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This study experimentally and numerically investigated the thermo-fluid dynamics of Taylor–Couette flow with an axial temperature gradient from the chemical engineering perspective. A Taylor–Couette apparatus with a jacket vertically divided into two parts was used in the experiments. Based on the flow visualization and temperature measurement for glycerol aqueous solutions with various concentrations, the flow pattern was classified into six modes: heat convection dominant mode (Case I), heat convection-Taylor vortex flow alternate mode (Case II), Taylor vortex flow dominant mode (Case III), fluctuation maintaining Taylor cell structure mode (Case IV), segregation between Couette flow and Taylor vortex flow mode (Case V) and upward motion mode (Case VI). These flow modes weremapped in terms of the Reynolds and Grashof numbers. Cases II, IV, V and VI are regarded as transition flow patterns between Case I and Case III, depending on the concentration. In addition, numerical simulations showed that in Case II, heat transfer was enhanced when the Taylor–Couette flow was altered by heat convection. Moreover, the average Nusselt number with the alternate flow was higher than that with the stable Taylor vortex flow. Thus, the interaction between heat convection and Taylor–Couette flow is an effective tool to enhance heat transfer. This article is part of the theme issue ‘Taylor–Couette and related flows on the centennial of Taylor’s seminal Philosophical transactions paper (Part 2)’.

The semi-batch operation effectively fabricated the ZIF-8 cover layer on silica hard-shell microcapsules.

A method to intensify the mixing process of scalar components within shear-thinning fluids was proposed. A conical Taylor–Couette flow enabled fluid elements to circulate in the entire fluid column owing to the global circulation flow (i.e., meridional flow) for keeping good local mixing within Taylor cells. The global convection and mixing characteristics were numerically investigated. The meridional flow was found to be enhanced with increasing shear-thinning. In addition, ......

The present chapter provides an overview of vortex dynamics in complex fluids by taking examples of Taylor vortex flow. As complex fluids, non-Newtonian fluid is taken up. The effects of these complex fluids on the dynamic behavior of vortex flow fields are discussed. When a non-Newtonian shear flow is used in Taylor vortex flow, an anomalous flow instability is observed, which also affects heat and mass transfer characteristics. Hence, the effect of shear-thinning on vortex dynamics including heat transfer is mainly referred. This chapter also refers to the concept of new vortex dynamics for chemical process intensification technologies that apply these unique vortex dynamics in complex fluids in Conclusions.

Polystyrene particles were dispersed in glycerol solution containing sodium chloride. The orthokinetic agglomeration process of the particles was observed in a mixing tank agitated by a six-blade Rushton turbine. It is found that the median diameter of agglomerates was initially increased and asymptotically approached a constant value. Bimodal particle size distributions were obtained within all of the experimental conditions and the stable size of produced agglomerates was independent of the rotational speed of the impeller. On the other hand, the amount of produced agglomerates was increased as the increase in the rotational speed of the impeller. Considering the experimental results, the population balance equation of a mathematical model to describe the evolution of the agglomerates was simplified. Then a representative shear rate taking into account the shear history of individual particles was proposed and its applicability was evaluated. It is showed that this shear rate is useful to predict agglomeration behavior of particles and a conventional representative shear rate in a mixing tank is overestimation.

The drying process of electrode slurry for LiB should be crucial to obtain higher electrochemical performance, but it has been a black box. Furthermore, the lack of sufficient information on slurry microstructure complicates solving this issue. In this study, the cathode slurries having different internal structures are prepared and characterized by rheological properties. The drying process of the coating layer is evaluated in terms of film shrinkage. When the coarse particles of active material and the network structure of acetylene-black particles are uniformly mixed, a low drying rate results in extensive particle segregation and poor cycle performance. On the other hand, it is found that insufficient dispersion of active materials causes poor rate performance. Under the optimal drying condition, the slurry microstructure is found not to affect battery performance. However, the optimization of drying conditions requires consideration of material mobility during drying.

This work experimentally investigated flow characteristics and mixing properties of the two-phase flow in a continuous Taylor-Couette flow reactor (CTCR) with narrow gap width. In the device with a gap width of 0.5mm, to the authors’ knowledge, the narrowest gap width device ever studied in CTCR systems, the present study revealed that slug flows with alternating gas and liquid phases, as observed in microchannels, appeared in a certain flow regime. This slug flow appeared mainly in the region of low rotational Reynolds and axial Weber numbers. The non-dimensional effective diffusion coefficient Deff/uL [-] of slug flow was also measured by a tracer response method. Deff/uL in the slug flow was on the order of 10⁻⁶ and it has been successfully found that ideal plug flow mixing characteristics could be achieved under this flow condition. Since the intensified and controllable mixing in the liquid phase due to Taylor vortex motion induced by the inner cylinder rotation is expected to be much better than the mixing in the liquid phase of slug flows in microchannels, this flow is expected to be one of the process intensification techniques that will outperform the performance of the conventional microreactors with microchannels.

