Impeller Agitation Speed Research Articles

The Impact of Gas-Liquid Dispersed Flow on Heat Exchanger Performance with Improvement Using CuO Nanofluid

Both the air-water dispersion coefficient and the air-nanofluid (CuO) dispersion coefficient were studied and measured in a double-pipe heat exchanger. Pumping air into a tank fitted with a Rushton turbulent impeller resulted in gas-liquid dispersion. In order to test the effects of varying operating conditions on the air-water and air-nanofluid dispersions, they were heated and pumped into the tube of a double-pipe heat exchanger. Reynolds numbers of Rec= 4750-13100 on the shell side and Reh=19900-64000 on the tube side were used to get the total heat transfer coefficient (Uo). The dispersion in the hot fluid tank was achieved by combining the two-phase fluids using a Rushton turbine impeller. It was discovered that the conscious phase saw a significant drop in the heat transfer coefficient when the air bubbles dissipated. Because the impeller's agitation speed affects the rate at which air bubbles are broken, the heat transfer coefficient in the case of dispersion rises as Reh and Rec rise. For all examined parameter values, CuO nanofluid showed significant heat transfer improvement. The heat transfer rate of gas-liquid dispersion increases by nanofluid by as much as 135.5% compared to gas-liquid dispersion which is considered the first attempt for heat transfer enhancement of two phase flow (gas-liquid dispersion) using Nano fluid.

Lagrangian wavelet analysis of turbulence modulation in particle–liquid mixing flows

A new experimental–theoretical framework has been developed to investigate turbulence and turbulence modulation in a two-phase multicomponent particle–liquid flow in a mechanically agitated vessel. A discrete wavelet transform is used to decompose long-term three-dimensional Lagrangian trajectories of flow phases, acquired by a technique of positron emission particle tracking, into their deterministic and stochastic sub-trajectories. The sub-trajectories are then used to construct the different-scale local velocity and turbulent kinetic energy (TKE) fields of the two-phase flow. The effects of the particle size and size distribution mode (mono, binary, and polydisperse), particle concentration, impeller agitation speed, and pumping mode on turbulence intensity are investigated. Amongst these factors, the particle size, impeller pumping mode, and particle size distribution mode have a significant impact on liquid turbulence. The presence of large particles enhances liquid turbulence and broadens the region in the vessel characterized by high local TKE values. Results also show that a down-pumping pitched-blade turbine generates significantly greater local maxima in the TKE field, which tend to be more localized in the impeller discharge stream. In addition, binary or polydisperse suspensions containing higher fractions of larger particles produce higher turbulence intensities in the carrier phase. The detailed information obtained on the turbulence intensity is crucial for better understanding of the dynamics of particle–liquid flows inside mixing vessels to aid the rational design of these units.

Simultaneous effect of nanoparticles and surfactant on emulsion liquid membrane: Swelling, breakage and mean drop size

In this study, the effect of multi-walled carbon nanotubes (MWCNTs) and Span-85 as a surfactant on drops breakup and coalescence rates of emulsion liquid membrane (ELM) due to hydrodynamic parameters was investigated which was not reported before. A single stage horizontal mixer-settler extractor with two 4-pitched blade turbine impellers with 45° inclined blades on one shaft was employed. The influences of MWCNTs, Span-85 and both of them at the same time on membrane swelling and breakage were studied in batch mode and dispersion Sauter mean diameter (D32) was compared to pure system for continuous mode experiments. Results indicated that simultaneous presence of MWCNTs and surfactant enhanced the ELM stability and the membrane swelling and breakage decreased about 46% and 63%, respectively. Also, it has the most influence on drop size compared to the presence of Span-85 and MWCNTs alone, respectively. Presence of MWCNTs and Span-85 at the same time caused to reduction in enhancing rate of D32 with dispersed phase volume fraction about 65.5%. Additionally, decreasing rate of D32 with impeller agitation speed diminished about 1.4%. Furthermore, in order to predict a mean drop size for all systems (with and without inorganic particles), a new modified correlation was proposed for the first time where the surfactant and nanoparticles concentrations were introduced as new independent parameters.

Platinum Extraction Modeling from Used Catalyst by Iodine Solutions

Platinum extraction from spent reforming catalysts in iodine solutions under atmospheric pressure at different temperatures, acid concentration, and iodine spices concentration, catalyst particle size, and impeller agitation speed have been studied in our group. In this system, platinum is oxidized from spent catalyst with I3¯ that is formed from the reaction of I2 and I¯ to produce PtI6-2 as its main product. It is obvious that some of the platinum ions in aqueous solution are precipitated as PtI4, especially at high temperatures. Power-law rate equation was used in extraction and precipitation reactions for kinetic modeling. The effect of temperature was studied using the Arrhenius equation. The activation energy for the platinum surface dissolution reaction was calculated as 53 kJ/mol in extraction reaction which indicated that the rate determining step is surface chemical reaction step. The reaction order was 3.01 for platinum concentration in solid and 0.45 for the hydrogen ion concentration, 0.1 for the iodine spices concentration in extraction reaction and 0.54 for platinum ions concentration in precipitation reaction. This model shows good agreement with experimental data.

