The dynamic viscosity of saturated liquid hydrogen at atmospheric pressure is roughly $\mu_{LH_2} = 1.3\times10^{-5}~Pa.s$. For the same conditions, its density is $\rho_{LH_2}=70.8~kg/m3$, so the kinematic viscosity of LH2 of saturated $LH_{2}$ is equal to $\nu_{LH2}= \mu_{LH_2}/\rho_{LH_2} = 1.8\times10^{-7}~ m²/s$. (source NIST)

If we look at air now, we see that at 15 °C, the viscosity of air is $ \mu_{air}=1.8 × 10^{-5}~Pa.s$ and its kinematic viscosity is $\nu_{air} = 1.5 × 10^{-5}~m^2 /s$.

So one can see that comparing those fluids for the conditions I provided that : $\mu_{LH_2} \approx \mu_{air}$ (very roughly) but $\nu_{LH_2} \ll \nu_{air}$.

Question : If my hand was at 20K, would waving my hand through this liquid hydrogen feels like waving my hand through the air because of the "similar" dynamic viscosity or would I feel way less resistance because of the very dissimilar kinematic viscosity ? This question Kinematic Viscosity touches on this topic but do not expand enough with its addendum since I am talking about a solid body through a fluid.


1 Answer 1


For Question 1, consider the drag flow of the respective fluids past a sphere. This is equivalent to observing from a frame of reference at rest with your hand.

For Question 2, assuming that in both cases, you have laminar flow, then yes. But, you would have to check the Reynolds numbers to be sure both were laminar.


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