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 ?