scholarly journals Centrifugal spinning of viscoelastic nanofibres

2022 ◽  
Vol 934 ◽  
Author(s):  
S. Noroozi ◽  
W. Arne ◽  
R.G. Larson ◽  
S.M. Taghavi
Keyword(s):  
Energy Equation ◽  
Dynamic Behaviour ◽  
Viscosity Ratio ◽  
Polymer Melt ◽  
String Model ◽  
Flow Parameters ◽  
Centrifugal Spinning ◽  
Spinning Process ◽  
Model Equations ◽  
Viscoelastic Constitutive Model

The centrifugal spinning method is a recently invented technique to extrude polymer melts/solutions into ultra-fine nanofibres. Here, we present a superior integrated string-based mathematical model, to quantify the nanofibre fabrication performance in the centrifugal spinning process. Our model enables us to analyse the critical flow parameters covering an extensive range, by incorporating the angular momentum equations, the Giesekus viscoelastic constitutive model, the air-to-fibre drag effects and the energy equation into the string model equations. Using the model, we can analyse the dynamic behaviour of polymer melt/solution jets through the dimensionless flow parameters, namely, the Rossby ( $Rb$ ), Reynolds ( $Re$ ), Weissenberg ( $Wi$ ), Weber ( $We$ ), Froude ( $Fr$ ), air Péclet ( $Pe^*$ ) and air Reynolds ( $Re^*$ ) numbers as well as the viscosity ratio ( $\delta _s$ ), corresponding to rotational, inertial, viscous, viscoelastic, surface tension, gravitational, air thermal diffusivity, aerodynamic and viscosity ratio effects. We find that the nonlinear rheology remarkably affects the fibre trajectory, radius and normal stresses. Increasing $Wi$ leads to a thicker fibre, whereas increasing $\delta _s$ shows an opposite trend. In addition, by increasing $Wi$ , the fibre curvature is enhanced, causing the fibre to spiral closer to the rotation centre.

scholarly journals Toward an understanding of the nonlinear nature of atmospheric photochemistry: Origin of the complicated dynamic behaviour of the mesospheric photochemical system

2000 ◽  
Vol 7 (1/2) ◽  
pp. 87-104 ◽  
Author(s):  
I. B. Konovalov ◽  
A. M. Feigin
Keyword(s):  
Atomic Oxygen ◽  
Dynamic Behaviour ◽  
Chemical Processes ◽  
Small Perturbations ◽  
Average Growth ◽  
Photolysis Rates ◽  
Abrupt Changes ◽  
Model Equations ◽  
Dimensional Mapping ◽  
Nonlinear Nature

Abstract. The methods of nonlinear dynamics are used to reveal the origin of complicated dynamic behaviour (CDB) of a dynamic model of the mesospheric photochemical system (PCS) perturbed by diurnal variations in photolysis rates. We found that CDB appearance during the multi-day evolution is unambiguously determined by two peculiarities in the model behaviour during its 24-hours evolution. These peculiarities are the presence of a stage of abrupt changes in reagent concentrations and the "humped" dependence of the end-night atomic hydrogen concentrations on those at the beginning of the night. Using a successive analysis we found that these two peculiarities are, in turn, conditioned by the specific features of the chemical processes involved in the model, namely, by the catalytic cycle whose net rate is independent of the concentration of the destroyed species (here, it is atomic oxygen). We believe that similar peculiarities inherent in other atmospheric PCSs indicate that under appropriate conditions they may also demonstrate CDB. We identified the mechanism of the CDB appearance and described it in two ways. The first one reveals a sequence of the processes causing the exponential (on the average) growth of a perturbation of the solution with time. In particular, we found that the behaviour of small perturbations of an arbitrary solution of model equations is identical to the behaviour of a linear oscillator excited parametrically. The second way shows the mechanism of CDB appearance by means of 1-dimensional mapping, which is, basically, the same as the well-known Feigenbaum mappings.

scholarly journals High Efficiency Fabrication of Chitosan Composite Nanofibers with Uniform Morphology via Centrifugal Spinning

