Tangential Mode Research Articles

Preparation and Characterization of Hybrids of Cellulose Acetate Membranes Blended with Polysulfone and Embedded with Silica for Copper(II), Iron(II) and Zinc(II) Removal from Contaminated Solutions

With the objective to assess the suitability of cellulose acetate (CA), polysulfone (PSF) and silica (SiO2) for wastewater treatment, this work presents the results of preparation and characterization of PSF blended CA hybrid filtration membranes (CA/PSF) as well as PSF blended and SiO2 embedded CA hybrid adsorption membranes (CA/PSF-SiO2) for copper(II), iron(II) and zinc(II) ions removal from contaminated aqueous solutions. The membranes were prepared by phase inversion, using granules of CA, PSF and SiO2 dissolved in N, N dimethyl formamide (DMF). From the scanning electron microscopy (SEM) used to determine the morphology of the membranes, different pore sizes are seen at their rough surfaces and cross sections. The porosity and pore sizes of the membranes, determined by differentiation varied from 26.8 ± 0.3 to 81.1 ± 0.3 µm and 1.26 to 1.38%, respectively. The contact angles of the membranes ranged between 49° and 76° on their glass side while their ranged between 56° and 77° on their air side. The hybrid filtration polymer membranes allowed the uptake of more than 90% of the metal ions initially present in the contaminated solutions which were concentrated at 40 mg L−1. Adsorption experiments were carried out with CA/PSF-SiO2 membranes. The adsorption capacity of these compounds was shown to be higher than numerous other literature-known adsorbents, reaching 70 mg g−1 for CA/PSF 85/15-SiO2 towards Cu(II). Finally, by coupling adsorption with ultrafiltration in the tangential mode, the removal of Cu(II), Fe(II) and Zn(II) was found to be improved, allowing to reach a removal efficiency of 95% towards Cu(II) at a metal concentration of 60 mg L−1, and a promising removal efficiency around 98% at a very high metal concentration of 900 mg L−1.

Air Supply Mode Effects on Ozone Production of Surface Dielectric Barrier Discharge in a Cylindrical Configuration

We investigated the air supply mode effects on ozone production of the surface dielectric barrier discharge in the cylindrical configuration. The air into the discharge volume between two coaxial cylinders was supplied through four nozzles axially or tangentially. Using tangential air supply, the vortex flow in the part of the discharge chamber was created. Because the active electrode was in the form of interconnected rings on the outer surface of the glass tube, we changed the airflow orientation concerning this electrode. The existence of vortex airflow affects the plasmachemical processes taking part in the discharge, and therefore, it affects discharge ozone production. We also paid attention to ozone concentration and temperature of output air measurements as a function of the duration of the experiment for both tangential and axial air supply modes. We found that the time required for the stabilization of generated ozone concentration depends on the discharge power, and for our experimental conditions, it smaller than approximately 70 s. Besides, in the case of tangential air supply into the discharge chamber, the concentration of ozone produced by the discharge is for higher discharge power increased in comparison with the concentration for the axial air supply mode.

Effect of the inner-surface baffles on the tangential acoustic mode in the cylindrical combustor

Abstract The combustion instability in a propulsion system is a ubiquitous problem. The radial baffles usually installed on the injector faceplate eliminate the combustion instability (acoustic pressure oscillation) in the propulsion system. In this article, the longitudinal baffles are installed on the inner surface of the combustor wall to control the combustion instabilities. The first-order and second-order tangential modes are induced in the experiments. The effects of the parameters of the baffle on the acoustic pressure oscillation in the cylindrical combustor are investigated. The effect of the combustor nozzle on the tangential modes has been systematically investigated. It is concluded that the eigen-frequency and amplitude of the first-order tangential mode decline with the increase in the longitudinal baffle number and height. For the second-order tangential mode, the eigen-frequency and amplitude monotonically increase until a maximum value (four baffles), subsequently decrease with the increase in the baffle number and height. The combustor without the nozzle obtains a lower frequency than that with the nozzle, especially for the low baffle height in the combustor.

