Apparent viscosity tests

Once a test 1s complete, another menu option provides the data analysis results 1n the form of a hard-copy report printed on the local line printer. The report Includes experiment identification Information and the apparent viscosities calculated for each data set. A subset of the data analysis program 1s scheduled automatically by the control programs while the experiment is 1n progress and provides immediate on-line analysis of apparent viscosities for each data set as It 1s collected. The results are viewed using the real-time data display program (Figure 5). 

For non-Newtonian liquids and suspensions, an apparent viscosity is determined using correlations which include power input and the Reynolds number. Scale-up comparisons based on heat generation data only were determined by comparison of results from RC1 experiments and from a 675-liter reactor [208]. In the experiments, a Bingham plastic fluid was used to determine the film heat transfer coefficient. This presents a worst case because of the low thermal conductivity of the Bingham plastic. Calculated inside film heat transfer coefficients determined in the RC1 tests were about 60% lower than the values determined in the pilot plant reactor, even though substantial effort was made to obtain both geometric and kinematic similarity in the pilot reactor. 

In this thin-film machine, the small clearance between heated wall and rotor blade, together with the high peripheral blade velocity, results in high shear gradients, whereby the apparent viscosity in the film is considerably reduced. The resulting increased turbulence and better surface renewal improve heat transfer, increase reaction velocities, and aid the required forced product flow on the wall. On the basis of test... 

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. 

Even with this equation, the end effects associated with the conical bottom end of the cylinder and the shaft extending from the top of the cylinder must be accounted for [5] [6]. The longer the cylinder, the less significant the error introduced by the end effects will be. Hence, by testing a fluid using cylinders of equal radius but increasing lengths the apparent viscosity ... 

D 2556 Test Method for Apparent Viscosity of Adhesives Having Shear Rate... 

If the foam phase is thought of as a pseudo continuous fluid with an apparent viscosity Vapp = it follows that Papp is greater than that of the aqueous liquid phase. (For the tests here, values of Uapp were on the order of 1 to 50 times that of water). Because of this, when foam and liquid move through a porous medium under an applied pressure drop, the foam, being the most viscous phase, must occupy a larger region of the pore space. Consequently, as observed, the gas saturation is increased over that of non-dispersed phase flow and the liquid permeability is correspondingly decreased. 

Laboratory tests with Alipal CD-128 indicated that a steady-state reciprocal apparent viscosity of 0.2-0.4 cP (about equal to that of the oil) could be obtained and that surfactant retention by the reservoir rock would not be excessive (0.00056 lb surfac-tant/ft of rock permanent adsorption). Eventually, the following injection sequence was planned (1) 15 kg of NH4SCN tracer in 371 bbl of water, followed by a water spacer between the tracer and the subsequent surfactant solution (2) 2,764 bbl of 0.1% surfactant, intended to satisfy the adsorption requirements of the rock ... 

A pressurized direct-drive concentric cylinder viscometer system (Figure 3-21) was used to obtain shear rate versus shear stress data on a tomato puree at several fixed temperatures between 76 and 120°C (Figure 3-22), and temperature versus apparent viscosity data at several shear rates on a 4% waxy rice (WR) starch dispersion during gelatinization over the temperature range 30 to 110°C (Figure 3-23) (Rao et al., 1998). The drive motor, torque unit, and concentric cylinder unit and temperature control vessel of a Haake RV2 viscometer system (Haake Inc.) were placed in a chamber (PRC) that could be pressurized to 0.2 MPa (two atmospheres). The temperature control vessel was insulated to minimize heat loss. A eopper-constantan (36 gage wires) thermocouple plaeed in the well of the inner eoneentric eylinder measured the temperature of the test sample. 

The viscosity obtained from the above equation in the linear region of a creep experiment can be used to extend the low-shear rate region of apparent viscosity versus shear rate data obtained in a flow experiment by about two decades (Giboreau et al., 1994 Rayment et al., 1998). The low shear rate region of about 10 -10 is often used for the characterization and differentiation of structures in polysaccharide systems through the use of stress controlled creep and non destructive oscillatory tests. The values of strain (y) from the creep experiment can be converted to shear rate from the expression y t) = y t)/t. 

Moskowitz and Arabic (1970) found that the taste intensity (sweetness, sourness, saltiness, and bitterness) was related to the apparent viscosity of carboxymethylcel-lulose solutions by a power function with a negative slope. Pangbom et al. (1973) observed that the influence of different hydrocolloids on the perception of some basic taste intensities (saltiness, bitterness, sourness) appeared to be more dependent on the nature of the hydrocolloid and the taste of the substance than on the viscosity level. In contrast, sweetness imparted by sucrose was found to be highly dependent on viscosity, that is, the hydrocolloid concentration above a certain viscosity threshold, it was shown that the sweetness intensity of sucrose was significantly depressed. Saltiness was the taste attribute less affected, sourness, imparted by citric acid, was significantly reduced by all hydrocolloids tested, and for the other taste substances, the presence of a hydrocolloid generally enhanced the taste intensity of saccharin and depressed that of sucrose and caffeine (bitterness). 

Figure 10.35. Temperature distributions before and after a 1.77 inch inside diameter six element Kenics HEM mixer performing thermal homogenization of polyethylene melt. The apparent viscosity of polyethylene used in the test was 11,000 poises. A homogeneous melt stream was obtained using a Kenics Mixer of six elements. It was found that thermal homogenization in the Kenics Mixer is independent of the initial radial temperature profiles and the size of the unit. A radial thermal gradient reduction from 100°F to less than 1 °F was obtained in a PVC cast film production. In general, the unit delivers a polymer melt stream with less than a 3°F radial temperature gradient.

For the evaluation of the rheology of the silica dispersions, different test methods were applied (a) a shear rate-controlled relaxation experiment at = 0.5 s (conditioning), 500 s (shear thinning), and 0.5 s (relaxation) to evaluate the apparent viscosity, the relaxation behavior, and thixotropy (b) shear yield-stress measurements using a vane technique introduced by Nguyen and Boger [5] (c) low deformation dynamic tests at a constant frequency of 1.6 s in a stress range of ca. 0.5 - 100 Pa. All samples contained 3 wt% of fumed silica. 

The test described above and the results obtained at a single stress value do not reveal anything about the stress dependence of flow rate. The apparent viscosity calculated from them is 3.6 x 10 dPa s. 

In order to facilitate rapid melt viscosity measurement and data analysis a modified Gflttfert capillary rheometer has been interfaced to a Hewlett-Packard data acquisition system. All test parameters (temperature, barrel pressure, etc) are monitored automatically and the data is stored on magnetic tape. After testing is complete, raw data is entered into an analysis program used to compute tables and draw plots of shear stress, shear rate, and apparent viscosity. Examples of the application of this system to commercial polymers are discussed. 

Another method (ASTM D-2669) is suitable for blends of wax and additives with apparent viscosities up to 20,000 cP at 177°C (350°F). Apparent viscosity is the measurement of drag produced on a rotating spindle immersed in the test liquid. A suitable viscometer is equipped to use interchangeable spindles and adjustable rates of rotation. The wax blend is... 

The cold crank simulator test, ASTM D2602/IP 383, measures the apparent viscosity of an oil sample at low temperatures and high shear rates, related to the cold starting characteristics of engine oils, which should be as low as possible. The oil sample fills the space between the rotor and the stator of an electric motor, and when the equipment has been cooled to the test temperature, the motor is started. The increased viscosity of the oil will reduce the speed of rotation of the motor and indicates the apparent viscosity of the oil. The test is comparative for different oil samples rather than an accurate prediction of the absolute performance of an oil in a specific engine. 

Winterburn, G. (1988) Cooperative Test Results of Apparent Viscosity Determination at Low Shear Rates using the Constant Pressure Viscometer, NLGI Spokesman LII (8), 365-372. PoweU, T. W. (1982) Activators for Organophilic Clays in Lubricating Greases, NLGI Spokesman XLVI (8) 269-277. 

In a similar round-robin test performed for low-density polyethylene at the highest set rate of 3162 s and stress of 320 kPa, apparent viscosity was 101.2 + 0.7 Pa.s for within-laboratory standard deviation of the average, and 101.2 + 5.2 Pa.s for between-laboratory standard deviation of the average, that is, 0.65 and 5.1%,... 

ASTM Method D 1092-62, Apparent Viscosity of Lubricating Greases, ASTM Standards Book, Part 17—Petroleum Products, American Society for Testing and Materials, Philadelphia. 

The use of surfactant-stabilized foams to counteract these kinds of problems was suggested several decades ago (7, 2) and has recently become actively pursued in laboratory and field tests (3—8). The use of foam is advantageous compared with the use of a simple fluid of the same nominal mobility because the foam, which has an apparent viscosity greater than the displacing medium, lowers the gas mobility in the swept or higher permeability parts of the formation. This lowered gas mobility diverts at least some of the displacing medium into other parts of the formation that were previously unswept or underswept. From these underswept areas, the additional oil is recovered. Because foam mobility is reduced disproportionately more in higher permeability zones, improvement in both vertical and horizontal sweep efficiency can be achieved. 

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