Volume–Geometry–Shear Rate ( VGS ) Coordinated Similarity Scale‐Up Method for Safe and Equivalent Mixing of Energetic Materials in Twin‐Screw Extrusion

Relative hydraulic resistance, shear rate, and pressure in a vascular network integrate the network's architecture via fluid flow, and determine vein dynamics, with a time delay, in the prototypical organism Physarum polycephalum.

The rate of breakage of duplex DNA molecules by laminar flow through a capillary has been studied. For λb2b5c DNA (molecular wt., M = 25 × 106) the point at which breakage occurs is normally distributed around the center of the molecule with a standard deviation of 12.5% of the molecular length. At constant shear stress or shear rate, the breakage rate is independent of ionic strength. Thus, shear induced local denaturation is not a rate limiting, preliminary step in breakage. In experiments at constant temperature with varying solvent viscosity (controlled by added sucrose) the breakage rate is a function of shear rate, not of shear stress. The rate of opening of hydrogenbonded circles into linear molecules by hydrodynamic shear is also shown to be a function of shear rate and not of shear stress. The breakage rate at constant shear rate is not greatly dependent on temperature. The shear rate required to achieve breakage is inversely proportional to M1,2. The breakage rate constant, k varies as a very high power of the shear rate; at 25°C, d In k/d In Gm ∼ 15; at 10°C, d In k/d In Gm ∼ 26, where Gm is the maximum shear rate at the capillary wall. The unexpected result that breakage rate is mainly dependent on shear rate, not shear stress, supports a model in which the DNA molecule is distorted with a driving force which depends on the hydrodynamic shear stress, ηG, but the rate limiting step is segment diffusion into a highly extended configuration. The characteristic time to achieve this configuration is proportional to solvent viscosity, η, hence the breakage rate is dependent on ηG/η or G, the shear rate.

In this article, a novel continuous twin‐screw kneader was proposed. The end‐cross section of the screw rotor consists of convex arcs and cycloidal curves and the rotors profiles were presented. The mixing performance of the novel twin screw kneader was simulated using finite element method (FEM) combined with mesh superimposition technique (MST). Statistical analysis was carried out for flow field using particle tracking technique to research the effect of geometry parameters and working parameters on the mixing performance. To study the dispersive mixing performance, specifically the maximum shear rate, maximum shear stress, maximum mixing index, residence time distribution (RTD) and RTD density function of tracer particles, and dispersive mixing is evaluated using the mixing index in combination with the shear stress. The results show that the changes of centre distance between female and male rotor have little influence on dispersive mixing performance, the lead of rotor has little effect on maximum shear stress and maximum shear rate, while it has an obvious effect on mixing index, cumulative RTD, and RTD density function. The rotor speed has obvious influence on mixing performance, and average residence time of material decreases greatly and the mixing ability is weakened, while the self‐cleaning performance of rotor improved obviously with the increasing of rotor speed. POLYM. ENG. SCI., 54:2407–2419, 2014. © 2013 Society of Plastics Engineers

The effect of particle shape and size on the mixing performance of a double barrel with differential velocity (DBDV) was investigated on the basis of a discrete element method (DEM). The mixing performance was determined on the basis of the velocity, mixing efficiency and mixing uniformity. The DBDV model, motion model and particle models of different shapes were constructed. The motion process of the particles was visualized by a DEM. The effect of particle shape, particle size and their coupling effect on the mixing performance of DBDV was analyzed. The simulation results were validated. The results indicate that the differential zone is less sensitive to particle shape than the nondifferential zone. In terms of mixing uniformity, choosing a lower linear velocity at low and medium inclinations is more appropriate; similarly, choosing a high linear velocity at a large inclination is more appropriate. In the differential region, the particle velocity decreases as the particle size decreases. The mixing uniformity increases but then decreases with increasing particle curvature and decreasing particle size. The particle size significantly affects the mixing time and mixing uniformity of particles. Choosing medium-sized ellipsoidal and square particles is better for achieving high mixing uniformity.