Development of multi-walled carbon nanotubes obtained from recycled plastics by single stage pyrolysis process

The development of nanofillers from plastic waste plays a significant role as an alternative plastic waste managing method. Multi-walled carbon nanotubes were produced by a single stage chemical vapor decomposition using polypropylene as carbon source in the presence of bimetallic catalyst. A mixture of Ar/H2 gas was used as a reducing agent for catalyst and at a later stage N2 was used to supply inert conditions for the pyrolysis product. Fe-Mn/Al2O3 catalyst was reduced at a temperature of 700 °C and PP waste was introduced at the same temperature to decompose at the surface of the catalyst to form the nanofillers. Tramission Electron Microscopy (TEM) and Raman characterization techniques were used to determine the properties of the nanofillers. The results showed that the developed nanofillers have a maximum diameter of 19.09 nm. TEM micrographs displayed lattice fringes at the magnitude of 20 nm indicating that the morphology of these nanofillers is crystalline. The Raman spectra showed the defect mode, D at the frequency of 1346 cm−1 and the tangential mode, G is at the frequency of 1588 cm−1. The intensity ratio ID/IG is 0,84 and signifies the quality of the nanofillers, as the ratio is the direct measure of the sample purity.The diameter obtained from the TEM analysis and the absence of the Radial Breathing Mode (RBM) on Raman spectra concluded that the nanofillers produced can be classified as Multi-Walled Carbon Nanotubes (MWCNT).

Thermoacoustic instability drivers and mode transitions in a lean premixed methane-air combustor at various swirl intensities

In this study, an in-house developed fully compressible solver utilizing high-order numerical discretization schemes is used to study the effects of swirl intensity on thermoacoustic instabilities in a lean premixed swirl stabilized combustor. Turbulent combustion modeling is achieved using large eddy simulations along with dynamically thickened flame combustion model. Obtained results reveal that there are two critical burner swirl numbers in which the combustor dynamics change drastically. Results show that the combustor is stable at low swirl numbers (S ≤ 0.5). However, as the swirl intensity increases, the combustor experiences thermoacoustic instabilities. The first critical swirl number lies within the range of 0.5–0.6, in which a transition occurs in the combustor dynamics from a state of stable operation to thermoacoustic instabilities. The second critical swirl number (S = 0.9) corresponds to the transition of different thermoacoustic instability modes. The combustor experiences limit cycle instabilities coupled with the first tangential acoustic mode of the combustor for 0.6 ≤ S < 0.9, while for S > 0.9 the instabilities are burst like and coupled with the second tangential acoustic mode of the combustor. The combustor experiences instabilities coupled with both the first and the second tangential modes, when the burner swirl number is 0.9. In order to evaluate key parameters inducing the thermoacoustic instabilities, heat release fluctuations are calculated through hydrodynamic flow features (central and side recirculation zones, coherent structures, and precessing vortex core). Investigations show that all the above features contribute almost equally in inducing heat release fluctuations in-phase with the acoustic perturbations at low swirl numbers. However, as the swirl number increases, side recirculation zone and coherent structures play the key role in producing heat release fluctuations in-phase with the acoustic perturbations, while central recirculation zone has the least effects on driving the instabilities.

Encapsulation effect of π-conjugated quaterthiophene on the radial breathing and tangential modes of semiconducting and metallic single-walled carbon nanotubes.

We developed a hybrid approach, combining the density functional theory, molecular mechanics, bond polarizability model and the spectral moment's method to compute the nonresonant Raman spectra of a single quaterthiophene (4T) molecule encapsulated into a single-walled carbon nanotube (metallic or semiconducting). We reported the optimal tube diameter allowing the 4T encapsulation. The influence of the encapsulation on the Raman modes of the 4T molecule and those of the nanotube (radial breathing modes and tangential modes) are analyzed. An eventual charge transfer between the 4T oligomer and the nanotube is discussed.

Nanofiltration as a robust method contributing to viral safety of plasma-derived therapeutics: 20 years' experience of the plasma protein manufacturers.