The sedimentation and flow characteristics of micro-encapsulated phase change materials have been investigated. As a phase change material, trimethylolethane clathrate hydrate having 218 kJ kg−1 of latent heat was used and encapsulated in silica hard-shell microcapsules, which size distribution has two peak at 15 µm and 59 µm. A cationic surfactant, oleylbishydroxyethylmethylammonium chloride with a counter-ion, sodium salicylate was used as drag reducing additives and poly vinyl alcohol was used as a stabilizer. From the results, it was found that the combination additive prevents effectively the microcapsule sedimentation. The drag reduction was also observed to occur in the high Reynolds number region. Thus, the present additive was concluded to be promising for the latent heat transportation by use of silica hard-shell microcapsules containing phase change materials.

This study numerically investigates the heat transfer characteristics, including the fluid flow, of a Taylor vortex flow system with shear-thinning fluids. Governing equations were solved using OpenFOAM® 4.0 code. The Carreau model was utilized as the rheological model. The parameter (n) in the Carreau model, which describes the slope of a decrease in viscosity with an increase in shear-rate, was varied from 1 to 0.3. The local Nusselt number (NuL) decreased with the increase in shear-thinning property. Furthermore, a correlation equation between the effective Reynolds number (Reeff) and a global Nusselt number (NuG) was proposed. Using this equation, NuG was evaluated within a ± 10% error in the case of n = 1, 0.7, 0.5, and within a ± 20% error in the case of n = 0.3. The size of the Taylor vortices became axially larger with an increase in the shear-thinning property. Furthermore, the thickness of the boundary layer of velocity and temperature increased with an increase in shear-thinning property. The ratio of the thickness of velocity boundary layer to the temperature boundary layer monotonically decreased with an increase in Reeff.

The material deposition in a mixing tank agitated by the MAXBLEND impeller in a turbulent state was quantified and compared between cases with and without baffle clearance. Magnesium hydroxide formed from the chemical reaction between calcium hydroxide and magnesium chloride was used as a model of scale formation. Flow velocity in the tank was investigated by employing computational fluid dynamics simulation and experimentally validated by an ultrasonic velocity profiler method. Results showed that the amount of scale decreased with the increase in the rotational speed of the impeller due to the erosion effect on the tank wall. In the case without baffle clearance, the smaller weight of the scale was deposited on the front of the baffle plate due to the flow impingement, which enhanced the removal of the scale deposition. However, the lower-velocity magnitude behind the baffles resulted in an enhancement in the formation of scale. Installation of baffle clearance caused a contraction flow in between the tank wall and baffles, and consequently, the higher flow velocity reduced the amount and thickness of the scale. Measurement of the torque showed that the baffle clearance did not affect the power consumption, so the installation of baffle clearance can be a promising approach to reduce scale deposition in terms of saving operational costs and increasing process efficiency and safety.

Pressure-driven membrane filtration processes such as microfiltration and ultrafiltration are still hindered by concentration polarization and membrane fouling. Generally in these filtration processes, concentration polarization causes decline of permeate flux and rejection, and fouling leads to permeate flux decline with the increase of rejection. The use of high shear stress for cross flow filtrations has long been considered one of the most efficient methods for overcoming these problems. However, circumferential fluid motion of the hollow fiber membrane surface is also important to avoid formation of a high concentration layer on the surface. In this study, ultrafiltration of humic acid aqueous solution using a polyethersulfone hollow fiber membrane was selected as a model case, and a membrane module with a helical baffle installed around the membrane was used. With the insertion of the baffle, normalized permeate flux and rejection became higher than those without the baffle at the wide range of the feed flow rate. In order to identify the cause of the improvement, CFD simulation was conducted for different baffle geometries. Swirling flow motion generated by the helical baffle around the membrane became more dominant with the lower aperture ratio of the cross sectional area, and there existed the optimum value for the swirling flow generation in terms of the variation of the helical baffle pitch length. The intensity of this fluid motion was characterized by Swirl number and it was found out that high separation performance was obtained at the high Swirl number.

