Efflux time

Steady-state, laminar, isothermal flow is assumed. For a given viscometer with similar fluids and a constant pressure drop, the equation reduces to 77 = Kt or, more commonly, v = r /p = Ct where p is the density, V the kinematic viscosity, and C a constant. Therefore, viscosity can be determined by multiplying the efflux time by a suitable constant. 

Gla.ss Ca.pilla.ry Viscometers. The glass capillary viscometer is widely used to measure the viscosity of Newtonian fluids. The driving force is usually the hydrostatic head of the test Hquid. Kinematic viscosity is measured directly, and most of the viscometers are limited to low viscosity fluids, ca 0.4—16,000 mm /s. However, external pressure can be appHed to many glass viscometers to increase the range of measurement and enable the study of non-Newtonian behavior. Glass capillary viscometers are low shear stress instmments 1—15 Pa or 10—150 dyn/cm if operated by gravity only. The rate of shear can be as high as 20,000 based on a 200—800 s efflux time. 

AH glass capillary viscometers should be caUbrated carefully (21). The standard method is to determine the efflux time of distilled water at 20°C. Unfortunately, because of its low viscosity, water can be used only to standardize small capillary instmments. However, a caUbrated viscometer can be used to determine the viscosity of a higher viscosity Hquid, such as a mineral oil. This oil can then be used to caUbrate a viscometer with a larger capillary. Another method is to caUbrate directly with two or more certified standard oils differing in viscosity by a factor of approximately five. Such oils are useful for cahbrating virtually all types of viscometers. Because viscosity is temperature-dependent, particularly in the case of standard oils, temperature control must be extremely good for accurate caUbration. 

Orifice. Orifice viscometers, also called efflux or cup viscometers, are commonly used to measure and control flow properties in the manufacture, processing, and appHcation of inks, paints, adhesives, and lubricating oils. Their design answered the need for simple, easy-to-operate viscometers in areas where precision and accuracy are not particularly important. In these situations knowledge of a tme viscosity is uimecessary, and the efflux time of a fixed volume of Hquid is a sufficient indication of the fluidity of the material. Examples of orifice viscometers include the Ford, Zahn, and Shell cups used for paints and inks and the Saybolt Universal and Furol instmments used for oils (Table 5). 

If it is necessary to calculate kinematic viscosities from efflux times, such as in a caUbration procedure, equation 20 should be used, where /is the efflux time and k and K are constants characteristic of the particular viscosity cup (see Table 5) (158,159). 

Linear equations of the type u = ct — C, where c and C are constants, relate kinematic viscosity to efflux time over limited time ranges. This is based on the fact that, for many viscometers, portions of the viscosity—time curves can be taken as straight lines over moderate time ranges. Linear equations, which are simpler to use in determining and applying correction factors after caUbration, must be appHed carefully as they do not represent the tme viscosity—time relation. Linear equation constants have been given (158) and are used in ASTM D4212. 

To achieve the desired cast density for Octol of 1.8g/cc it is necessary that the ratio of HMX TNT be 3 1. However, at this ratio the apparent viscosity, or efflux, is strongly dependent on the polymorphic variety of HMX used and on its particle size distribution. In the initial pilot production of Octol (Ref 3) it was found that for the desired efflux of < 15 sec, 60—70% of the solid HMX must consist of the beta-polymorph having particle diameters in the range of 500—800 microns. Such precise control of particle size was not possible at that time and early Octol casts were made at approximately 50 secs efflux. The economical production of Octol with a satisfactorily short efflux time continues to present a problem in loading shells with this expl (Refs 4, 11 29)... 

In practice we do not measure viscosity directly. Instead, what is measured is time of flow for solutions and pure solvent in a capillary viscometer, the so-called efflux time. If the same average hydrostatic head is used in all cases, and since for very dilute solutions the density differences between the different concentrations are negligible, then the ratio of the efflux time of the solution, t, to that of the pure solvent, tg, may be taken as a measure of the ratio of the viscosities, i.e. 

