Oscillatory Flow Mixing Research Articles

Protein Crystallization As a Process Step in a Novel Meso Oscillatory Flow Reactor: Study of Lysozyme Phase Behavior

In the present work, it is reported for the first time the study of the applicability of a novel meso oscillatory flow reactor (meso-OFR) for protein crystallization as a process step. Crystallization assays carried out in the designed device enabled to derive a two-dimensional lysozyme phase diagram (lysozyme concentration against sodium chloride concentration). Results evidence the formation of several types of crystals (different size and shape), with a strong influence of salt concentration on crystal shape. Results also show that lysozyme remains active at the end of the experiments. Furthermore, it was possible to verify the reduction of the metastability zone when compared to lysozyme crystallization conducted under quiescent conditions. Induction times were also measured by online monitoring of the turbidity of the crystallization solution, obtained values being between 41 and 900 min. Beyond providing improved understanding of protein phase behavior under oscillatory flow mixing, the results are ...

Synthesis of palm based biolubricant in an oscillatory flow reactor (OFR)

Plant-based oils are drawing great attention as potential alternative biodegradable lubricant base stocks with their attractive properties of being renewable, non-toxic and environmentally friendly. In the present study, oscillatory flow mixing (OFM) technology was applied in the production of palm biolubricant via transesterification of palm methyl ester (PME) with trimethylolpropane (TMP) by using sodium methoxide (CH3ONa) as the catalyst under vacuum conditions. The optimum operating temperature was recorded at 140°C, based on the maximal conversion of PME to trimethylolpropane ester (TE) achieved and the reaction was found to follow a second order reaction with 99.6kJ/mol as the total activation energy required. OFR can effectively promote uniform mixing and enhance the engineering performance within the reactor, thus leading to a time saving of more than two-fold compared to the reports of previous researchers. The properties of the synthesized palm biolubricant were also found to be comparable to the other plant based biolubricants.

The functionalization of carbon nanotubes using a batch oscillatory flow reactor

This paper describes an efficient method for the functionalizing of multi-walled carbon nanotubes (MWCNT) using oscillatory flow mixing (OFM). A 3 l batch oscillatory flow reactor (OFR) was designed and constructed for pilot scale functionalization of MWCNT in order to potentially improve their compatibility within a thermoplastic polyphenylene sulphide (PPS) matrix. The OFM batch reactor consisted of a jacketed cylindrical vessel with a vertical axial oscillator that contained a series of baffled mixing plates. MWCNTs dispersed in dimethylformamide (DMF) were introduced into the reactor and a two stage reaction for functionalizing MWCNTs with PPS compatible groups was carried out under oscillation of baffles at elevated temperatures. Fluid mixing observations in the reactor showed that MWCNTs formed a uniform dispersion of aggregated flocs before and during the functionalization reaction. On completion of the reaction and cessation of the oscillation, the aggregated flocs of MWCNT rapidly sedimented at the bottom of the reactor; hence could be collected as a concentrated mass thereby facilitating the separation of functionalized MWCNTs from the solvent. The functionalized MWCNTs were dried and then characterized by transmission electron microscopy, infrared spectroscopy as well as thermal gravimetric analysis in order to investigate the extent of MWCNT functionalization. The characterization results confirmed the effective and relatively uniform functionalization of the MWCNTs despite formation of aggregates, indicating that OFM provides a viable approach for functionalizing MWCNTs.

Aqueous two-phase micellar systems in an oscillatory flow micro-reactor: study of perspectives and experimental performance

BACKGROUND: Aqueous two-phase micellar systems (ATPMS) are micellar surfactant solutions with physical properties that make them very efficient for the extraction/concentration of biological products. In this work the main proposal that has been discussed is the possible applicability and importance of a novel oscillatory flow micro-reactor (micro-OFR) envisaged for parallel screening and/or development of industrial bioprocesses in ATPMS. Based on the technology of oscillatory flow mixing (OFM), this batch or continuous micro-reactor has been presented as a new small-scale alternative for biological or physical-chemical applications. RESULTS: ATPMS experiments were carried out in different OFM conditions (times, temperatures, oscillation frequencies and amplitudes) for the extraction of glucose-6-phosphate dehydrogenase (G6PD) in Triton X-114/buffer with Cibacron Blue as affinity ligand. CONCLUSION: The results suggest the potential use of OFR, considering this process a promising and new alternative for the purification or pre-concentration of bioproducts. Despite the applied homogenization and extraction conditions have presented no improvements in the partitioning selectivity of the target enzyme, when at rest temperature they have influenced the partitioning behavior in Triton X-114 ATPMS. Copyright © 2011 Society of Chemical Industry

