Dynamic Flow Curves Research Articles

Hempseed polysaccharide (Cannabis sativa L.): Physicochemical characterization and comparison with flaxseed polysaccharide

The whole hempseed contains about 27.6% of fiber, of which 5.4% and 22.2% are soluble and insoluble fiber, respectively. The defatted hempseed meal contains about 42.6% of total fiber. Despite the abundant amount of fiber in the hempseed, the application of hempseed polysaccharides (HSP) is currently limited in the food industry. It is necessary to understand their physicochemical properties to extend their food applications. Hence, the objective of the current study is to investigate the physicochemical properties of soluble hempseed polysaccharides in comparison with flaxseed polysaccharides. The physicochemical properties, including molecular weight distribution, shape conformation, total sugar content, uronic acid content, rheological properties, and emulsification properties, were evaluated. The results indicated that the HSP contains about 33% uronic acids, 53% total sugars, and possesses an oblate ellipsoidal shape (Rg = 23.07 nm, Rh = 22.61 nm). Compared to flaxseed polysaccharides and pectin, the HSP showed a high surface active behavior at concentrations above 0.5% (w/v). The dynamic flow curves demonstrated the shear thinning behavior of HSP at the low shear rate range (0.01–10 s−1), followed by a Newtonian behavior at the high shear rate range. The HSP exhibited a weak gel property and an elastic nature. The emulsion stability of HSP and flax polysaccharide did not show a significant difference. The effects of pH and heat treatment on HSP stabilized emulsion were insignificant compared to flax polysaccharides. Finally, the freeze-thaw stability of HSP was inferior compared to flaxseed polysaccharides and pectin. The study has revealed that the HSP could be a potential emulsifying agent in the food system.

A Novel Approach for Semiautomated Three-Dimensional Quantification of Mitral Regurgitant Volume Reflects a More Physiologic Approach to Mitral Regurgitation

Quantification of mitral regurgitation (MR) by echocardiography is integral to assessing lesion severity and entails the integration of multiple Doppler-based parameters. These methods are founded primarily upon the principle of proximal isovelocity surface area (PISA), a two-dimensional (2D) method known to involve several assumptions regarding MR jet characteristics. The authors analyzed the results of a semiautomated method of three-dimensional (3D)-based regurgitant volume (RVol) estimation that accounts for jet behavior throughout the cardiac cycle and compared it with conventional 2D PISA methods for MR quantification. A total of 50 patients referred for transesophageal echocardiography for evaluation of primary (n=25) and secondary (n=25) MR were included for analysis. Three-dimensional full-volume color data sets were acquired, along with standard 2D methods for PISA calculation. A 3D semiautomated MR flow quantification algorithm was applied offline to calculate 3D RVol, with simultaneous temporal curves generated from the 3D data set. Three-dimensional RVol was compared with 2D RVol. Three-dimensional vena contracta area was also performed in all cases. There was a modest correlation between 2D RVol and 3D RVol (r=0.60). The semiautomated 3D approach resulted in significantly lower values of RVol compared with 2D PISA. Real-time and dynamic flow curve patterns were used for integral estimates of 3D RVol over the cardiac cycle, with a distinct bimodal pattern in functional MR and a brief and solitary peak in primary MR. Using a semiautomated 3D software for the quantification of MR allows the simultaneous calculation of 3D RVol with an automated generation of dynamic flow curves characteristic of the underlying MR mechanism. The present flow curve pattern results highlight well-known differences between MR flow dynamics in degenerative MR compared with functional MR.

Method and System for Testing the Working Characteristics of Vehicle Fuel Injector

