High Centrifugal Acceleration Research Articles

A numerical scale-up study of annular fluidized bed reactor with high centrifugal acceleration

A rotating fluidized bed imposes a strong centrifugal force to form the dense annular bed with high interphase slip velocity for significantly enhanced gas-solids contact. The fundamental fluidization behaviors in rotating fluidized beds have been well understood in small-scale systems. The current study focuses on the scale-up of a rotating fluidized bed from lab-scale to commercial-scale through computational fluid dynamics modeling. The computational model was first validated against a lab-scale horizontal rotating fluidized bed for the general flow behavior and pressure drop. The validated computational model with a column diameter of 0.12 m was then scaled up to 0.48 m and 1.92 m to investigate the flow hydrodynamics at larger scales. By comparing the solids distribution and other flow field variables, major limitations in the stable operation of a rotating fluidized bed at large scales were identified. The challenges faced in the scale-up of an annular fluidized bed with centrifugal acceleration are discussed and ways to overcome such challenges are explored.

Centrifugal balance for the detection of mass fluctuations in advanced propulsion concepts

Propellantless propulsion with a greater thrust-to-power ratio than photon rockets and functioning independently from the Sun or Earth-based lasers promise to revolutionize interstellar space travel. Claims of micronewtons in force for a Mach-Effect-Thruster on a torsion balance in vacuum, along with theories predicting mass fluctuations in a device with large fluctuations in internal energy, have paved the way for experimental investigations. In this experiment originally conceived by Woodward, devices are subjected to high centrifugal acceleration for direct measurement of mass fluctuations using an embedded force transducer. The test devices included a capacitor stack, a toroid and a pre-stressed, multi-layer piezoelectric stack in which electromechanical energy was varied. This paper first describes the design of a centrifugal balance: a rotating apparatus with low eccentricity and maximal angular frequency of 3600 rpm, capable of applying an acceleration above 1000 g's to the test device. The piezoelectric force transducer was characterized and calibrated under quasi-static conditions using an electrodynamic test instrument. The second harmonic response of the force transducer was then examined at different rotational rates to identify the presence of mass fluctuations. The experiment revealed a maximal resolution of 40 μg over a 100 kHz measurement bandwidth. Results with the electrostatic and inductive devices did not show mass fluctuations, orders of magnitude below the prediction. Even if the measurement resolution with the piezoelectric stack was more strongly affected by the centrifugal force, electromagnetic interaction, and nonlinear behavior, the measured noise reached one order of magnitude below the mass fluctuation prediction as well. Despite some limitations with the calibration and with the piezoelectric test device, the experiments have successfully demonstrated the feasibility of the centrifugal balance for high-frequency and high-precision mass variation measurements and have ruled out the postulated Mach-Effect mass fluctuations.

The Effects of High Centrifugal Acceleration on Bluff-Body Stabilized Premixed Flames

Abstract An experimental study is conducted on bluff-body stabilized premixed flames in a curved, square cross section duct. High flow velocities coupled with a small radius of curvature of the duct induce high centrifugal acceleration normal to the flame sheet. A cylindrical flame holder spans the width of the square cross section and is positioned at the channel midheight. Flame shear layers are stabilized on the radially inward (upper) and outward (lower) edges of the flame holder. Side-view high-speed Schlieren images and high-speed pressure measurements are captured. Static stability, overall pressure loss, and statistics and velocimetry results from the Schlieren images are reported, and results are compared to a straight configuration with no centrifugal acceleration. Two bluff-body diameters are studied to show the effect of flame holder diameter on static stability. For the curved configuration, blowout velocities are higher for the smaller bluff-body diameter, likely due to flow acceleration effects. Blowout velocities are lower for the curved configuration compared to the straight configuration which may be due to the destabilizing Rayleigh–Taylor (RT) effect on the upper flame layer. Overall pressure loss is slightly higher for the curved configuration than the straight configuration. High-speed Schlieren results show centrifugal acceleration causes significant structural and velocimetric asymmetry in the bluff-body wake. In the curved configuration, the upper flame layer displays destabilizing RT instabilities, and the lower flame layer displays stabilizing RT effects. The upper flame shows vigorous RT instabilities which broaden the flame brush and sustain a flame leading edge independent of inlet Reynolds number or velocity. Conversely, the lower flame exhibits suppression of Kelvin–Helmholtz and flame-generated instabilities in the wake, which confines the flame brush and significantly reduces transverse flame velocities. The lower flame edge profile moves toward the channel centerline with increasing inlet Reynolds number. The upper flame in the curved configuration shows higher flame edge velocities than the straight configuration while the lower flame shows velocities closer to zero. The empirical constant to the power law relation for upper flame edge velocities agrees with RT-dominated flame growth theory for this experimental scale and agrees with other RT-dominated flame studies.