Scaling-up fermentation of Escherichia coli for production of recombinant P64k protein from Neisseria meningitidis

P64k is a Neisseria meningitidis high molecular weight protein present in meningococcal vaccine preparations. The lpdA gene, which encodes for this protein, was cloned in Escherichia coli and the P64k recombinant protein was expressed in E. coli K12 GC366 cells under the control of a tryptophan promoter. P64k was expressed as an intracellular soluble protein about 28% of the total cellular protein. Several scale-up criteria of fermentation processes were studied to obtain the recombinant P64k protein at the pilot production scale. The best operational conditions at a larger scale production of P64k recombinant protein were studied and compared using the four following criteria: Constant Reynold's number (Re constant), Constant impeller tip speed (n di constant), Constant power consumption per unit liquid volume (P/V constant) and Constant volumetric oxygen transfer coefficients (KLa/k constant). The highest production of the recombinant protein was achieved based on the constant KLa/k scale-up fermentation criterion, calculating the aeration rate (Q) and the impeller agitation speed (n) by iterative process, keeping constant the KLa/k value from bench scale. The P64k protein total production at the 50 l culture scale was 546 mg l-1 in comparison with the 284 mg l-1 obtained at 1.5 l bench scale. The methodology described herein, for the KLa/k scale-up fermentation criterion, allowed us to obtain the P64k protein at 50 l scale. A fermentation process for the production of P64k protein from N. meningitidis was established, a protein to be used in future vaccine formulations in humans. How to cite: Espinosa R, García J, Narciandi E, et al. Scaling-up fermentation of Escherichia coli for production of recombinant P64k protein from Neisseria meningitidis. Electron J Biotechnol 2018;33. https://doi.org/10.1016/j.ejbt.2018.03.004.

Experimental investigation of hydrodynamic and heat transfer effects on scaling in an agitated tank

Scale formation on process equipment is a major problem in the mineral industry because of lost production from equipment downtime required in de-scaling maintenance and its high cleaning cost. Scale formation in the Bayer process mainly occurs from crystallisation of Bayer liquor which is not fully understood. This study investigated the hydrodynamic and heat transfer effects on crystallisation scale growth and its suppression, using a novel experimental approach in a newly fabricated lab-scale agitation tank. A series of experiments were undertaken using laboratory-made potassium nitrate (KNO3) aqueous solutions.Experiments were conducted with different size impellers at varying rotational speeds using various concentrations of KNO3 solutions. It was observed that the impeller agitation speed plays a critical role in the scale growth and suppression mechanisms as the scale growth rate is enhanced at the lower and is reduced at the higher agitation rate. The effects of baffles on scale growth rate and suppression and the bottom settled scale accumulation rate were also examined. The wall scale growth rate decreased with time ranging from 58.06% to 6.79% and the corresponding bottom settled scale increased ranging from 4.19% to 80.2% depending on the agitation rate, impeller size, solution concentration and tank conditions.

Scaling-up fermentation of Escherichia coli for production of recombinant P64k protein from Neisseria meningitidis

Background: P64k is a Neisseria meningitidis high molecular weight protein present in meningococcal vaccine preparations. The lpdA gene, which encodes for this protein, was cloned in Escherichia coli and the P64k recombinant protein was expressed in E. coli K12 GC366 cells under the control of a tryptophan promoter. P64k was expressed as an intracellular soluble protein about 28% of the total cellular protein. Several scale-up criteria of fermentation processes were studied to obtain the recombinant P64k protein at the pilot production scale. Results: The best operational conditions at a larger scale production of P64k recombinant protein were studied and compared using the four following criteria: Constant Reynold's number (Re constant), Constant impeller tip speed (n di constant), Constant power consumption per unit liquid volume (P/V constant) and Constant volumetric oxygen transfer coefficients (KLa/k constant). The highest production of the recombinant protein was achieved based on the constant KLa/k scale-up fermentation criterion, calculating the aeration rate (Q) and the impeller agitation speed (n) by iterative process, keeping constant the KLa/k value from bench scale. The P64k protein total production at the 50 l culture scale was 546 mg l-1 in comparison with the 284 mg l-1 obtained at 1.5 l bench scale. Conclusions: The methodology described herein, for the KLa/k scale-up fermentation criterion, allowed us to obtain the P64k protein at 50 l scale. A fermentation process for the production of P64k protein from N. meningitidis was established, a protein to be used in future vaccine formulations in humans.

