Rotor-stator Spinning Disc Reactor Research Articles

Epoxidation of methyl oleate in a rotor-stator spinning disc reactor

The intensification of the epoxidation of methyl oleate with hydrogen peroxide and formic acid in a rotor-stator spinning disc reactor (RSSDR) was studied in dependence of temperature, rotational disc speed and reactor throughput. The application of TiO2 as heterogeneous catalyst immobilized with Nafion® as adhesive on the rotor disc was also examined. Optimum values for the regarded parameters with respect to conversion and yield were 80 °C, 1000 min−1 and 50 mL min−1. The use of TiO2 as catalyst yielded no beneficial results as opposed to a plain steel rotor. A significant increase in yield and conversion were achieved with the RSSDR in comparison to comparative batch experiments. The average rates of epoxide production in the RSSDR are about a factor four higher than the batch experiments. In comparison with literature results of similar reaction systems, but different reactors, in particular microreactors, the RSSDR shows values in the same order of magnitude and even outperforms catalyst coated microreactor systems. This study shows that the RSSDR with its very good heat and mass transfer properties allows to significantly intensify epoxidation of fatty acid methyl esters.

CFD simulation of single-phase heat transfer in a rotor-stator spinning disc reactor

A computational fluid dynamics (CFD) study on hydrodynamics and heat transfer in a rotor-stator spinning disc reactor (RSSDR), an inventive reactor technology engineered within the frame of process intensification, was performed with OpenFOAM®. This allows the investigation of locally resolved temperature profiles and heat transfer coefficients in the reactor gap, which is experimentally difficult for RSSDRs with small dimensions, while keeping computational costs low. The retrieved radial and tangential velocity and temperature profiles are in agreement with literature. Local stator-side heat transfer coefficients were determined, which increase with higher disc speeds and with increasing throughputs. Area-averaged heat transfer coefficients across the reactor gap were calculated and validated against experimental results performed on the setup simulated in this study; the numerical and experimental data are in qualitative agreement. This study presents the possibility to characterize an RSSDR in terms of hydrodynamics and heat transfer properties by means of a two-dimensional axisymmetric geometry and Reynolds-averaged Navier-Stokes (RANS) turbulence modeling in OpenFOAM®. Expensive measurements, which are difficult to perform particularly for RSSDRs with small dimensions, could thus be avoided, simulating industrial applications at the conditions of interest and designing the RSSDR setup accordingly.

Convective mixing of miscible liquids in a rotor-stator spinning disk reactor

Convective mixing of two miscible liquids injected into a rotor-stator spinning disk reactor (RS-SDR) has been studied using an LIF technique and CFD simulations. The fluids are ammonia water and fluorescein ammonia water solutions. The RS-SDR has a rotor 100 mm in diameter and a thin circular cavity 0.10–0.15 mm in height between the rotor and stator. Laminar flow conditions for rotation speeds up to 120 rpm and total flow rates up to 8 mL/min are considered. The fluorescein solution is injected from the second off-center hole into the cavity filled with the ammonia water supplied from the central hole. The LIF technique visualizes a spiral streak pattern formed downstream of the second injection hole. This streak pattern is analyzed to calculate the local mixedness of the two fluids. It is determined that the mixedness increases for lower flow rates, while it is less sensitive to rotation speed and cavity height. The CFD simulations indicate that the spiral streak pattern is deformed and stretched in the radial direction to form a densely layered structure of the two fluids. The development of the mixedness along the streak pattern is correlated well with Reinlet/Recavity, where Reinlet and Recavity are the Reynolds numbers for the injected flow and the azimuthal flow in the cavity, respectively. This Reynolds number ratio is shown to be related to the Rossby number and the position and radius of the second injection hole. The proposed correlation is based on a linear combination of injection mixing and rotation mixing. The mixedness decreases with Reinlet/Recavity because the injection mixing decreases with Reinlet while the rotation mixing increases with Recavity.

Micromixing in a Rotor-Stator Spinning Disc Reactor.

