THE EFFECT OF THICKENER ON THE RHEOLOGY OF COATING COLORS

The effect of type and amount of thickener on the shear and extensional rheological properties of paper coating colors was studied. A coarse delaminated kaolin clay was used as pigment and either a carboxy methylcellulose (CMC) or an associative gum was used as thickener. The shear properties were evaluated with a stress controlled rheometer and the extensional properties were obtained at high strain rates using an orifice flow meter. The apparent extensional viscosity was compared to the shear viscosity in terms of the Trouton ratio, which was shown to exceed considerably the theoretical value of 3 expected for Newtonian fluids. Suspensions formulated with the associative gum exhibited more pronounced strain hardening at high strain rates than those prepared with CMC.     

THE EFFECT OF THICKENER ON THE RHEOLOGY OF COATING COLORS

The effect of type and amount of thickener on the shear and extensional rheological properties of paper coating colors was studied. A coarse delaminated kaolin clay was used as pigment and either a carboxy methylcellulose (CMC) or an associative gum was used as thickener. The shear properties were evaluated with a stress controlled rheometer and the extensional properties were obtained at high strain rates using an orifice flow meter. The apparent extensional viscosity was compared to the shear viscosity in terms of the Trouton ratio, which was shown to exceed considerably the theoretical value of 3 expected for Newtonian fluids. Suspensions formulated with the associative gum exhibited more pronounced strain hardening at high strain rates than those prepared with CMC.     

A pressure drop correlation for low Reynolds number Newtonian flows through a rectangular orifice in a similarly shaped micro-channel

Current microfabrication methods mean that rectangular orifices in similarly shaped micro-channels are often found in microfluidic devices. The power required to overcome the pressure drop across such orifices is often of importance. In the contribution reported here, numerical results for low Reynolds number incompressible Newtonian fluid flow through rectangular orifice in similarly shaped micro-channel have been used to develop a correlation for pressure drop arising from the orifice. The correlation, which was motivated by theoretical developments, indicates that the pressure drop is proportional to the average velocity through the orifice, and a function of the orifice contraction ratio, length-to-width ratio and, most particularly, aspect ratio.     

Laminar mixing of shear thinning fluids in a SMX static mixer

Flow and mixing of power-law fluids in a standard SMX static mixer were simulated using computational fluid dynamics (CFD). Results showed that shear thinning reduces the ratio of pressure drop in the static mixer to pressure drop in empty tube as compared to Newtonian fluids. The correlations for pressure drop and friction factor were obtained at Re_MR?100. The friction factor is a function of both Reynolds number and power-law index. A proper apparent strain rate, area-weighted average strain rate on the solid surface in mixing section, was proposed to calculate pressure drop for a non-Newtonian fluid. Particle tracking showed that shear thinning fluids exhibit better mixing quality, lower pressure drop and higher mixing efficiency as compared to a Newtonian fluid in the SMX static mixer.     

Shear and extensional rheology and flow‐induced orientation of carbon nanofiber/polystyrene melt composites

The rheological behavior and morphology of polystyrene/carbon nanofiber (PS/CNF) composites in their melt phase have been characterized through experimental measurements. Viscosity measurements of the PS/CNF composites in the linear viscoelastic regime show the ratio of the transient extensional viscosity to the transient shear viscosity to be greater than three, the Trouton ratio. This behavior is due to differences in the flow‐induced orientation of CNFs in shear and extensional flow. The orientation development of the CNFs in shear and extensional flow was analyzed through a method utilizing transmission electron microscopy and was used to explain observed rheological phenomena. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Shear and extensional properties of short glass fiber reinforced polypropylene