Dynamics of a planetary needle roller bearing considering the waviness

A dynamic model of a planetary needle roller bearing (PNRB) considering the waviness is proposed. This model can formulate the PNRB dynamic motions under high centrifugal acceleration conditions, which are more complicated than those of shaft-fixed bearings. The waviness distributed on the surfaces of races and needle rollers can change the contact conditions between the needle rollers and races. In this study, the effect of the waviness on the roller-race contact forces, roller-cage impact forces, and the PNRB elements’ dynamics are discussed, which were not studied in the listed literature for the PNRB models. Moreover, a case of a PNRB in a single row planetary gear train is used to analyze the relationship between the needle roller-cage impact force and cage speed variation. The effect of the waviness on the vibration characteristics frequency of PNRB races are also studied.

Experimental analysis and rate-based stage modeling of multicomponent distillation in a Rotating Packed Bed

Rotating Packed Beds (RPBs) offer increased flexibility and the potential of significant size-reductions for distillation processes through mass transfer intensification. This may be of interest for example for retrofits or off-shore applications. However, validated models for process design of multicomponent distillation in RPBs are not available up to now. To bridge this gap, distillation of binary and ternary mixtures at total reflux was experimentally investigated in an RPB test rig. Depending on the flowrate and rotational speed, up to 10 theoretical stages were achieved in the investigated RPB, corresponding to an HETP (height equivalent of a theoretical plate) of as low as 17mm at the best operating point. With increasing centrifugal acceleration, separation efficiency increased at first, but decreased again at high centrifugal accelerations. Using the rate-based stage approach, a correlation for gas-side volumetric mass transfer coefficient in the RPB is developed. It is capable of reproducing the observed maximum of separation efficiency. Coefficients are fitted for this correlation, based on results obtained from distillation of ethanol/n-propanol. The model is validated using data obtained from distillation of ethanol/water and ethanol/n-propanol/water. Overall volumetric mass transfer coefficients and numbers of theoretical stages are described for most of the data within ±30%.

Soft Sensor Development for Real-Time Process Monitoring of Multidimensional Fractionation in Tubular Centrifuges.

High centrifugal acceleration and throughput rates of tubular centrifuges enable the solid–liquid size separation and fractionation of nanoparticles on a bench scale. Nowadays, advantageous product properties are defined by precise specifications regarding particle size and material composition. Hence, there is a demand for innovative and efficient downstream processing of complex particle suspensions. With this type of centrifuge working in a semi-continuous mode, an online observation of the separation quality is needed for optimization purposes. To analyze the composition of fines downstream of the centrifuge, a UV/vis soft sensor is developed to monitor the sorting of polymer and metal oxide nanoparticles by their size and density. By spectroscopic multi-component analysis, a measured UV/vis signal is translated into a model based prediction of the relative solids volume fraction of the fines. High signal stability and an adaptive but mandatory calibration routine enable the presented setup to accurately predict the product’s composition at variable operating conditions. It is outlined how this software-based UV/vis sensor can be utilized effectively for challenging real-time process analytics in multi-component suspension processing. The setup provides insight into the underlying process dynamics and assists in optimizing the outcome of separation tasks on the nanoscale.

Investigation on the role of drainage structure in preventing the mass accumulation induced by shock/boundary-layer interactions in supersonic separators

The occurrence of shock wave in nozzle and the blockage of fluid at the so called "second throat" are closely related to the drainage structure of supersonic separator, which result from the thickening of the boundary layer owing to the interaction between boundary layer and shock waves. Two types of drainage structures are proposed to solve the above problems and promote the separation performance for gas purification. The CFD modeling is used to optimize and evaluate the different drainage structures. The results show that the cylindrical drainage and the cascade drainage can efficiently alleviate or remove the mass accumulation at the "second throat". The cascade drainage with reflux channel and oblique openings is superior to other drainage structures, due to the low flow velocity and high centrifugal acceleration in the drainage section. The flow velocity and temperature in the cascade drainage chamber with reflux channel are opposing for separation performance of the supersonic separator. It means that high flow rate in cascade drainage section will lead to lower temperature, but increase the number of droplets carried by airflow, and vice versa.

