What is viscosity?
Viscosity is really a measure of the resistance of fluid to an applied stress. In everyday terms it is like the thickness of a fluid or gas. By way of example, water has a low viscosity so it appears thin. In comparison honey has a higher viscosity so it appears thick. Viscosity essentially describes a liquids internal resistance to flow and might be thought of as a measure of its internal friction.
The measurement of viscosity can be a fairly simple test and the result reported is generally a single number. For the results of a viscosity test to be relevant, they should be compared to the results of tests done in the identical temperature. It truly is normal for fluids to turn into a lot more viscous at colder temperatures and much less viscous at higher temperatures.
What is rheology?
Rheology is actually a more complicated study of the flow of matter; mainly liquids, but additionally soft solids, gels, pastes as well as sold materials that exhibit some level of flow (ie. do not just deform elastically). Rheology applies to substances that have a complex structure, which includes: muds, sludges, suspensions, polymers, petrochemicals and biological supplies. The flow of these complicated materials cannot be characterized by a single value of viscosity, instead viscosity modifications with changing conditions. By way of example;
Ketchup’s viscosity lowers when it truly is shaken
Cornflour’s viscosity increases when it really is struck
In practice, rheology is concerned with supplies whose properties are among purely elastic material and Newtonian fluids, where mechanical behavior cannot be described by classic theories.
Do I need a viscometer or a rheometer?
There are a number of ways to measure the viscosity and rheological properties of a material. In both instances one of the most common testing methods are based about rotational devices that rotate a spindle immersed in a sample. By applying a controlled force or strain and measuring the resulting force or strain, it is feasible to know measure viscosity and realize rheological properties of a material.
The distinction in between a viscometer and rheometer is essentially the quality of components and control capabilities. Basically, a rheometer is much more versatile and has a wider range of applications than a viscometer does.
A rotational viscometer is easy device that rotates a spindle in a single direction. Most viscometers have mechanical bearings that limit the range of applications to more viscous materials. A viscometer can be a low cost instrument that’s appropriate for easy material, approach or production tests that call for simple flow measurements. A viscometer is extremely appropriate for top quality control testing and is often portable so offer the ability to complete remote or field testing.
A rotational rheometer allows far greater characterization of flow and deformation behavior. Rheometers can apply oscillatory motion to the spindles and may also apply big step alterations in stress and strain to determine viscoelastic properties together with flow properties. Rheometers typically use ultra-low friction air bearings which enable a lot greater sensitivity for low viscosity samples to become measured. Rheometers also tend to offer a wider range of sampling accessories such as temperature control units to study materials below a wider range of conditions.
A rheometer typically represents a greater investment, but may be vital for the true simulation of real processes and complete material characterization. The increased versatility of a rheometer makes it an excellent tool for investigation, product and process development in addition to high quality control testing.
Both instruments are complimentary and it really is not uncommon to see viscometers and rheometers in a single organization.