The objective of the present study is to experimentally investigate the transient rheological behavior of concentrated xanthan gum solutions in start-up shear flow fields. Using a strain-controlled rheometer, a number of constant shear rates were suddenly imposed to aqueous xanthan gum solutions with different concentrations and the resultant shear stress responses were measured with time. The main findings obtained from this study can be summarized as follows: (1) For all shear rates imposed, however low it may be, the shear stress is rapidly increased with time (stress overshoot) upon inception of steady shear flow before passing through the maximum stress value and then gradually decreased with time (stress decay) until reaching a steady state flow. (2) As the imposed shear rate is increased, a more pronounced stress overshoot takes place and the maximum stress value becomes larger, whereas both times at which the maximum stress is observed and needed to reach a steady state flow are shortened. (3) The maximum shear stress is linearly increased with shear rate in a double logarithmic scale and becomes larger with increasing concentration at equal shear rates. In addition, the time at which the maximum stress occurs exhibits a linear relationship with the inverse of shear rate in a double logarithmic scale for all xanthan gum solutions, regardless of their concentrations. (4) The shear stress is sharply increased with an increase in strain until reaching the maximum stress at small range of deformations. The maximum stress is observed at similar strain values, irrespective of the imposed shear rates lower than 10 1/s. (5) The Bird-Leider model can be successfully used with regard to quantitatively predicting the transient behavior of concentrated xanthan gum solutions. However, this model has a fatal weakness in terms of describing a decrease in shear stress (stress decay).

By means of a cone and plate rheometer the relaxation of the shear stress and the first normal stress difference in polymer liquids upon cessation of a constant shear rate were examined. The experiments were conducted mostly in a high shear rate region of relevance for the processing of these materials. The relaxation behavior at these shear rates can only be measured accurately under extremely precise specifications of the rheometer. To determine under which conditions the integral normal thrust is a convenient measure for the relaxing local first normal stress difference the radial distribution of the pressure in the shear gap was measured. The shape of relaxation of both the shear stress and the first normal stress difference could be closely approximated for the entire measured shear rate and time range by a two parameter statistical function. In the range of measured shear rates, one of the parameters, the standard deviationS, is equal for the shear and the normal stress, and is independent of the shear rate within the limit of experimental error. The second parameter, the mean relaxation timet′50,τ of the shear stress andt′50,σ of the first normal stress difference, can be calculated approximately from the viscosity function and only a single relaxation experiment.

In a previous paper, we reported for the first time the lamellar-to-onion transition with increasing temperature at around 67 °C under a constant shear rate (0.3-10 s(-1)) in a nonionic surfactant C(16)E(7)/water system. In this study, the first temperature-shear rate diagram has been constructed in a wider range of shear rate (0.05-30 s(-1)) than in our previous study based on the temperature dependence of the shear stress at constant shear rate. The results suggest that the critical temperature above which the transition begins does not depend on the shear rate very much, although it takes a very shallow minimum. Then we have performed simultaneous measurements of small-angle X-ray scattering/shear stress (rheo-SAXS) with a stepwise increase in temperature of 0.1 K per 15 min at a constant shear rate of 3 s(-1) near the transition temperature. When the temperature exceeds 67 °C, just before the increase in the shear stress, the intensity of the Bragg peak for the velocity gradient direction (approximately proportional to the number of lamellae with their normal along this direction) is suddenly increased. As the temperature increases by 0.2 K, the shear stress begins to increase. At the same time, the peak intensity in the velocity gradient direction rapidly decreases and instead the intensity in the neutral direction increases. As the temperature increases further, the intensities in both the neutral and gradient directions decrease whereas the intensity in the flow direction increases, corresponding to the formation of onions. We have also performed rheo-SAXS experiments with a stepwise increase in shear rate at 72 °C. The sequence of the change in the intensity in each direction is almost the same in the temperature scan experiments at constant shear rate, suggesting that the transition mechanisms along these two paths are similar. The abrupt enhancement of the lamellar orientation with the layer normal along the velocity gradient direction just before the transition is the first finding and strongly supports the coherent buckling mechanism in the lamellar-to-onion transition proposed by Zilman and Granek (Zilman, A. G.; Granek, R. Eur. Phys. J. B 1999, 11, 593).

The yield stress of mud is the key to the starting analysis of debris flow. Taking the clay in Longquan District of Chengdu as the experimental object, slurries with different solid volume concentrations were prepared. Using the blade rotor system of MCR301 rheometer, the continuous increasing shear rheological test of mud is carried out, and the dynamic change process of shear stress with the increase of shear rate is recorded. According to the results, the following conclusions are drawn: Chengdu clay mud is a non-Newtonian fluid with yield stress. When the solid volume concentration exceeds 35%, the shear rate is less than 1s-1, and the shear stress increases rapidly with the increase in shear rate. When shear rate is higher than 1s-1, the shear stress decreases with the increase in shear rate, and finally tends to be stable. There is a maximum shear stress near 1s-1. When the solid volume concentration is less than 35%, the shear rate is less than 0.1s-1, and the shear stress increases with increase in shear rate. When the shear rate is higher than 0.1s-1, the shear stress changes little with the increase in shear rate. An exponential relationship between mud (dynamic and static) yield stress and solid volume concentration can be seen.

