Question

Viscosity of a fluid vary with temperature?

Answer 1

Viscous forces in fluid are outcome of intermolecular cohesion & molecular momentum transfer.

For liquids :

Increase in temperature causes a decrease in viscosity of liquid.

Now, in liquid molecules are closely packed. So, we neglect molecular momentum transfer. Another criteria we consider is cohesion force. Now, as temperature increases cohesion force decrease. So, fluid can easily flow that means viscosity decrease.

For gases :

Increase of temperature causes a increase the viscosity of gases.

Now, in gas cohesion forces between molecules are less, so we can neglect it. Another criteria we consider is molecular momentum transfer.

As temperature increases molecular momentum transfer increase. So, we know we consider resultant vector of all molecular velocity for fluid velocity. But molecules moves randomly as temperature increases. So, fluid can not easily flow. So, viscosity is increase as temperature increases for gases.

Hope, this helps.

Answer 2

Explanation:

In general, the viscosity of a simple liquid decreases with increasing temperature. As temperature increases, the average speed of the molecules in a liquid increases and the amount of time they spend "in contact" with their nearest neighbors decreases.

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