Numerical Study of High-Frequency Oscillatory Air Flow and Convective Mixing in a CT-Based Human Airway Model

High-frequency oscillatory ventilation (HFOV) is considered an efficient and safe respiratory technique to ventilate neonates and patients with acute respiratory distress syndrome. HFOV has very different characteristics from normal breathing physiology, with a much smaller tidal volume and a higher breathing frequency. In this study, the high-frequency oscillatory flow is studied using a computational fluid dynamics analysis in three different geometrical models with increasing complexity: a straight tube, a single-bifurcation tube model, and a computed tomography (CT)-based human airway model of up to seven generations. We aim to understand the counter-flow phenomenon at flow reversal and its role in convective mixing in these models using sinusoidal waveforms of different frequencies and Reynolds (Re) numbers. Mixing is quantified by the stretch rate analysis. In the straight-tube model, coaxial counter flow with opposing fluid streams is formed around flow reversal, agreeing with an analytical Womersley solution. However, counter flow yields no net convective mixing at end cycle. In the single-bifurcation model, counter flow at high Re is intervened with secondary vortices in the parent (child) branch at end expiration (inspiration), resulting in an irreversible mixing process. For the CT-based airway model three cases are considered, consisting of the normal breathing case, the high-frequency-normal-Re (HFNR) case, and the HFOV case. The counter-flow structure is more evident in the HFNR case than the HFOV case. The instantaneous and time-averaged stretch rates at the end of two breathing cycles and in the vicinity of flow reversal are computed. It is found that counter flow contributes about 20% to mixing in HFOV.

Phase transfer wet oxidation

The photocatalysed mineralisation of methylene blue, a common organic dye, has been carried out in a novel Pulsed Baffled Tube Photochemical Reactor (PBTPR). The fluid hydrodynamics of the PBTPR is based on oscillatory flow mixing, which essentially exploits the phenomenon of flow separation resulting from fluid flow past sharp edges. The PBTPR has excellent solids handling capacity, and is capable of effecting complete dispersion and mixing of the photocatalyst slurry. The effects of oscillatory flow mixing are reported on properties such as adsorption and the reaction rate. A kinetic study has also been undertaken and kinetic parameters are reported for this system. A catalyst loading of 0.143 g/l has been found to be optimal for this system.

The intensification of gas–liquid flows with a periodic, constricted oscillatory-meso tube

The experimental study of gas dispersion in a vertical periodically, constricted, oscillatory meso-tube (OMT) is herein presented. Water was continuously pumped through the OMT in the laminar flow regime along with an oscillatory flow component superimposed into the net flow in a range of fluid oscillation frequency ( f ) and centre-to-peak amplitude ( x 0 ) of 0 – 20 s - 1 and 0–3 mm, respectively, in the presence of a very low superficial gas velocity ( 0.37 mm min - 1 ) . Bubble images were recorded with a CCD camera and analysed with Visilog ® software. A bimodal distribution of bubble size was in general observed but the bubble size was found strongly dependent on the oscillatory flow mixing conditions imposed into the fluid. A number fraction of micro-bubbles (with an equivalent diameter, D eq , equal or bellow 0.2 mm) up to 60% was generated with increasing values of x 0 (i.e. 3 mm) and values of f in the range 10 – 15 s - 1 . Furthermore, it is demonstrated that the Sauter mean diameter, D 32 , and the specific interfacial area, a, can be fined tune by setting both f and x 0 in this studied range. The high number fraction of micro-bubbles was concluded to have a positive impact in enhancing the liquid-side mass transfer coefficient, k L . Globally, the differences in bubbles sizes were found to play a marginal effect in the global enhancement of the k L a in the meso-tube in comparison with the intensive contact experimented by the bubbles rising in the oscillatory flow. The higher order of magnitude of the k L values found in this work (up to 0.0021 m s - 1 ) is promising for running numerous industrial gas–liquid flows processes through smaller and better, while aeration of biotransformations can be run more efficiently, as supported by our recent proof-of-concept studies carried out in the platform.

An Experimental Investigation into the Scale-up of Oscillatory Flow Mixing in Baffled Tubes

This paper describes results from an experimental investigation into the scale-up of oscillatory flow mixing (OFM) in geometrically scaled baffled tubes ranging from 24 mm to 150 mm diameter and from 1 m to 4.5 m in length. Measured axial dispersion coefficients are reported together with case studies and an empirical correlation. An alternative multi-orifice reactor geometry with the potential for use in large-scale plant was also constructed and tested from which it was concluded that OFM is a technology which lends itself readily to scaling-up from laboratory to pilot plant scale, and to industrial scale. Experiments performed on small laboratory OFM apparatus containing less than one litre of fluid can with confidence be used to predict mixing behaviour in much larger plant containing hundreds of litres of fluid.