BackgroundNanofiltration entails the filtering of protein solutions through membranes with pores of nanometric sizes that have the capability to effectively retain a wide range of viruses.Study Design and MethodsData were collected from 754 virus validation studies (individual data points) by Plasma Protein Therapeutics Association member companies and analyzed for the capacity of a range of nanofilters to remove viruses with different physicochemical properties and sizes. Different plasma product intermediates were spiked with viruses and filtered through nanofilters with different pore sizes using either tangential or dead‐end mode under constant pressure or constant flow. Filtration was performed according to validated scaled‐down laboratory conditions reflecting manufacturing processes. Effectiveness of viral removal was assessed using cell culture infectivity assays or polymerase chain reaction (PCR).ResultsThe nanofiltration process demonstrated a high efficacy and robustness for virus removal. The main factors affecting nanofiltration efficacy are nanofilter pore size and virus size. The capacity of nanofilters to remove smaller, nonenveloped viruses was dependent on filter pore size and whether the nanofiltration process was integrated and designed with the intention to provide effective parvovirus retention. Volume filtered, operating pressure, and total protein concentration did not have a significant impact on the effectiveness of virus removal capacity within the investigated ranges.ConclusionsThe largest and most diverse nanofiltration data collection to date substantiates the effectiveness and robustness of nanofiltration in virus removal under manufacturing conditions of different plasma‐derived proteins. Nanofiltration can enhance product safety by providing very high removal capacity of viruses including small non‐enveloped viruses.

Modulation of transmembrane pressure in manufacturing scale tangential flow filtration N-1 perfusion seed culture.

Mammalian cells were grown to high density in a 3,000 L culture using perfusion with hollow fibers operated in a tangential flow filtration mode. The high-density culture was used to inoculate the production stage of a biomanufacturing process. At constant permeate flux operation, increased transmembrane pressures (TMPs) were observed on the final day of the manufacturing batches. Small scale studies suggested that the filters were not irreversibly fouled, but rather exposed to membrane concentration polarization that could be relieved by tangential sweeping of the hollow fibers. Studies were undertaken to analyze parameters that influence the hydrodynamic profile within hollow fibers; including filter area, cell density, recirculation flow rate, and permeate flow rate. Results indicated that permeate flow rate had the greatest influence on modulating TMP. Further evaluation showed a significant decrease in TMP when permeate flow was reduced, and this occurred without any negative effect on cell growth or viability. Hence, a 30% reduction of permeate flow rate was implemented at manufacturing scale. A stable operation was achieved as TMP was successfully reduced by 75% while preserving all critical factors for performance in the perfusion bioreactor.

Numerical Analysis of Self-Excited Combustion Instabilities in a Small MMH/NTO Liquid Rocket Engine

Combustion instabilities in a small MMH/NTO liquid rocket engine used for satellite attitude and course control are numerically investigated. A three-dimensional Navier-Stokes code is developed to simulate two-phase spray combustion for cases with five different droplet Sauter Mean Diameters. As the droplet size increases from 30 microns to 80 microns, pressure oscillations are stronger with larger amplitudes. But an increase of the droplet size in the range of 80 microns to 140 microns indicates a reduction in the amplitudes of pressure oscillations. This trend is the same as the Hewitt criterion. The first tangential (1T) mode and the first longitudinal (1L) mode self-excited combustion instabilities are captured in the 60-micron and 80-micron cases. Abrupt spikes occur in the mass fraction of MMH and coincide with abrupt spikes in the mass fraction of NTO at the downstream regions just adjacent to the impinging points. Thus, local combustible high-dense mixtures are formed, which result in quasiconstant volume combustion and abrupt pressure spikes. The propagation and reflection of pressure waves in the chamber stimulate the combustion instability. When the droplet size is too small or too large, it is difficult to form local high-dense premixtures and combustion is stable in the chamber.

Experimental investigation of self-excited combustion instabilities in a small Earth storable bipropellant rocket combustor

A 1000 N scale liquid rocket combustion experiment was designed and conducted to investigate high-frequency combustion instabilities in small Earth storable bipropellant engines. The propellants were injected through unlike impingement injectors. Based on the Hewitt stability correlation, the first tangential combustion instabilities could be spontaneously initialized. As combustion instabilities grew, standing tangential modes gradually shifted to spinning modes. This eventually yielded limit-cycle instabilities with peak-to-peak amplitudes of 40 bar, about four times the static combustor pressure. One single pressure wave characterized by steep rising and falling edges rotated around the chamber at supersonic velocity during spinning mode, which could be defined as a detonation-like wave. However, the pressure oscillated in-phase in the axial direction of the combustor. The frequency of the spinning mode was about 10.9 kHz and was minimally influenced by operation conditions. In a series of test campaigns, the instabilities boundary was identified by the parameters of the Hewitt correlation coefficient (HCC) and the oxidizer/fuel mixing ratio (ROF). When the HCC of oxidizer was less than 0.101 and the HCC of fuel was less than 0.075, self-excited tangential combustion instabilities could be developed easily. The combustion instability with moderate amplitude was not observed.

