of a shock wave turbulent boundary layer interaction
Experiments in Fluids, 2007Co-Authors: R A Humble, Fulvio Scarano, B W Van OudheusdenAbstract:Particle image velocimetry is used to investigate the interaction between an incident shock wave and a turbulent boundary layer at Mach 2.1. A particle response assessment establishes the fidelity of the tracer particles. The undisturbed boundary layer is characterized in detail. The mean velocity field of the interaction shows the incident and reflected shock wave pattern, as well as the boundary layer distortion. Significant Reversed Flow is measured instantaneously, although, on average no Reversed Flow is observed. The interaction instantaneously exhibits a multi-layered structure, namely, a high-velocity outer region and a low-velocity inner region. Flow turbulence shows the highest intensity in the region beneath the impingement of the incident shock wave. The turbulent fluctuations are found to be highly anisotropic, with the streamwise component dominating. A distinct streamwise-oriented region of relatively large kinematic Reynolds shear stress magnitude appears within the lower half of the redeveloping boundary layer. Boundary layer recovery towards initial equilibrium conditions appears to be a gradual process.
H C Carlson - One of the best experts on this subject based on the ideXlab platform.
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Reversed Flow events in the cusp ionosphere detected by superdarn hf radars
Journal of Geophysical Research, 2011Co-Authors: K Oksavik, J Moen, E H Rekaa, H C Carlson, Mark LesterAbstract:[1] We present several examples of Reversed Flow events (RFEs) from the cusp ionosphere. RFEs are 100–200 km wide Flow channels opposing the background plasma convection. RFEs were discovered a few years ago by the incoherent scatter European Incoherent Scatter Svalbard Radar. In this paper we show that coherent scatter Super Dual Auroral Radar Network (SuperDARN) HF radars can also see RFEs. We report a close relationship between RFEs and the development of HF backscatter power and spectral width. Wide spectra were seen near the edges of the RFEs (i.e., associated with the Flow shear), and there was a significant increase in SuperDARN HF backscatter power when the RFE expanded. This increase in power is much faster than anticipated from the gradient drift instability alone, supporting the hypothesis that RFE Flow shears foster rapid growth of Kelvin-Helmholtz instabilities. That decameter-scale irregularities form so rapidly should be an important guide to the development of instability theory for cascade of plasma irregularities from larger to smaller scale sizes.
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on the relationship between thin birkeland current arcs and Reversed Flow channels in the winter cusp cleft ionosphere
Journal of Geophysical Research, 2008Co-Authors: K Oksavik, J Moen, H C Carlson, Y Rinne, Ryoichi Fujii, H J OpgenoorthAbstract:[1] In this paper we study Reversed Flow events (RFEs) that seem regulated by Birkeland current arcs in the winter cusp ionosphere above Svalbard. An RFE is a longitudinally elongated, 100–200 km wide channel, in which the Flow direction is opposite to the background convection, persisting for 10–20 min. The RFE onset occurs with the brightening of a discrete arc near the open-closed boundary. The auroral arc is situated exactly at a sharp clockwise Flow reversal, consistent with a converging electric field and an upward field-aligned current. One category of RFEs propagates into the polar cap in tandem with poleward moving auroral forms, while another category of RFEs moves with the cusp/cleft boundary. The RFE phenomenon is addressed to a region void of electron precipitation, and in lack of direct sunlight the E-region conductivity will be very low. We propose two possible explanations: (1) the RFE channel may be a region where two MI current loops, forced by independent voltage generators, couple through a poorly conducting ionosphere and (2) the Reversed Flow channel may be the ionospheric footprint of an inverted V-type coupling region. Electron beams of <1 keV will not give rise to significant conductivity gradients, and the form of a discontinuity in the magnetospheric electric field will be conserved when mapped down to the ionosphere, although reduced in amplitude. These two explanations may be related in the sense that the boundary discontinuity in the magnetospheric electric field in (1) may be the driver for the inverted V in (2).
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Reversed Flow events in the winter cusp ionosphere observed by the european incoherent scatter eiscat svalbard radar
Journal of Geophysical Research, 2007Co-Authors: Y Rinne, K Oksavik, J Moen, H C CarlsonAbstract:[1] High-resolution fast azimuth sweeps by the European Incoherent Scatter (EISCAT) Svalbard radar provide an unparalleled opportunity to study small-scale Flow disturbances in the cusp ionosphere. Observations from 11 days of the winter cusp ionosphere of highresolution ion Flow data have been analyzed. Transient channels of Reversed plasma Flow appear to be a regular feature of the cusp, and they were seen in 16% of 767 analyzed EISCAT Svalbard Radar (ESR) scans. We introduce a new descriptive term, Reversed Flow events (RFEs), for this class of events. RFEs are defined as longitudinally elongated segments of transiently enhanced ion Flow in the direction opposite to the background Flow. RFEs typically occurred near the cusp inFlow region in association with enhancements in the polar cap convection observed by the Super Dual Auroral Radar Network (SuperDARN). Their lifetime was found to be � 19 min on average. Their longitudinal dimension typically exceeded the ESR field of view (>400–600 km), and ranged from � 50 to 250 km in latitude. The occurrence rate of RFEs appears independent of the BZ and BY component polarity of the interplanetary magnetic field (IMF), and RFEs occurred for clock angles between 40 and 240. RFE ion Flow was in 95% of the cases documented to oppose the magnetic tension force, and RFEs cannot be interpreted in terms of newly opened flux. RFEs formed one by one and never simultaneously in pairs. To explain these observations, we propose an asymmetric version of the Southwood (1987) twin cell flux transfer event model to account for significant IMF BY, in which only the poleward cell located on open field lines develops.
