The Experts below are selected from a list of 1818 Experts worldwide ranked by ideXlab platform
Radovan Omorjan - One of the best experts on this subject based on the ideXlab platform.
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predicting hydrodynamic parameters and volumetric gas liquid mass transfer coefficient in an external loop airlift reactor by support vector regression
Chemical Engineering Research & Design, 2017Co-Authors: Predrag S Kojic, Radovan OmorjanAbstract:Abstract For modeling, design and scale-up of the airlift reactors, it is crucial to estimate hydrodynamic parameters and volumetric gas–liquid mass transfer coefficient for different flow regimes. Prediction of these variables had begun by applying empirical power low correlations and later evolved in use of the artificial neural networks (ANN) as the best option available in the literature. The objective of this study was to present the support vector regression (SVR) model that predicts the gas holdup, Downcomer liquid velocity and volumetric gas–liquid mass transfer coefficient values in the external-loop airlift reactor better than ANN. Furthermore, to demonstrate the applicability of the SVR model, it was used on the different literature data sets with wide-ranging databanks. The statistical error analysis revealed that the proposed generalized SVR model had more precisely prediction than ANN with an average absolute relative error (AARE) of 2.17%, 1.32% and 9.64% for gas holdup, Downcomer liquid velocity and volumetric gas-liquid mass transfer coefficient values, respectively.
Predrag S Kojic - One of the best experts on this subject based on the ideXlab platform.
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predicting hydrodynamic parameters and volumetric gas liquid mass transfer coefficient in an external loop airlift reactor by support vector regression
Chemical Engineering Research & Design, 2017Co-Authors: Predrag S Kojic, Radovan OmorjanAbstract:Abstract For modeling, design and scale-up of the airlift reactors, it is crucial to estimate hydrodynamic parameters and volumetric gas–liquid mass transfer coefficient for different flow regimes. Prediction of these variables had begun by applying empirical power low correlations and later evolved in use of the artificial neural networks (ANN) as the best option available in the literature. The objective of this study was to present the support vector regression (SVR) model that predicts the gas holdup, Downcomer liquid velocity and volumetric gas–liquid mass transfer coefficient values in the external-loop airlift reactor better than ANN. Furthermore, to demonstrate the applicability of the SVR model, it was used on the different literature data sets with wide-ranging databanks. The statistical error analysis revealed that the proposed generalized SVR model had more precisely prediction than ANN with an average absolute relative error (AARE) of 2.17%, 1.32% and 9.64% for gas holdup, Downcomer liquid velocity and volumetric gas-liquid mass transfer coefficient values, respectively.
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volumetric gas liquid mass transfer coefficient in an external loop airlift reactor with inserted membrane
Chemical Industry & Chemical Engineering Quarterly, 2016Co-Authors: Predrag S Kojic, Ivana M Sijacki, Natasa Lj Lukic, Dragica Z Jovicevic, Svetlana S Popovic, Dragan Lj PetrovicAbstract:The effects of the inserted membrane in the Downcomer of an external-loop airlift reactor, the gas sparger type (single orifice and sinter plate) and added alcohol (ethanol, n-butanol, or n-hexanol) on the volumetric gas-liquid mass transfer coefficient (kLa) were studied. Due to the presence of the membrane in the Downcomer, kLa did not change significantly; the differences were smaller than 10%. The highest values of the kLa were obtained using the sinter plate. It was found that the addition of small amounts of alcohol increased the mass transfer. Using our experimental results and the data of other authors, the feed-forward back propagation neural network for prediction of kLa in external-loop airlift reactors with alcohol solutions was proposed. [Projekat Ministarstva nauke Republike Srbije, br. 172025]
Shyhjye Hwang - One of the best experts on this subject based on the ideXlab platform.
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Gas holdup and liquid velocity in three-phase internal-loop airlift reactors
Chemical Engineering Science, 1997Co-Authors: Shyhjye Hwang, Yi-lung ChengAbstract:Abstract The liquid velocities and gas holdups in the riser and Downcomer of three-phase internal-loop airlift reactors with Newtonian and non-Newtonian fluids were studied. The reactor was constructed of 19 cm ID Plexiglas column and 250 cm in height. The inside diameters of the draft tube were 9, 12, and 14 cm (wall thickness is 0.5 cm), which made the ratio of the cross-sectional area of the riser to the Downcomer equal to 0.69, 1.33 and 3.22, respectively. The draft tube heights used in this study were 70, 110 and 150 cm. Water and various concentrations of carboxymethyl cellulose (CMC) aqueous solutions were employed as the liquid phases. Air and polystyrene particles were used as the gas and solid phases, respectively. The liquid velocities and gas holdups in the riser and Downcomer were measured by tracer response and manometric techniques, respectively. It was found that the gas holdups and the liquid velocities generally decreased with an increase in the concentration of CMC or the solids loading. In addition, the gas holdup in the riser decreased but that in the Downcomer increased with increasing draft tube length. The liquid velocities increased with increasing draft tube length. Furthermore, the gas holdup and the liquid velocity in the riser increased but those in the Downcomer decreased with decreasing draft tube diameter. Based on the drift-flux model and energy balance, a hydrodynamic model was developed. It was shown that using a correlation equation for the gas holdup in the Downcomer, the proposed model could predict satisfactorily the gas holdup in the riser and the liquid velocities in the riser and Downcomer of the internal-loop airlift reactors with Newtonian and non-Newtonian fluids.