Fractionation of ultrafine particles: Evaluation of separation efficiency by UV–vis spectroscopy

Centrifugation is an established tool in solids process technology to handle classification of particulate products. However, dispersions with strict specifications for product-relevant properties often require a different approach. Fractionation is necessary when both geometric and material properties matter. Due to their high throughput and centrifugal acceleration, semi-continuous tubular centrifuges are suitable for the effective performance of such tasks. In order to monitor this mechanism for several size and density fractions, the separation efficiency is correlated with optical properties. Titanium dioxide and pigment particles serve as experimental products. Coarser size fractions are separated and overflow samples are analysed with analytical centrifugation and UV–vis spectroscopy. Each extinction spectrum is labeled with distinctive target values and a regression model is build. Finally, mixtures are processed and targets determined using the machine learning algorithm. It is discussed to what extent the advanced methodology can be applied to multidimensional unit operations such as density fractionation.

Numerical simulation of supersonic separator with axial or tangential outlet in reflow channel

In the separation process of the conventional supersonic separator, the shock wave easily appears in diverging section of the nozzle and the swirling flow occurs in subsonic conditions with poor efficiency, which make the low temperature section short and the cooling effect dissatisfied. In this paper, a novel supersonic separator with reflow channel that has axial outlet or tangential outlet has been designed. The fluid can be drawn into the nozzle by the differential pressure between the discharge clearance on the wall and the throat zone near the centerline. Axial and radial distribution of the main parameters and the effect of pressure ratio are investigated with Reynolds Stress Mode (RSM) turbulence model. The results show that compared with the device without reflow channel, the pressure recovery in the diffuser with reflow channel is faster, the centrifugal acceleration is higher and the temperature is lower, which manifest the new device has a better refrigeration and separation performance. The supersonic separator with axial reflow outlet can obtain the better performance with pressure ratio of 1.5 that has a low temperature (221 K) and high centrifugal acceleration (2.2 × 107 m/s2), while the high centrifugal acceleration (9.89 × 109 m/s2) and low temperature (223 K) can be achieved in the device with tangential reflow outlet when pressure ratio is 2.0. Moreover, the structure with axial reflow outlet enlarges the supersonic region in the novel device and has a better ability to resist flow fluctuation and backmixing under the same condition when pressure ratio is 1.5. As the pressure ratio increases, the position of shock wave shifts downstream and the centrifugal acceleration and the reflow impetus increase, while the minimum temperature decreases, which prove that the increasing pressure ratio can improve the fluid expansion characteristics.

Concept of modernization of input device of oil and gas separator

The process of defoaming in oil production is discussed. This technology is important in oil and gas fields. Today, the technology of separating the gas fraction is based on chemical catalysis. The use of mechanical technologies improves the economics of the process. Modernization of the separator input device is based on the use of long thin tubes. The chosen length of the tubes is two orders of magnitude larger than the diameter. The separation problem is solved by creating a high centrifugal acceleration. The tubes of the input device are connected in parallel and divide the input stream into several arms. The separated fluid flows are directed tangentially into the working tubes to create a vortex motion. The number of tubes connected in parallel is calculated in accordance with the flow rate of the fluid. The connection of the working tubes to the supply line is made in the form of a flange. This connection allows carrying out maintenance without stopping the flow of fluid. An important feature of this device is its high potential for further modernization. It is concerned with the determination of the parameters of the tubes and the connection geometry in the construction of a single product.

Theoretical analysis for the centrifugal effect on premixed flame speed in a closed tube

A theoretical analysis is described to study the effect of centrifugal acceleration, especially high centrifugal acceleration, i.e. more than 200 times of gravity acceleration (200g), on the premixed flame speed in a rotating closed tube. Based on one-dimensional (1-D) steady adiabatic flame model, simplified governing equations are directly solved by integration method in the reaction zone. A theoretical prediction that describes the premixed flame speed in a rotating closed tube is obtained. The theoretical prediction agrees well with the experimental data obtained by Lewis & Smith. The result verifies that the flame speed accelerated by the centrifugal force is nearly proportional to the square root of the centrifugal acceleration. It is shown by theoretical analysis that the flame speed in a rotating closed tube is determined by the initial temperature, the critical ignition temperature, the adiabatic flame temperature and the thicknesses of reaction zone. The premixed flame speed in a rotating closed tube increases nearly linearly with the increasing of the initial temperature or square root of the thicknesses of reaction zone, or with decreasing of the critical ignition temperature or the adiabatic flame temperature.