Polymers ◽  
2019 ◽  
Vol 11 (10) ◽  
pp. 1550 ◽  
Author(s):  
Zhen Li ◽  
Shunqi Mei ◽  
Yajie Dong ◽  
Fenghua She ◽  
Lingxue Kong
Keyword(s):  
Empirical Model ◽  
Composite Nanofibers ◽  
High Efficiency ◽  
Industrial Applications ◽  
High Yield ◽  
High Productivity ◽  
Chemical Structures ◽  
Centrifugal Spinning ◽  
Spinning Process ◽  
Chitosan Composite

While electrospinning has been widely employed to spin nanofibers, its low production rate has limited its potential for industrial applications. Comparing with electrospinning, centrifugal spinning technology is a prospective method to fabricate nanofibers with high productivity. In the current study, key parameters of the centrifugal spinning system, including concentration, rotational speed, nozzle diameter and nozzle length, were studied to control fiber diameter. An empirical model was established to determine the final diameters of nanofibers via controlling various parameters of the centrifugal spinning process. The empirical model was validated via fabrication of carboxylated chitosan (CCS) and polyethylene oxide (PEO) composite nanofibers. DSC and TGA illustrated that the thermal properties of CCS/PEO nanofibers were stable, while FTIR-ATR indicated that the chemical structures of CCS and PEO were unchanged during composite fabrication. The empirical model could provide an insight into the fabrication of nanofibers with desired uniform diameters as potential biomedical materials. This study demonstrated that centrifugal spinning could be an alternative method for the fabrication of uniform nanofibers with high yield.

scholarly journals In-Situ X-Ray Characterization of Fiber Structure during Melt Spinning

2008 ◽  
Vol 3 (3) ◽  
pp. 155892500800300 ◽  
Author(s):  
Michael S. Ellison ◽  
Paulo E. Lopes ◽  
William T. Pennington
Keyword(s):  
Melt Spinning ◽  
Simultaneous Detection ◽  
Polymer Melt ◽  
Polymer Chains ◽  
Degree Of Crystallinity ◽  
Structure Evolution ◽  
X Ray ◽  
Spinning Process

The properties of a polymer are strongly influenced by its morphology. In the case of fibers from semi-crystalline polymers this consists of the degree of crystallinity, the spacing and alignment of the crystalline regions, and molecular orientation of the polymer chains in the amorphous regions. Information on crystallinity and orientation can be obtained from X-ray analysis. In-situ X-ray characterization of a polymer during the melt spinning process is a major source of information about the effects of material characteristics and processing conditions upon structure evolution along the spinline, and the final structure and properties of the end product. We have recently designed and installed an X-ray system capable of in-situ analysis during polymer melt spinning. To the best of our knowledge this system is unique in its capabilities for the simultaneous detection of wide angle and small angle X-ray scattering (WAXS and SAXS, respectively), its use of a conventional laboratory radiation source, its vertical mobility along the spinline, and its ability to simulate a semi-industrial environment. Setup, operation and demonstration of the capabilities of this system is presented herein as applied to the characterization of the melt spinning of isotactic poly(propylene). Crystallinity and crystalline orientation calculated from WAXS patterns, and lamellar long period calculated from SAXS patterns, were obtained during melt spinning of the polymer along the spinline.

Parameter study and characterization for polyacrylonitrile nanofibers fabricated via centrifugal spinning process

2013 ◽  
Vol 49 (12) ◽  
pp. 3834-3845 ◽  
Author(s):  
Yao Lu ◽  
Ying Li ◽  
Shu Zhang ◽  
Guanjie Xu ◽  
Kun Fu ◽  
...  
Keyword(s):  
Parameter Study ◽  
Centrifugal Spinning ◽  
Spinning Process

scholarly journals Regularized string model for nanofibre formation in centrifugal spinning methods

