Rotational viscosimeter

The p, p, K and n are usually determined with the Fann rotational viscosimeter. The Herschel and Buckley model is not considered in this manual. 

Another well documented, but less widely used method for formulation development is the measurement of electrokinetic properties [14]. These tests require more disdnc-tive/elaborate sample preparation and are mosdy restricted to use during development. Also widely used and relied on are rheological measurements. The scope of rheological measurements ranges from viscosity measurements to the determination of yield points or oscillatory properties, such as the G and G -modules [15]. Since suspoemulsions are not ideal viscous but mostly viscoelastic or dilatant, a wide range of characterization techniques exists. Instrumentation required for this are simple rotary viscosimeters (Brookfield) or more sophisticated stress or shear controlled rotational viscosimeters. 

Measurement and analysis. The viscosity of tomato juice was measured using Tokyokelkl BH type disc rotating viscosimeter. 

Figure 6 represents the relationship between tomato juice viscosity and flow velocity. The measurement was done with the juice prepared from canned paste, using a disc rotating viscosimeter. The value, viscosity multiplied by velocity was nearly Independent of the velocity. This suggests that the effect of flow velocity on the pressure drop would be small. This allows the variation of juice feed velocity in a wide range without significant change in pressure drop. 

Figure 7. The effect of tomato juice concentration on the viscosity observed at 20°C by using a disc-rotating viscosimeter...

The viscosity of a bioprocess liquid is an important factor, affecting mass transfer, heat transfer, and power consumption. It is affected by the concentrations and types of microorganisms, substrates, products, and solids present in the liquid, and can vary during a fermentation or separation process. Unfortunately, on-line viscosity measurements are difficult, especially when significant amounts of air bubbles and suspended solids are present, and thus viscosity probes are not in widespread use. Sensors that have been applied for viscosity determination (usually in laboratory studies) are often various types of rotational viscosimeters [42]. 

In situ rotational viscosimeters have also been used for biomass estimation [135]. This technique utilizes the fact that the viscosity of the medium increases with increasing biomass concentration. However, the application of such devices is relatively rare. 

Viscosity measurement (xy), density (p), and conductivity (k) The measurement of PCM viscosity is a key point in flowage, taking into account that the higher the temperature, the lower the viscosity. Also, it is important to measure it at different temperatures with a rotation viscosimeter. An increase of the viscosity will give rise to the increase of pump energy consumption, which will counteract the positive effect to some extent. 

There are roughly three classes of viscosimeters available the capillary viscosimeter, the rotational viscosimeter, and the falling-ball viscosimeter. Both the capillary and the rotational viscosimeters are built in different versions that allow for the exact determination of the viscosity in well-defined flow fields. Especially rotational viscosimeters allow the exact adjustment of a constant flow profile, thus are available in high precision and expensive versions as rotational rheometers. Capillary viscosimeters are the best compromise between the exact determination of viscosity and a well-priced measurement device, and are therefore the most commonly found type of viscosimeters. Both rotational and capillary viscosimeters are available in simple and inexpensive versions as Brookfield viscosimeters and flow... 

According to DIN 53018, simple rotational viscosimeter have a coaxial cylinder system with a cup (inner radius R ) and a cylinder with an outer radius Rj and a length h, that is lowered into the cup. For the Couette system, the outer cup is moved and the measurement of the torque T takes place at the inner cylinder. For the Searle system on the other hand, the inner cylinder is moved. 

Because of centrifugal forces in the Searle System, crosscurrents can arise, that are called Taylor vortices. Couette Systems on the other hand have the disadvantage that temperature control of the rotating outer cylinder is achieved only with complicated equipment. Most rotational viscosimeters are therefore built in the Searle Type. 

The option of shear rate control in rotational viscosimeters makes it possible to detect shear rate dependent flow phenomena. Variants with high-precision motors and torque sensors are called rheometers and are used in research projects above and beyond the viscosimetry (see also 115, 17, 18]). In these instruments, other measurement systems besides the cylinder geometries are used, that are described in the following chapters. 

Brookfield viscosimeters also belong to the group of rotational viscosimeters. In contrast to the devices described earlier, this viscosimeter does not generate a defined shear field. The Brookfield viscosimeter consists mainly of a disc or a pin that is rotating with a defined velocity in the sample fluid. The torque that is required to achieve this rotational speed directly yields a viscosity through comparison with a calibration fluid. The range of measurable viscosities can be adjusted by variation of the disc geometry. 

A plot of red against c+iCy (where K is an arbitrary constant) allows for a better determination of the intersection with they-axis for the determination of the intrinsic viscosity (see Fig. 5.9). The rotational viscosimeters introduced in Chap. 3 have the possibility to vary the shear rate over a wider range and are able to allow for measurements at a defined and constant shear rate. 

Figure 1 Melt viscosity (rotation viscosimeter, shear rate 3.27 s ) in function of the weight-average molecular weight (M ) for various aPP fractions.

The shift of the resonance frequency due to the viscous adjacent medium can be used in determining the viscosity-density product of the adjacent layer. Thus, the viscosity of solutions can be determined by using usually small volumes of liquids when compared to typical rotational viscosimeters. 

A rotational viscosimeter and an Engler Viscoimeter were employed to measure the polymer latex viscosity. The surface tension was measured by the bubble pressure method at 25 + 0.10°C. 

The dispersion of low-substituted, acetylated starches in water increased as the number of acetate groups was increased and as the temperature was raised. The viscosity of starch-acetate pastes was lower than that of native starch pastes at all temperatures. The viscosity decreased until an acetyl content of 2.36% was reached, after which it changed only slightly. The reduced ability of starch acetates to form gels could be expressed in terms of the ratio of the viscosities at low and high temperatures. A rotation viscosimeter Rheotest was used to study the viscosities and the rheological properties of starch acetates. 

Rotation viscosimeter Shear flow within a channel required torque Newtonian/non- Newtonian fluids (e.g., polymeric solutions, VES) Costly... 

Dynamic viscosity of geopolymer resins was measured intermittently (every 15 minutes) with rotation viscosimeter Reotest 2 at 20°C. Between subsequent measurements resin was not stirred... 

FIGURE 4 A schematic of die rotational viscosimeter. N - sample, H - electro-magnet,... 

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