Viscosity changes

When sulphur is melted viscosity changes occur as the temperature is raised. These changes are due to the formation of long-chain polymers (in very pure sulphur, chains containing about 100 (X)0 atoms may be formed). The polymeric nature of molten sulphur can be recognised if molten sulphur is poured in a thin stream into cold water, when a plastic rubbery mass known as plastic sulphur is obtained. This is only slightly soluble in carbon disulphide, but on standing it loses its plasticity and reverts to the soluble rhombic form. If certain substances, for example iodine or oxides of arsenic, are incorporated into the plastic sulphur, the rubbery character can be preserved. 

ASTMD1286 mixed fungal culture fungal growth, viscosity change... 

Fig. 18. Viscosity change of industrial petroleum oils with irradiation (72). To convert Gy to rad, multiply by 100.

Viscous Hquids are classified based on their rheological behavior characterized by the relationship of shear stress with shear rate. Eor Newtonian Hquids, the viscosity represented by the ratio of shear stress to shear rate is independent of shear rate, whereas non-Newtonian Hquid viscosity changes with shear rate. Non-Newtonian Hquids are further divided into three categories time-independent, time-dependent, and viscoelastic. A detailed discussion of these rheologically complex Hquids is given elsewhere (see Rheological measurements). 

Commercial condensed phosphoric acids are mixtures of linear polyphosphoric acids made by the thermal process either direcdy or as a by-product of heat recovery. Wet-process acid may also be concentrated to - 70% P2O5 by evaporation. Liaear phosphoric acids are strongly hygroscopic and undergo viscosity changes and hydrolysis to less complex forms when exposed to moist air. Upon dissolution ia excess water, hydrolytic degradation to phosphoric acid occurs the hydrolysis rate is highly temperature-dependent. At 25°C, the half-life for the formation of phosphoric acid from the condensed forms is several days, whereas at 100°C the half-life is a matter of minutes. 

Controlled Stress Viscometer. Most rotational viscometers operate by controlling the rotational speed and, therefore, the shear rate. The shear stress varies uncontrollably as the viscosity changes. Often, before the stmcture is determined by viscosity measurement, it is destroyed by the shearing action. Yield behavior is difficult to measure. In addition, many flow processes, such as flow under gravity, settling, and film leveling, are stress-driven rather than rate-driven. 

Solutions of HEC are pseudoplastic. Newtonian rheology is approached by very dilute solutions as well as by lower molecular-weight products. Viscosities change Httie between pH 2 and 12, but are affected by acid hydrolysis or alkaline oxidation under pH and temperature extremes. Viscosities of HEC solutions change reversibly with temperature, increasing when cooled and decreasing when warmed. 

For lubricated plug cocks, the lubricant must have limited viscosity change over the range of operating temperature, must have low solubility in the fluid handled, and must be applied regularly. There must be no chemical reaction between the luBricant and the fluid which... 

For a quick estimate of viscosity change with temperature, simply place a point on the graph shown as Figure... 

Viscosity changes make conventional water pipe sizing tables useless these must be upgraded by the application of appropriate correction factors. 

There are two distinct stages in viscosity change with the addition of NBR in the blend. First, there is a rapid rise of viscosity with the initial addition of NBR, then beyond 50% of NBR, viscosity increases slowly, except for the preheated blends where viscosity decreases marginally at the higher level of NBR. 

Variation of melt viscosity for both the preblends and preheated blends with the blend ratio are shown in Fig. 19. There are two distinct regions in viscosity change with the addition of polyacrylic rubber (ACM) in the blends. First, in the higher shear rate region, the viscosity increases with the addition of the ACM (up to 40% ACM) in the blend and then it decreases. In the lower... 

HETP values for random dumped packing have been found to be 25% greater at a greater ascosity than a lower viscosity, i.e., viscosity change from 0.15 cps to 0.44 cps. 

Care necessary in commissioning and in heat-up rates due to viscosity changes in medium. 

Two effects on pump performance must be discussed viscosity and gas content. Figures 32.23 and 32.24 illustrate the effects of viscosity change on centrifugal and... 

Figure 40.18 Viscosity Index (VI) is a relative measure of viscosity change with temperature change...

Some water-thinned industrial paints exhibit anomalous viscosity changes during drying and therefore need careful control of air flow and humidity to ensure satisfactory film formation. 

Einstein coefficient b, in (5) for viscosity 2.5 by a value dependent on the ratio between the lengths of the axes of ellipsoids. However, for the flows of different geometry (for example, uniaxial extension) the situation is rather complicated. Due to different orientation of ellipsoids upon shear and other geometrical schemes of flow, the correspondence between the viscosity changed at shear and behavior of dispersions at stressed states of other types is completely lost. Indeed, due to anisotropy of dispersion properties of anisodiametrical particles, the viscosity ceases to be a scalar property of the material and must be treated as a tensor quantity. 

Fig. 6-4 Viscosity changes during the processing of TS. The B-stage represents the start of the heating cycle followed by a chemical reaction (cross-linking) and solidification of the plastic.

NPei and NRtt are based on the equivalent sphere diameters and on the nominal velocities ug and which in turn are based on the holdup of gas and liquid. The Schmidt number is included in the correlation partly because the range of variables covers part of the laminar-flow region (NRei < 1) and the transition region (1 < NRtl < 100) where molecular diffusion may contribute to axial mixing, and partly because the kinematic viscosity (changes of which were found to have no effect on axial mixing) is thereby eliminated from the correlation. 

FIGURE 16.5 Viscosity changes per mixing step demonstrate QDI reduces the viscosity of natural rubber (NR) compounds. (Note that the viscosities reported are MS(1 +4) or small rotor viscosities.)... 

Carboxypolymethylene exhibits a stabilizing effect against separation and viscosity change of a cetyl alcohol-stearic acid-sodium lauryl sulfate system. Samples 1 and 2 are identical, except that the former contains carboxypolymethylene (adjusted to pH 7). Sample 1 shows no separation, while sample 2 shows 13% separation after 6 months. Figure 8 shows the viscosity characteristics of the above samples. The broken line represents the viscosities of sample 1 at different time intervals, and the unbroken line, the viscosities at the same time intervals for sample 2. Apparently the carboxypolymethylene prevents the agglomeration and precipitation of stearic acid, which would result in separation and loss of viscosity. 

Given the loading of solid poison that will be used, consider whether this will drastically alter your reaction conditions. Is the system still well-mixed Are there phase separation problems Does the viscosity change appreciably when adding the poison, as was observed by one group (23)... 

Rheological Property Determination. The rheology of an emulsion is often an important factor in determining its stability. Any variation in droplet size distribution, degree of flocculation, or phase separation frequently results in viscosity changes. Since most emulsions are non-Newtonian, the cone-plate type device should be used to determine their viscosity rather than the capillary viscometer. 

---