This paper presents the micromixing times in a rotor–stator spinning disc reactor. Segregation indices are obtained at different rotational speeds performing the Villermaux–Dushman parallel-competitive reaction scheme. Consequently, the corresponding micromixing times are calculated using the engulfment model, while considering the self-engulfment effect. It was found that the segregation index decreases with an increasing disc speed. Furthermore, for the investigated operational conditions, the estimated micromixing times are in the range of 1.13 × 10–4 to 8.76 × 10–3 seconds, in agreement with the theoretical dependency on the energy dissipation rate of ε–0.5. In a rotor–stator spinning disc reactor it is thus possible to further continue the theoretical trend of decreasing micromixing times with very high levels of energy dissipation rates that are unattainable in traditional types of process equipment.

Numerical Analysis of The Effect of Hydrodynamics and Operating Conditions on Biodiesel Synthesis in a Rotor-Stator Spinning Disk Reactor

AbstractA rotor-stator spinning disk reactor for intensified biodiesel synthesis is described and numerically simulated in the present research. The reactor consists of two flat disks, located coaxially and parallel to each other with a gap ranging from 0.1 mm to 0.2 mm between the disks. The upper disk is located on a rotating shaft while the lower disk is stationary. The feed liquids, triglycerides (TG) and methanol are injected into the reactor from centres of rotating disk and stationary disk, respectively. Fluid hydrodynamics in the reactor for synthesis of biodiesel from TG and methanol in the presence of a sodium hydroxide catalyst are simulated, using convection-diffusion-reaction multicomponent transport model with the CFD software ANSYS©Fluent v. 13.0. Effect of operating conditions on TG conversion is particularly investigated. Simulation results indicate that there is occurrence of back flow close to the stator at the outlet zone. Small gap size and fast rotational speed generally help to intensify mixing among reagents, and consequently enhance TG conversion. However, increasing rotational speed of spinning disk leads to more backflow, which decreases TG conversion. Large flow rate of TG at inlet is not recommended as well because of the short mean residence time of reactants inside the reactor.

Liquid–solid mass transfer to a rotating mesh electrode in a rotor–stator spinning disc configuration

Here we present the mass transfer coefficient for liquid–solid mass transfer to a rotating mesh electrode and a smooth flat disc electrode in a rotor–stator spinning disc reactor. The mass transfer coefficients are measured with the limiting current density technique. Additionally, the torque is measured and the energy dissipation rate in the system is calculated. The volumetric mass transfer coefficient of the mesh electrode increases a factor 5 compared to that of the flat disc electrode at virtually equal energy dissipation rates. Due to the characteristics of the mesh, the mesh electrode offers 2.77 times higher electrode area than the flat disc. The mass transfer coefficients measured for the rotating mesh electrode are a factor 1.74 higher compared to the flat disc. Average Sherwood numbers are reported and a correlation is presented that predicts mass transfer rates of rotating meshes in rotor–stator spinning disc reactor configurations.

Convective condensation in a stator–rotor–stator spinning disc reactor

Centrifugal intensification of condensation heat transfer in the rotor–stator cavities of a stator–rotor–stator spinning disc reactor (srs‐SDR) is studied, as a function of rotational velocity ω, volumetric throughflow rate , and average temperature driving force . For the current range of ω, heat transfer from the vapor bubbles to the condensate liquid is limiting, due to a relatively low gas–liquid interfacial area aGL. For rad s−1, a strong increase of aGL, results in increasing the reactor‐average condensation heat transfer coefficient hc from 1600 to 5600 W m−2 K−1, for condensation of pure dichloromethane vapor. Condensation heat transfer in the srs‐SDR is enhanced by rotation, independent of the vapor velocity. The intensified condensation comes at the cost of relatively high energy dissipation rates, indicating condensation in the srs‐SDR is more suited as a means to supply heat (e.g. in an intensified reactor‐heat exchanger), rather than for bulk cooling purposes. © 2016 American Institute of Chemical Engineers AIChE J, 62: 3784–3796, 2016

Forced convection boiling in a stator–rotor–stator spinning disc reactor

Boiling of a pure fluid inside the rotor–stator cavities of a stator–rotor–stator spinning disc reactor (srs‐SDR) is studied, as a function of rotational velocity ω, average temperature driving force and mass flow rate . The average boiling heat transfer coefficient hb increases a factor 3 by increasing ω up to 105 rad s−1, independently of and . The performance of the srs‐SDR, in terms of hb vs. specific energy input ϵ, is similar to tubular boiling, where pressure drop provides the energy input. The srs‐SDR enables operation at Wm , yielding values of hb not practically obtainable in passive evaporators, due to prohibitively high pressure drops required. Since hb is increased independently of the superficial vapor velocity, hb is not a function of and the local vapor fraction. Therefore, the srs‐SDR enables a higher degree of control and flexibility of the boiling process, compared to passive flow boiling. © 2016 American Institute of Chemical Engineers AIChE J, 62: 3763–3773, 2016