Two correlations for the prediction of the rheological behaviour of thixotropic crude oils are described and tested on a set of data. A comparison shows that the Perkins-Turner correlation, which Is simpler to use, n-ill give adequate predictions over the range of their data, whereas the more complex correlation of Ritter and Govier reproduces the shear stress - shear rate - shear duration relationships for shear rates greater than 0.1 sec−1 for all values of shear durations with good accuracy. Introduction THE LAST FEW YEARS have seen the publication of a number of papers on various aspects of the rheological behaviour of thixotropic materials including crude oils. Several of these deal with the general nature of thixotropic behaviour(1–6). The thixotropic behaviour is usually described by a "model" or a set of constitutive equations in-volving several material constants which may be evaluated from rheological measurements. A successful model permits the construction of the shear stress shear rate shear duration (T - S - U) relationships from the material constants. Several models are reviewed by Govier and Aziz.(7). Another group of papers(6–10) deals with practical aspects of pipeline flow characteristics of thixotropic crude oils, including the starting behaviour after the oil has gelled in the pipeline. The pressure drop required to start flow is related to the yield value or "gel strength" of the crude oil Some actual data on the rheological behaviour of specific crude oils, or their pressure drop - flow rate relationship in pipelines, are included in both groups of papers. The Data And Correlation Of Perkins And Turner Recently, Perkins and Turner (10) presented data on the flow behaviour of crude oil from the Prudhoe Bay field. Their data were carefully taken in precision rotational viscometers over an exceptionally wide range of shear rates. For the Prudhoe Bay crude oil the observed the same general features, some in accentuated form, observed by Govier and Ritter(11) for the Pembina crude oil, i.e.: sensitivity to previous thermal history shear history and aging: sensitivity to temperature; existence of yield value; decay of shear stress with time at constant shear rate; pseudoplastic behaviour of the zero-time shear stress. Perkins and Turner correlated their data covering a range of temperatures and a variety of previous thermal and shear treatments in terms of (Equation Available In Full Paper) Equation (1) may therefore be considered an interpolation formula for the evaluation of τ at any value of θ based on the above limiting values. Equation (2) is of reasonable form to describe a yield-pseudoplastic fluid. Equation (3) is the Newtonian equation; its applicability even to the infinite-time behaviour of a thixotropic yield - pseudoplastic crude oil is questionable in principle. Its suitability for the Prudboe Bay crude oil is not supported by the trend of the data. This is discussed further later. The correlation also presupposes that the effect on the rheological behaviour of shear rate, γ and shear duration, θ, is expressible through γ itself and the product E = γ θ, i.e., that the effect of shear duration, θ, is fully expressible through.

Simulation analysis and parameter optimization are performed for the loading and mixing devices of a self-propelled total mixed ration mixer. To reveal the three-dimensional movement of silage material under the action of the loading cutter roller, the latter is modeled using SolidWorks software. ANSYS/LS-DYNA software is used to simulate the process of silage cutting, which is modeled using smoothed particle hydrodynamics coupled with the finite element method. The cutting force and power consumption are simulated, and the behavior of the equivalent strain of the silage is determined. The results showed that silage was broken up mainly by extrusion and shear force due to the loading cutter roller. The power consumption according to the simulation is consistent with the value from an empirical formula, confirming the validity of the proposed modeling method. To study the mixing performance and obtain the optimum parameters of the mixing device, the Hertz–Mindlin model is used for the interaction between material particles and mixing device. A three-factor, five-level method is used to optimize the mixing performance. Material-mixing time, loading rate, and auger speed are chosen as experimental factors and mixed uniformity as an evaluation index. It is found that auger speed and material mixing time have significant effects on mixing uniformity. These results provide reference values allowing the analysis of the crushing of silage and selection of the optimum parameters for mixing performance.

Numerous cell functions are accompanied by phenotypic changes in viscoelastic properties, and measuring them can help elucidate higher level cellular functions in health and disease. We present a high-throughput, simple and low-cost microfluidic method for quantitatively measuring the elastic (storage) and viscous (loss) modulus of individual cells. Cells are suspended in a high-viscosity fluid and are pumped with high pressure through a 5.8 cm long and 200 µm wide microfluidic channel. The fluid shear stress induces large, ear ellipsoidal cell deformations. In addition, the flow profile in the channel causes the cells to rotate in a tank-treading manner. From the cell deformation and tank treading frequency, we extract the frequency-dependent viscoelastic cell properties based on a theoretical framework developed by R. Roscoe [1] that describes the deformation of a viscoelastic sphere in a viscous fluid under steady laminar flow. We confirm the accuracy of the method using atomic force microscopy-calibrated polyacrylamide beads and cells. Our measurements demonstrate that suspended cells exhibit power-law, soft glassy rheological behavior that is cell-cycle-dependent and mediated by the physical interplay between the actin filament and intermediate filament networks.

