Question

How is flow rate related to viscosity?

Answer 1

Viscosity is a major property of oils and lubricants which is used in many machines to reduce friction. Viscosity tells the property of resistance to flow. If the oil or liquid has a high flow rate then it will have low viscosity.

Complete answer:
There are many properties of the fluid or oil that tells the flowing property of the liquid and viscosity is one of the major properties of oils and lubricants which is used in many machines to reduce the friction. Viscosity tells the property of resistance to flow. We can relate the flow rate and viscosity as follows:
The flow rate can be denoted with F and it is equal to the pressure drop or difference in the pressure divided by the R (resistance to flow).
$F=\dfrac{\Delta p}{R}=\dfrac{{{p}_{1}}-{{p}_{2}}}{R}$
Since viscosity is the resistance to flow, so it will be directly proportional to the resistance to flow. And its equation is given as:
$R=\dfrac{8\eta L}{\pi {{r}^{4}}}$
So, we can put the value of R in the equation of the flow rate, we get a new formula:
$F=\dfrac{\pi {{r}^{4}}\Delta p}{8\eta L}$
Now, in this formula if we take the difference in pressure constant, r constant, and L constant, then we can write:
$F=\dfrac{k}{\eta }$
$\eta$ is the viscosity.
So, we can see that if the flow rate will increase the viscosity will decrease therefore, we can say that the rate flow is inversely proportional to the viscosity.

Note:
In heavy machines, the lubricants that have high viscosity or very low flow rate are used, so the machines can be used for a long duration and there are very few wear and tear movements.