In this study, the flow dynamics of a Taylor–Couette flow with an axial distribution of temperature was experimentally investigated. The flow can be classified into three patterns based on the balance between the centrifugal force and the buoyancy. If the buoyancy is dominant, global heat convection is observed instead of Taylor vortices (Case I). When the buoyancy is comparable to the centrifugal force, the Taylor vortices and global heat convection appear alternately (Case II). If the centrifugal force is sufficiently high to suppress the buoyancy, stable Taylor vortices are observed (Case III). The characteristics of the mixing/diffusion are investigated by conducting a decolorization experiment on a passive tracer. In Case II, the tracer is rapidly decolorized in the presence of the global heat convection instead of the Taylor vortices. This result implies that the interaction between the centrifugal force and the buoyancy would induce an anomalous transport. This article is protected by copyright. All rights reserved.

In this paper, thermal processing of starch slurry in a Couette-Taylor flow (CTF) apparatus was investigated. Gelatinized starch dispersion, after treatment in the CTF apparatus, was characterized using such parameters like starch granule diameters (or average diameter), starch granule swelling degree (quantifying the amount of water absorbed by starch granules) and concentration of dissolved starch. These parameters were affected mostly by the process temperature, although the impact of the axial flow or rotor rotation on them was also observed. Moreover, the analysis of results showed a relatively good correlation between these parameters, as well as, between those parameter and apparent viscosity of gelatinized starch dispersion. Meanwhile, the increase in the value of the apparent viscosity and in shear-tinning behaviour of dispersion was associated with the progress of starch processing in the CTF apparatus. Finally, the CTF apparatuses of different geometries were compared using numerical simulation of the process. The results of the simulation indicated that the apparatus scaling-up without increasing the width of the gap between cylinders results in higher mechanical energy consumption per unit of processed starch slurry.

In food industries, enzymatic starch hydrolysis is an important process that consists of two steps: gelatinization and saccharification. One of the major difficulties in designing the starch hydrolysis process is the sharp change in its rheological properties. In this study, Taylor–Couette flow reactor was applied to continuous starch hydrolysis process. The concentration of reducing sugar produced via enzymatic hydrolysis was evaluated by varying operational variables: rotational speed of the inner cylinder, axial velocity (reaction time), amount of enzyme, and initial starch content in the slurry. When Taylor vortices were formed in the annular space, efficient hydrolysis occurred because Taylor vortices improved the mixing of gelatinized starch with enzyme. Furthermore, a modified inner cylinder was proposed, and its mixing performance was numerically investigated. The modified inner cylinder showed higher potential for enhanced mixing of gelatinized starch and the enzyme than the conventional cylinder.

The objective of this study is to model the transport phenomena in packed column distillation with the aid of experiment and computer-aided process simulation. The main concept is in that local distillation efficiency HETP is considered as the height of control volume for shell balance of mass and enthalpy, so that it becomes possible to bridge between the ideal and real processes. Distillation experiment was conducted under the total-reflux condition. Determination of local HETPs was performed by comparing the vertical temperature distribution experimentally observed with the stage-by-stage temperature distribution calculated by computer process simulation. In a manner similar to the analogy analysis of a single-phase boundary layer flow over a flat plate, a semi-empirical model of local similarity between simultaneous interphase mass and enthalpy transfer was successfully built by experiment collaborating with a computer-aided process simulation.

Biological Liquid Crystal, a rich set of soft materials with rod-like structures widely existed in nature, possess typical lyotropic liquid crystalline phase properties both in vitro (e.g. cellulose, peptides and protein assemblies), and in vivo (e.g. cellular lipid membrane, packed DNA in bacteria and aligned fibroblasts). Given the ability to undergo phase transition in response to various stimuli, numerous practices have been exercised to spatially arrange biological liquid crystals. In this mini-review, the fundamental understanding of interactions between rod-shaped biological building blocks and their orientational ordering across multiple length scales is addressed. Discussions are made with regard to the dependence of physical properties of non-motile objects on the first-order phase transition and the coexistence of multi-phases in passive liquid crystalline systems. This review also focuses on how the applied physical stimuli drives the reorganization of constituent passive particles for a new steady-state alignment. A number of recent progresses in the dynamics behaviours of active liquid crystals are presented, and particular attention has been given to those self-propelled animate elements, like the formation of motile topological defects, active turbulence, correlation of orientational ordering and cellular functions. Finally, future implications and potential applications of the biological liquid crystalline materials are discussed.

