Search results

The purpose of this paper is to study numerically the rheological properties of fiber suspensions flowing through turbulent pipe flows.

The work presented in this paper is derived the fluctuating equation for fiber orientation distribution function (FODF) in turbulent flows and solved using the method of characteristics. The FODF is predicted numerically. The numerical results of root-mean-square velocities generated by kinetic simulation sweeping model and are compared with the experimental data.

The fiber orientation distribution becomes wider with increasing Re. The components of the fourth-order orientation tensor increase with the increase of Re, and also increase along the radial direction and reach the maximum at the center line. The first normal stress difference is much less than the shear stress. For different Re the shear stress increases rapidly in the region far from the pipe center, and reaches its maximums at center, while the first normal stress difference decreases rapidly in the region far from the pipe center, and reaches its minimum at center finally.

By solving numerically the equation in a turbulent pipe flow with Reynolds number ranging from 2,500 to 1,000, the authors obtain the mean FODF which is in agreement with the experimental one qualitatively. Then the shear stress and first normal stress difference of suspensions are calculated based on the mean FODF.

Modelling of fiber suspension in injection molding cavities is very complex, with fluid flow, fiber orientation, and heat transfer effects taking place at the same time. Moreover, the flow is modified by the presence of fibers and vice versa. Therefore, the aim of the paper is to develop a Computational Fluid Dynamics (CFD) model to simulate and characterise the fiber suspension flow in two dimensional mold cavities. The model is intended to describe the fluid flow and heat transfer aspects of the suspension, and to predict the fiber orientation. The Navier-Stokes equations and the Jeffery (1922) equation are the governing equations for the velocity field and fiber motion respectively. The flow is considered to be two-dimensional incompressible, non-isothermal, transient and behave as non-Newtonian fluid containing suspension of short-fibers. The Finite Volume Method (FVM) combined with Control Volume Method is used to simulate the flow field by solving the momentum, energy and fiber orientation equations. To validate the numerical model, the numerical results are compared with available experimental findings. A good agreement between the numerical results and the experimental data is achieved. Since the behaviour of fiber suspension has great significance on the quality of the final product, this study has wide background of engineering application.

This paper seeks to explore the fiber orientation distribution and rheological properties of turbulent fiber suspensions flowing through a contraction.

The Reynolds averaged Navier‐Stokes equation was solved with the Reynolds stress model to get the mean fluid velocity and the turbulent kinetic energy in the turbulent flow of a contraction with rectangular cross‐section. The turbulent velocity fluctuations were represented as a Fourier series with random coefficients. Then the slender‐body theory was used to predict the fiber orientation distribution, orientation tensor, additional shear stress and first normal stress difference of suspensions in the flow.

It is found that the longer fibers tend to align the streamline easily. Increased contraction ratio results in higher fiber alignment in the direction of flow. The fibers are weakly and strongly aligned in the direction of flow in the region near the inlet and the exit, respectively. Fibers are significantly more aligned in the plane of the contraction than in the x‐z plane. Contraction ratio and fiber length were shown to strongly and weakly affect the distributions of additional shear stress and first normal stress difference.

It is the first time that the fiber orientation distribution and rheological properties of turbulent fiber suspensions flowing through a contraction have been computed numerically. The computational approach and results are valuable to the design and operation of contraction used in the industrial processes.

The purpose of this paper was to show that the generalised viscosity model can correctly characterise suspension data over both a wide range of concentration as well as a wide range of temperature. A second objective of this study was to show theoretically and experimentally how the interaction coefficient from the generalised viscosity model also appears to have some thermodynamic properties.

In this study, many well‐known suspension equations were shown mathematically to be subsets of the generalised viscosity equation. The generalised viscosity equation was also found to be able to be reduced mathematically to two well‐known dilute solution equations (Huggins and Kramer's equations) as well. The relationship between Huggins and Kramer's constants and the interaction coefficient from the generalised viscosity equation yielded the potential to evaluate the solubility characteristics of the interaction coefficient. The value of the interaction coefficient was then found to be able to be evaluated as a function of temperature to enhance an understanding of the thermodynamic characteristics of the interaction coefficient using the data of Bueche.

In this study, a polymer plasticiser system involving polymethyl methacrylate in the plasticiser diethyl phthalate yielded an interaction coefficient, σ, primarily in the expected plasticiser range from 0< σ<1. It was also found that the generalised viscosity equation fit Bueche's polymer plasticiser data remarkably well over the whole concentration range for temperatures ranging from 30°C to 140°C. This study also appeared to show that the interaction coefficient from the generalised viscosity model can apparently characterise thermal transitions as well as thermodynamic solubility for a polymer solute (i.e. polymethyl methacrylate) when viscosity is evaluated over a wide temperature range. This result was particularly significant since Bueche's data covered 25 decades of viscosity on a log scale.

This is the first paper to successfully explore the thermodynamic characteristics of the interaction coefficient of the generalised viscosity equation. This opens up new avenues for evaluating the solubility and thermodynamic characteristics of various additives in solutions and polymeric formulations.

