Viscometer calibration

Table entries were calculated from the following empirical relationships from measurements in viscometers calibrated with water at 20°C (and 1 atm), modified to agree with the currently accepted value for the viscosity at 20° of 1.002cP ... 

Apparent viscosity is usually measured by a capillary viscometer calibrated with viscous oils the pressure affecting the outflowing liquid is variable within certain limits. 

R. C. Hardy, NBS Viscometer Calibrating Liquids and Capillary Tube Viscometers, Monograph 55, Nat. Bur. Stand. (1962)... 

The dynamic viscosity (q) (in Pa-s) is calculated by multiplying the efflux time t) (in seconds) by the viscometer calibration factor (K) (in Pa). 

Cannon-Fenske viscometer n. Capillary viscometer (calibrated) used for measuring relative flow time for liquids, useful for determining relative, specific and inherent viscosities of polymer solutions and extrapolation of intrinsic viscosities. It is convenient to clean and calibrate, but lacks correction due to different volume levels leading to weight due to gravity in the viscometer See image). 

Calibration of a rotational viscometer with a standard should be done regularly and recorded. ASTM D-2196 considers a viscometer calibrated if the viscosity reading is within 5% of the stated viscosity. 

Intrinsic Viscosity. Intrinsic viscosities were determined from single, dilute decahydronapthalene solutions (ca. 0.05 g/dl) with a Viskotek Corp. (Houston) model 100 Differential Viscometer calibrated with NBS 1475 linear polyethylene (h - 1.18 dl g ). 

If the determined kinematic viscosity does not agree within 0.35 % of the certified value, recheck each step in the procedure, including thermometer and viscometer calibration, to locate the source of error. Annex A1 gives details of standards available. 

Note 4 Caution—It is essential that alkaline cleaning solutions are not used as changes in the viscometer calibration can occur. 

The time is measured for a fixed volume of the liquid to be drawn up through a capillary tube by means of vacuum, under closely controlled conditions of vacuum and temperature. The viscosity in poises is calculated by multiplying the flow time in seconds by the viscometer calibration factor. 

Use of alkaline glass cleaning solutions may result in a change of viscometer calibration, and is not recommended. 

X4.3.2 Calibration of Vacuum Viscometer by Means of Standard Vacuum Viscometer—Calibrate the vacuum viscometer as follows ... 

Thus, by simply measuring t, the kinematic viscosity v = q/p of any low-viscosity Newtonian liquid can be determined. It is important to note that because the lower bulb contains liquid during the measnrement, h depends on the liquid level in both arms of the viscometer. Calibration experiments must therefore be performed with the same initial head of liquid as the actual measuranents to yield accurate results. In practice, Equation 7.17 leads to small but systanatic errors in viscosity data, particularly for low viscosity liquids. The source of errors can be traced to omission of the energy required to accelerate the liquid as it enters and leaves the capillary. When this effect is taken into account, Equation 7.17 reads [30]... 

Since viscometer drainage times are typically on the order of a few hundred seconds, intrinsic viscosity experiments provide a rapid method for evaluating the molecular weight of a polymer. A limitation of the method is that the Mark-Houwink coefficients must be established for the particular system under consideration by calibration with samples of known molecular weight. The speed with which intrinsic viscosity determinations can be made offsets the need for prior calibration, especially when a particular polymer is going to be characterized routinely by this method. 

The equations and methods for determining viscosity vary greatly with the type of instmment, but in many cases calculations may be greatly simplified by calibration of the viscometer with a standard fluid, the viscosity of which is known for the conditions involved. General procedures for calibration measurement are given in ASTM D2196. The constant thus obtained is used with stress and shear rate terms to determine viscosity by equation 25, where the stress term may be torque, load, or deflection, and the shear rate may be in rpm, revolutions per second (rps), or s F... 

If a solution tends to be independent of shear, then the measurement of viscosity (q) is based on Poiseuille s law can be made easy by grouping all those terms related to a specific viscometer as a calibration constant A. 

The MUF resin pH was determined using pH meter model pH 340-A/SET l-MTM. The pH meter was calibrated before it was used to determine the pH of the resin. The viscosity was determined using the Cole-Parmer 98936-15 viscometer (R2 spindle, lOOrpm speed). The storage life was a test of shelf life of the MUF resin under the ambient environment. Resin was first stored at ambient room temperature. Viscosity of the resin was checked for every three to four days. The ratio of water that can be added into resin before it turned turbid or precipitated is called resin solubility. The resin solubility was determined by divide the weight of resin and the weight of water added into resin before it turned turbid or precipitated. The curing period of a resin was defined as the time period for the resin to be hardened after application in a 30°C and 1.0% of NH4CI powder (as hardener). 

At the moment, one recommends to determine the molecular characteristics of pectins using SEC chromatography equipped with a differential refractometer, a multiangle laser light scattering detector and a viscometer as previously described [25]. This technique needs no calibration with the usual molecular weight standards such dextrans and pullulans... 

Molecular weight distribution was analysed by gel chromatography (0.5 % AG) equipped with a Shodex Ohpak B 805 column (500 8 mm) with phosphate buffer (pH 6.5) using diffe-rential-refractometer/viscometer detection (Knauer). For calibration a pectin series from vibration milling was applied. 

Mills has concluded in his review article on molten slags that (1) most viscosity measurements were subject to experimental imcertainties of 25% (2) in some cases experimental uncertainties could be > 50% and (3) experimental uncertainties as low as 10% could be achieved by careful calibration of viscometers with high and low temperature reference materials. 

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). 

With the aim to establish an [rj]-M relation (Equation (36)) for universal calibration and for the determination of the persistence length, intrinsic viscosities were measured with an Ubbelohde capillary viscometer. The respective data are also included in Table 3. 

Novolac molecular weights were measured in THF at 35°C by high pressure size exclusion chromatography using a Waters Model 510 pump (flow rate=1.0 ml/min), 401 differential viscometer detector and a set of Dupont PSM 60 silanized columns. A universal calibration curve was obtained with a kit of 10 narrow molecular weight distribution, linear polystyrene standards from Toya Soda Company. Data acquisition and analysis were performed on an AT T 6312 computer using ASYST Unical 3.02 software supplied with the Viscotek instrument. 

Viscosity depends on temperature. The higher the temperature, the lower the viscosity Pancake syrup, for example, flows more freely when heated. For reasonable accuracy when measuring viscosity, the temperature must be very carefully controlled. This means that the viscometer and sample must be immersed in a constant temperature bath and the temperature given time to equilibrate before the measurement is recorded. A calibrated thermometer must be used to measure the temperature. 

In order to calculate the kinematic viscosity, the calibration constant for the viscometer in question must be known. This calibration constant is often determined by the vendor before it is shipped, but it is also often checked by the user. In the calibration procedure, a fluid of known viscosity is tested so that the calibration constant can then be calculated ... 

A given calibration liquid is known to have a kinematic viscosity of 15.61 cS at 25°C. Testing this liquid in a capillary viscometer gave a time of 139 sec. An unknown liquid was then tested with the same viscometer and found to give a time of 238 sec. What is the kinematic viscosity of the unknown liquid ... 

First, the calibration constant of the viscometer is determined from the calibration data ... 

Obtain a capillary viscometer with a known calibration constant. Also obtain samples of the following alcohols methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, and any others your instructor may suggest. 

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