2017 ◽  
Vol 822 ◽  
pp. 202-234 ◽  
Author(s):  
S. Noroozi ◽  
H. Alamdari ◽  
W. Arne ◽  
R. G. Larson ◽  
S. M. Taghavi
Keyword(s):  
Surface Tension ◽  
String Model ◽  
Inviscid Limit ◽  
Arc Length ◽  
Viscous Forces ◽  
Spiral Trajectory ◽  
Viscous Shear ◽  
Centrifugal Spinning ◽  
Power Law Index ◽  
Arc Lengths

We develop a general regularized thin-fibre (string) model to predict the properties of non-Newtonian fluid fibres generated by centrifugal spinning. In this process the fibre emerges from a nozzle of a spinneret that rotates rapidly around its axis of symmetry, in the presence of centrifugal, Coriolis, inertial, viscous/shear-thinning, surface tension and gravitational forces. We analyse the effects of five important dimensionless groups, namely, the Rossby number ($Rb$), the Reynolds number ($Re$), the Weber number ($We$), the Froude number ($Fr$) and a power-law index ($m$), on the steady state trajectory and thinning of fibre radius. In particular, we find that the gravitational force mainly affects the fibre vertical angle at small arc lengths as well as the fibre trajectory. We show that for small $Rb$, which is the regime of nanofibre formation in centrifugal spinning methods, rapid thinning of the fibre radius occurs over small arc lengths, which becomes more pronounced as $Re$ increases or $m$ decreases. At larger arc lengths, a relatively large $We$ results in a spiral trajectory regime, where the fibre eventually recovers a corresponding inviscid limit with a slow thinning of the fibre radius as a function of the arc length. Viscous forces do not prevent the fibre from approaching the inviscid limit, but very strong surface tension forces may do so as they could even result in a circular trajectory with an almost constant fibre radius. We divide the spiral and circular trajectories into zones of no thinning, intense thinning and slow or ceased thinning, and for each zone we provide simple expressions for the fibre radius as a function of the arc length.

Non-contact detection of polyester filament yarn tension in the spinning process by the laser Doppler vibrometer method

2021 ◽  
pp. 004051752110342
Author(s):  
Dongjian Zhang ◽  
Qihua Ma ◽  
Yuan Tan ◽  
He Liao ◽  
Chenhui Lu ◽  
...  
Keyword(s):  
Differential Equations ◽  
Natural Frequencies ◽  
Laser Doppler Vibrometer ◽  
String Model ◽  
Contact Detection ◽  
Polyester Filament ◽  
Axially Moving String ◽  
Spinning Process ◽  
Polyester Filament Yarn ◽  
Axially Moving

The precise detection of polyester filament yarn (PFY) tension in the spinning process is critical to ensure product quality. The laser Doppler vibrometer (LDV) method is proposed to achieve non-contact detection of PFY tension in this paper. By employing the Hamilton principle, the transverse dynamics differential equations of PFY are derived, which are discretized and solved by the Galerkin method and Runge–Kutta method, respectively. In the equations, the PFY between two adjacent rollers is simplified as an axially moving string to verify the generality of calculating natural frequencies. The calculated natural frequencies from the axially moving string model are compared with solved results from the transverse dynamics differential equations. It is shown that the approximation of natural frequencies can be obtained from the axially moving string model. This study attempts to establish an approximate generic model among the PFY tension, the spinning speed and the first natural frequency based on axially moving string model, from which the PFY tension can be calculated efficiently by employing the measured natural frequencies. The LDV method is used to measure the natural frequencies. A major advantage of the proposed method is to realize non-contact detection of PFY tension. The method is more useful under high-speed spinning conditions where contact tension detectors are not available. An experimental analysis is carried out to verify the effectiveness and accuracy of the proposed method. Therefore, it is believed that the non-contact detection of PFY tension in the spinning process by the LDV method is feasible.