Shear and extensional properties of a commercial short glass fiber reinforced polypropylene were carefully investigated using commercial rheometers and a novel on‐line rheometer. This on‐line slit rheometer, installed on an injection molding press, has been designed to measure the steady shear viscosity, the first normal stress difference, and the apparent extensional viscosity of polymer melts and composites for high strain rates up to 10⁵ s⁻¹ in shear and 200 s⁻¹ in extension. Our results show that the steady‐state viscosity measurements using the on‐line rheometer are in excellent agreement with those obtained using commercial rheometers. The steady‐state and the complex viscosities of the composites were found to be fairly close to that of the matrix, but the Cox‐Merz rule was not verified for the composites at high rates. The elasticity of the composites was found to be equal to that of the polypropylene matrix. The apparent extensional viscosity was obtained from the pressure drop in the planar converging die of the slit rheometer using the analyses proposed by Cogswell [1] and Binding [2]. The extensional viscosity of the polypropylene was found to be much larger than the shear viscosity at low strain rates with a Trouton ratio of about 40 that decreased rapidly with increasing strain rate down to the value of 4 at 200 s⁻¹. The extensional viscosity of the composites was also found to be close to that of the matrix, with values 35 and 5% larger for the 30 and 10 wt% reinforced polypropylenes, respectively. These results are compared with the predictions of the Goddard model [3], which are shown to overpredict our experimental results. POLYM. COMPOS. 26:247–264, 2005. © 2005 Society of Plastics Engineers.     

Rheological characterisation of hydroxyapatite filled polyethylene composites. Part 1 – Shear and extensional behaviour

Abstract

The shear and extensional properties of injection moulding grade hydroxyapatite–polyethylene composites developed for orthopaedic applications have been studied. The composite was prepared without processing aids owing to concerns over the potential biological responses to such additives. The composite containing 20 vol.-% hydroxyapatite filler showed typical pseudoplastic behaviour. However, that containing 40 vol.-% hydroxyapatite filler tended to exhibit yield. The Maron–Pierce equation was found to be useful in predicting the viscosities of the composite systems. The activation energy of the composite and the unfilled polymer were equal, indicating that the 20 vol.-% system exhibits the same flow mechanism as the unfilled polymer. A qualitative assessment of extensional properties was made following Cogswell's method. The extensional stress of the unfilled polymer decreases with increasing temperature whereas the composites behave in a complex manner. For all the systems the Trouton ratios tend to increase with apparent shear rates. The Trouton ratio also indicates that at higher temperatures the flow of these composites is dominated by extensional properties.     

The effect of shear‐thickening on the stability of slot‐die coating

Slot‐die coating is an economical roll‐to‐roll processing technique with potential to revolutionize the fabrication of nano‐patterned thin films at high throughput. In this study, the impact of shear‐thickening of the coating fluid on the stability of slot‐die coating was investigated. For the coating fluid, a model system fumed silica nanoparticles dispersed in polypropylene glycol was chosen. These dispersions exhibit shear and extensional thickening characterized through steady shear and capillary break‐up measurements. The critical web velocity for the onset of coating defect for different flow rates was measured, while the type of coating defect was visualized using a high speed camera. For the shear thickening particle dispersions, the coating failed through the onset of a ribbing instability. The critical web velocity for the onset of coating defect was found to decrease with increasing particle concentration and increasing fluid viscosity. The minimum wet thickness was studied as a function of capillary number for the particle dispersions and compared with a series of Newtonian fluids with similar viscosities. In all cases, shear‐thickening behavior was found to stabilize coating by reducing the minimum wet coating thickness when compared against a Newtonian fluid with similar viscosity at the same capillary number. Conversely, the shear‐thinning fluids tested destabilized the coating by increasing the minimum wet thickness when compared against a Newtonian at the same capillary number. The impact of shear‐thickening on slot‐die coating was further studied by quantifying the evolution of the ribbing instability with increasing web speed and by conducting tests over a wide range of coating gaps. © 2016 American Institute of Chemical Engineers AIChE J, 62: 4536–4547, 2016     

