Capillary/tube viscometer glass

More recent developments in the rolling ball area include an automated micro viscometer, the Paar AMV 200, from Paar Physica. The specimen to be measured is introduced into a glass capillary down which a gold-covered steel ball roUs. The rolling time is measured automatically. The shear stress may be varied by changing the inclination angle of the capillary tube. The shear rate range is 10 1000, which makes the instmment useflil for... 

Viscometers Devices for measuring viscosity are called viscometers. The most common viscometer consists of a Cannon-Fenske tube, which is a U-shaped glass tube (see Figure 5.6), one arm of which consists of a capillary tube through which liquids flow slowly. The more viscous the liquid, the longer it takes for a given volume to flow through the capillary. This time is related to the viscosity of the liquid in poise or centipoise, which can be calculated from the measured time, a calibration constant, and the liquid s... 

This unit describes a method for measuring the viscosity (r ) of Newtonian fluids. For a Newtonian fluid, viscosity is a constant at a given temperature and pressure, as defined in unit hi. i common liquids under ordinary circumstances behave in this way. Examples include pure fluids and solutions. Liquids which have suspended matter of sufficient size and concentration may deviate from Newtonian behavior. Examples of liquids exhibiting non-Newtonian behavior (unit hi. i) include polymer suspensions, emulsions, and fruit juices. Glass capillary viscometers are useful for the measurement of fluids, with the appropriate choice of capillary dimensions, for Newtonian fluids of viscosity up to 10 Pascals (Newtons m/sec 2) or 100 Poise (dynes cm/sec 2). Traditionally, these viscometers have been used in the oil industry. However, they have been adapted for use in the food industry and are commonly used for molecular weight prediction of food polymers in very dilute solutions (Daubert and Foegeding, 1998). There are three common types of capillary viscometers including Ubelohde, Ostwald, and Cannon-Fenske. These viscometers are often referred to as U-tube viscometers because they resemble the letter U (see Fig. HI.3.1). 

Figure H1.3.1 Schematic of a glass capillary (U-tube) viscometer. Contributed by Jody Renner-Nantz...

The use of these empirical procedures is being superseded by the more precise kinematic viscosity method (ASTM D-445, IP 71), in which a fixed volume of fuel flows through the capillary of a calibrated glass capillary viscometer under an accurately reproducible head and at a closely controlled temperature. The result is obtained from the product of the time taken for the fuel to flow between two etched marks on the capillary tube and the calibration factor of the viscometer and is reported in centistokes. Because the viscosity decreases with increasing temperature the temperature of test must also be reported if the viscosity value is to have any significance. For distillate fuel oils the usual test temperature is 38°C (100°F). 

Viscosity can also be measured with viscometers where the movement or the developed force is due to gravity, by the fluid s own weight. Such a system is developed when the fluid flows in special glass tubes (capillary tubes). In this case, the kinematic viscosity (qj or v) is measured, and the measurement unit is in square millimetres per second. This unit is also known as centistoke (cSt). However, when the fluid is forced to flow under negative pressure (vacuum), then the dynamic viscosity (Pa-s) is measured. 

The automatic relative viscometer is ideally suited for measuring dilute polymer viscosities. It provides faster analysis and greater precision than is obtainable with conventional glass tube viscometers (Ubbelohde or Cannon-Fenske), which it replaces. The principle of operation is based on measurement of pressure drops due to the continuous forced flow of solvent and sample through two stainless steel capillary tubes placed in series. The pressure drop across each capillary tube obeys Poiseuille s law. The pressme drop is measured by a differential pressure transducer. The sample solution is loaded into a sample loop via a syringe pump and then pushed into one of the two capillaries. A steady-state condition is reached when the sample solution completely fills capillary 2, solvent remaining in capillary 1 at all times. The relative viscosity of the sample solution is determined simply and directly by the ratio of the pressure drops. From the measured relative viscosity, all other solution viscosity measurements can be calculated. Solution viscosities are determined by the viscosity of the sample relative to the reference solvent. The relative viscometer measures the solvent and sample viscosity simultaneously, so errors due to temperatme fluctuation and solvent variations are avoided. The main advantages of this approach are ... 

Capillary Viscometers sed for concentrated solutions or polymer melts and described just above, the other, described here, used for measuring dilute-solution viscosities. The most widely used of the latter types employ a glass capillary tube and means for timing the flow of a measured volume of the solution (e.g., polymer in solvent) through the tube under the force of gravity. This time is then compared with the time taken for the same volume of pure solvent, or of another liquid of known viscosity, to flow through the same capillary. Relevant tests are from ASTM (www.astm.org). See also Dilute-Solution Viscosity and Viscometer. 

Capillary viscometers are simple and inexpensive. They are normally constructed from glass and resemble a U-tube with a capillary section between two bulbs. The initial design originated with Ostwald and is shown as part A in Figure 3.2-1. The Cannon-Fenske type, a popular modification of the Ostwald design that moves the bulbs into the same vertical axis, is shown as part B in Figure 3.2-1. 

Viscosity. The viscosity of ozone-fluorine mixtures was determined in a modified Ostwald viscometer (1) which was used with a variable volume of liquid. The viscometer was made from precision-bore glass tubing (4 mm. i.d.) with a capillary section 0.203 mm. in diameter and 12 on. long. 

A flow-through viscometer developed for application as a sensor in automated analyses consisted of a glass capillary connected to the sample flow circuit with thin-walled tubes at both ends. These tubes separate the fluid to be tested from a hydraulic fluid, and this construction ensures the absence of dead space and a minimal test volume. Development of a mathematical model describing the enzymatic degradation of macromolecules resulted in a reciprocal equation allowing rectilinear presentation of the calibration data. The application of the enzyme to the assay of amylase was described. 

For accurate measurements on mineral oils, glass capillary viscometers are used. The driving force is provided by the head of the test oil flowing vertically down the tube and is given by... 

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