Reynolds Number–Strouhal Number Relationship for Cylindrical Bluff Body with Variation of Aspect Ratio in High Reynolds Number

2014 ◽  
Vol 69 (3) ◽  
Author(s):  
Nor Azwadi Che Sidik ◽  
Tey Wah Yen
Keyword(s):  
Reynolds Number ◽  
Aspect Ratio ◽  
Strouhal Number ◽  
Bluff Body ◽  
Flow Parameters ◽  
Ansys Cfx ◽  
Sst Model ◽  
Model Equations ◽  
High Reynolds ◽  
Volume Method

The effect between Reynolds number and bluff body aspect ratio to the flow parameters such as Strouhal number and drag coefficient are studied. The range of Reynolds number applied is within 10000 and 200000 while three aspect ratio (Ar) where Ar = 1.0, 1.5 and 2.0 are implemented. Finite volume method with the aid of ANSYS CFX codes is deployed using the turbulence SST model. Equations of Re-St relationship for Ar 1.0 and 1.5 are then hypothesized as well in this paper for the range of 10000<Re<100000.

Temperature Simulation on Rotor and Stator of Hydro-Generator

2011 ◽  
Vol 383-390 ◽  
pp. 2411-2416
Author(s):  
Qun Feng Zhang ◽  
Hui Min Cui ◽  
Jin Li Yan ◽  
Min Wang ◽  
Zhi Xiang Chen
Keyword(s):  
Rational Design ◽  
Unstructured Mesh ◽  
Energy Equation ◽  
Flow Characteristic ◽  
Navier Stokes ◽  
Gap Size ◽  
Insulating Layer ◽  
Frame Method ◽  
Model Equations ◽  
Volume Method

Reynolds averaged Navier-Stokes (RANS) equations, energy equation and V2f turbulence model equations governing the flow field of the rotor frame, magnetic yoke and the pole, the stator were solved with finite volume method(FVM) based on unstructured mesh. The MRF(multiple implicit rotating frame) method was used to simulated the rotating motion of the rotor frame, magnetic yoke and the pole. The flow characteristic of different parts was analyzed. The influence of the gap size between insulating layer of bar core, the gap size between insulating layer of pole and coil to the temperature distributions on the solid parts was studied. The results show that the temperature on the windward of the pole is lower than the temperature on the leeward. With the gap size between the insulating layer of bar and core varying from 0.0mm to 0.3mm,the temperature of insulating layer of bar rise increases 9.2 degrees, So the gap size is important for the life of insulating layer. With the gap size between the insulating layer of pole and the coil varying from 0.25mm to 0.75mm, the temperature of coil increases 16.5 degrees. The results provide a reference for the rational design of the gap size.

Scaling and parameterization of stratified homogeneous turbulent shear flow

2000 ◽  
Vol 412 ◽  
pp. 1-20 ◽  
Author(s):  
LUCINDA H. SHIH ◽  
JEFFREY R. KOSEFF ◽  
JOEL H. FERZIGER ◽  
CHRIS R. REHMANN
Keyword(s):  
Richardson Number ◽  
Energy Equation ◽  
Reynolds Numbers ◽  
Turbulent Shear ◽  
Turbulent Shear Flow ◽  
Stratified Turbulence ◽  
Final Value ◽  
Stationary Flows ◽  
Flow Parameters ◽  
Turbulent Kinetic Energy Equation

Homogeneous sheared stratified turbulence was simulated using a DNS code. The initial turbulent Reynolds numbers (Re) were 22, 44, and 89, and the initial dimensionless shear rate (S*) varied from 2 to 16. We found (similarly to Rogers (1986) for unstratified flows) the final value of S* at high Re to be ∼ 11, independent of initial S*. The final S* varies at low Re, in agreement with Jacobitz et al. (1997). At low Re, the stationary Richardson number (Ris) depends on both Re and S*, but at higher Re, it varies only with Re. A scaling based on the turbulent kinetic energy equation which suggests this result employs instantaneous rather than initial values of flow parameters.At high Re the dissipation increases with applied shear, allowing a constant final S*. The increased dissipation occurs primarily at high wavenumbers due to the stretching of eddies by stronger shear. For the high-Re stationary flows, the turbulent Froude number (Frt) is a constant independent of S*. An Frt-based scaling predicts the final value of S* well over a range of Re. Therefore Frt is a more appropriate parameter for describing the state of developed stratified turbulence than the gradient Richardson number.

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