Correlation forkLaPrediction of Airlift Loop Reactors Including the Gas Phase Residence Time Effect

2015 ◽  
Vol 38 (11) ◽  
pp. 2002-2010 ◽  
Author(s):  
Ulrich Mießner ◽  
Ulf D. Kück ◽  
Viviane Dujardin ◽  
Susanne Heithoff ◽  
Norbert Räbiger
Keyword(s):  
Gas Phase ◽  
Residence Time ◽  
Time Effect ◽  
Airlift Loop

Comparative Study of GaN Growth Process by MOVPE

1999 ◽  
Vol 572 ◽  
Author(s):  
Jingxi Sun ◽  
J. M. Redwing ◽  
T. F. Kuech
Keyword(s):  
High Temperature ◽  
Comparative Study ◽  
Gas Phase ◽  
Residence Time ◽  
Gas Flow ◽  
Flow Sheet ◽  
Flow Zone ◽  
High Quality ◽  
Phase Temperature ◽  
High Temperature Gas

ABSTRACTA comparative study of two different MOVPE reactors used for GaN growth is presented. Computational fluid dynamics (CFD) was used to determine common gas phase and fluid flow behaviors within these reactors. This paper focuses on the common thermal fluid features of these two MOVPE reactors with different geometries and operating pressures that can grow device-quality GaN-based materials. Our study clearly shows that several growth conditions must be achieved in order to grow high quality GaN materials. The high-temperature gas flow zone must be limited to a very thin flow sheet above the susceptor, while the bulk gas phase temperature must be very low to prevent extensive pre-deposition reactions. These conditions lead to higher growth rates and improved material quality. A certain range of gas flow velocity inside the high-temperature gas flow zone is also required in order to minimize the residence time and improve the growth uniformity. These conditions can be achieved by the use of either a novel reactor structure such as a two-flow approach or by specific flow conditions. The quantitative ranges of flow velocities, gas phase temperature, and residence time required in these reactors to achieve high quality material and uniform growth are given.

Effect of Particle Residence Time on Particle Dispersion in a Plane Mixing Layer

1993 ◽  
Vol 115 (4) ◽  
pp. 751-759 ◽  
Author(s):  
Tsuneaki Ishima ◽  
Koichi Hishida ◽  
Masanobu Maeda
Keyword(s):  
Gas Phase ◽  
Residence Time ◽  
Time Scale ◽  
Characteristic Time ◽  
Mixing Layer ◽  
Particle Dispersion ◽  
Laser Doppler Velocimeter ◽  
Characteristic Time Scale ◽  
Two Phase ◽  
Particle Residence Time

A particle dispersion has been experimentally investigated in a two-dimensional mixing layer with a large relative velocity between particle and gas-phase in order to clarify the effect of particle residence time on particle dispersion. Spherical glass particles 42, 72, and 135 μm in diameter were loaded directly into the origin of the shear layer. Particle number density and the velocities of both particle and gas phase were measured by a laser Doppler velocimeter with modified signal processing for two-phase flow. The results confirmed that the characteristic time scale of the coherent eddy apparently became equivalent to a shorter characteristic time scale due to a less residence time. The particle dispersion coefficients were well correlated to the extended Stokes number defined as the ratio of the particle relaxation time to the substantial eddy characteristic time scale which was evaluated by taking account of the particle residence time.

scholarly journals Molecular mechanisms for the gas-phase conversion of intermediates during cellulose gasification under nitrogen and oxygen/nitrogen

2016 ◽  
Vol 22 (4) ◽  
pp. 343-353 ◽  
Author(s):  
Asuka Fukutome ◽  
Haruo Kawamoto ◽  
Shiro Saka
Keyword(s):  
Gas Phase ◽  
Residence Time ◽  
Molecular Mechanisms ◽  
High Efficiency ◽  
Experimental Setup ◽  
Phase Conversion ◽  
Gas Phase Reactions ◽  
Secondary Reaction Zone ◽  
Hydrocarbon Gas ◽  
Molten Phase