Proof-of-concept of a novel micro-bioreactor for fast development of industrial bioprocesses

The experimental performance of a novel micro-bioreactor envisaged for parallel screening and development of industrial bioprocesses has been tested in this work. The micro-bioreactor with an internal volume of 4.5 mL is operated under oscillatory flow mixing (OFM), where a controllable mixing and mass transfer rates are achieved under batch or continuous laminar flow conditions. Several batch fermentations with a flocculent Saccharomyces cerevisiae strain were carried out at initial glucose concentrations (S(0)) range of approximately 5-20 g/L and compared to yeast growth kinetics in a stirred tank (ST) bioreactor. Aerobic fermentations were monitored ex situ in terms of pH, DO, glucose consumption, and biomass and ethanol production (wherever applicable). An average biomass production increase of 83% was obtained in the micro-bioreactor when compared with the ST, with less 93.6% air requirements. It also corresponded to a 214% increase on biomass production when compared with growth in a shaken flask (SF) at S(0) = 20 g/L. Further anaerobic fermentations at the same initial glucose concentration ranges gave the opportunity to use state-of-the-art fiber optics technology for on-line and real-time monitoring of this bioprocess. Time profiles of biomass concentration (measured as optical density (OD)) were very similar in the ST bioreactor and in the micro-bioreactor, with a highly reproducible yeast growth in these two scale-down platforms.

Crystallization of Paracetamol under Oscillatory Flow Mixing Conditions

There has been an increasing effort in designing pharmaceutical particles with controllable properties (quality) such as chemical purity, morphology, size distribution, surface characteristics, and microstrain content. In this paper, we explore the feasibility of oscillatory flow mixing (OFM) in improving the quality of pharmaceutical precipitates, using paracetamol (4-acetamidophenol) as a model system. In-situ atomic force microscopy (AFM) and optical microscopy were applied to observe the growth of {110} faces of single paracetamol crystals. These studies showed that (a) the bunching and macrostep formation occur at all values of supersaturation; and (b) the oscillation of solution with respect to the growing interface and its relative velocity are the critical parameters for the minimization of the interfacial instabilities, and in turn, for maintaining structural quality. These findings were tested in a conventional impeller driven batch crystallizer (IDBC) and in an oscillatory baffled batch crystallizer (OBBC), in which, apart from hydrodynamics, all external conditions such as initial supersaturation and crystallization temperature were kept constant. The physical properties (the quality) of the precipitates were characterized by low angle laser light scattering (LALLS), scanning electron microscopy (SEM), and X-ray powder diffraction (XRPD), respectively. The analysis of obtained results and their comparison for these two types of mixing shows clearly that particles precipitated in OBBC are of significantly higher quality than those produced in IDBC. A computational fluid dynamics (CFD) software package, Fluent 5, was used to model dynamical fluid patterns in both crystallizers.

Characterisation of impeller driven and oscillatory mixing by spatial and temporal shear rate distributions

Computational fluid dynamics (CFD) technique was used to model spatial and temporal behaviour of flow patterns in an impeller-driven stirred vessel (IDSV) and in an oscillatory flow baffled vessel (OFBV). The spatial and temporal shear rate distributions were assessed for IDSV based on k– ε model, appropriate for classical mixing, while the distributions for OFBV were calculated based on large eddy simulation suitable for oscillatory flow mixing. In addition, the real parameters of the vessels such as geometry, physical dimensions, impeller speed, oscillation frequency and amplitude, and density and viscosity of the fluid (water), were taken into account. Under given operating conditions the spatial shear rate distribution appears to be quite distinct for two different methods of mixing. For OFBV, the volume-averaged shear rate was found to be of one order of magnitude larger than that of IDSV. In addition, a marked distinction between the temporal shear rate distributions was observed. In OFBV, the modelling shows that particles spend most of their residence time in the high shear regions, while in IDSV, particles reside mainly in the region of considerably lower shear rates.

Heat transfer performance for batch oscillatory flow mixing

Abstract Experimental heat transfer data is presented for two batch operations of oscillatory flow mixing. In one case fluid is oscillated within a baffled tube and in the second case baffles are oscillated within a process fluid. For both situations the heat transfer coefficient depends on the intensity of oscillation, and the energy performance of each configuration corresponds to that of an equivalent net turbulent flow in a pipe or a batch stirred vessel. The results indicate that oscillatory flow batch mixing is as energy efficient as other conventional mixing configurations and the heat transfer performance indicates that each oscillatory flow mixing configuration could be satisfactorily used as a batch reactor system.