Application of magnetic bearing technology in high-speed centrifugation

Centrifuges represent a well-established tool in separation technology to handle high throughputs of suspensions with micron-sized particles. However, extraordinarily high centrifugal accelerations are required for even smaller particles. For this purpose, we make use of magnetic bearing and drive technology. We report the first application of this contactless technique in separation experiments. The presented prototype is based on a semi-continuous principle, where sediment is built up within the rotor while the liquid (which contains the fine fraction in case of classification) is discharged at the overflow weir. The new centrifuge allows rotational speeds of more than 64kmin−1. A broad variation of parameters with centrifugal accelerations of up to C=100,000 and flow rates of up to 0.4l/min provides a sound experimental basis for this study. The cut size and the product loss of three particle systems between 10nm and 1µm (silver nanoparticles, silica nanoparticles, and polystyrene) are precisely adjustable via the mentioned parameters. Furthermore, a good comparability with a commercially available device was found regarding the specific efficiency. We consider our approach to be a promising contribution to nanoscale separation technology where scalable high-throughput methods are rare.

A novel lab-on-a-chip design by sequential capillary–gravitational valves for urinary creatinine detection

For the first time, instead of the high centrifugal acceleration (or force) by high speed rotation as the driving source that commonly used in the literature, a novel design of capillary–gravitational valves has been developed in a disposable plastic chip by simple control of the balance between capillary and gravitation forces for sequential functions of fluid material delivery, metering and mixing with much less needed power in this study. An integrated lab-on-a-chip (LOC) module with full functions from the sampling to detection for the urinary creatinine measurement has been further tested and verified its use by simply adjusting the LOC tilt angle. The sequential operation can be even operated by hand in the cases of unstable electricity or for regions without AC electric power. Furthermore, the concentration of urinary creatinine was measured by the transmitting optical density (O.D.) change for a Jaffe reaction and calibrated with the coefficient of variations (CV) less than 3.5%. Real urine samples were also tested and showed highly consistent in compare with clinical method.

Measurement of heat transfer coefficients at up to 25,500 g – A sensor test at a rotating free disk with complex telemetric instrumentation

Heat transfer coefficients (HTC) are important for the design of efficient energy machines as for instance gas turbines for industrial, power generation and propulsion applications. Published HTC measurement data considering geometries and operating conditions which are relevant for these applications are very rare or not available.This study presents an experimental investigation using a telemetric setup for the direct HTC measurement at metallic boundaries with gaseous flow. The rotor rig has a complex instrumentation using one of the in house developed telemetry systems. The experimental investigation relies on a recent measurement/sensor concept tested for the first time in the rotating frame with high centrifugal acceleration. The measurement setup has miniaturized sensor dimensions and low energy consumption. Therefore, the sensor concept is suitable for integration in a telemetry system as necessary for turbomachinery research. The sensor setup features good local resolution, short response time and a high resolution versus temperature and HTC.Measurements of the radial distribution of the heat transfer coefficient of a rotating free disk are presented. Additionally a comparison with correlations found in literature as well as a calibration of the HTC sensors for the test case forced convection at the flat plate is included.

Process monitoring and control for constant separation conditions in centrifugal classification of fine particles

Due to their high centrifugal acceleration tubular bowl centrifuges enable the separation and classification of fine particles. However, this type of centrifuge which is operated in a semi-continuous mode has a major disadvantage: sediment buildup in the rotor leads to a successive degradation of separation conditions over process time. In this study, a light scattering sensor was used to monitor this mechanism online by measuring the solids concentration in the overflow. Polyvinylchloride (low micrometer range) and fumed silica particles (nanometer range) served as experimental products. By incorporating the sensor signal in a control loop with the speed of the centrifuge, the mentioned drawback was compensated. As a result, grade efficiency and product loss were kept constant up to a high filling level of the rotor. It is outlined how this technology can be used for very demanding classification tasks, especially in case of fine, low-density materials.

