Variable viscosity

In summary, the conversation discusses the relationship between viscosity and pressure in different types of flow. For liquids, both dynamic and kinematic viscosities are independent of pressure, but for gases, only dynamic viscosity remains constant at low to moderate pressures. Viscosity is caused by internal frictional forces and varies greatly with temperature, decreasing in liquids and increasing in gases.
  • #1
hoomanya
90
0
Hi,
I think I'm mixing things up... For a flow with low compressibility, I know density varies but does viscosity also vary? Does that depend on whether the flow is laminar or turbulent.
Thanks,
H
 
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  • #2
For liquids, both the dynamic and kinematic viscosities are practically independent of pressure, and any small variation with pressure is usually disregarded, except at extremely high pressures.

For gases, this is also the case for dynamic viscosity (at low to moderate pressures), but not for kinematic viscosity since the density of a gas is proportional to its pressure


Viscosity is due to the internal frictional force that develops between different
layers of fluids as they are forced to move relative to each other.

Viscosity is caused by the cohesive forces between the molecules in liquids and by
the molecular collisions in gases, and it varies greatly with temperature.

The viscosity of liquids decreases with temperature, whereas the viscosity of
gases increases with temperature
 

1. What is variable viscosity?

Variable viscosity is the property of a fluid to change its resistance to flow based on its temperature, pressure, and shear rate. This means that the viscosity (thickness) of the fluid can change depending on external factors.

2. How does variable viscosity affect fluid flow?

Variable viscosity can significantly impact fluid flow because the thickness of the fluid affects its ability to move through a system. If the viscosity changes, it can alter the velocity and direction of the flow, potentially leading to inefficiencies or disruptions in the system.

3. What are some examples of fluids with variable viscosity?

Some common examples of fluids with variable viscosity include motor oil, honey, and lava. These fluids have different viscosities at different temperatures and pressures, which can affect their flow properties.

4. How is variable viscosity measured?

Variable viscosity can be measured using various techniques, such as a viscometer or rheometer. These devices apply a force or shear stress to the fluid and measure its response, providing information about its viscosity at a specific condition.

5. What are the practical applications of understanding variable viscosity?

Understanding variable viscosity is crucial in many industries, such as food processing, oil and gas, and pharmaceuticals. It helps engineers and scientists design more efficient systems and predict the behavior of fluids in different conditions.

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