Home About us Contact
|
Home About us Contact | ||
|
|
||
Hydrodynamic Parameters (hydrodynamic + parameter)
Selected AbstractsEffect of a gas,liquid separator on the hydrodynamics and circulation flow regimes in internal-loop airlift reactorsJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 5 2001Jaroslav Klein Abstract The role of the gas,liquid separator on hydrodynamic characteristics in an internal-loop airlift reactor (ALR) was investigated. Both gas holdup and liquid velocity were measured in a 30,dm3 airlift reactor with two different head configurations: with and without an enlarged separator. A magnetic tracer method using a neutrally buoyant magnetic particle as flowfollower was used to measure the liquid velocity in all sections of the internal-loop airlift reactor. Average liquid circulation velocities in the main parts of the ALR were compared for both reactor configurations. At low air flow rates the separator had no influence on gas holdup, circulation velocity and intensity of turbulence in the downcomer and separator. At higher superficial air velocities, however, the separator design had a decisive effect on the hydrodynamic parameters in the downcomer and the separator. On the other hand, the gas holdup in the riser was only slightly influenced by the separator configuration in the whole range of air flow. Circulation flow regimes, characterising the behaviour of bubbles in the downcomer, were identified and the effect of the separator on these regimes was assessed. © 2001 Society of Chemical Industry [source] Volume-of-fluid-based model for multiphase flow in high-pressure trickle-bed reactor: Optimization of numerical parametersAICHE JOURNAL, Issue 11 2009Rodrigo J. G. Lopes Abstract Aiming to understand the effect of various parameters such as liquid velocity, surface tension, and wetting phenomena, a Volume-of-Fluid (VOF) model was developed to simulate the multiphase flow in high-pressure trickle-bed reactor (TBR). As the accuracy of the simulation is largely dependent on mesh density, different mesh sizes were compared for the hydrodynamic validation of the multiphase flow model. Several model solution parameters comprising different time steps, convergence criteria and discretization schemes were examined to establish model parametric independency results. High-order differencing schemes were found to agree better with the experimental data from the literature given that its formulation includes inherently the minimization of artificial numerical dissipation. The optimum values for the numerical solution parameters were then used to evaluate the hydrodynamic predictions at high-pressure demonstrating the significant influence of the gas flow rate mainly on liquid holdup rather than on two-phase pressure drop and exhibiting hysteresis in both hydrodynamic parameters. Afterwards, the VOF model was applied to evaluate successive radial planes of liquid volume fraction at different packed bed cross-sections. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Effect of hydrodynamic multiplicity on trickle bed reactor performanceAICHE JOURNAL, Issue 1 2008Werner van der Merwe Abstract Multiple hydrodynamic states in trickle bed reactors have been the subject of numerous hydrodynamic investigations. The extent of variation in the hydrodynamic parameters (like holdup and pressure drop) is large and this variation can be expected to have a significant impact on the conversion in a reaction system. This study presents reaction data for ,-methyl styrene hydrogenation in a trickle bed reactor over a range of conditions that include gas and liquid limitations. It is seen that liquid flow rate variation induced hysteresis has a large impact on the conversion. For gas-limited reactions, the upper branch of the pressure drop hysteresis loop has a higher conversion than the lower branch at the same linear fluid velocities and catalyst weight, while for liquid-limited reactions the lower branch has a higher conversion than the upper branch (the difference in productivity being up to 20%). These trends cannot be explained by differences in wetting efficiency. Instead, it is proposed that for this system the gas,liquid mass transfer rate is the limiting step in gas-limited reactions, while the liquid,solid mass transfer rate is the limiting step in liquid-limited reactions. © 2007 American Institute of Chemical Engineers AIChE J, 2008 [source] Hydrodynamic characteristics of gas,solid fluidization at high temperatureTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2010Shabnam Sanaei Abstract Effect of temperature on the hydrodynamics of bubbling gas,solid fluidized beds was investigated in this work. Experiments were carried out at different temperatures ranged of 25,600°C and different superficial gas velocities in the range of 0.17,0.78,m/s with sand particles. The time-position trajectory of particles was obtained by the radioactive particle tracking technique at elevated temperature. These data were used for determination of some hydrodynamic parameters (mean velocity of upward and downward-moving particles, jump frequency, cycle frequency, and axial/radial diffusivities) which are representative to solids mixing through the bed. It was shown that solids mixing and diffusivity of particles increases by increasing temperature up to around 300°C. However, these parameters decrease by further increasing the temperature to higher than 300°C. This could be attributed to the properties of bubble