Effect of thixotropy and segregation on centrifuge modelling

In this paper, segregation related to the application of high centrifugal acceleration and the effect of thixotropy in modelling the settling behaviour of slurry/soft soils using a centrifuge are examined. Settling column and centrifuge tests were conducted on slurry/soft soils at various sand fines ratios (SFR) to define a segregation boundary using the ternary diagram. A segregation boundary based on centrifuge and settling column tests are established and the results indicate that the application of high gravity in centrifuge tests prompts and enhances segregation. It is also found that the segregation boundary of high gravity tests is a function of applied acceleration level, grain size of sand, the percentage fines and clay contents. The application of formulas that estimate the maximum size of sand that remain in suspension are evaluated and found conservative at high gravity tests. The shear strength of slurry/soft soils at various SFR and age were evaluated to assess the effect of non-gravity, time-dependent behaviour on strength and settling behaviour of slurry/soft soils. The results of the shear strength tests at various ages and composition indicate that strength gain is mainly due to thixotropy. The gain in shear strength due to thixotropy may not be properly modelled in centrifuge testing and may create difficulty in extrapolating centrifuge test results to prototype.

The Effects of an Unexpected Ceramic Coating Phase at the Head of a Pipe on Joining and Postprocessing of a Ceramic-Lined Composite Pipe

Produced ceramic-lined steel pipe using the self-propagating high-temperature synthesis (SHS) method has found uses in many applications. A SHS-centrifugal machine was designed to produce a ceramic-lined steel pipe from ferric oxide and aluminum powder (thermite mixture) under high centrifugal acceleration. The obtained products are expected to be Al2O3 ceramic in the innermost layer and a Fe layer in a region between the outer steel pipes. In the present work, specific regions of a pipe was particularly observed to investigate the stuck (dead) spaces at the pipe head because of its importance in further processes (joining, welding, etc.) which may affect the quality of the next operations. In this article, the product’s composition, phase separation, microhardness, and surface finish were studied on three zones of the pipe.

High Performance BaTiO3‐Based BME‐MLCC Nanopowder Prepared by Aqueous Chemical Coating Method

Dispersion plays an important role in aqueous chemical coating process for the preparation of BaTiO3‐based powder for base‐metal‐electrode multilayer ceramic capacitors (BME‐MLCCs) in our previous research. In this article, a powerful sand mill (SC‐milling) machine is utilized instead of traditional ball milling to produce BaTiO3 MLCC nanopowder, in which small ZrO2 beads help to achieve high centrifugal accelerations and avoid BaTiO3 agglomerates. As much as 1 kg BaTiO3 nanopowder has been effectively dispersed very well in one time, then a uniform coating of additives on BT nanoparticles has been achieved by aqueous chemical coating method. High performance X7R BaTiO3 nanoceramics with the average grain size of about 96 nm are obtained. The experimental result indicates that this technology can be feasible to the industry for manufacturing next generation BME‐MLCCs.

A multiplexed immunoassay system based upon reciprocating centrifugal microfluidics

A novel, centrifugal disk-based micro-total analysis system (μTAS) for low cost and high throughput semi-automated immunoassay processing was developed. A key innovation in the disposable immunoassay disk design is in a fluidic structure that enables very efficient micro-mixing based on a reciprocating mechanism in which centrifugal acceleration acting upon a liquid element first generates and stores pneumatic energy that is then released by a reduction of the centrifugal acceleration, resulting in a reversal of direction of flow of the liquid. Through an alternating sequence of high and low centrifugal acceleration, the system reciprocates the flow of liquid within the disk to maximize incubation/hybridization efficiency between antibodies and antigen macromolecules during the incubation/hybridization stage of the assay. The described reciprocating mechanism results in a reduction in processing time and reagent consumption by one order of magnitude.

Surface modification of porous scaffolds with nanothick collagen layer by centrifugation and freeze‐drying

Three-dimensional (3D) porous scaffolds constructed from biodegradable synthetic polymers are frequently used in tissue engineering. Their surfaces are hydrophobic and require treatment to be changed to hydrophilic before use in cell culture. We developed a novel surface modification for 3D porous scaffolds made of synthetic polymers by coating the surfaces of the pores with a nanothick collagen layer. First, a collagen aqueous solution was introduced under reduced pressure to fully fill the pores of the PLGA sponges. The collagen-containing sponges were then centrifuged to remove any excess collagen solution. Finally, the sponges were freeze-dried to form a thin collagen layer. Scanning electron microscopy observation and water absorption tests demonstrated that the excess collagen was removed; the effect of modification was evident when the collagen-containing sponges were centrifuged at high centrifugal acceleration. Scanning probe microscopy analysis demonstrated the formation of a nanometer-thick collagen layer on the PLGA surface. The collagen-coated PLGA sponges facilitated cell seeding and spatial distribution. The method will be useful for the surface modification of 3D porous scaffolds.