Gas-phase conversions of volatile intermediates from cellulose (AvicelPH-101) were studied using a two-stage experimental setup and compared with those of levoglucosan (1,6-anhydro-b-D-glucopyranose). Under N2or 7% O2/N2flow, vapors produced from the pyrolysis zone (500?C) degraded in the secondary reaction zone at 400,500, 600 or 900?C (residence time:0.8-1.4 s). The 69.3% (C-based) of levoglucosan was obtained at 400?C under N2flow along with 1,6-anhydro-b-D-glucofuranose (8.3 %, C-based), indicating that these anhydrosugars are the major volatile intermediates from cellulose pyrolysis. Levoglucosan and other volatiles started to fragment at 600?C, and cellulose was completely gasified at 900?C. Most gas/tar formations are explained by gas-phase reactions of levoglucosan reported previously, except for some minor reactions originating from the molten-phase pyrolysis, which produced benzene, furans and 1,6-anhydro-b-D-glucofuranose. Synergetic effects of O2and volatiles accelerated fragmentation and cellulose gasification was completed at 600?C, which reduced benzene and hydrocarbon gas productions. The molecular mechanisms including the action of O2as a biradical are discussed. These lines of information provide insights into the development of tar-free clean gasification that maintains high efficiency.

KINETICS OF LEAD ADSORPTION/DESORPTION ON GOETHITE: RESIDENCE TIME EFFECT

Soil Science ◽  
1999 ◽  
Vol 164 (1) ◽  
pp. 28-39 ◽  
Author(s):  
Matthew J. Eick ◽  
John D. Peak ◽  
Patrick V. Brady ◽  
John D. Pesek
Keyword(s):  
Residence Time ◽  
Time Effect ◽  
Lead Adsorption ◽  
Adsorption Desorption ◽  
Kinetics Of

Gas-phase residence time distribution in a falling-film microreactor

2006 ◽  
Vol 61 (2) ◽  
pp. 597-604 ◽  
Author(s):  
J.-M. Commenge ◽  
T. Obein ◽  
G. Genin ◽  
X. Framboisier ◽  
S. Rode ◽  
...  
Keyword(s):  
Gas Phase ◽  
Residence Time ◽  
Time Distribution ◽  
Residence Time Distribution ◽  
Falling Film

Cobalt, Cadmium, and Lead Sorption to Hydrous Iron Oxide: Residence Time Effect

1994 ◽  
Vol 58 (6) ◽  
pp. 1615 ◽  
Author(s):  
Calvin C. Ainsworth ◽  
Paul L. Gassman ◽  
James L. Pilon ◽  
William G. Van Der Sluys
Keyword(s):  
Iron Oxide ◽  
Residence Time ◽  
Time Effect ◽  
Hydrous Iron Oxide ◽  
Lead Sorption ◽  
Cadmium And Lead

scholarly journals Influence of Particle Size, Reactor Temperature and Gas Phase Reactions on Fast Pyrolysis of Beech Wood

2010 ◽  
Vol 8 (1) ◽  
Author(s):  
Li Chen ◽  
Capucine Dupont ◽  
Sylvain Salvador ◽  
Guillaume Boissonnet ◽  
Daniel Schweich
Keyword(s):  
Particle Size ◽  
Gas Phase ◽  
Residence Time ◽  
Beech Wood ◽  
Tubular Reactor ◽  
Gaseous Product ◽  
Drop Tube ◽  
Gas Phase Reactions ◽  
Molar Ratios ◽  
Reactor Temperature

In the present work, a drop tube reactor (DTR) and a horizontal tubular reactor (HTR) were used to study the pyrolysis behaviour of beech wood particles of different sizes under the conditions encountered in industrial fluidized bed gasifiers, namely high external heat flux (105 – 106 W.m-2) and high temperature (800 – 1000°C). The influence of the reactor temperature (800 and 950°C), of particle size (from 350 µm to 6 mm), and of gas residence time (from 1 to 10 s) were examined. Under the explored conditions, when pyrolysis is finished, more than 80 wt.% of virgin wood is converted into gas and less than 13 wt.% remains in solid. In the gas phase, CO is the main gaseous product (50 wt.% of virgin wood), followed by H2 (molar ratios of H2/CO are between 0.35 to 0.55), H2O, CO2 and CH4. Species C2H2, C2H4, C2H6 and C6H6 are present in much lower amounts. The increase of temperature increases the rate of solid devolatilization and favours the cracking reactions of hydrocarbons. The increase of particle size increases the required time for completing pyrolysis. Meanwhile, the results obtained at 950°C show that the final products distribution at the end of pyrolysis is almost the same for the particles between 350 and 800 µm. The increase of the particle size from 800 µm to 6 mm seems to have some influence on the final products distribution. The gas phase reactions mainly change the yields of light hydrocarbons and H2: the increase of gas residence time favours the cracking reactions of hydrocarbons and thus leads to a higher H2 yield.

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