Rheological measurements capillary viscometers

Various methods are used to examine the viscosity characteristics of metallized gels. Two types that have received extensive application are the cone and plate viscometer and the capillary viscometer. Both instruments can measure rheological characteristics at high shear rates, and the former is useful for low shear rate measurements as well. 

In a pressure capillary viscometer, such as a rheological die, pressure is used to force fluid through a capillary tube at constant volumetric flow rate Q, as shown in Figure 6.4. The pressure difference AP is measured between points A and B spaced apart a distance 1 along the tube. The basic rheological equations are as follows for shear stress and shear rate taken to be very near the wall in a tube of radius r ... 

Frequently used single-point viscosity tests in the starch plant are orifice pipettes,56 orifice funnels,57 the Hot Scott viscometer, and various methods to determine alkaline fluidity.58 For absolute measurements of the rheological properties, rotating viscometers with coaxial cylinders are used.59 The paper industry uses mainly the Brookfield viscometer and the Hercules viscometer for determining shear-dependent viscosity, pseudoplasticity, and thixotropy. Oscillatory and capillary viscometers are used for more detailed viscosity characterization, such as yield value, elastic properties, and viscoelasticity.60... 

Factors have been reported in the literature (Johnston and Brower 1966) for the conversion of Brookfield viscometer scale readings to yield value or viscosity. Saravacos (1968) has also used capillary viscometers for rheological measurements of fmit purees. 

The rheological properties of slips are usually measured by rotary viscomete while capillary viscometers are used for routine checks. 

Instrumental quality control before, during, and after manufacture is one area to which food rheology makes important contributions. For example, the measurement of apparent viscosity and yield stress of ketchup helps to predict how well tomato ketchup drains from a bottle. A number of tests have been developed using either basic rheological instruments (rotational viscometer, capillary viscometers, etc.) or instruments simulating the situation in which the rheological properties are of importance (Bostwick... 

The main focus of the measurement programme was the rheological measurements with the high-pressure capillary viscometer. In addition, a number of measurements were performed with the aim of permitting statements about the dispersion state (pyrolysis, microscopic investigations) and determining (conductivity measurements). 

Rheological measurements were carried out using a capillary viscometer and the studies were conducted with and without application of nltrasonic oscillation. The results obtained are shown in Figure 5.3 and indicate the dependence of the effective flow state (p f on the stress shear. The definition of the toughness depends on the arguments about the influence of the ultrasonic oscillations using the expression ... 

Consequently, the rheological measurements of MPSs should be carried out such that the dimension of the flow channel is significantly larger than the size of the flow element. For example, the relative viscosity, jjr, of diluted spherical suspensions measured in a capillary instrument depends on the (d/D) factor, where 7) is the sphere diameter and d that of the capillary—for d 107), the error is around 1% [Happel and Brenner, 1983]. Thus, if 1% error is acceptable, the size of the dispersion should be at least 10 times smaller than the characteristic dimension of the measuring device (e.g., diameter of a capillary in capillary viscometers, distance between stationary and rotating cylinders or plates). Following this recommendation is not always possible, which lead to the decline and fall of continuum mechanics [Tanner, 2009]. 

For characterization of polymer blends, low strain dynamic rheological measurements are preferred over steady-state shearing (e.g., in a capillary viscometer). Since... 

As an example, consider the data aspect of the situation. The first requirement in applying rheology is, of course, the need for rheological data. Such data can be determined from sophisticated rheological devices, such as capillary viscometers and rotational devices. Data, however, can also be determined from operating process data or by making certain in-line measurements. 

Based on this approach, the apparent viscosity of the polymer solution, uapp corrected if the apparent viscosity of the corresponding hypothetical Newtonian fluid flowing in the same capillary with the same total pressure drop is known. There are two procedures to determine the apparent viscosity of such a Newtonian fluid. The direct experimental procedure is to measure the apparent viscosity of the appropriate Newtonian fluid in the high-shear capillary viscometer. This experimental calibration technique was employed by Graham and co-workers (20). Although this experimental technique is direct, in practice it is difficult to perform. It is difficult to find a Newtonian fluid with the identical rheological properties as exhibited by the polymer solution at low-shear rates. 

The isothermal rheological measurements (at T = 190, 205 and 220/C) were carried out in a capillary viscometer, HKV 7901, at shear rates varying from 10 to 2500 (1/s). The constant-stress viscosities of the component pol)miers and their blends were determined from the primary flow curves t = f( y ). These were used to calculate the constant-stress viscosity ratios and capillarity numbers. 

The rheology of K30-water solutions are characterized by measurements with rotational and capillary viscometers (Fig. 19.1 left). The measurements have been conducted by Schroder et al. [6]. The elongational deformation mechanisms of PVP-water solutions have been determined by a CaBER-device (Fig.19.1 right). 

Figure 14.10 Viscosity functions for samples A, B, and C at 150°C. la, IVa Weissenberg rheogoniometer (la measures at 130°C and shifts the data) II Kepes rotational rheometer (cone-and-plate) Ih, IVb capillary viscometers. MF denotes the onset of melt fracture. (From Ref. 4.) (Reprinted with permission from Meissner, J. Basic Parameters, Melt Rheology, Processing and End-Use Properties of Three Similar Low Density Polyethylene Samples, Pure Appl. Chem., vol. 42, pp. 553-612, 1975.)...

In a series of experiments on the flow of flocculated kaolin suspensions in laboratory and industrial scale pipelines(26-27-2Sl, measurements of pressure drop were made as a function of flowrate. Results were obtained using a laboratory capillary-tube viscometer, and pipelines of 42 mm and 205 mm diameter arranged in a recirculating loop. The rheology of all of the suspensions was described by the power-law model with a power law index less than unity, that is they were all shear-thinning. The behaviour in the laminar region can be described by the equation ... 

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