In this study, a Taylor-Couette flow reactor (TCFR) was applied to starch hydrolysis accompanied with an intricate viscosity change during reaction for the purpose of process intensification. In industries, several reactors are used in starch hydrolysis, namely gelatinization, liquefaction, and saccharification. It was possible to conduct a continuous starch hydrolysis with one TCFR. In addition, a sufficient reducing sugar yield was obtained in the Taylor vortex flow regime. However, the yield decreased at a higher effective Reynolds number (Reeff) due to axial dispersion through a bypass flow generated by the wavy motion of Taylor cells. In order to immobilize Taylor vortex flow at this condition, a ribbed inner cylinder was employed which suppressed axial dispersion at the higher Reeff. As a result, a higher reducing sugar yield was successfully obtained than that by using a standard cylinder, demonstrating that the optimization of TCFR geometry has the potential for process intensification.

The definition of Reynolds number (Re) in a Taylor-Couette flow for a shear-thinning fluid is discussed in this paper. Since the shear-thinning property causes spatial distribution of fluid viscosity in a Taylor-Couette flow reactor (TCFR), a method to determine Re by using a numerical simulation is suggested. The effective viscosity (η eff) in Re was the average viscosity using a weight of dissipation function $$ {\eta}_{\mathrm{eff}}={\displaystyle \sum_{i=1}^N{\overset{\cdot }{\gamma}}_i^2{\eta}_i\Delta {V}_i}/{\displaystyle \sum_{i=1}^N{\overset{\cdot }{\gamma}}_i^2\Delta {V}_i}, $$ where N is the total mesh number, η i (Pa·s) is the local viscosity, $$ {\overset{\cdot }{\gamma}}_i $$ (1/s) is the local shear-rate, and ΔV i (m3) is the local volume for each cell. The critical Reynolds number, Re cr, at which Taylor vortices start to appear, was almost the same value with the Re cr obtained by a linear stability analysis for Newtonian fluids. Consequently, Re based on η eff could be applicable to predict the occurrence of Taylor vortices for a shear-thinning fluid. In order to understand the relation between the rotational speed of the inner cylinder and the effective shear rate that resulted in η eff, a correlation equation was constructed. Furthermore, the critical condition at which Taylor vortices appear was successfully predicted without further numerical simulation.

Background: The intensification of fermentation in stirred bioreactors is an attractive approach for commercial interests and industries that work with biochemical products. Alpha amylase is an enzymatic bio-products that is produced largely from Aspergillus oryzae. Using adaptable agitator can be an efficient way for stirred fermentation. Objective: This study, concentrated on enhancing the mixing process in order to intensify Aspergillus oryzae fermentation. A straight type of Maxblend® impeller was used as an agitator to investigate the incubation parameters compared with the use of a 6-blade double Rushton turbine. Method: Stirred fermentation was done in batch condition. Effect of flow pattern of mixing on fermentation parameters was investigated after each sampling. Results: The results showed that the Maxblend® significantly intensified both enzyme activity and growth rate at low and moderate rates of power consumption (P). The main reason for the decreases in the growth rate and the enzyme activity during agitation by the Rushton turbine at low and high Pv was the lack of oxygen and mycelial damage, respectively. Additionally, use of the Maxblend® significantly intensified the KLa at low and moderate rates of power consumption. Conclusion: Axial and uniform mixing by Maxblend® impeller was resulted in improving the fermentation characteristics and enzyme activity.

This study investigated the effect of pretreatment of ultrasonic irradiation on emulsion polymerization of styrene to propose a process intensification method which gives high conversion, high reaction rate, and high energy efficiency. The solution containing styrene monomer was irradiated by a horn mounted on the ultrasonic transducer with the diameter of 5 mm diameter and the frequency of 28 kHz before starting polymerization. The pretreatment of ultrasound irradiation as short as 1 min drastically improved monomer dispersion and increased reaction rate even under the agitation condition with low rotational speed of impeller. Furthermore, the ultrasonic pretreatment resulted in higher monomer concentration in polymer particles and produced larger polymer particles than conventional polymerization without ultrasonic pretreatment.

Homogeneous dispersion of particles is crucial for many processes where the reaction rate is highly dependent on relative rates of mixing or degree of homogenization. These processes include crystallization, polymerization, and some mineral-refining processes. Complete particle dispersion in high-concentration slurries is researched experimentally and numerically. Computation fluid dynamics results suggest that cloud height is an excellent indicator for mixing homogeneity, and energy efficiency can be enhanced by removing baffles over a range of solids concentrations under the complete dispersion condition. The power required to maintain a high cloud height in a stirred tank can be predicted via a simple power number analysis. The proposed unbaffled design can be potentially beneficial to some industrial processes like crystallization.

