Wikipedia:Reference desk/Archives/Science/2016 August 26

= August 26 =

A liquid other than water that is safe to put on your skin
Suppose that it's 50 C outside and the relative humidity is 95%. It would then be difficult to keep your body cool by sweating. But if you take a bottle with a liquid other than water with you with a sufficiently high latent heat and a sufficiently high rate of evaporation, you could spray that on your skin where it would evaporate quire rapidly and keep you cool. There are a few problems with this solution. One problem is that most compounds that are liquid at room temperature tend to be poisonous when put on the skin in large quantities, but perhaps some here know of some compound that is not going to kill you. Another problem is that water vapor from the atmosphere could condense on the liquid, so the Gibbs free energy for water-liquid mixture needs to be sufficiently high for this method to work. Count Iblis (talk) 02:26, 26 August 2016 (UTC)
 * Isopropanol? It's very drying if you keep doing it and hurts like Satan if it gets on mucous membranes though so you might want to dilute it with um, water. Or maybe not – it's very hot. I have no idea how hot that feels and it must depend on exposure time but 50C/95%RH doesn't actually occur on Earth. Maybe in a sauna. This will use up liquid fast! Sagittarian Milky Way (talk) 02:52, 26 August 2016 (UTC)
 * That article doesn't say it doesn't occur, just that if it did it would be extremely dangerous. And the other word to insert here is --- YET.  We'll see where we are five years from now... Wnt (talk) 19:25, 26 August 2016 (UTC)
 * SMW is correct -- this value is far outside the observed range. 50C with 95% relative humidity corresponds to a dew point temperature of 49C. The global record high observed dew point is 35C. Shock Brigade Harvester Boris (talk) 04:24, 27 August 2016 (UTC)
 * Thanks for finding the number. Now we'll have to check and see if this here clathrate gun is loaded...  there's nothing like a string of 10 Warmest Months Ever to make a person wonder if a tipping point really has been reached. Wnt (talk) 18:13, 29 August 2016 (UTC)
 * Perfluorocarbons could do what you want. They may not be good for global warming, but you should be able to select one.  Perhaps Perfluoroheptane or Perfluorohexane which is biologically inert. Graeme Bartlett (talk) 10:24, 26 August 2016 (UTC)
 * There isn't much that matches water for heat capacity, and I doubt that it takes nearly as much energy to boil perfluorocarbons either. Though then again, lacking these properties, Liquid nitrogen seems like a fair solution here since it starts off cold, if you can just arrange to atomize it a bit better with some kind of sprayer, and invent some kind of surfactant so it wets skin better (once you have it in small enough drops that you're not burning yourself if it does).  What the hell can you use for a surfactant for liquid nitrogen?  I definitely stumped Google with that phrase. :) Wnt (talk) 19:30, 26 August 2016 (UTC)
 * In this case the relevant property is not heat capacity, but latent heat of vaporization. Shock Brigade Harvester Boris (talk) 04:24, 27 August 2016 (UTC)
 * Hyperthermia may or may not help you. -- Jayron 32 12:26, 26 August 2016 (UTC)


 * Thinking a bit more about this problem, it seems to me that the condensation of water vapor from the atmosphere will be a big problem. Even if it doesn't dissolve well in the liquid, the fact that it's evaporation has a cooling effect will cause water vapor to condense of the surface of the liquid, causing it to absorb the latent heat of the water. Count Iblis (talk) 23:10, 27 August 2016 (UTC)


 * Short of wearing a containment suit, I don't see a way to prevent water from condensing on you if your skin temp is below the dew point. I'd say you should just embrace the water, and douse yourself in cool water continuously to stay cool, letting it drip off you.  Obviously not a good choice if you are working with electricity, though, so I'd go with the suit in such cases, since you don't want sweat or condensation dripping into the works.  And, in any case, items you keep with you that can't get wet, like your wallet, should be sealed in a plastic bag. StuRat (talk) 14:02, 29 August 2016 (UTC)


 * Polyethylene glycol (PEG) is as biocompatible as such things get, you can even swig modest amounts of it (I've had it prescribed for medical conditions). However, and it's a big however, you'd not want it on your skin if ultrasound or any other highly energetic sound source were in the neighborhood, as PEG degrades on exposure to intense or energetic sound to ethylene glycol, which will poison your kidneys if taken into your body, including through cuts on your skin.  I'd try as low a molecular weight a form as possible to allow optimum energy transfer from your skin.  It'd have the advantage of cooling your skin (hopefully) while forming a solution with the water in your sweat that might provide a wicking effect if the water evaporates from the air/PEG layer - and which also could be modulated with proper selection of molecular weight. loupgarous (talk) 00:12, 31 August 2016 (UTC)