I would like to compare the viscosity of "chilled" RP-1 as it is used for Falcon 9 launches to that of some everyday fluids. However, I am unable to find this information elsewhere. Would you please help me out? Thanks a lot!
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How cold do you want it? – Organic Marble Sep 25 '19 at 19:06
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2@OrganicMarble Falcon 9 Full Thrust cools it to -7°C – called2voyage Sep 25 '19 at 19:14
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different but viscosity-related question: Does the NK-33 engine require subcooled kerosene so cold that it turns to wax? – uhoh Sep 25 '19 at 22:29
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According to this nasaspaceflight.com forum post, the dynamic viscosity of Falcon 9 chilled RP-1 is about 3.3 cP.
The table here lists the viscosities of some maybe-not-so-everyday fluids; Falcon fuel is kept twice as viscous as ordinary kerosene at room temperature (1.64 cP), comparable to milk or blood. Water at room temperature is 0.89 cP.
I tried to find a more authoritative reference for the 3.3 cP figure, but had only partial success. Wikipedia gives the fuel temperature for Falcon as 266.5 K (-6.6º C). This NIST document contains extensive information on RP-1's properties, including its kinematic viscosity across a broad range of temperatures -- kinematic viscosity being the ratio of dynamic viscosity to density. Unfortunately, the density information in the document only goes down to 0º C. The temperature-density relationship is very close to linear over the measured range, however, and if I extrapolate the density down to the target temperature I get 0.819 g/cc. The kinematic viscosity for Falcon juice is about 3.7 mm^2/s, implying a dynamic viscosity of 3.7 * 0.819 = 3.0 cP, which is at least in the ballpark of the unreferenced 3.3 cP.
Russell Borogove
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Thanks a lot. I think this answer is fine. However I'd prefer a more authoritative source than a forum post ... is there any? – Everyday Astronaut Sep 26 '19 at 08:33
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@EverydayAstronaut Added some more info; no hard reference but 3.3 cP seems at least plausible. – Russell Borogove Sep 26 '19 at 17:02
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1Thank you for the rabbit hole I just got sent down figuring out what the heck a Poise is. Cool answer :)! – Magic Octopus Urn Sep 27 '19 at 16:58