Swirling flow is widely used in gas turbine burners to promote fuel/air mixing uniformity and to stabilize lean premixed flames. In this study, numerical and experimental methods are utilized to investigate the effects of burner geometry on fuel/air mixing and combustion performance and to optimize the burner geometry. The premixed burner geometry parameters including air swirling angle and fuel injection diameter/angle are modified to achieve fuel/air mixture uniformity. Laser Doppler Velocimetry (LDV) and Particle Image Velocimetry (PIV) are adopted to examine the flow field, Planar Laser Induced Fluorescence (PLIF) for detecting OH radical distribution thus investigating the characteristics of the reaction field. Burners of different configurations are manufactured to conduct combustion experiments. The burner with the worst mixing performance can‘t ignite successfully. However, burners with better mixing performance have a homogeneous reaction field with less perturbance, and the NOX emission stays at a relatively low level around 2.5 ppm (15% O2) at the designed operating condition.

Apparent flow activation energies evaluated from viscosity changes with temperature can be calculated in the non‐Newtonian region at either constant shear rate, E, or at constant shear stress, E. For many linear, amorphous polymere, it can be shown that E is independent of stress over the full range for which shear stress data tire reported. This conclusion also holds for solutions of several polymer types. Anomalous results are documented only for branched polyethylene. E decreases with shear in the non‐Newtonian region approaching a lower limit corresponding to the “power law” region. The relative changes in E with shear rate can be expressed in terms of reduced variables. The absolute change in E with shear rate can he used as a measure of polymer molecular weight distribution.

Introduction: Inflammation has been proposed as a possible mechanism involved in the degradation and weakening of the walls of intracranial aneurysms. Hypothesis: Abnormal wall shear stress (WSS) levels induce wall inflammation which then affects the wall structure and mechanics Methods: A total of 20 aneurysms which underwent surgical clipping were studied. Patient-specific computational fluid dynamics models were constructed from pre-surgical CTA images. Numerical simulations were carried out using pulsatile flows. After clipping the aneurysm, a tissue sample was resected from the dome and analyzed histologically with CD45 to search for evidence of wall inflammation. For analysis, the aneurysm series was divided in two different manners. First, aneurysms were classified into an “inflammation” group if the number of CD45+ cells was larger than the median of CD45+ cells in the entire sample of 20 aneurysms; otherwise they were classified as “no-inflammation”. Hemodynamic variables were then statistically compared between these two groups. Secondly, aneurysms were subdivided into three groups according to their mean WSS: 1) “low WSS” if WSS<0.5*median(WSS), 2) “high WSS” if WSS>2*median(WSS), and 3) “mid WSS” otherwise. The numbers of CD45+ cells in each group were then statistically compared. Results: Aneurysms in the “inflammation” group had significantly larger mean WSS (p=0.018), shear rate (p=0.015), vorticity (p=0.018), and viscous dissipation (p=0.015) than aneurysms in the “no-inflammation” group. Conversely, aneurysms in the “high WSS” group had significantly larger numbers of CD45+ cells (p=0.0046) than the “mid WSS” and “low WSS” groups. Interestingly, aneurysms with stable flow patterns also tended to have larger numbers of inflammatory cells (p=0.040) than aneurysms with unstable flows. Conclusion: These preliminary results suggest that there is a connection between intra-aneurysmal flow characteristics and wall inflammation in cerebral aneurysms. In particular, inflamed walls seem to be associated with higher levels of wall shear stress.

This study investigates the blending characteristics of natural gas (NG) and hydrogen in a Kenics static mixer using computational fluid dynamics. The effectiveness of the adopted numerical model is experimentally validated. The scenario of high-pressure, long-distance NG pipelines is considered, and the Soave–Redlich–Kwong equation of state is applied. The mixing uniformity and pressure loss are adopted as evaluation criteria to analyze the impact of factors such as the deflection angle of spiral blades, the number of blades, the length-to-diameter ratio, the hydrogen blending ratio (HBR), the pipeline pressure, and the temperature on mixer performance, followed by structural optimization of the mixer. It is found that a Kenics static mixer with two spiral blades, a length-to-diameter ratio of 2, and a deflection angle of 135° can achieve a mixing uniformity of 95% at the blade outlet while minimizing pressure loss. Increasing the HBR helps improve the mixing uniformity but also increases the pressure loss of the mixer. Increasing the pipeline pressure while keeping the hydrogen mole fraction constant enhances the mixing uniformity but also increases the pressure loss. Increasing the gas temperature reduces the mixing uniformity and the pressure loss. Overall, pipeline pressure and temperature changes have a minimal impact on the mixing characteristics. Under high-pressure conditions, the use of a real gas model is essential. This study provides theoretical guidance for the design of static mixers for hydrogen blending in high-pressure NG pipelines.