RHEOLOGICAL CHARACTERIZATION OF NON-NEWTONIAN FLUIDS WITH A NOVEL VISCOMETER

A hydrostatic head viscometer and its novel viscosity equation were developed to determine flow characteristics of Newtonian and non-Newtonian fluids. The objective of this research is to test capabilities of the hydrostatic head viscometer and its novel non-Newtonian viscosity equation by characterizing rheological behaviors of well-known polyethylene oxide aqueous solutions as non-Newtonian fluids with 60 wt.% sucrose aqueous solution as a reference/calibration fluid. Non-Newtonian characteristics of 0.3-0.7 wt.% polyethylene oxide aqueous solutions were extensively investigated with the hydrostatic head viscometer and its non-Newtonian viscosity equation over a 294-306 K temperature range, a 0.14-40 Reynolds number range, and a 55-784 s^-1 shear rate range at atmospheric pressure. Dynamic viscosity values of 60 wt.% sucrose aqueous solution were determined with the calibrated hydrostatic head viscometer and its Newtonian viscosity equation over a 3-5 Reynolds number range at 299.15 K and atmospheric pressure and compared with the literature dynamic viscosity value.     

RHEOLOGICAL CHARACTERIZATION OF NON-NEWTONIAN FLUIDS WITH A NOVEL VISCOMETER

A hydrostatic head viscometer and its novel viscosity equation were developed to determine flow characteristics of Newtonian and non-Newtonian fluids. The objective of this research is to test capabilities of the hydrostatic head viscometer and its novel non-Newtonian viscosity equation by characterizing rheological behaviors of well-known polyethylene oxide aqueous solutions as non-Newtonian fluids with 60 wt.% sucrose aqueous solution as a reference/calibration fluid. Non-Newtonian characteristics of 0.3–0.7 wt.% polyethylene oxide aqueous solutions were extensively investigated with the hydrostatic head viscometer and its non-Newtonian viscosity equation over a 294–306 K temperature range, a 0.14–40 Reynolds number range, and a 55–784 s^?1 shear rate range at atmospheric pressure. Dynamic viscosity values of 60 wt.% sucrose aqueous solution were determined with the calibrated hydrostatic head viscometer and its Newtonian viscosity equation over a 3–5 Reynolds number range at 299.15 K and atmospheric pressure and compared with the literature dynamic viscosity value.     

Effect of elongational viscosity on axisymmetric entrance flow of polymers

A finite element simulation of the flow in a channel with an abrupt contraction is presented. The effects of the shear and elongational viscosities of a polymer on the entrance flow are analyzed employing a truncated power‐law model. The power‐law index and the strain rate characterizing the transition from Newtonian to power‐law behavior for the elongational viscosity are treated as being independent of the values of these two parameters for the shear viscosity. The effect of flow rate on entrance flow is also analyzed. It is confirmed that the Trouton ratio is important in determining the recirculating vortex and the extra pressure loss in entrance flow. Extra pressure loss and vortex length predicted by a finite element simulation of entrance loss are compared with the corresponding predictions from Binding's approximate analysis.     

Energy Dissipation Rates of Newtonian and Non‐Newtonian Fluids in a Stirred Vessel

Energy dissipation rates of water and glycerol as Newtonian fluids and carboxyl methyl carbonate solution as non‐Newtonian fluid in a stirred vessel are investigated by 2D particle image velocimetry and compared. Mean velocity profiles reflect the Reynolds (Re) number similarity of two flow fields with different rheological properties, but the root mean square velocity profiles differ in rheology at the same Re‐number. Energy dissipation rates are estimated by direct calculation of fluctuating velocity gradients. The varying energy dissipation rates of Newtonian and non‐Newtonian fluids result from the difference in fluid rheology and apparent viscosity distribution which decides largely the flow pattern, circulation intensity, and rate of turbulence generation.     