Background: The vehicle fuel injector directly affects the power performance, emission characteristics and economic efficiency of the engine. At present, several testing standards are stipulated on accurate measurement of the working characteristics of fuel injectors. Objective: The purpose of this study is to provide an efficient patent about the method and system for testing the working characteristics of a vehicle fuel injector. Methods: Two key techniques are significant to establish a standard test environment. The patent about the pressure control approach and the injector driving method was proposed. The adaptive fuzzy PID approach was applied to control pressure. An adaptive multi-functional driver was designed and developed for both the voltage-driven and current-driven port fuel injectors. Results: The experiments on the two key technologies were conducted. During the dynamic flow test, the settling time using the system was 1ms. For the static flow test, the settling time was 1 s. The maximum changing rate of pressure fluctuation was 1%. Then, the system was verified by test on the flow characteristics and dynamic response of the voltage-driven and current-driven injectors. The linear deviation of each dynamic flow curve was between ± 3% to ± 6%. Furthermore, the deviation of the dynamic flow curves from the repeated test was small. The maximum deviation of the static flow results was less than 4% and the dynamic response of the injector varied with the change of the pressure. Conclusion: The system meets the requirements of the related standards. The experimental results prove that the system is stable and reliable.

Linear and nonlinear rheology of oil in liquid crystal emulsions

While the majority of experimental and numerical studies focus on yield stress fluids with short-range repulsive interactions, the effect of long-range interaction is rarely known. In this work, we studied the linear and nonlinear rheological behavior of a model oil in nematic liquid crystal emulsions, which exhibit long-range droplet-droplet interaction. The characteristic of long-range interaction, attractive at large droplet separation and repulsive at a small surface distance, was inferred from the morphology and thixotropy of emulsions. We suggested a model accounting for the plateau modulus purely due to the long-range repulsive interaction. We further illustrated that neither the yield stress nor the relaxation time followed a simple power-law scaling with respect to the distance to jamming. The rescaled steady and dynamic flow curves could not collapse on master curves above jamming transition when the long-range and short-range repulsive interactions contribute simultaneously.

Dynamic compressive response of electron beam melted Ti–6Al–4V under elevated strain rates: Microstructure and constitutive models

Cylindrical rods of Ti–6Al–4V (Ti64) alloy were additively produced using the electron beam melting (EBM) process in the horizontal and vertical directions. Optical microscopy, electron microscopy (scanning and transmission), X-ray diffraction (XRD), and electron backscatter diffraction (EBSD) techniques were employed to characterize the microstructure and phases of the EBM–Ti64 alloy. The microstructure consists of α and β phases, where in the vertical sample, the average α-width decreased, and the finer microstructure was formed. Both horizontal and vertical samples were subjected to several dynamic compression tests at various strain rates between 150 s−1 and 1100 s−1 using a Split-Hopkinson pressure bar apparatus to characterize the effect of the build direction. Peak stress increased with the increase in strain rate for both orientations. The dynamic compressive strength of the alloy in both directions was strain-rate dependent, where the maximum of 1880 MPa and 2000 MPa was attained for horizontal and vertical samples, respectively. Under similar loading conditions, the strength of the vertical specimens was consistently higher than that of the horizontal ones. This was attributed to the finer microstructure and near-parallel orientation of prior β-boundaries to the impact loading axis in the vertical samples. Furthermore, a constitutive mathematical model was developed to encompass the results of dynamic flow curves for both directions to interpret the elevated strain rate behavior of EBM–Ti64. Model predictions were in good agreement with the experimental data.

The study on calculating flow pressure for tight oil well

This paper presents a new method to calculate flow pressure for tight oil well with partial penetration fracture. The solution to the diffusivity equation can be obtained using dimensionless transformation, Laplace transformation, Fourier cosine transformation and other mathematical methods. The calculation results of relative simple system are in good agreement with Kuchuk and Brighan’s analytical solution, suggesting that this method in this paper is accurate. The pressure dynamic flow curve can be divided into four stages: transient flow, first linear flow, first radial flow, and boundary dominated flow. The effect of parameters including fracture orientation, fracture length, the degree of penetration, reservoir boundary anisotropy, reservoir boundary conditions and reservoir width on the pressure and pressure derivative was fully investigated in detail. The fracture length mainly affects the early linear flow, and permeability anisotropy mainly affects the mid-radial flow, and the degree of penetration in the reservoir and fracture orientation mainly affect the late spherical flow, and the boundary conditions and reservoir border width mainly affect the control flow. The method can be used to determine the optimal degree of opening shot, vertical permeability and other useful parameters.