Solids Suspension Study in a Side-Entering Stirred Tank Through CFD Modeling

Abstract Computational fluid dynamics (CFD) technique was employed to study solids suspension in a stirred tank equipped with three side-entering impellers. Simulations of solid–liquid flow were performed by using an Eulerian-Granular Multiphase (EGM) model coupling with standard k–ε mixture turbulence model and Reynolds stress model, respectively. A multiple reference frame (MRF) approach was used to model the impeller rotation. The CFD predictions have been verified by comparing the predicted results with the experimental just suspended impeller speed and solid sediment pattern at the tank bottom. The solid distribution and liquid-phase velocity vectors throughout the tank for two cases with and without solid phase were investigated to understand the characteristics of solid–liquid flow. The solid suspension quality has been assessed by employing three criterions: the just suspended impeller speed Njs, cloud height h, and suspension homogeneity. The effects of impeller agitation speed, particle size, and solid loading on suspension quality have been investigated. The computational model and results discussed in this study would be useful to understand the solid–liquid dispersion process in side-entering stirred tanks and extend the application of CFD models for equipment design and process optimization.

Mean drops size in the presence of cetyl trimethyl ammonium bromide in horizontal mixer settler

ABSTRACTThe mean drop size of toluene/water dispersion in the presence of cetyl trimethyl ammonium bromide (CTAB) as a cationic surfactant has been studied in a horizontal mixer settler. Two 45°‐pitched blade turbine impellers with four blades on a shaft were used to have completed mixing. Additionally, the influences of hydrodynamic parameters such as impeller agitation speed and dispersed phase volume fraction on the drops size were investigated. The results indicate that the presence of CTAB leads to a decrease in D32 by about 46%, averagely. Furthermore, increase in the impeller speed from 450 up to 650 rpm causes D32 to reduce by about 30%, and the decreasing rate of D32 diminishes with increasing impeller speeds. Increase in the dispersed phase volume fraction gives rise to increase in the drops size. Finally, in order to predict the mean drop size, new modified correlations were provided, wherein the influence of CTAB concentration was introduced as a new parameter. © 2013 Curtin University of Technology and John Wiley & Sons, Ltd.

Mixing and Dissolution Processes of Pharmaceutical Bulk Materials in Stirred Tanks: Experimental and Numerical Investigations

Numerical analysis of mixing and dissolution processes is becoming increasingly important for gaining a process understanding and thus optimizing the production. Due to the increasing costs and shortage of raw materials, in-silicotechniques are currently employed together with standard experimental analyses. Numerical simulations have proven to be a useful tool for understanding and optimizing industrial mixing problems. However, such simulations are still in the research phase. Although Computational Fluid Dynamics (CFD) is a well-developed and validated method, for more complex applications (e.g., industrial mixing)muchworkisstillrequiredtoobtainreliableresultsquicklyenough.Inthisworkwefocusedonthesimulationofmixingand dissolution of a bulk powder in a moderately viscous solution in an unbaffled stirred tank reactor typically used in the chemical and pharmaceutical industries. Estimations were made with regard to optimizing batch sizes, tank geometry, impeller type, and placement and process variables, such as the impeller agitation speed. In addition, the vortex formation of the liquid surface, the feeding position of the bulk powder, and the dissolution process of the solid particles that represent the bulk powder were manipulated.Finally,aquantitativecomparisonofdifferentstirringsystems andscale-up studieswas prepared. Thetime-dependent and turbulent flow of the mixture was studied by solving the Reynolds-averaged NavierStokes equations. The numerical predictions of the flow field were validated by means of high-speed camera images and particle image velocimetry postprocessing techniques.

Factors affecting platinum extraction from used reforming catalysts in iodine solutions at temperatures up to 95 °C

Platinum extraction from the spent reforming catalysts in iodine–iodide solutions at temperatures from 25 to 95 °C was investigated. The reforming catalyst mostly consists of a porous gamma alumina support with metallic platinum finely dispersed on the walls of the nano-pores of the catalyst support. The effect of a variety of factors, including catalyst particle size, impeller agitation speed, reactant concentrations, liquid to solid mass ratio, temperature and the solution pH on the Pt extraction rate and recovery were investigated. It was found that the catalyst particle sizes less than 106 µm and impeller agitation speed higher than 700 rpm eliminated the effects of catalyst size and agitation level, respectively, on platinum leaching. The initial iodine–iodide concentrations and the liquid to solid ratio were mostly affecting the solution pH and the concentration of “active” iodine species, which in turn, affected the rate of Pt extraction. Higher acidities, generated by adding concentrated HCl, resulted in faster Pt extractions. Increasing the reaction temperature also produced faster platinum extraction kinetics. The “active” iodine species (HIO, I 2(aq), and I 3 −) concentration decreased mostly due to conversion to “inactive” iodine–oxygen species and evaporation from the solution.