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liquid velocity and gas holdup in three phase internal loop airlift reactors with low density particles
Chemical Engineering Science, 1995Co-Authors: Wenjang Lu, Shyhjye Hwang, Chunmin ChangAbstract:Abstract Liquid velocity and gas holdup in three-phase internal loop airlift reactors were investigated. Air and water were used as the gas and liquid phase, respectively, and the solid particles used were calcium alginate beads with different particle size. The liquid velocity in the riser and the Downcomer were obtained by tracer analysis. The gas holdup in the riser and the Downcomer were determined by manometric technique. It was found that the liquid velocity did not show any significant variations with top clearance. The liquid velocity increased with an increase in aeration rate or draught tube length, whereas it decreased as the diameter of the particles was increased. Moreover, the liquid velocity and the gas holdup decreased with increasing solids loading. A hydrodynamic model based on the drift-flux model was developed to describe satisfactorily the liquid velocity and gas holdup in air-water-calcium alginate internal loop airlift reactors.
R Z Tudose - One of the best experts on this subject based on the ideXlab platform.
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modelling mixing parameters in concentric tube airlift bioreactors part ii axial dispersion
Bioprocess Engineering, 1999Co-Authors: Maria Gavrilescu, R Z TudoseAbstract:Axial dispersion of the liquid phase was investigated in a concentric-tube airlift bioreactor (RIMP: V L = 0.70 m 3 ) as a whole and in the separate zones (riser, Downcomer, gas-separator) using the axial dispersion model. The axial dispersion number Bo and the axial dispersion coefficient, D ax were determined from the output curves to an initial Dirac pulse, using the tracer response technique. They were analyzed in relation to process and geometrical parameters, such as: gas superficial velocity, υ SGR ; top clearance, h S ; bottom clearance, h B : and resistances at Downcomer entrance expressed as A d /A R ratio. Correlations between Bodenstein numbers in the overall bioreactor and riser and Downcomer sections (Bo T , Bo R . Bo D ) and the geometrical and process parameters were developed, which can allow to assess the complex influence of these parameters on liquid axial dispersion.
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concentric tube airlift bioreactors part i effects of geometry on gas holdup
Bioprocess Engineering, 1998Co-Authors: Maria Gavrilescu, R Z TudoseAbstract:Gas holdup investigations were performed in three concentric-tube airlift reactors of different scales of operation (RIMP: 0.070 m3; RIS-1: 2.5 m3; RIS-2: 5.2 m3; nominal volumes). The influences of the top and bottom clearances and the flow resistances at the Downcomer entrance were studied using tap water as liquid phase and air as gaseous phase, at atmospheric pressure. It was found that the gas holdup in the individual zone of the reactor: riser, Downcomer and gas-separator, as well as that in the overall reactor is affected by the analyzed geometrical parameters in different ways, depending on their effects on liquid circulation velocity. Gas holdup was satisfactorily correlated with Fr, Ga, bottom spatial ratio (B), top spatial ratio (T), gas separation ratio (Y) and Downcomer flow resistance ratio (A d /A R ). Correlations are presented for gas holdup in riser, Downcomer, gas separator and for the total gas holdup in the reactor. All the above stressed the importance of the geometry in dynamic behaviour of airlift reactors.
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Concentric-tube airlift bioreactors. Part II: Effects of geometry on liquid circulation
Bioprocess Engineering, 1998Co-Authors: Maria Gavrilescu, R Z TudoseAbstract:Liquid circulation velocity was investigated in three concentric-tube airlift reactors of different scales (RIMP, V L = 0.07 m 3 ; RIS-1, V L = 2.5 m 3 ; RIS-2, V L =5.20 m 3 ). The effects of top and bottom clearance and resistance in flow pathway at Downcomer entrance on the riser liquid superficial velocity, the circulation time, the friction coefficient and flow radial profiles of the gas holdup and the liquid superficial velocity in riser, using water-air as a biphasic system, were studied. It was found that the riser liquid superficial velocity is affected by the analyzed geometrical parameters in different ways, depending on their effects on the pressure loss. The riser liquid superficial velocity, the friction coefficient and the parameters of the drift-flux model were satisfactorily correlated with the bottom spatial ratio (B), gas separation ratio (Y) and Downcomer flow resistance ratio (A d /A D ), resulting empirical models, with correlation coefficients greater than 0.85.
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study of the liquid circulation velocity in external loop airlift bioreactors
Bioprocess Engineering, 1995Co-Authors: Maria Gavrilescu, R Z TudoseAbstract:Liquid circulation velocity was studied in externalloop air-lift bioreactors of laboratory and pilot scale, respectively for different gas input rates, Downcomer-to-riser cross-sectional area ratio, AD/AR and liquid phase apparent viscosities.
Xuedong Jiang - One of the best experts on this subject based on the ideXlab platform.
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cfd simulation of internal loop airlift reactor using emms drag model
Particuology, 2015Co-Authors: Xuedong Jiang, Ning Yang, Jiahua ZhuAbstract:The simulation of internal-loop airlift reactors is challenging because complex meso-scale structures exist in different sections of the reactor, separated by the draft tube. This paper reports on the computational fluid dynamics (CFD) simulation of internal-loop airlift reactors using a new drag model derived from the dual-bubble-size COBS) model, an extended energy-minimization multi-scale (EMMS) approach for gas-liquid flows. Compared with the traditional Schiller-Naumann (S-N) correlation, the new model improves the simulation of gas holdup in the riser and Downcomer significantly. In particular, gas holdup and circulation of two-phase flow can be modeled successfully using the new model, whereas traditional drag models such as the S-N correlation show an absence of gas in the Downcomer. The simulation demonstrates the advantage and potential of this new model for internal-loop airlift reactors. (C) 2014 Published by Elsevier B.V. on behalf of Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences.