Viscometer, Brookfield rotational

OtherRota.tiona.1 Viscometers. Some rotational viscometers employ a disk as the inner member or bob, eg, the Brookfield and Mooney viscometers others use paddles (a geometry of the Stormer). These nonstandard geometries are difficult to analy2e, particularly for an infinite bath, as is usually employed with the Brookfield and the Stormer. The Brookfield disk has been analy2ed for Newtonian and non-Newtonian fluids and shear rate corrections have been developed (22). Other nonstandard geometries are best handled by determining iastmment constants by caUbration with standard fluids. 

Set the viscometer to rotate at 20 rpm, and allow the spindle to rotate until a constant dial reading is obtained. The viscosity, in centipoise, is the dial reading on the 0 to 100 scale multiplied by the appropriate factor (for a Brookfield RVF, spindle No. 4, 20 rpm, the factor is 100). 

Probably the most widely used type of viscometer in the food industry is the Brookfield rotational viscometer. An example of this instrument s application to a non-Newtonian food product is given in the work of Sarava-cos and Moyer (1967) on fruit purees. Viscometer scale readings were plotted against rotational speed on a logarithmic scale, and the slope of the straight line obtained was taken as the exponent n in the following equation for pseudoplastic materials ... 

Viscosity There are many different methods of determining the viscosity of a fluid, however, the quickest method for running routine QC checks is to use a Brookfield rotational viscometer either the RV or LV models are suited to the range of viscosities normally encountered for magnesium hydroxide slurry. 

While various methods and equipment can be used to measure viscosity, the most common uses the Brookfield viscometer (Fig. 7.1). ASTM D2196, Rheological Properties of Non-Newtonian Materials by Rotational (Brookfield) Viscometer, covers this method for Model LVF and Model RVF viscometers. Brookfield LV viscometers are used for low-viscosity materials, RV for medium-viscosity formulations, and HV for high-viscosity formulations. Test Method ASTM D2556, Apparent Viscosity of Adhesives HavingShear-Rate Dependent Flow Properties also specifies... 

S. Flow Properties of a Non-Newtonian Fluid from Rotational Viscometer Data. Following are data obtained on a fluid using a Brookfield rotational viscometer. 

The viscosity (cps) of samples was measured with a digital viscometer (Brookfield, USA) at the rotation speed of 100 rpm with a No. 21 spindle. 

The resulting reaction mixture (8.0 ml) was transferred into the Teflon cup reservoir of a Brookfield LVDVTI-PRO digital rotational viscometer (Brookfield Engineering Labs. Inc., Middleboro, MA, USA). Recording of the viscometer ontpnt parameters started 2 min after the onset of the experiment. The changes of dynamic viscosity of the system were measured at 25.0 0.1°C at 3-min intervals for up to 5 h. The viscometer Teflon spindle rotated at 180 rpm, i.e., at the shear rate of 237.6 s [26]. 

The Cannon Instmment Company produces a line of rotational viscometers, most of which are quite specialized, eg. Cold Cranking Simulators (ASTM D5293) and Mini-Rotary viscometers (ASTM D3829 and D4684) for automotive engine oils. They also have a general use instmment similar to Brookfield s basic viscometer. 

The Nametre Rotary B rotational viscometer measures torque in terms of the current needed to drive the d-c motor at a given speed while a material is under test. The standard sensors are coaxial cylinders or Brookfield disk-type spindles, but a cone—plate system is also available. The viscosity range for the coaxial cylinder sensors is 5 to 5 x 1(T mPa-s, and the maximum shear rate is 200. ... 

Hydrolysis rate measurements. Hydrolysis rates were examined by mixing polymer solutions with hydrochloric acid, in apparatus previously described (5). Solutions of polymer and acid are mixed rapidly, and the torque on a rotating PTFE coated fork, attached to a Brookfield LVTD viscometer, recorded as a function of time. Decreases in viscosity were approximated to first-order, and half-lives for viscosity loss calculated. 

The viscosity of a liquid can also be determined by measuring the torque needed to rotate a cylinder in the liquid. Brookfield viscometers and rheometers fall into this class of instrument (Fig. 3.7). The viscometer measures the torque produced when a spindle is rotated at constant velocity in a liquid. The Rheometer produces a constant torque... 

A number of techniques have been developed to measure melt viscosity. Some of these are listed in Table 3.8. Rotational viscometers are of varied structures. The Couette cup-and-bob viscometer consists of a stationary inner cylinder, bob, and an outer cylinder, cup, which is rotated. Shear stress is measured in terms of the required torque needed to achieve a fixed rotation rate for a specific radius differential between the radius of the bob and the cup. The Brookfield viscometer is a bob-and-cup viscometer. The Mooney viscometer, often used in the rubber industry, measures the torque needed to revolve a rotor at a specified rate. In the cone-and-plate assemblies the melt is sheared between a flat plate and a broad cone whose apex contacts the plate containing the melt. 

