How does viscosity of liquids vary with temperature?
The former effect causes a decrease in the shear stress while the latter causes it to increase. The result is that liquids show a reduction in viscosity with increasing temperature. With high temperatures, viscosity increases in gases and decreases in liquids, the drag force will do the same.
Fluid viscosity changes with temperature. Pressure has a small impact on gas viscosity and the pressure impact on the viscosity of a liquid is very small. When studying multiphase liquids (a mixture of gas, liquid and solids) there are other factors that come into play.
- The SI unit of kinematic viscosity is m2/s. The cgs physical unit for kinematic viscosity is the stokes (St), named after George Gabriel Stokes. It is sometimes expressed in terms of centistokes (cSt). In U.S. usage, stoke is sometimes used as the singular form.
- Viscosity is the measure of a substance's resistance to motion under an applied force. The result is typically expressed in centipoise (cP), which is the equivalent of 1 mPa s (millipascal second). Shear stress is the force per unit area required to move one layer of fluid in relation to another.
- Viscosity and density are not related. Liquids with similar densities may have very different viscosities. Density remains essentially the same regardless of the temperature of a liquid, but viscosity generally changes quite dramatically with temperature.
Pressure Effects. Changes in presure have very little effect on the volume of a liquid. Liquids are relatively incompressible because any increase in pressure can only slightly reduce the distance between the closely packed molecules. If the pressure above a liquid is increased sufficiently, the liquid forms a solid.
- The pressure law states that for a constant volume of gas in a sealed container the temperature of the gas is directly proportional to its pressure. This can be easily understood by visualising the particles of gas in the container moving with a greater energy when the temperature is increased.
- When there is an increase in pressure, the equilibrium will shift towards the side of the reaction with fewer moles of gas. When there is a decrease in pressure, the equilibrium will shift towards the side of the reaction with more moles of gas.
- Heat is the total energy contained within a substance. As a solid is heated, its temperature increases as the molecules move faster. During the phase change, when solid melts into liquid, its temperature remains constant as the heat energy is stored as potential energy.
Even for a Newtonian fluid, the viscosity usually depends on its composition and temperature. For gases and other compressible fluids, it depends on temperature and varies very slowly with pressure. The viscosity of some fluids may depend on other factors.
- "In most cases, a fluid's viscosity increases with increasing pressure. Compared to the temperature influence, liquids are influenced very little by the applied pressure. The reason is that liquids (other than gases) are almost non-compressible at low or medium pressures.
- It is the ratio of the dynamic viscosity to its density, a force independent quantity. Kinematic viscosity can be obtained by dividing the absolute viscosity of a fluid with the fluid mass density. Kinematic Viscosity Formula Questions: First calculate the density mass of mercury using the formula ρ = mass/volume.
- The former effect causes a decrease in the shear stress while the latter causes it to increase. The result is that liquids show a reduction in viscosity with increasing temperature. With high temperatures, viscosity increases in gases and decreases in liquids, the drag force will do the same.
Updated: 19th September 2018