A robust separation strategy using novel particle-flow-instability physics is successfully developed for a difficult-to-separate suspension in which there is some combination of a small density difference between solid and liquid, high viscosity, and small-sized particles. The method we propose here requires no dilution for medium, high or extremely high viscosity slurries and can produce effective solid–liquid separation with low capital and operational inputs. The results have relevance for many biotechnological and/or chemical processes. We anticipate that further optimizations could lead to a more effective separation process with even lower energy input.

Starch gelatinization and enzymatic hydrolysis was carried out in a continuous Couette–Taylor flow reactor with a water jacket. The degree of gelatinization and the concentration of reducing sugars produced via enzymatic saccharification were evaluated by varying operational variables: rotation speed of an inner cylinder, initial concentration of starch and reaction temperature. At the initial concentration of the starch suspension, 50 kg m−3, starch saccharification proceeded sufficiently even at low rotation speed of the inner cylinder and saccharification temperature. At the higher initial concentration, 100 and 150 kg m−3, a higher rotation speed of the inner cylinder and temperature of the saccharification section were required to obtain sufficient starch saccharification. Even in the case of C0 = 100 and 150 kg m−3, the more reducing sugar was obtained by choosing an adequate rotation speed of the inner cylinder and a reaction temperature.

Couette–Taylor flow (CTF), which is characterized by the presence of Taylor vortices, ensures effective mixing, fast heat transfer and improved rheological properties of starch slurry. Therefore, this type of flow can be expected to provide favorable conditions for starch processing. In order to check how to intensify the process, starch gelatinization has been studied experimentally and using computer simulation in two CTF apparatuses of different volumes. The results show that, when the volume of apparatus was small, high value of degree of starch gelatinization could be achieved at relatively low temperature or at relatively low rotor rotation frequency. The increase in the apparatus volume ensures higher rate of gelatinized starch production and the reduction in dissipation of mechanical energy connected with rotor rotation, however, it also amplifies the detrimental inlet and gravitation effects. To overcome both of these negative effects, the increase in the rotor frequency is required. Practical Application Starch gelatinization is a process frequently encountered in food industry, e.g., food sterilization or starch hydrolysis. Therefore, a new way of starch processing could be interesting in the context of growing consumer interest in natural food. It is expected that CTF apparatus could enable to process much more concentrated starch slurry than a jet cooker or coil heater typically used in industrial setting. Starch granules should also be less damaged during treatment in CTF apparatus than in an extruder. The results presented in this paper are relevant for process intensification and scale-up of starch gelatinization in CTF apparatus and will be extended to simultaneous starch gelatinization with enzymatic hydrolysis in the future work.

The mixing of viscous Newtonian fluids was investigated in experiments by means of decolorization visualization. Various inclined shaft and offset impeller configurations were tested to develop complete mixing with less energy consumption. It was found that isolated mixing regions could be more easily destroyed with larger angles of inclination, for example, 30°. A specific energy parameter was introduced to quantify the energy required for complete homogenization based on the mixing time and the specific power input. It was found that an increased shaft angle reduces the specific energy required for complete mixing. The results suggested that operating an angled-shaft system at higher speeds is more energy-efficient. It was also found that increased eccentricity and reduced impeller-to-bottom clearance generally lead to reduced specific energy consumption for homogenization. The CFD results confirmed that breaking the spatial symmetry in an angled-shaft system leads to destruction of the regular regions ...

In this study, it was shown that how rheology and fluid dynamics effected the behavior of cell growth and L-Lactic acid productivity during cultivation of filamentous fungi (Aspergillus oryzae) in a stirred-tank. Submerged culture of A. oryzae was a shear-thinning fluid with complex rheology and morphology. It is a shear-sensitive fluid. The scope of this study, was enhancing the gas-liquid flow of fermentation fluid to improve the liquid-gas mass transfer, L-lactic acid production and stagnant zone reduction at low energy consumption by effective shear rate generation using multi-large blade agitator with global axial pattern of mixing. Due to this reason, the advantage of Fullzone® (FZ), and impeller was investigated. Experimental results when using multi-large and multi-radial impeller, showed that the same volumetric power consumption of the dissolved oxygen concentration, Re, macro and micro-morphology size, biomass and L-lactic acid production when using multi large impeller was higher and more stable than that of the multi radial impeller. Most of above positive properties were due to the reduction in viscosity and apparent consistence index of fermented fluid.