Elongational,hysteresis, and oscillatory flows of complex fluids

The simple model proposed earlier to describe te rheological properties of complex fluids is used to calculate (a) the extensional viscosity, (b) the hysteresis loops, and (c) the complex viscosity. It has been found that the rheological properties predicted by the model agree with experimental observations. It is shown that for some viscoelastic fluids the extensional viscosity is always finite and for some other fluids the extensional viscosity tends t infinity at finite extensional rate. In the latter case, steady flow is not attainable. The shape of the hysteresis loops depends on the maximum shear-rate. It also depends on the material properties. In a small amplitude oscillatory flow, our model reduces t a linear viscoelastic fluid.     

Steady flow of ionic liquid through a cylindrical microfluidic contraction-expansion pipe: Electroviscous effects and pressure drop

Electroviscous effects in steady, pressure-driven flow of a symmetric 1:1 electrolyte in a cylindrical microfluidic 4:1:4 contraction-expansion at low Reynolds number are investigated numerically by solving the field equations using a finite volume method. Predicted profiles of electrical potential, charge distribution, pressure drop and apparent viscosity are qualitatively similar to those for the slit-like contraction-expansion studied previously by the authors. However, the changes in electrical potential and pressure drop along the channel are greater than those for a corresponding slit-like geometry. The apparent viscosity is lower in the cylindrical contraction-expansion than it is in the equivalent slit-like geometry, whereas the converse is found for uniform channels except when the electrical double layers (EDLs) overlap. As for the slit-like case, a simple model is developed to calculate the pressure drop, and hence the apparent viscosity, by adding the pressure drops over the inlet, outlet and contracted sections of the channel (based on the fully developed flow in a uniform pipe), and an extra pressure drop due to contraction-expansion using the low Reynolds number analytical solution for a circular orifice. For the parameter range considered, the predictions of the simple model overestimate the apparent viscosity by up to 5-12% compared with that obtained by a finite volume numerical solution. The differences become smaller when the thickness of the EDL or the surface charge density are reduced.     

Shear and extensional flow of a thermotropic liquid crystalline polymer

The flow of a thermotropic liquid crystalline polymer (unfilled and glass fiber filled) was studied using a capillary rheometer and an instrumented injection molding machine. Despite different thermal histories, the techniques gave similar results. From 330 to 350°C, viscosity was independent of temperature. At 340°C, where most measurements were carried out, pronounced shear-thinning occurred and the shear flow curves were nonlinear, the power law exponent decreasing from 0.51 at a shear rate of 10 s⁻¹ to 0.35 at 10⁴ s⁻¹. A previously reported model was used to derive elongational flow curves from die entry pressure data. Because of the nonlinearity of the flow curves, quadratic log-stress vs. log-strain rate plots were needed to model behavior over the strain rate region studied. The elongational flow curves were similar in shape to the shear flow curves, with an effective Trouton ratio of 30. Despite orientation and structure present in the melt, the extensional viscosities and Trouton ratios were within the range found with normal thermoplastic melts. The results suggest that extensional flow may be inhomogeneous, the flowing units possibly being partially ordered domains.     

表面活性剂虫状胶束流体中颗粒沉降负尾迹模拟

颗粒在剪切稀释黏弹性表面活性剂形成的蠕虫状胶束流体中沉降时会产生负尾迹,负尾迹的形成对该种复杂流体与固体颗粒之间的相互作用具有重要影响。基于Giesekus本构方程,采用POLYFLOW软件模拟了黏弹性表面活性剂(Viscoelastic Surfactant, VES)蠕虫状胶束流体中单颗粒的沉降过程,分析了流体松弛时间和迁移因子对颗粒周围速度场及应力场的影响,重点研究了颗粒尾部速度负尾迹的产生原因及其对颗粒曳力的影响。结果表明,Giesekus本构方程能够描述VES流体的非线性剪切变稀行为和弹性导致的拉伸变形。流体弹性导致颗粒尾部产生较大的拉伸变形,剪切稀化和流体弹性的共同作用使颗粒尾部产生拉伸变形,导致负尾迹出现。表征流体弹性的De(黛博拉数)越大,流体拉伸黏度的Tr(特劳顿数)越小,负尾迹越长。负尾迹的出现使VES流体中颗粒所受曳力减小,沉降速度开始增加。模拟结果为此种流体的进一步应用提供了一定的研究基础。     

