On Mon, 11 Feb 2019, Lux, Jim (337K) via Beowulf wrote:
Stu reports swimming, but perhaps he was really more wading.
A beautiful summary below. I should keep it to use with my students when we cover Archimedes' Principle and buoyancy. I hadn't even thought about this danger from dealing with large tanks of low density fluid, but it makes sense -- you can drown in CO2 if you go down in a crater full of CO2 because you don't float to the top and surely can't swim to the top... OTOH, in the Dead Sea or the Great Salt Lake (or even just the Mediterranean) the density is greater than that of fresh water, and it is correspondingly easier to tread water or swim, harder to drown. I don't think you could "drown" in a well-ventilated vat of mercury unless you deliberately rolled face down on it, although breathing in the mercury vapor over its surface would certainly be a problem. Very nice! rgb
A significant problem with large vats of liquid, whether used for cooling electronic equipment, or just storage, is that if the density is significantly less than that of water, you don?t float. Humans are just slightly positively buoyant in water (with full lungs). Change that to oil or corn syrup or scotch whisky with a density of 0.9, and it?s like having 5-10 kg of weight on you, and that takes a lot of work to stay on the surface. This is a well known hazard in the petroleum processing industry (aside from the fact that the air above the tank?s liquid surface is probably full of all manner of unhealthy things and not oxygen) ? you fall in the big tank, you die. Diala AX (a HV insulating oil I?ve used) has a specific gravity of 0.885, and is somewhat more viscous than water (not a lot) ? if you fell into it, and couldn?t support yourself by standing on the bottom or equipment within the tank, you?d need to be rescued pretty quickly. The increased viscosity would also mean that it?s more work to keep ?treading oil? to stay above the surface. USP white mineral oil is about 0.85 g/cc. We had a thousand gallon tank of this where I used to work, and there was a whole discussion about safety ? it was a wide flat tank, so in theory, if you fell in, you could stand up (except that the tank was polyethylene and it *is* oil.. there were questions about whether you could stand up on the slippery surface) Of course, you can get oil in all densities ? the stuff they use for road surfacing is quite dense. Fluorinert FC-40 (which I?ve also used) is quite dense ? 1.85 g/cc ? you?d float well above the surface like a cork. A quick glance at the line card for Novec? shows they?re all pretty dense - 1.4g/cc is the least dense. --
Robert G. Brown http://www.phy.duke.edu/~rgb/ Duke University Dept. of Physics, Box 90305 Durham, N.C. 27708-0305 Phone: 1-919-660-2567 Fax: 919-660-2525 email:r...@phy.duke.edu _______________________________________________ Beowulf mailing list, Beowulf@beowulf.org sponsored by Penguin Computing To change your subscription (digest mode or unsubscribe) visit http://www.beowulf.org/mailman/listinfo/beowulf
