# Lowest Kinematic Viscosity Fluid - High Pressure Gas

• Timtam
In summary, a lowest kinematic viscosity fluid is a fluid with low resistance to flow and shearing forces, measured by dividing dynamic viscosity by density. In high pressure gas systems, it can improve efficiency and reduce friction and damage to equipment. While gases can have a kinematic viscosity, their values are typically much lower than those of liquids. This type of fluid can greatly enhance the performance of a high pressure gas system by enabling smoother and more efficient flow, reducing energy consumption, and preventing clogs or blockages.
Timtam
I am trying to determine which fluid to use in an experiment.
An important aspect of the experiment is the ratio of inertial forces (due to mass) vs the viscous forces that the fluid will experience

Amongst common liquids the lowest I can see is Acetone with a kinematic viscosity of 0.41 cSt
(Abs Viscosity0.3mpa.s, Temp 20'c, Density 0.791 g cm−3, Pressure 1 atm)

Amongst gases absolute viscosities are a magnitude less (eg Air 0.005 cSt) but as the densities are also way less. (Again eg: Air 0.00035kg/m3) We actually end up with a higher Kinematic viscosity - the ratio of inertial to viscous is worse.

What interests me is the statement that gas viscosity is independent of pressure ( by the reason that as pressure increases, density increases and the mean free path inversely falls - from good old Wiki

"Maxwell's calculations show that the viscosity coefficient is proportional to the density, the mean free path, and the mean velocity of the atoms. On the other hand, the mean free path is inversely proportional to the density. So an increase in density due to an increase in pressure doesn't result in any change in viscosity"

My question is if I want to improve the inertial forces the fluid flow carries (by way of its mass) without increasing viscosity -Should I use a high pressure Gas (increase its density~mass) as I would only see a weak affect on its Dynamic Viscosity

Higher density for same Dynamic Viscosity would equate to a lower Kinematic Viscosity ?

My fluid carries higher inertia for same viscosity, Is this correct ?

I would first like to commend you for considering the ratio of inertial to viscous forces in your experiment. This is an important factor to consider when choosing a fluid for an experiment.

Based on the information you have provided, it does seem that using a high pressure gas would be a good option for your experiment. As you mentioned, increasing the pressure of a gas would increase its density, which would in turn increase its mass and therefore its inertial forces. This would result in a higher ratio of inertial to viscous forces, which aligns with your goal of improving the inertial forces in your fluid flow.

Additionally, as you pointed out, the viscosity of a gas is independent of pressure, so increasing the pressure would not significantly affect its dynamic viscosity. This means that you would not have to worry about the gas becoming too viscous and affecting the flow in your experiment.

In terms of the kinematic viscosity, it is correct that a higher density for the same dynamic viscosity would result in a lower kinematic viscosity. This is because kinematic viscosity is calculated by dividing the dynamic viscosity by the density.

In summary, it seems that using a high pressure gas would be a good option for your experiment if you want to improve the inertial forces without significantly increasing the viscosity. However, as with any experiment, it is important to carefully consider all factors and conduct thorough testing to determine the best fluid for your specific experiment.

## 1. What is the definition of a lowest kinematic viscosity fluid?

A lowest kinematic viscosity fluid refers to a fluid with a low resistance to flow, meaning it has a low resistance to shearing forces. This is typically seen in liquids, but can also be found in gases with very low molecular weights. In scientific terms, kinematic viscosity is the ratio of a fluid's dynamic viscosity to its density.

## 2. How is kinematic viscosity measured?

Kinematic viscosity is measured by dividing the dynamic viscosity of a fluid by its density. The resulting unit is usually either centistokes (cSt) or square meters per second (m^2/s). This measurement is important in determining the behavior and flow characteristics of a fluid.

## 3. What is the significance of a lowest kinematic viscosity fluid in high pressure gas systems?

In high pressure gas systems, a lowest kinematic viscosity fluid is important because it can help reduce friction and improve the efficiency of the system. Low viscosity fluids are also less likely to cause damage to equipment and piping, as they are less abrasive and easier to control.

## 4. Can a gas have a kinematic viscosity?

Yes, it is possible for a gas to have a kinematic viscosity. This is most commonly seen in gases with very low molecular weights, such as helium or hydrogen. However, the kinematic viscosity of a gas is usually much lower than that of a liquid.

## 5. How does a lowest kinematic viscosity fluid affect the performance of a high pressure gas system?

A lowest kinematic viscosity fluid can greatly improve the performance of a high pressure gas system. This is because it allows for smoother and more efficient flow of the gas, which can reduce energy consumption and increase system longevity. Low viscosity fluids are also less likely to cause clogs or blockages in the system, which can lead to costly repairs.

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