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An investigation of the plasma jet generated by a dc argon–nitrogen plasma torch, operated in association with a controlled-pressure chamber, is presented. The purpose of this article is to describe a study of the properties of a subsonic plasma jet under such operating conditions, when its transition to supersonic flow regime is nearly complete. The goal is that of performing plasma diagnostics not only in the initial region of the jet but also in the downstream region where the plasma emission is weak. For this purpose two different diagnostic methods are used. The first approach is based on non-intrusive optical emission spectroscopy, which yields both excitation and rotational temperatures as well as electron number density fields. The zone investigated by this method extends from the torch exit to about 10 nozzle diameters downstream. The second approach consisted of the use of the intrusive enthalpy probe technique for the measurement of the plasma gas temperature, mainly in the tail region of the plasma jet. In the present work, the effects of axial and radial distances across the jet, on the temperature and electron density profiles are discussed for subsonic flow conditions. Interesting features revealed are the data shown for the various diagnostic methods, which either disagree or overlap with each other. Finally, our results show the need for involving non-equilibrium models for the argon–nitrogen plasma due to the presence of significant differences between the temperatures of light and heavy particles.  相似文献   
2.
Rheological properties of suspensions of fibers in polymeric fluids are influenced by fiber–polymer interactions. In this paper, we investigate this influence from both experimental and modeling standpoints. In the experimental part of this investigation, we have changed the fiber–polymer interactions by treating the surface of the fibers. The resulting effects are observed using scanning electron microscopy and dynamic mechanical analysis techniques and quantified from the measurements of the viscosity in the start-up of shear flows and dynamic tests in the linear viscoelastic range region. The results are interpreted with the help of a mesoscopic rheological model developed for suspensions of fibers in viscoelastic fluids.  相似文献   
3.
Mixing of solid nanoparticles in viscous fluids is a key stage in synthesis of nanocomposites and can affect their final properties. A multi-step preparatory mixing is developed to synthesize the nanocomposites of layered silicate in thermosetting polymers. This study aims to investigate the influences of mixing conditions and steps taken to process the thermosetting nanocomposites on the viscoelastic properties of suspensions. We also examine subsequent influences of mixing on the microstructure and dispersion state of cured hybrids of organically modified clays in a polyester resin. The nanocomposites were prepared in a sequential mixing process developed for the model nanocomposites of organoclays and thermoset resin. Depending on the mixing conditions, the final nanocomposites showed mixed intercalated and moderately to highly delaminated structure. TEM images show that the nanoclay galleries are dispersed in the polymer phase after curing reactions. The startup viscosities and linear viscoelastic properties of the nanocomposites are significantly influenced by the extent and the time duration of mixing. These observations indicate that extensive mechanical mixing combined with a stationary step followed by moderate shear mixing can improve the polymer and nanoparticle interactions at the interface. In the last part of this work, we develop a simple but efficient mathematical formulation on the flow of oblate spheroids in viscous media and compare selected model predictions with the measured startup shear viscosities of suspensions.  相似文献   
4.
The influence of nano‐scale particles on the viscoelastic properties of polymer suspensions is investigated. We have developed a simulation technique for the particle orientation and polymer conformation tensors to study various features of the suspensions. The nano‐particles are modeled as thin rigid oblate spheroid particles and the polymers as FENE‐P type viscoelastic and Newtonian fluid. Both interparticle and polymer‐particle interactions have been taken into account in our numerical computations. The nonlinear viscoelastic properties of nanocomposites of layered silicate particles in non‐Newtonian fluids are examined at the start‐up of shear flow and are interpreted using the model to examine the effects of model parameters as well as flow conditions on particle orientation, viscosity, and first normal stress difference of the suspensions. We have studied the microstructure of polymer‐clay nanocomposites using X‐ray diffraction (XRD) scattering and transmission electron microscopy (TEM). The rheology of these nanocomposites in step‐shear is shown to be fairly well predicted by the model. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 2003–2011, 2010  相似文献   
5.
The diagnostics study on supersonic argon/nitrogen plasma jets expanded into a low-pressure test chamber is carried out by means of emission spectroscopy and enthalpy probe measurement techniques. The spatial distributions of electron density, temperatures, and associated shock structure effects in plasma jets are investigated in conjunction with their direct dependency upon the chamber pressure. The experimental results show the occurrence and the position of different zones; i.e., supersonic expansion, stationary shock waves and subsonic jet at pressures below 51 kPa. Flow fluctuations due to the oblique shock wave at 39 kPa background pressure are observed and discussed. The electron density profiles show variations along the plasma axis that coincide with the position of the shock waves. The experimental results show the transition from the moderately under-expanded to the strongly under-expanded jet structure induced by lowering of the chamber pressure.  相似文献   
6.
We study the rheological characteristics of nanocomposites containing nano-sized plate like particles in a viscoelastic fluid at the startup of steady state in the simple shear flow mode. The nanocomposites of organoclay-polypropylene with different nanoclay contents were prepared by melt mixing. A rheological equation of state, originally formulated to predict the orientation state and viscoelastic behavior of suspensions of ellipsoidal particles in polymer melts, has been modified to describe the observed phenomena for the nanoclay/poly(propylene) composites. The rotational particle motion and alignment for a group of symmetric ellipsoids with the applied flow field are investigated. Additionally, model calculations of the macroscopic rheological properties for a simple flow case suggest the presence of nano-particles significantly modify the suspended fluid at volume concentrations as low as 0.5%. The model calculations for the startup viscosity are reasonably in agreement with the experimental results at the experimental range covered in this study. At the shear rate of , we observe pronounced stress overshoots at the three nanoclay loadings level tested which are found to be related to the fast alignment of the silicate layers with the shear direction in the polymer melt.  相似文献   
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A mesoscopic rheological model of suspensions of semiflexible fibers in polymeric fluids is formulated. Consequences of the model are compared with results of experimental observations of the rheological properties in a simple shear flow. The model takes into account the fiber-fiber and fiber-polymer interactions (in the free energy and the mobility coefficients) and the semiflexible nature of the fibers (in the choice of the Khokhlov-Semenov entropy).  相似文献   
9.
Transient elongational rheology of two commercial-grade polypropylene (PP) and the organoclay thermoplastic nanocomposites is investigated. A specifically designed fixture consisting of two drums (SER Universal Testing Platform) mounted on a TA Instruments ARES rotational rheometer was used to measure the transient uniaxial extensional viscosity of both polypropylene and nanoclay/PP melts. The Hencky strain rate was varied from 0.001 to 2 s − 1, and the temperature was fixed at 180°C. The measurements show that the steady-state elongational viscosity was reached at the measured Hencky strains for the polymer and for the nanocomposites. The addition of nanoclay particles to the polymer melt was found to increase the elongation viscosity principally at low strain rates. For example, at a deformation rate of 0.3 s − 1, the steady-state elongation viscosity for polypropylene was 1.4 × 104 Pa s which was raised to 2.8 × 104 and 4.5 × 104 Pa s after addition of 0.5 and 1.5 vol.% nanoclay, respectively. A mesoscopic rheological model originally developed to predict the motion of ellipsoid particles in viscoelastic media was modified based on the recent developments by Eslami and Grmela (Rheol Acta 47:399–415, 2008) to take into account the polymer chain reptation. We show that the orientation states of the particles and the rheological behavior of the layered particles/thermoplastic hybrids can be quantitatively explained by the proposed model.  相似文献   
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