Bubble formation in co-fed gas–liquid flows in a rotor-stator spinning disc reactor

The gas–liquid flow in a rotor-stator spinning disc reactor, with co-feeding of gas and liquid, is studied for high gas volumetric throughflow rates and high gas/liquid volumetric flow ratios. High speed imaging and spectral analysis of pressure drop signals are employed to analyse the flow. Two mechanisms of bubble formation are observed, one due to gas overpressure leading to large irregular bubbles, and one due to liquid turbulent vortices leading to small, well-defined bubbles. The two mechanisms lead to three distinct gas dispersion regimes, distinguished by their characteristic oscillations in pressure drop. At low rotational Reynolds numbers (Reω < 0.4 · 106), in the gas spillover regime, the gas is dispersed as large bubbles only. Above this critical Reω, small bubbles are sheared off as well, thus forming a heterogeneous dispersion. At sufficiently high Reω, depending on the gas flow rate, the gas is homogeneously dispersed as small bubbles. The maximum gas flow that can be dispersed as small bubbles is linearly proportional to the local energy dissipation rate. The understanding of the bubble formation mechanisms and pressure signature allows prediction and detection of the prevailing hydrodynamic regime in scaled up spinning disc reactors and for different reaction fluids.

Gas–Liquid mass transfer in a rotor–stator spinning disc reactor: Experimental study and correlation

The gas–liquid mass transfer of rotor–stator spinning disc reactors is studied for various operating conditions and different reactor geometries with rotor radii between 0.065 and 0.135 m. A new reactor setup with a perforated disc containing 119 narrow channels for direct dispersal of gas into the reactor cavity is examined. High volumetric mass transfer coefficients of up to 12ml3mR−3s−1 can be observed due to the large energy input at high rotational disc speeds of up to 2000rpm. The combination of high turbulence and small gas bubbles as a result of the large shear forces in the cavity is identified to be responsible for the acceleration of the mass transfer at high rotational disc speeds. Correlation with an extended power law model equation allows the first-time quantification of the impact of the main operating parameters such as gas and liquid flow rate and rotational disc speed on the volumetric mass transfer coefficients for different reactor geometries.

Intensification of convective heat transfer in a stator–rotor–stator spinning disc reactor

A stator–rotor–stator spinning disc reactor is presented, which aims at intensification of convective heat‐transfer rates for chemical conversion processes. Single phase fluid‐rotor heat‐transfer coefficients hr are presented for rotor angular velocities rad s−1 and volumetric throughflow rates m3s−1. The values of hr are independent of and increase from 0.95 kWm−2K−1 at ω = 0 rad s−1 to 34 kWm−2K−1 at ω = 157 rad s−1. This is a factor 2–3 higher than values achievable in passively enhanced reactor‐heat exchangers, due to the 1–2 orders of magnitude larger specific energy input achievable in the stator–rotor–stator spinning disc reactor. Moreover, as hr is independent of , the heat‐transfer rates are independent of residence time. Together with the high mass‐transfer rates reported for rotor–stator spinning disc reactors, this makes the stator–rotor–stator spinning disc reactor a promising tool to intensify heat‐transfer rates for highly exothermal chemical reactions. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2307–2318, 2015

A numerical study on gas–liquid mass transfer in the rotor–stator spinning disc reactor

The gas–liquid mass transfer coefficient was investigated in a novel multiphase reactor: the rotor–stator spinning disc reactor. Direct Numerical Simulations of the flow field around a single bubble in the reactor showed that vortex stretching invoked the presence of turbulence inside the thin liquid film surrounding the bubble. The Direct Numerical Simulations further provided a measure for the eddy diffusivity in the thin liquid film caused by this increase in vorticity. An expression was subsequently derived from a mass balance using these eddy diffusivities in order to estimate the order of magnitude of gas–liquid mass transfer coefficients. These estimates were found to lie more in line with experimental results in literature than previously used mass transfer models based on Higbie׳s penetration theory.