The application of oscillatory flow mixing to photocatalytic wet oxidation

The photocatalysed mineralisation of methylene blue, a common organic dye, has been carried out in a novel Pulsed Baffled Tube Photochemical Reactor (PBTPR). The fluid hydrodynamics of the PBTPR is based on oscillatory flow mixing, which essentially exploits the phenomenon of flow separation resulting from fluid flow past sharp edges. The PBTPR has excellent solids handling capacity, and is capable of effecting complete dispersion and mixing of the photocatalyst slurry. The effects of oscillatory flow mixing are reported on properties such as adsorption and the reaction rate. A kinetic study has also been undertaken and kinetic parameters are reported for this system. A catalyst loading of 0.143 g/l has been found to be optimal for this system.

The Effects of Oscillatory Flow and Bulk Flow Components on Residence Time Distribution in Baffled Tube Reactors

A characteristic of oscillatory flow mixing in a baffled tube is that the residence time distribution performance can be affected independently of net flow conditions. The effects of both the oscillatory velocity and the throughput velocity on the residence time distribution performance has been investigated in a 24 mm diameter, 2.8 m long, baffled tube oscillatory flow reactor. The experiments were performed by applying the tanks-in-series model to ’perfect pulse’ tracer experiments over a wide range of oscillatory conditions and flow rates. An optimum set of oscillatory and net flow conditions was found which resulted in near plug flow behaviour, usually 50 tanks-in-series ( N ) or greater. For a throughput velocity, N was found to be sensitive to both the amplitude and frequency of oscillation, and this dependence could be expressed by means of the oscillatory flow Reynolds number ( Re 0 ), which combines both parameters. A unique value for Re 0 for each value of the net flow Reynolds number ( Re n ) gave the closest approach to a plug flow RTD. To relate the oscillatory and net flows, a dimensionless velocity ratio, ψ, was used, defined as Re o / Re n . In order to relate the RTD performance for different flow rates, the tanks-in-series model was non-dimensionalized by the use of a stage-wise efficiency term,η, defined as the ratio of N to the theoretical number of stages. Over the range of oscillatory and net flow conditions studied, it was found that the range 2 ≤ψ ≤ 4 corresponded to the optimum RTD conditions, where efficiencies close to 1 were achieved. It was concluded that these dimensionless parameters were sufficient to select, a priori, the oscillatory parameters necessary to obtain the optimum RTD in an oscillatory flow reactor based on a desired throughput specification.

The quantitative description of fluid mixing using Lagrangian- and concentration-based numerical approaches

We report on two numerical approaches to quantify mixing—method I is based on kinematic mixing rates (i.e. the mixing rates due to the fluid mechanics only) and method II is based on the evolution of the concentration distribution of a passive tracer. For method I, kinematic mixing rates are established from the way infinitesimal fluid line elements are stretched by the flow and, from method II, the mixing rate is determined from the rate at which the variance of the concentration of a particle cloud decreased, during the mixing process. For method II, concentrations were calculated by tracking a large number of diffusive particles using a Langevin-type equation (i.e. introducing a random walk term to model molecular diffusion) and by dividing the domain into small regions. The two approaches were applied to a case study, oscillatory flow mixing (OFM) within baffled tubes, which is an inertial flow that has been shown to provide an efficient alternative to conventional mixing processes and is a viable candidate for technological application. A numerical solution for this flow field was calculated by solving the full axisymmetric Navier–Stokes equations which is valid up to a value of the oscillatory flow Reynolds number of order 200. The results of the two mixing methods are compared and their applicability and usefulness in the characterisation of the mixing ranked. The effect of fluid oscillation conditions are also quantified, for the flow field examined.

Computation Transport Phenomena in Chemical Engineering. Self-Sustained Oscillatory Flow and Fluid Mixing in Grooved Channels.

くぼみ付き流路内の自律振動と流体混合を, 実験と数値解析によって研究した.自律振動は, くぼみ上部のはく離せん断層によって励起されたトルーミン・シュリヒティング波から生じ, 臨界レイノルズ数はくぼみ長さの増大とともに低下する.流れの変動成分による運動量輸送過程の解析は, リブ上面で逆カスケード現象を示す.くぼみと主流部間の流体交換は自律振動によって開始され, 粒子軌跡追跡法の結果は可視化実験の観察とよく一致した.