Sweat is a pretty good way to cool off and I know to drink lots and lots of water. But is there a way I can make the sweat evaporation process “better” so that I cool off more? I’m thinking maybe there’s some substance that I could rub on my skin which would make the evaporation take even more heat away from my body. Anything like that out there?
a fan
Rub the fan on your skin? Better make it a female fan.
Just thinking out loud here:
The latent heat of vaporization of water is (IIRC) 539 cal/gram - a substantial cooling, when you consider that it only takes about 100 cal to raise liquid water from its freezing point to its boiling point. This is both the amount of energy that a gram of water must acquire to evaporate, and most of the heat it carries away. How does a gram if water acquire so much heat? It’s a statistical matter: in any sample of water, differnt molecules have differnt energies, and the temperature is only an average. If an unusually energetic molecule is at the surface, it escapes like an embezzing executive, taking a disproportionate amount of energy with it, leaving behind a sample that is “poorer” (cooler) on average.
The boiling point of a liquid reflects its tendency to evaporate (it’s the temperature at which the partial pressure equals atmospheric pressure), and as a general rule, substances dissolved in water tend to *increase[/ the boiling by (IIRC) 1.86 °C/molal (1 molal is 1 mole of solute dissoved in 1 kg of water) – the opposite of what you want. Even if you did smear yourself with an exotic chemical that decreased the boiling point of water, the effect would be small: the amount of heat required to raise the temperature a few extra degrees would only be a few calories.
(The 539 cal/g heat of vaporization would be unchanged, because that’s also the heat that id “refunded” when water vapor condenses. Water molecules have no memory, and can’t remember they flew off on a “discount fare” when the time comes to refund it.)
How do you decrease the boiling point of water? well, I can’t think of any wexamples at the moment, but the general principle would be: by decreasing the attraction between water molecules. I’m pretty sure you wouldn’t want that on your skin, because it would interfere withthe thermodynamics of every reaction inside your mostly aqueous skin cells (and all your other cells).
Any molecular biologist would tell you that’s a Bad Thing. Cells are delicate balances. You’d be amazed how many things would be affected: for example, the lipid bilayer (fatty, oily chemicals) that primarily make up your cell membranes would not stick together as well. Oil doesn’t actually repel water - it’s just that water attracts itself so much that the oil is excluded as the water tries to increase the water-water interaction. You don’t want to mess with all your cell membranes! Nerves might be particularly affected, because action potantials -the signals on neurons- are ion imbalances across the highly specialized neuron membrane.
In short - the answer is “no”. There’s almost certainly nothing that would work safely. If something is marketed, it won’t work.
However, if you have ample excess water, your sweat might be somewhat more dilute, and its boiling pointy wouldn’t be elevated as much by the dissolved salt. This would be a tiny effect, because, mole for mole, there isn’t very much salt in your sweat anyway, and your kidneys would get rid of any substantial excess water anyway.
Indeed, if I ever have fans, I prefer they be female fans. Groupies, even.
Increase the surface area from which your perspiration evaporates, by putting on a thin cotton t-shirt. Perspiration wicks away and evaporates, rather than dripping or running off = More efficient cooling. Ever notice what the Saudis wear in the desert? Much cooler than bare skin.
Cotton doesn’t wick away sweat. It absorbs it. There are materials that do, such as polypropolene (olefin). I’ve found that wearing no shirt, as opposed to a thin T-shirt or even a mesh singlet is the coolest. I believe it’s against the Saudi’s religion to go naked.
A shirt does not increase the surface area from which your sweat evaporates. In the first place, in spite of some dripping, your body will have much more sweat than the T-shirt, which absorbs only some of the sweat. In the second place, you are not concerned about cooling off your shirt, but cooling off your body. In the third place, a shirt, no matter how thin, adds additional heat to the body.
Your brain controls body temperature. Almost all of your body heat is eliminated through your skin and that is the way most of the calories you consume are eliminated. Calories are a measure of heat, and your body must eliminate most of the calories you consume, and does so through your skin. Therefore, the more you eat the hotter you will feel. Evaporation is by far the greatest agent in cooling your core temperature, but not the only one. There are 3 others: conduction, convection, and radiation.
There are two main ways your brain can effect heat loss thru your skin: increase the blood flow through the skin, and increased sweat. When blood reaches the surface of your skin, calories are lost to the surrounding environment, and calories are a measure of heat. You are also cooled by evaporation of invisible sweat. But when your temperature rises more, the brain turns on the sweat glands, increasing the sweating.
The exchange of heat from the skin to the environment depends on several factors. Radiation is the most important, accounting for 60% of heat loss under resting conditions. Your body is a metabolic furnace that constantly radiates heat. You can also gain heat by the sun’s radiation.
You also lose or gain heat by conduction. If you sit on a hot surface, you will gain heat. In contrast, cold water causes heat from the skin to be conducted to the water.
Closely related to conduction is convection, which is moving the warmed water or air away from the skin and replacing it with cooler water or air. That is why a cool breeze helps, but not a hot breeze.
At room temperatures at rest, about 25% of your calories of heat are eliminated by insensible perspiration. As you exercise and increase the need to eliminate heat, you sweat more and the heat loss is increased. That is why humidity causes heat stress. It limits your ability to cool by evaporation. In humid environments, the body must rely mostly on radiation, conduction, and convection to cool.
95% of the calories you consume and eliminate are eliminated through your skin. Only about 25% of the calories expended with exercise are used for the mechanical effort. The other 75% are from heat produced by the muscles. That is why vigorous exercise causes the body temperature to rise.
(Source: August 1991 issue of The Health Letter.)