A stable extended/generalized finite element method with Lagrange multipliers and explicit damage update for distributed cracking in cohesive materials

A flexible, general and stable mixed formulation is developed to model distributed cracking in cohesive grain-based materials in the framework of the extended/generalized finite element method. The displacement field is discretized on each grain separately, and the continuity of the displacement and traction fields across the interfaces between grains is enforced by Lagrange multipliers. The design of the discrete Lagrange multiplier space is detailed for bilinear quadrangular elements with the potential presence of multiple interfaces/discontinuities within an element. We give numerical evidence that the designed Lagrange multiplier space is stable and provide examples demonstrating the robustness of the method. Relying on the stable discretization, a cohesive zone formulation equipped with a damage constitutive formulation expressed in terms of the traction is used to model propagation of multiple cracks at the interfaces between grains. The damage formulation makes use of an explicit solution procedure, couples the normal and tangential failure modes, accounts for different tension and compression behaviours and takes into account a compression-dependent fracture energy in mixed mode. The framework is applied to complex 2D problems inspired by indirect tension tests of heterogeneous rock-like materials.

A method to decouple the geometric errors for rotary axis in a five-axis CNC machine

When using a ball-bar to measure rotary axis error, to keep the posture of the bar constant, a linkage motion of two linear axes with the rotary axis is required, which will cause the ball-bar length to contain both rotation axis error and linear axis error. In order to get the accurate rotary axis error, a decoupling strategy based on the actual position of the double balls on both ends of the ball-bar is proposed in a CFXYZA-type five-axis machine tool. Three measurement modes, axial, radial and tangential mode, are designed with a ball-bar instrument. Six groups of length variations of the ball-bar are measured by changing both the position and the height of the ball base mounted on the rotary table. Center offset error in measurement of the ball bar length is eliminated. The relationship between geometric error parameters of the rotary axis and ball-bar length variations is derived by the homogeneous coordinate matrix transformation from which the parameters can be identified. The displacement deviation aroused from the linkage motion of the linear axis with the rotary axis is also derived. Mathematical matching is operated between the feed rate of the rotary axis and acquisition speed of the ball-bar software. Center offset of the ball-bar length data acquired is eliminated to reduce the influence of installation. An obvious scaling mismatch between the axes diagnosed from the polar plot of ball-bar length variation shows that the C-axis has the tilt error around the X- or Y-axes. Experiment results show that the proposed method can improve the identification accuracy. The decoupling method is both effective and convenient for identifying geometric error of the rotary axis in a five-axis machine tool.

Effects of the fresh mixture temperature on thermoacoustic instabilities in a lean premixed swirl-stabilized combustor

This numerical study investigated the effects of the fresh mixture temperature on thermoacoustic instabilities in a lean premixed swirl-stabilized combustion chamber by utilizing high-fidelity, fully compressible large eddy simulations. At low fresh mixture temperatures, the side recirculation zone stabilized the premixed flame on the boundary of the burner rim, while the central part of the flame was detached from the burner due to the inability of the central recirculation zone to assist in flame stabilization. However, the central recirculation zone became stable enough to stabilize the central portion of the flame near the burner rim as the fresh mixture temperature increased. Moreover, the coherencies and penetration depths of the coherent structures and precessing vortex cores in the combustor increased with the fresh mixture temperature. Analyses showed that the limit cycle instabilities that occurred at low fresh mixture temperatures resulted from coupling between heat release fluctuations and the first tangential acoustic mode of the combustor. However, as the fresh mixture temperature increased, a combustor dynamics transition occurred, through which the coupling between heat release and pressure fluctuations shifted toward the mixed tangential and radial acoustical modes of the combustor. During this mode transition, limit cycle oscillations were replaced by burst oscillations. The results revealed that recirculation zones are the key features that trigger thermoacoustic instabilities at low fresh mixture temperatures, while coherent structures and precessing vortex cores are the main combustion instability drivers at high fresh mixture temperatures.