The ageing test measures the torque necessary to induce the rotation of a special spindle in the slurry. The measure must be done before the first rotation is completed in order to prevent destruction of the gel network. We measure gel after 25 seconds using a Brookfield viscometer with a special spindle (Helipath type), rotating at 1 rpm. 

For viscometers having a cup-to-bob diameter ratio which is essentially infinite, as for the case of the Brookfield Synchrolectric cylindrical-bob viscometers rotating in a large beaker or tank, the shear rate at the bob is given (A3, Kl) by the relation... 

Since the apparent viscosity of a non-Newtonian fluid holds only for the shear rate (as weii as temperature) at which it is determined, the Brookfield viscometer provides a known rate of shear by means of a spindle of specified configuration that rotates at a known constant speed in the fluid. The torque imposed by fluid friction can be converted to absolute viscosity units (centipoises) by a multiplication factor. See viscosity, shear stress. The viscosities of certain petroleum waxes and wax-polymer blends in the molten state can also be determined by the Brookfield test method ASTM D 2669. 

Two Brookfield viscometers were used to collect the data necessary for rheologic property studies of wet grains a Brookfield RVDV III viscometer with a cone-and-plate spindle and a Brookfield HBDV III viscometer with a double helical ribbon impeller attachment. The Brookfield RVDV III had a full-scale torque of 7187 dyn-cm, and the HBDV III had a full-scale torque of 57,496 dyn-cm. Each viscometer had a maximum rotational speed of 250 rpm. Both viscometers had accuracy limits of 5% full-scale torque. 

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... 

Viscosities of liquid epoxy systems are usually measured with a rotating spindle instrument, such as a Brookfield viscometer. Solid resins are usually dissolved in solvent for viscosity measurement by these instruments. Temperature and spindle speed are important... 

The most popular viscosity test for products ranging in viscosity from 50 to 200,000 cP uses a rotating spindle instrument such as the Brookfield viscometer. The equipment used for this measurement is shown in Fig. 20.1. The instrument measures the resistance of the fluid to a spindle of certain size that is rotating at a predetermined rate. The method is relatively simple and quick. It can be adapted to either the laboratory or production floor. 

Measuring Viscosity Several common methods are available for measuring viscosity. Two very common ones are the use of capillary tubes such as Ubbelohde, Ostwald, or Cannon-Fenske viscometer tubes and the use of a rotating spindle such as the Brookfield viscometer. 

Apparatus Use a Brookfield Model LV series viscometer, analog or digital, or equivalent type viscometer for the determination of viscosity of aqueous solutions of cellulose gum within the range of 25 to 10,000 centipoises at 25°. Rotational viscometers of this type have spindles for use in determining the viscosity of different viscosity types of cellulose gum. The spindles and speeds for determining viscosity within different ranges are tabulated below. 

The behavior of melt viscosity of sulfur-dicyclopentadiene solutions is of obvious interest from the point of sprayable coatings. The melt viscosity behavior has been reported recently, but only qualitatively and over a narrow range of compositions (18). The viscosity of sulfur measured by the capillary method by Bacon and Fanelli (19, 20) is considered to be the best (21). Recently, however, the viscosity of sulfur has been measured by an apparatus containing an electric motor and a rotating cylinder (22). Viscosity of the sulfur-DCP solutions are measured here with the help of a Brookfield synchro-lectric viscometer, which is of the later kind. Viscosity measurements have been carried out to follow the copolymerization reaction and to analyze the viscosity behavior. 

Dense-phase flow properties can be predicted by measuring the viscosity and deaeration rate of a fluidized bed in a laboratory test (117). This method appears to be especially useful for evaluating the flow characteristics in standpipes. The viscosity is measured by means of a Brookfield viscometer, which consists of a cylindrical wire-screen spindle rotated about its axis by an electric motor through a torsion spring. The torque required to rotate the spindle is measured by displacement of the... 

Pseudoplastic and thixotropic liquid detergents as emulsions are the subjects of U.S. Patent 5,851,979. Equilibrium viscosity values measured using a Brookfield viscometer with Spindle no. 2 at 20°C are cited at 12, 30, and 60 r/min. For one example containing hydrogen peroxide, the viscosity is 1020, 400, and 220 cP at 12, 30, and 60 r/min, respectively. Pseudoplasticity is clearly evident, as the viscosity decreases with increasing rotational speed. 

The viscosity is typically measured by a viscometer. The SI unit of viscosity is the pascal second (Pa s). However, the widely used unit is poise (P) or centipoise (cP) (1 cP = 1 mPa s). The routine laboratory testing of viscosity is typically done using Brookfield viscometers and reported in cP. For non-Newtonian fluids such as those discussed above, the viscosity is dependent on the spindle size and type (number) and speed of rotation (rotation per minute or r/min) of the viscometer. 

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