and emulsion phases. Results of this study indicated that the bubbles grow up to a maximum diameter by increasing the temperature up to 300°C, after which the bubbles become smaller. The results showed that due to the wall effect, there is no significant change in the mean velocity of downward-moving clusters. In order to explain these trends, surface tension of emulsion between the rising bubble and the emulsion phase was introduced and evaluated in the bubbling fluidized bed. The results showed that surface tension between bubble and emulsion is increased by increasing temperature up to 300°C, however, after that it acts in oppositely. L'effet de la température sur l'hydrodynamique de lits fluidisés de gaz-solide bouillonnants a fait l'objet de l'étude de cet ouvrage. Des expériences ont été faites à différentes températures se situant entre 25 et 600°C et différentes vélocités de gaz superficiels sur une plage de 0,17 à 0,78,m/s avec particules de sable. La trajectoire temps-position des particules a été obtenue à l'aide d'une technique de repérage par particules radioactives à haute température. Ces données ont été utilisées pour déterminer certains des paramètres hydrodynamiques (vélocité moyenne des particules ascendantes et descendantes, la fréquence de sauts bonds, la fréquence de cycles et les diffusivités axiales et radiales), lesquels sont représentatifs de solides se mélangeant dans le lit. Il a été démontré que le mélange de solides et la diffusivité des particules augmentent en haussant la température à environ 300°C. Cependant, ces paramètres diminuent en accroissant davantage la température au-delà de 300°C. Cela pourrait être attribué aux propriétés des phases de bouillonnement et d'émulsion. Les résultats de cette étude indiquent que les bulles croissent pour atteindre un diamètre maximum en augmentant la température jusqu'à 300°C. Au-delà de cette température, les bulles deviennent plus petites. Les résultats démontrent qu'en raison de l'effet de paroi, il n'y a pas de changement significatif à la vélocité moyenne des grappes descendantes. Afin d'expliquer ces tendances, la tension de surface de l'émulsion entre la bulle ascendante et la phase émulsion a été introduite et évaluée dans le lit fluidisé bouillonnant. Les résultats ont démontré que la tension de surface entre la bulle et l'émulsion augmente en haussant à température jusqu'à 300°C; cependant, après cette température, elle agit inversement. [source] Flow characterization of a wavy-walled bioreactor for cartilage tissue engineeringBIOTECHNOLOGY & BIOENGINEERING, Issue 6 2006Bahar Bilgen Abstract Cartilage tissue engineering requires the use of bioreactors in order to enhance nutrient transport and to provide sufficient mechanical stimuli to promote extracellular matrix (ECM) synthesis by chondrocytes. The amount and quality of ECM components is a large determinant of the biochemical and mechanical properties of engineered cartilage constructs. Mechanical forces created by the hydrodynamic environment within the bioreactors are known to influence ECM synthesis. The present study characterizes the hydrodynamic environment within a novel wavy-walled bioreactor (WWB) used for the development of tissue-engineered cartilage. The geometry of this bioreactor provides a unique hydrodynamic environment for mammalian cell and tissue culture, and investigation of hydrodynamic effects on tissue growth and function. The flow field within the WWB was characterized using two-dimensional particle-image velocimetry (PIV). The flow in the WWB differed significantly from that in the traditional spinner flask both qualitatively and quantitatively, and was influenced by the positioning of constructs within the bioreactor. Measurements of velocity fields were used to estimate the mean-shear stress, Reynolds stress, and turbulent kinetic energy components in the vicinity of the constructs within the WWB. The mean-shear stress experienced by the tissue-engineered constructs in the WWB calculated using PIV measurements was in the range of 0,0.6 dynes/cm2. Quantification of the shear stress experienced by cartilage constructs, in this case through PIV, is essential for the development of tissue-growth models relating hydrodynamic parameters to tissue properties. © 2006 Wiley Periodicals, Inc. [source] Turbulence Transfer Processes in Adiabatic and Condensing Film Flow in an Inclined TubeCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 4 2003R. Würfel Abstract For the description of transfer processes in separated turbulent two-phase flow, knowledge is necessary about interactions at the interface. Particularly experimental studies were performed of the two-phase-friction coefficient, film thickness, entrainment and heat transfer for adiabatic and condensing conditions. Working systems were n-heptane/air, water/air and condensing n-heptane. The measurement of the liquid film thickness was successful with the ultrasonic method and the entrainment was measured with an isokinetic technique. Quantitative connections between hydrodynamic parameters were discussed and compared with literature models. Based on experimental data, special models are proposed. Partly the influence of the mass transfer intensity cannot be neglected for calculation of the two-phase-friction coefficient. For the description of the heat transfer for film condensation in turbulent flow the interface shear stress and the inclination angle of the tube have proved useful. [source] | ||||||||||