Refers to how the mechanical properties of polymer‐based composite objects produced via rapid layered fabrication methods can be improved significantly using short discontinuous fibres as reinforcements. Notes in this context, that the viscosity of the uncured fibre‐photopolymer composite liquids affects the raw‐material handling, the layer formation and the draining operations. Assesses the effects of aspect ratio, surface coating and volume fraction of short glass fibres on the viscosity of the fibre‐photopolymer composite liquids. Based on extensive experimentation and analysis, concludes that the shear viscosity of the composite liquids increases with increasing fibre‐volume fraction, showing that this effect is more pronounced at low shear rates than at high shear rates. Reveals, similarly, that the aspect ratio of the dispersed fibres has a stronger effect on the increase of viscosity at low shear rates and that the surface coating of the dispersed fibres also affects the viscosity of the composite liquids.

The purpose of this paper is to examine the macroscopic and microscopic fields of fiber suspensions in the non‐isothermal situations, also to examine the effect of fiber on this non‐isothermal system.

Control equations are coupled and simultaneously solved by collocated finite volume method on fully triangular meshes.

Temperature dependence and wall temperature have significant effect on both macroscopic and microscopic fields of fiber suspensions. Moreover, the influence of fiber on the non‐isothermal system is similar to that of the isothermal system.

This is the first time that the microstructures of both molecules and fibers are presented in the non‐isothermal condition and it is hoped that the results will provide more insight into the microscopics of complex flows.

A model is presented for the flow of inkjet-printed fluids into textiles based on capillary flow between fibers and diffusion of solvent into the fibers. Dispersions of PEDOT (Poly 3, 4 ∓ ethylenedioxythiophene), a conducting polymer, can be inkjet-printed onto fabric to form piezoresistive sensors. A problem is to get proper penetration of PEDOT into the fabric so that it does not easily flake off the surface. This penetration depends on a balance between wetting, evaporation and viscous flow of printed PEDOT suspensions between the fibers of the textile substrate.

This study addresses how these liquids flow within a yarn after being printed onto the fabric. Loss of liquid into the fiber limits spreading of the ink as the residual solids level builds up. Ink predominantly follows the path of a yarn but is treated as crossing between yarns at narrow crossing points. This model yields predictions for the distribution of conducting ink when printed onto fabric.

The orientation behavior of fiber is of great significance in improving the performance of fiber-reinforced polymer products. Generally, the Folgar–Tucker equation can accurately describe the variation of orientation vector of fiber, whereas the stability of numerical algorithms was the major challenge. This paper aims to propose an accurate, stable algorithm to solve the Folgar–Tucker equation for the fiber orientation behavior.

First, the mismatch problem between the strain rate and the pressure field was solved by using the integral transformation method. Then, an accurate, stable algorithm to solve the Folgar–Tucker equation based on the invariant-based optimal fitting method was proposed. The equation was discretized by finite element/finite difference method, and the Lagrange multiplier method was applied to ensure stability.

The proposed algorithm is proven to accurately and steadily coincide with the experimental results for different cases, including the fiber orientation behaviors under combined flow field, rectangular sheet, three-dimensional computed tomography imaging of tensile specimen and box cases.

The fiber orientation behavior during the injection molding can be accurately predicted, which plays a significant role in determining the mechanical properties of products.

The purpose of this paper is to study the effect of particle shapes (spherical particle and nonspherical fiber) on their orientation distributions in indoor environment.

This paper adopted a particle model to predict the fibrous particle flow and distribution, and analyzed the orientation distributions of nonspherical fiber particles and spherical particles in airflows like indoor places. Fokker-Planck model was employed to solve the orientation behavior of nonspherical fiber particles.

The simulation results discover that the nonspherical airborne fiber particles have very different characteristics and behaviors and their orientation distributions are totally different from the uniform distribution of spherical particles. The investigation of the particle orientation tensor and orientation strength indicates that the airflow field becomes more anisotropic due to the suspended fibers. The airborne fiber particles increase the viscosity of the room airflow due to the fiber induced additional viscosity.

Orientation tensor, strength and additional viscosity in fibrous flow are seldom investigated indoor. This research reveals that the particle shape has to be considered in the analysis of particle transport and distribution in indoor places as most suspended indoor particles are nonspherical.

This paper aims to address the production of biocomposite nanofibers using luffa natural fibers and polyaniline conductive polymer/polyethylene oxides (PANI/PEO).

In this study, luffa natural fibers are extracted by chemical method. After mixing the treated luffa (TL) with the PANI/PEO solution, TL/PANI/PEO nanofibers were produced by electrospinning (ES) method under different ES parameters to examine the optimal conditions for nanofiber production. Then TL/PANI/PEO biocomposite nanofibers prepared in different weight ratios were produced to analyze the effects of luffa in the morphology and thermal properties of the biocomposite nanofibers. The characterization analysis of TL/PANI/PEO biocomposite nanofibers was performed by scanning electron microscopy, Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) analysis methods.

The analysis shows that different weight ratios of TL to PANI/PEO changed the morphology of the membrane. When increasing the weight ratio of TL, the morphological structure of TL/PANI/PEO transformed from nanofiber structure to thin film structure. The appearance of O—H peaks in the FTIR results proved the existence of TL in PANI/PEO nanofibers (membrane). Moreover, an increase in the weight ratio of luffa from 2% to 7.5% leads to an increase in the peak intensity of the O—H group. Regarding DSC analysis, biocomposite nanofibers improved the thermal properties. According to all results, 2%wt TL/PANI/PEO showed optimal morphological properties.

Plant cellulose was extracted from the luffa, one of the natural fibers, by method of alkali treatment. A new type of biocomposite nanofibers was produced using TL blend with PANI via electrospinning method.