CFD Numerical Simulation of Hydrodynamics in a Rotor-Stator Reactor for Biodiesel Synthesis

In this paper a rotor-stator spinning disk reactor for intensified biodiesel synthesis is described and numerically simulated. The reactor consists of two flat disks, located coaxially and parallel to each other with a gap ranging from 0.1 mm to 0.2 mm between the disks. The upper disk is located on a rotating shaft while the lower disk is stationary. The feed liquids, triglycerides (TG) and methanol are introduced coaxially along the center line of rotating disk and stationary disk, respectively. Fluid hydrodynamics in the reactor for synthesis of biodiesel from TG and methanol in the presence of a sodium hydroxide catalyst are simulated, using convection-diffusion-reaction species transport model by the CFD software ANSYS? Fluent v. 13.0. The effects of upper disk’s spinning speed and gap size are evaluated.

Single phase fluid-stator heat transfer in a rotor–stator spinning disc reactor

Single phase fluid-stator heat transfer coefficients for a multi-stage rotor–stator spinning disc reactor are presented. The overall heat transfer coefficient is obtained by fitting experimentally obtained steady state outlet temperatures to an engineering model for the fluid flow inside the rotor–stator cavities. Heat transfer measurements are done for gap ratios of G=0.017 and 0.03, rotational Reynolds numbers of Reω=0 to 12×105 and superposed dimensionless throughflow rates of Cw=211–421. From the overall heat transfer coefficient values for the fluid-stator Nusselt number Nus are obtained. For all values of Cw and G, Nus increases more than a factor of 4 by increasing Reω from 0 to 1.3×105. A throughflow dominated regime occurs for Reω<0.2×105, where Nus increases with increasing Cw and decreasing G. For Reω>0.2×105, rotation dominates the heat transfer and no influence of Cw and G on Nus is observed. The thermal performance of the multi-stage rotor–stator spinning disc reactor, quantified in the volumetric overall heat transfer coefficient, increases from UovAVR−1=0.46±0.2 to 0.93±0.16MWm−3K−1 by increasing Reω from 0 to 4.5×105. The volumetric overall heat transfer coefficient of the multi-stage rotor–stator spinning disc reactor is more than a factor of 5 higher than in conventional tubular reactors.

Engineering model for single-phase flow in a multi-stage rotor–stator spinning disc reactor

An engineering model for single-phase flow in a multi-stage rotor–stator spinning disc reactor is presented. The model is based on residence time distribution data, obtained by tracer injection experiments. Measurements are done for gap ratios of G=0.017 and 0.03, rotational Reynolds numbers of Re=4.4×104 to 2.05×106 and superposed dimensionless throughflow rates of Cw=127–421. A single rotor–stator cavity can be described by regions of radial plug flow at low radial disc positions, in combination with a single ideally mixed region at high radial positions. The radial position where transition between plug flow and ideally mixed regions occurs decreases with increasing rotational Reynolds number and gap ratio, and increases with increasing superposed throughflow rate. The resulting flow model is explained by the throughflow and rotation dominated regions observed in rotor–stator cavities with superposed throughflow. The model can be used to quantify performance characteristics of rotor–stator spinning disc reactors, without application of extensive numerical simulations. Results indicate that the model can be scaled up with any number of rotor–stator cavities in series, as well as with increasing disc radius and gap ratio. This makes it a valuable tool in scaling up production capacity of the spinning disc reactor.

Residence time distribution in a single‐phase rotor–stator spinning disk reactor

A reactor model for the single‐phase rotor–stator spinning disk reactor based on residence time distribution measurements is described. For the experimental validation of the model, the axial clearance between the rotor and both stators is varied from 1.0 × 10−3 to 3.0 × 10−3 m, the rotational disk speed is varied from 50 to 2000 RPM, and the volumetric flow rate is varied from 7.5 × 10−6 to 22.5 × 10−6 m3 s−1. Tracer injection experiments show that the residence time distribution can be described by a plug flow model in combination with 2–3 ideally stirred tanks‐in‐series. The resulting reactor model is explained with the effect of turbulence, the formation of Von Kármán and Bödewadt boundary layers, and the effect of the volumetric flow rate. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2686–2693, 2013