In the SI system, the theoretical unit of v is m2/s or the commonly used Stoke (St) where 1 St = 0.0001 m2/s = 100 cSt = 100 centiStoke. Similarly, 1 centiStoke = 1 cSt = 0.000001 m2/s = 0.01 Stoke = 0.01 st. The specific gravity of water at 20.2°C (68.4°F) is almost 1. The kinematic viscosity of water at 20.2°C (68.4°F) is for all practical purposes equal to 1 cSt. For a liquid, the kinematic viscosity will decrease with higher temperature. For a gas, the kinematic viscosity will increase with higher temperature. Another commonly used kinematic viscosity unit is Saybolt universal seconds (SUS), which is the efflux time required for 60 mL of petroleum product to flow through the calibrated orifice of a Saybolt universal viscometer, as described by ASTM-D88. Therefore, the relationship between dynamic viscosity and kinematic viscosity can be expressed as... 

Saybolt Universal Seconds (SUS) are used to measure viscosity. The efflux time is the SUS required for 60 mL of a petroleum product to flow through the calibrated orifice of a Saybolt Universal viscometer, under carefully controlled temperature and as prescribed by test method ASTM D 88. This method has largely been replaced by the kinematic viscosity method. SUS is also called the SSU number (Seconds Saybolt Universal) or SSF number (Saybolt Seconds Furol). 

Viscosity measurements were carried out using Cannon-Fenske viscometers of appropriate capillary diameter so as to keep the efflux time between 200-300 seconds. Approximate shear rate at the wall was calculated using the equation... 

In the Ostwald viscometer, the solution is introduced through the tube a and is then sucked through the tube 7/ until its level is above mark C, the efflux time of the solution from mark c to mark d is then noted. 

The error in the determination of the efflux time because of the deflection of the viscometer from the vertical is much larger in Ostwald viscometer than in Ubbelohde viscometer. 

In the case of Intrinsic viscosity measurements, the measurements will be in the form of pressure drop or a ratio of efflux times. In either case, the interpretation equation is of the form... 

Ubbelohde viscometer with efflux times greater than 100 sec for the solvent... 

Irradiation Studies in Solution. The degradation studies on both PIPTBK and PMIPK in solution were carried out in an automatic UV irradiation-viscometer apparatus that has been described elsewhere (10). Each solution was irradiated at 313 nm for a fixed time period and then automatically transferred to a viscometer, where nine repetitive measurements of the efflux time were performed. The solution was then returned to the UV cell for further irradiation, and the cycle was repeated seven times. The intrinsic viscosity of... 

Meyerhoff (4) and Goedhart and Opschoor (5) have measured the viscosity of each eluting GPC fraction by coupling an automatic capillary tube viscometer with the GPC syphon. The low polymer concentration in each fraction necessitated an extremely accurate efflux time measurement to 0.01 second since the flow time of each fraction containing polymer has flow times, th greater than that of pure solvent, t0, by at most 2.00 seconds. The specific viscosity sv. of the ith polymer fraction is calculated from the flow times of the pure solvent and the polymer fraction. 

The solvent and solution efflux times were determined by means of the Hewlett-Packard Autoviscometer system. The intrinsic viscosity [rj] was... 

SAYBOLT UNIVERSAL VISCOSITY. The efflux time in seconds (SUS) of 60 mL of sample flowing through a calibrated Universal onfice in a Saybolt viscometer under specified conditions. 

At the optimal sodium pectate concentration, the efflux time of the substrate solution in the viscometer should be in the range of 115 to 120 sec. 

Determine an efflux time immediately after initiating the reaction (using a second timer) and then at suitable intervals to allow graphical determination of the time to reach a 50% reduction in viscosity. 

Set up a second reaction system as described above, but use a heat-inactivated enzyme. Use the efflux time of this reaction as the zero-time data point (U0). 

Set up a third reaction system using heat-inactivated enzyme diluted in 20 mM sodium acetate buffer alone (no sodium pectate substrate solution). Use the efflux time of this reaction as V%. 

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