Micromixing performance in a rotating bar reactor

AbstractA rotating bar reactor (RBR) was designed for adjusting micromixing efficiency. It consists of two concentric cylinders of inner rotating and outer fixed cylinders. Two feeding modes, named as radial and tangential feeding modes, were applied to modify the feeding at the bottom section of the RBR. The influence of feeding modes on the micromixing performance was measured with different rotational speeds, flow rates, viscosities, volumetric flow ratios, and hydrogen ion concentrations. Experimental results reveal that the RBR with tangential feeding mode has better micromixing performance than that with radial mode. The higher rotational speed has a positive impact on the segregation index (Xs). The values of Xs increased with the decrease of the flow rate, and the increase of the viscosity, volumetric flow ratio, and hydrogen ion concentration. The micromixing time, estimated by using an incorporation model, was in the range of 5.00 × 10−6‐1.13 × 10−5 seconds in the RBR with a tangential feeding mode, which indicates a promising prospect of the RBR for process intensification of fast and complex reactions.

An FFT-based spectral solver for interface decohesion modelling using a gradient damage approach

This work presents a fast Fourier transform (FFT) based method that can be used to model interface decohesion. The inability of an FFT solver to deal with sharp interfaces discards the use of conventional cohesive zones to model the interfacial mechanical behaviour within this framework. This limitation is overcome by approximating sharp interfaces (e.g. grain/phase boundaries) with an interphase. Within the interphase, the background plastic constitutive behaviour is inherited from the respective adjacent grains. The anisotropic kinematics of the decohesion process is modelled using a damage deformation gradient that is constructed by mapping the opening strains (in normal and tangential modes) to the associated projection tensors. The degradation (damage) of the interfacial opening resistances is modelled via a dimensionless nonlocal damage variable that prevents localisation of damage within the interphase. This nonlocal variable results from the solution of a gradient damage based regularisation equation within the interphase subdomain. The damage field is constrained to the interphase region by applying a relatively large penalisation on the damage gradients inside the interphase. The extent of nonlocality ensures that the damage is largely uniform in the direction perpendicular to the interphase, thus making its thickness the theoretical lengthscale for dissipation. To achieve model predictions that are objective with respect to the interphase thickness, scaling relations of the model parameters are proposed. The numerical performance is shown for a uniform opening case and then for a propagating crack. Finally, an application to an artificial polycrystal is shown.

A Flow Dynamic Characteristic Analysis of A Single Radial Swirler Combustor

Abstract A diffusion combustor with a single radial swirler in non-reacting condition is investigated via a large eddy simulation (LES). Three dynamic analysis methods – the fast Fourier transform (FFT), proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD) – are implemented to investigate the flow dynamic characteristics of the combustor. The kerosene-air combustor analyzed in the study was designed by the German Aerospace Center (DLR). It has a square cross-section and uses kerosene as fuel, which is modeled as a pre-vaporized and surrogated fuel consisting of 242 species. The first tangential(1T) mode in combustor caused by the swirler emerges dominantly in the combustor. This 1T mode exhibits the largest amount energy in the combustor dynamics, as verified by POD, and the DMD analysis determines the frequency of 1876.8 Hz. The fuel injector dynamics is associated with Helmholtz resonator frequency of 816.5 Hz. To analyze the instability, the DMD method is employed to investigate the growth rate of the most dominant dynamic structure.

Nonlinear Combustion Instability in a Multi-Injector Rocket Engine

A computational study is presented of the nonlinear combustion instability of a multi-injector rocket engine. The study addresses a choked nozzle and a combustion chamber with 10 and 19 coaxial injector ports. Computations using a three-dimensional unsteady shear-stress transport delayed detached-eddy simulation method provide detailed time-resolved information about the combustion instability. The spontaneous longitudinal-mode instability is observed for the 10- and 19-injector geometries with a combustion-chamber diameter of 28 cm. The triggered tangential and longitudinal instability modes are obtained for the 19-injector geometry with a combustion-chamber diameter of 43 cm by pulsing the injector mass flux. It is shown that an oscillating combustion-chamber flow can be triggered to a new mode with a larger disturbance amplitude. The streamwise vorticity created by the instability impacts the heat release in a manner that supports the instability. A preliminary study of injector-size scaling effects is performed by comparison of the 10- and 19-injector combustors.