Kinetics of platinum extraction from spent reforming catalysts in aqua-regia solutions

Platinum content of two commercial spent reforming catalysts were extracted in aqua-regia solutions under atmospheric pressure and at temperatures up to 100 °C. Three factors, including presence of coke, catalyst particle size, and impeller agitation speed were first tested to study the relative importance of mass-transfer resistances during Pt extraction reaction. Catalyst particle sizes < 100 µm and agitation speeds > 700 rpm eliminated the internal and external mass-transfer resistances, respectively. The effect of other factors, including HNO 3-to-HCl volume ratio, liquid-to-solid mass ratio, and the reaction temperature on the extraction rate of platinum were then examined. Pt extraction rate was significantly increased by increasing liquid-to-solid mass ratio and the reaction temperature. Kinetic modeling using power-law rate equation for Pt extraction revealed that increasing liquid-to-solid mass ratio increases the acid concentration, as a major reactant. This quantitatively accounted for the increased Pt extraction rate. The effect of temperature on Pt extraction kinetics was studied using the Arrhenius equation. The activation energy for the platinum surface dissolution reaction was calculated as 72.1 kJ/mol. This large value indicates that Pt extraction in aqua-regia solution is controlled by surface chemical reaction. The reaction order was 1.5 for Pt concentration in solid and 1.3 for the hydrogen ion molarity in solution.

Effect of mixing time on taxoid production using suspension cultures of Taxus chinensis in a centrifugal impeller bioreactor

The effects of fluid mixing on the cell growth and secondary metabolite production of plant cells were investigated in a low-shear centrifugal impeller bioreactor (CIB) system. Suspension cultures of Taxus chinensis cells producing taxuyunnanine C (Tc), a physiologically active secondary metabolite, were used as a model system for this investigation. The mixing time ( t m) and volumetric oxygen transfer coefficient ( k La ) in the bioreactor were characterized at various cell densities and operating conditions. A constant t m of 5 s or 10 s was maintained during cultivation by adjusting the impeller agitation speed with no detrimental effect on the cultured cells. A higher cell density, Tc content and total Tc production were obtained under the shorter mixing time of 5 s. The favorable effect of more rapid mixing on Tc production was also confirmed when the Tc accumulation was significantly increased through culture elicitation using 100 μM methyl jasmonate (MJA). The lower Tc production at the longer t m of 10 s was mainly attributed to oxygen transfer limitation in the dead zones and larger cell aggregates resulting from poor mixing.

Effect of Mixing Time on Taxoid Production Using Suspension Cultures of Taxus chinensis in a Centrifugal Impeller Bioreactor

The effects of fluid mixing on the cell growth and secondary metabolite production of plant cells were investigated in a low-shear centrifugal impeller bioreactor (CIB) system. Suspension cultures of Taxus chinensis cells producing taxuyunnanine C (Tc), a physiologically active secondary metabolite, were used as a model system for this investigation. The mixing time (t(m)) and volumetric oxygen transfer coefficient (k(L)a) in the bioreactor were characterized at various cell densities and operating conditions. A constant t(m) of 5 s or 10 s was maintained during cultivation by adjusting the impeller agitation speed with no detrimental effect on the cultured cells. A higher cell density, Tc content and total Tc production were obtained under the shorter mixing time of 5 s. The favorable effect of more rapid mixing on Tc production was also confirmed when the Tc accumulation was significantly increased through culture elicitation using 100 microM methyl jasmonate (MJA). The lower Tc production at the longer t(m) of 10 s was mainly attributed to oxygen transfer limitation in the dead zones and larger cell aggregates resulting from poor mixing.

Mass transfer studies in batch fermentation: Mixing characteristics

Studies have been undertaken to investigate the mass transfer parameters due to mixing effects during fermentation using Candida utilis in a 2·0-dm 3 batch fermentor. Mechanical agitation and mixing via air flow have been studied and each varied independently of the other. Oxygen transfer rates were found to increase up to a limiting value when both air flow rate and agitation were increased. Aerobic fermentation is characterised by the specific oxygen rate which increased with agitation and air flow rate. It was found, however, that agitation and aeration had no effect on the carbon dioxide production rate but the mass transfer coefficient increased markedly with increasing agitation. Values for all the mass transfer terms were determined. The mass transfer coefficient, k La, has been correlated with the impeller agitation speed, N, as follows: k L a=1·079×10 −3 N 1·96