Water and n-Heptane Volume Fractions in a Rotor-Stator Spinning Disc Reactor

This paper presents the volume fractions of n-heptane and water measured in a rotor-stator spinning disc reactor. The volume fractions were measured using γ-ray tomography and photographic image analysis. The volume fractions were determined as a function of rotational disc speed, flow ratio, position in the reactor, and rotor material. In addition, the effect of the density difference between water and n-heptane was determined by dissolving potassium iodide in the water phase. Below a rotational disc speed of 75 rpm the volume fraction measured by tomography and photographic image analysis are within 10% deviation. For low rotational disc speeds, the n-heptane volume fraction decreases slightly with increasing rotational disc speed: the centrifugal force accelerates the larger n-heptane droplets to the center. At higher rotational disc speeds the droplets become smaller accordingly, the friction between the phases determines the flow, and the n-heptane volume fraction becomes equal to the n-heptane to total flow ratio. An increase in density difference from 0.31 to 0.79 kg dm–3 did not influence the volume fractions.

Liquid–liquid mass transfer in a rotor–stator spinning disc reactor

This paper presents the liquid–liquid flow behaviour and the liquid–liquid mass transfer rates for a rotor–stator spinning disc reactor, with an axial disc spacing of 1mm, a rotor radius of 0.066m, and rotational disc speeds up to 1600rpm. The liquid–liquid mass transfer rate is determined from extraction experiments of benzoic acid from n-heptane to water. For the calculation of the overall mass transfer rate the dimerization and acid dissociation equilibria are taken into account. Three flow patterns are characterized. Up to 100rpm continuous radially inwards spiralling n-heptane patterns are observed. Between 100rpm and 300rpm this continuous spiral changes to spiralling n-heptane droplets. Above 300rpm fully dispersed phase flow is observed. The overall mass transfer rate increases from 0.17 mORG3 mR−3 s−1 at 100rpm and a water flow rate of 2.5×10−6 mAQ3 s−1 (water: n-heptane=1.1:1) to 51.47 mORG3 mR−3s−1 at 1600rpm and a water flow rate of 12.5×10−6 mAQ3 s−1 (water: n-heptane=5.6:1). These mass transfer rates are at least 25 times higher compared to those in packed columns, and at most 15 times higher compared to mass transfer rates in state of the art microchannels.

Effect of rotor–stator distance and rotor radius on the rate of gas–liquid mass transfer in a rotor–stator spinning disc reactor

Abstract This paper describes the effect of rotor radius, rotor–stator distance, liquid flow rate and rotational disc speed on the rate of gas–liquid mass transfer in a rotor–stator spinning disc reactor. A rotor radius of 0.135 m is studied with rotor–stator distances of 1, 2 and 5 mm, at rotational disc speeds up to 209 rad s −1, and compared with a rotor radius of 0.066 m. At rotational disc speeds lower than 70 rad s −1, elongated gas bubbles are formed, that are larger than the rotor–stator distance. At rotational disc speeds above 100 rad s −1, spherical gas bubbles are formed that are smaller than the rotor–stator distance. The volumetric gas–liquid mass transfer coefficient increases with increasing rotational disc speed and decreases with increasing liquid flow rate. This decrease is larger than predicted by the Wallis drift flux model because of the complex two-phase flow pattern. The rate of gas–liquid mass transfer per unit of reactor volume increases with decreasing rotor–stator distance. The maximum observed volumetric mass transfer coefficient in case of the 0.135 m rotor is a factor 3 higher than in case of the 0.066 m rotor, while the rate of energy dissipation is a factor 15 higher.

Gas–liquid mass transfer in a rotor–stator spinning disc reactor

This paper describes a new multiphase reactor, the rotor–stator spinning disc reactor, which shows high rates of gas–liquid mass transfer in comparison to conventional multiphase reactors. The volumetric gas–liquid mass transfer coefficient k GL a GL in the rotor–stator spinning disc reactor increases with increasing rotational disc speed, due to the higher surface renewal rate caused by the increasing turbulence, and with increasing gas flow rate. Measured k GL a GL values are as high as 0.43 m L 3 m R - 3 s - 1 at 7.3 × 10 - 6 m 3 s - 1 gas flow and a rotational disc speed of 179 rad s - 1 , and are expected to increase even further at increasing rotational disc speed. This is twice as high as for conventional reactors as bubble columns, in spite of the low gas holdup of 0.021 m G 3 m R - 3 with only one gas inlet. The volumetric mass transfer per unit volume of gas, k GL a GL / ɛ G , of 20.5 m L 3 m G - 3 s - 1 is 40 times higher than 0.5 m L 3 m G - 3 s - 1 for a bubble column.