Aeroacoustic characteristics of subsonic flow from axisymmetric pipe-cavities

A detailed experimental study on the acoustic characteristics of an axisymmetric pipe-cavity jet is conducted for different ratios of cavity depth to length, over a range of subsonic Mach numbers. Power spectral analysis and Scalogram are implemented to unravel the physics of the pipe-cavity resonance. Proper Orthogonal Decomposition analysis is used to understand the flow dynamics of the pipe-cavity jet. The results show that the pipe-cavity resonates close to the first tangential mode for a wide range of Mach numbers. However, an increase in the depth and Mach number leads to the onset of combined resonance modes. Experimentally obtained resonance frequencies are validated against numerical simulations and theoretical predictions. Scalogram results show the existence of nonlinear interactions and mode shifting of resonance modes. A parametric space plot demarcates the domains of operation of various oscillation modes, over the relevant parametric range. The results reveal that the upstream cavity significantly affects the downstream jet flow dynamics, and its far-field noise radiation. Deeper cavities have a stronger influence on the far-field acoustics compared to shallow cavities.

Simulation of dust deposition process in ceramic filter under different filtration modes by a novel CFD-based method

In this study, the dust deposition process in the ceramic filter of the updraft, tangential, and downdraft flow filtration mode was modeled by a novel CFD-based method, in which a unique mesh grid zone referred to as “dust cake zone” was created to simulate the actual dust cake layer, and grid cells located in the same line were linked together by a fast neighborhood search algorithm to model the actual dust cake growth path. Next, a simulation of the updraft flow filtration (UFF) mode was first carried on and compared to the related experiment in detail to determine the optimal simulation setting. Then, the simulations of the tangential flow filtration (TFF) and downdraft flow filtration (DFF) mode were performed based on the verified CFD settings of the UFF mode, which was able to reduce the pressure drop relative error to less than 6%. Furthermore, the simulation results of these three kinds of filtration modes were carefully analyzed and compared. It was found that the dust cake distribution varied dramatically among different filtration modes, which was due to different patterns of the vortex-flow forming near the candle surface. Some less-particle-deposition-zones can be found on the ceramic candles’ lower portion, middle-lower portion and upper portion in the UFF, TFF and DFF mode, respectively. Moreover, the TFF mode had the lowest pressure drop growth rate, while the most uniform dust cake layer was formed in the DFF mode.

Quantum dynamics and geometric phase in E⊗e Jahn-Teller systems with general Cnv symmetry.

E ⊗ e Jahn-Teller (JT) systems are considered the prototype of symmetry-induced conical intersections and of the corresponding geometric phase effect (GPE). For decades, this has been analyzed for the most common case originating from C3v symmetry and these results usually were generalized. In the present work, a thorough analysis of the JT effect, vibronic coupling Hamiltonians, GPE, and the effect on spectroscopic properties is carried out for general Cnv symmetric systems (and explicitly for n = 3-8). It turns out that the C3v case is much less general than often assumed. The GPE due to the vibronic Hamiltonian depends on the leading coupling term of a diabatic representation of the problem, which is a result of the explicit n, α, and β values of a CnvEα ⊗ eβ system. Furthermore, the general existence of n/m (m∈N depending on n, α, and β) equivalent minima on the lower adiabatic sheet of the potential energy surface (PES) leads to tunneling multiplets of n/m states (state components). These sets can be understood as local vibrations of the atoms around their equilibrium positions within each of the local PES wells symmetrized over all equivalent wells. The local vibrations can be classified as tangential or radial vibrations, and the quanta in the tangential mode together with the GPE determine the level ordering within each of the vibronic multiplets. Our theoretical predictions derived analytically are tested and supported by numerical model simulations for all possible Eα ⊗ eβ cases for Cnv symmetric systems with n = 3-8. The present interpretation allows for a full understanding of the complex JT spectra of real systems, at least for low excitation energies. This also opens a spectroscopic way to show the existence or absence of GPEs.