Viscosity, viscosity or viscosity (in English: Viscosity), is a resistance to fluid shear stress. In a fluid flow (moving), that different layers which are displaced relative to each other, the resistance value of the slip on the viscosity of the fluid is called fluid layers. The fluid viscosity is greater, for the same deformation, the shear stress is needed. For example, the viscosity of milk and honey viscosity is much greater.
Fluid viscosity decreases with increasing temperature liquid Yabdvly in gases, it is the contrary, the percentage changes for different fluids
ترجمه به فارسی
گِرانرَوی ،لِزْجَت یا ویسکوزیته(به انگلیسی: Viscosity)، عبارت است از مقاومت یک مایع در برابر اعمال تنش برشی. در یک سیال جاری (در حال حرکت)، که لایههای مختلف آن نسبت به یکدیگر جابجا میشوند، بهمقدار مقاومت لایههای سیال در برابر لغزش روی هم گرانروی سیال میگویند. هرچه گرانروی مایعی بیشتر باشد، برای ایجاد تغییر شکل یکسان، به تنش برشی بیشتری نیاز است. بهعنوان مثال گرانروی عسل از گرانروی شیر بسیار بیشتر است.
با افزایش دما لزجت سیالات مایع کاهش می یابدولی در گازها، قضیه برعکس است، البته درصد تغییرات آن برای سیالات مختلف متفاوت است.
برای اطلاعات بیشتر به ادامه مطلب مراجعه کنید.
Rheology is a more complex study of the flow of matter; mainly liquids, but also soft solids, gels, pastes and even sold materials that exhibit some level of flow (ie. do not just deform elastically). Rheology applies to substances that have a complex structure, including: muds, sludges, suspensions, polymers, petrochemicals and biological materials. The flow of these complex materials cannot be characterized by a single value of viscosity, instead viscosity changes with changing conditions. For example, ketchup’s viscosity lowers when it is shaken and cornflour’s viscosity increases when it is struck.
In practice, rheology is concerned with materials whose properties are between 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 several ways to measure the viscosity and rheological properties of a material. In both cases the most common testing methods are based around 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 possible to understand measure viscosity and understand rheological properties of a material.
The difference between a viscometer and a rheometer is essentially the quality of components and control capabilities. Basically, a rheometer is more versatile and has a wider range of applications than a viscometer does.
A rotational viscometer is a simple 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 is a low cost instrument that is suitable for simple material, process or production tests that require simple flow measurements. A viscometer is highly suitable for quality control testing and is often portable so offer the ability to do 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 can also apply large step changes in stress and strain to determine viscoelastic properties as well as flow properties. Rheometers usually use ultra-low friction air bearings which enable much greater sensitivity for low viscosity samples to be measured. Rheometers also tend to offer a wider range of sampling accessories such as temperature control units to study materials under a wider range of conditions.
A rheometer usually represents a greater investment, but can be essential for the true simulation of real processes and complete material characterization. The increased versatility of a rheometer makes it an excellent tool for research, product and process development as well as quality control testing.
Both instruments are complimentary and it is not uncommon to see viscometers and rheometers in a single organization.