AN EXPERIMENTAL INVESTIGATION OF INITIATION AND CESSATION OF FLOW IN A TUBE FOR NEWTONIAN FLUIDS

An experimental investigation of sudden initiation and cessation of laminar flow in a tube following the opening and closure of a direct acting solenoid valve is reported for Newtonian fluids in the viscosity range 0.9 ≤ μ ≤ 39.5 centipoise. A non-contact probing Laser Doppler Anemometer and a high speed data logging system are used to make local axial velocity measurements at 85 tube diameters from the entrance to a test section, 1.36 cm I.D. and 1.4 meters long. Some qualitative measurements of the pressure gradient over the test section are also made.

The results show that for Newtonian fluids, with μ ≤ 27.1 cp, the sudden opening or closure of the solenoid valve is not equivalent to a step input in either pressure drop or flow rate. Both show overshoots, the magnitude of which decreases with increasing viscosity of the fluid. The normalized time for a 90% development or decay increases with the viscosity of the fluid. For fluids with μ ≥ 39.5 cp, the behavior appears to approach that due to a step input in pressure gradient.     

PIV技术测试聚合物流体拉伸流动的实验研究

针对低相对分子质量、低黏度的牛顿流体（如聚异丁烯）和非牛顿流体（如3 %苯甲酸钠溶液）,采用粒子成像速度仪（PIV）系统测试了2种流体在同一流率下流经渐变收缩流道时的速度分布,并研究比较了壁面处的纯剪切流动与流道中心轴线上的拉伸流动。通过实验测试与有限元模拟比较发现,牛顿流体和非牛顿流体的速度分布形态具有一定的差异。在确定速度分布的情况下,根据渐变收缩流动的特点,可以得到流体流动时中心轴线上的拉伸速率和边界处的剪切速率。     

AN EXPERIMENTAL INVESTIGATION OF INITIATION AND CESSATION OF FLOW IN A TUBE FOR NEWTONIAN FLUIDS

An experimental investigation of sudden initiation and cessation of laminar flow in a tube following the opening and closure of a direct acting solenoid valve is reported for Newtonian fluids in the viscosity range 0.9 ≤ μ ≤ 39.5 centipoise. A non-contact probing Laser Doppler Anemometer and a high speed data logging system are used to make local axial velocity measurements at 85 tube diameters from the entrance to a test section, 1.36 cm I.D. and 1.4 meters long. Some qualitative measurements of the pressure gradient over the test section are also made.

The results show that for Newtonian fluids, with μ ≤ 27.1 cp, the sudden opening or closure of the solenoid valve is not equivalent to a step input in either pressure drop or flow rate. Both show overshoots, the magnitude of which decreases with increasing viscosity of the fluid. The normalized time for a 90% development or decay increases with the viscosity of the fluid. For fluids with μ ≥ 39.5 cp, the behavior appears to approach that due to a step input in pressure gradient.     

聚乳酸熔体流变性的研究

研究了聚 L -乳酸熔体的流变性 ,并与 PET熔体流变性进行了比较 ,发现聚 L -乳酸流体为切力变稀流体 ,当温度达 2 2 5℃ ,流动曲线上出现了第二牛顿区 ;粘流活化能高达 12 3k J/m ol;随着熔体温度的增大 ,其流动曲线下移 ,表观粘度下降 ,非牛顿指数增大 ,在 2 0 5～ 2 15℃区域内上升速率较大 ,其结构粘度指数变小 ,同时特性粘数的下降高达 39%。