Viscosity of a Liquid
To know the factors affecting viscosity of a liquid, it is important to know what it is. Liquid viscosity is basically the measure of stickiness of a fluid. It refers to molecular friction caused by pushing of molecules past one another. While viscosity of water is low, other liquids such as shampoo or syrup have high viscosity.
Several factors affect viscosity of a liquid. Flow conditions are among the factors that affect the viscosity of a liquid.
The two main flow conditions of a liquid are laminar and turbulent. Laminar flow is when the liquid moves in the thin imaginary layers without changing of molecules from one layer to the other.
This flow is usually orderly. On the other hand, turbulent flow does not have a recognizable structure and layers cannot be observed. Fluid develops cortices. When tested under this flow condition, liquid depicts higher viscosity.
Shear rate is another factor that influences liquid viscosity. Liquids that have internal flow that does not depend on external forces, that is the shear rate that act on the fluid, they are ideally viscous. Such fluids are called Newtonian fluids.
On the other hand, there are non-Newtonian liquids that are ideally not viscous. Viscosity of the non-Newtonian liquids changes with shear rate. Apparent viscosity of such liquids is specified. Some of them show shear-thinning behavior with their viscosity decreasing with increasing shear rate. Others have viscosity that increases with an increase in shear rate, a characteristic called shear thickening.
Temperature is another factor that affects viscosity of a liquid. Along with shear rate, for most liquids temperature has dominating influence in their viscosity. Most liquids have low viscosity when temperatures are high. As such, decreased temperature causes increased liquid viscosity. Viscosity and temperature have an inversely relationship in liquids.
This implies that temperature changes will always have inverse effects on the viscosity of a liquid. The level of influence that temperature has on the liquid depends on its type and level of temperature change. For instance, in some liquids, a 1 degree centigrade decrease in temperature causes a 10 percent increase in their viscosity.
Pressure also affects viscosity of most liquids. Compared to temperature, pressure has very little influence on the viscosity of liquids. This is because compressing liquids at medium or low pressures is almost impossible. In most liquids, changing pressure from about 0.1 to 30MPa can cause a similar viscosity change with a change in temperature of approximately 1 degree centigrade.
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Sources
http://www.azom.com/article.aspx?ArticleID=10035
http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch14/property.php#viscosity
http://www.corvallis.k12.mt.us/middle/staff/jillw/Volcanoes/Viscosity%20Lab.htm
http://www.viscopedia.com/basics/factors-affecting-viscometry/