Strain rate effects of dynamic compressive deformation on mechanical properties and microstructure of CoCrFeMnNi high-entropy alloy

In this work, the effects of strain rate on mechanical deformation and microstructural evolution of CoCrFeMnNi high-entropy alloy (HEA) under quasi-static and dynamic compression were investigated. The HEA exhibited high strain-rate sensitivity values (m = 0.028) of yield strength under quasi-static conditions. In particular, due to the viscous drag effect, the variation of yield strength with strain rate under dynamic compression was much larger than that under quasi-static compression. Microstructural analysis using electron backscatter diffraction shows profuse twinning under both conditions. The dynamically deformed specimens exhibited strongly localized deformation regions (i.e., adiabatic shear bands). The process of dynamic compressive behavior in this HEA is competitive between hardening by dislocation and twinning, and thermal softening. To analyze numerically the flow behavior of the HEA under dynamic conditions, the modified Johnson-Cook model considering adiabatic temperature rise was employed. The modified Johnson-Cook model offered good agreement with experimental results regarding dynamic flow curves of this HEA.

Influence of shear rheometer measurement systems on the rheological properties of microfibrillated cellulose (MFC) suspensions

Flow curve and viscoelastic measurements were performed on microfibrillated cellulose (MFC) suspensions of different solids content using both cylinder and cup (smooth and rough) as well as vane in cup geometries. To compare the data quantitatively from amplitude sweep measurements and dynamic flow curves several descriptors were newly introduced to parameterize the observed two-zone behaviour separated by a transition region. It was observed that the cylinder cup geometries are prone to erroneous effects like slip, wall depletion and/or shear banding. However, those effects were not observed when the MFC suspension was not stressed beyond the dynamic critical stress (yield) point, i.e. when still in the linear viscoelastic regime. The vane in cup system on the other hand, seems to be less affected by flow inhomogeneities. By following the rheological properties as a function of the MFC suspension solids content, it could be shown that the global property trends remained alike for all investigated measurement systems, despite the presence of erroneous effects in some geometries. The observed effects were linked to recent model hypotheses in respect to the morphology of MFC suspensions under changing shear situations.

Influence of Strain Rate, Temperature, Plastic Strain, and Microstructure on the Strain Rate Sensitivity of Automotive Sheet Steels

AbstractThis work identifies the influence of strain rate, temperature, plastic strain, and microstructure on the strain rate sensitivity of automotive sheet steel grades in crash conditions. The strain rate sensitivity m has been determined by means of dynamic tensile tests in the strain rate range 10−3–200 s−1 and in the temperature range 233–373 K. The dynamic flow curves have been tested by means of servohydraulic tensile testing. The strain rate sensitivity decreases with increasing plastic strain due to a gradual exhausting of work hardening potential combined with adiabatic softening effects. The strain rate sensitivity is improved with decreasing temperature and increasing strain rate, according to the thermally activated deformation mechanism. The m‐value is reduced with increasing strength level, this decrease being most pronounced for steels with a yield strength below 400 MPa. Solid solution alloying with manganese, silicon, and especially phosphorous elements lowers the strain rate sensitivity significantly. Second phase hardening with bainite and martensite as the second constituent in a ferritic matrix reduces the strain rate sensitivity of automotive sheet steels. A statistical modeling is proposed to correlate the m‐value with the corresponding quasistatic tensile flow stress.

Steady and Dynamic Shear Properties of Aqueous Polymer Solutions

The steady and dynamic shear properties of dilute aqueous solutions of Separan AP30, xanthan gum, carboxymethyl cellulose, and Polyox WSR301 at different concentrations and temperatures were investigated. These polymer solutions exhibit both shear thinning (“power‐law”) and elastic characteristics under steady and oscillatory measurements even at polymer concentrations as low as 50 ppm. The temperature and concentration superposition principles using reduced variables are applicable to both steady and dynamic shear data. The steady‐shear viscosity data are fitted with the Carreau viscosity equation. The dynamic results agree qualitatively with the trend predicted by the Zimm molecular model. However, the longest relaxation time evaluated from the dynamic flow curve is an order of magnitude longer than the predicted value from the Zimm theory. The disagreement could be attributed to the differences in the molecular weight distribution or polydispersity, ionic interaction, and solvent chemistry. The relatio...