Viscometer Design

The new viscometer design utilizes two sets of the capillary and pressure transducer assemblies like the one shown in Figure 1. 

Fig. 3.19. Vacuum viscometer design. A solvent reservoir, B hanging burette, C site for freeze seal, F killing agent in break-seal phial, G stainless steel ball bearing in appendix, H coarse frit to retain glass fragments, J phial breaker, K stirrer, P initiator phial.

Viscometer design to fill simultaneously the needs of quality-control and production personnel as well as development engineers would appear to be a stimulating and rewarding field to which, evidently, little intelligent attention has been given to date. 

We begin with a brief discussion of Newton s law of viscosity and follow this with a discussion of Newtonian flow (i.e., the flow of liquids that follow Newton s law) in a few standard configurations (e.g., cone-and-plate geometry, concentric cylinders, and capillaries) under certain specific boundary conditions. These configurations are commonly used in viscometers designed to measure viscosity of fluids. 

McKennell, R. 1960. Influence of viscometer design on non-Newtonian measurements. Anal. Chem. 32, 1458. 

It is clear then, that the measurement of non-Newtonian materials presents special challenges for a viscometer. Many industrial viscometers designed to give a single point determination have a deceptively simple operating principle. Examples include the speed at which a liquid flows out of a container through a known orifice, a bubble rises in a column of fluid, or a ball falls in a column of fluid. These simple devices are actually very complex in terms of the shear field that is generated. The shear field is the variation of shear stress or shear rate as a function of position within the... 

Figure 3-16 Tube Viscometer Design Considerations (Vitali and Rao, 1982).

The last differential viscometer design is the Waters Corporation detector [9], which is in the Alliance GPCV2000 high-temperature instrument. It is composed of three capillaries, two differential pressure transducers, and two holdup reservoirs it is represented in Fig. Id. The pressure transducers are connected flow-through this eliminates the need for frequent purges. This detector provides, at the same time, relative viscosity information and relative flow information. This design does not require a perfect matching of the capillaries. 

As mentioned earlier, viscometric manipulations are simplified considerably by using a capillary instrument of the Ubbelohde type, as modified by Davis and Elliott, rather than one of the Ostwald or Fenske t3q)e. This viscometer has a side arm at the base of the capillary which breaks the liquid flow to form a suspended level, and also reduces kinetic-energy corrections. The latter are very important, but can be made negligible by careful viscometer design. Kinetic-energy corrections are inversely proportional to the flow time, and so the viscometer should be designed so that solvent flow-times of 150-200 seconds are achieved. Full details of viscometric techniques can be found elsewhere. ... 

Mariotte Tube. An orifice-type viscometer designed by E. Mariotte (Paris, 1700). One such instrument with a tube diameter of 54 mm and a 3 mm orifice has been used for the assessment of the fluidity of clay slips (/. Amer. Ceram. Soc., 27, 99,1944). 

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