Submitted by OvidPerl t3_121eza5 in todayilearned
Reply to comment by ahecht in TIL: Thanks to poor internal communication at NASA, information about a spacesuit water leak wasn't properly communicated. Later, Astronaut Luca Parmitano almost drowned on a July, 2013 ISS space walk, his helmet filling with several liters of water before they could get him back inside. by OvidPerl
The energy required for the water to boil would come from the thermal energy of the water itself.
This is just not how fluids work. Boiling fluids do not suck the thermal energy from surrounding fluids to do so, that would defy rules of entropy.
This is literally how sweat works.
Entrophy isn't an issue because it would still take energy to revert to its original liquid form.
Sweat regulates temperature, it doesn't actively cool the body to lower than the temperature of the sweat. Your skin and sweat equalise in temperature until the sweat evaporates or is wicked away.
It's the same in all liquid cooling, the substance being cooled cannot be cooled beneath the temperature of the coolant.
Assuke the water in the space suit would be relatively consistent throughout its volume. The drop in pressure from being exposed to hard vacuum drastically decreases the amount of energy it needs to boil. So for each water molecule, some of its thermal energy will essentially be used to change state. It won't suck energy out of neighbouring particles to do so unless they are significantly hotter.
If the water were in a sealed chamber you might observe what you described, because the now cooler vapour would be contained with any remnants of liquid water. In open space however, the vapor would disperse too quickly for the vapor to take any meaningful amount of heat away.
I say this ironically while writing a report on the nitrogen cooled cryostat I made for a uni project.
>Your skin and sweat equalise in temperature until the sweat evaporates or is wicked away.
That doesn't even make sense. Your sweat literally comes from your body. It starts at the exact same temperature as your body. It can't take warmth from your body until it's the same temperature as the rest of your body since it was already at body temperature to begin with.
Sweating is entirely a form of evaporative cooling. Even the wikipedia articles says as much.
Buy a bottle of canned air and spray it. You can feel the bottle cool down dramatically to the point where it can cause frostbite as the compressed liquid inside turns to vapor. To the point where the bottle will stop working if you run it for too long.
Take a cooler full of ice, place a thermometer in it, and add salt. Since the ice will melt without heat being added the water will drop in temperature dramatically compared to the ice you started with.
Here is a god damn youtube video of someone freezing water by boiling it in a vacuum.
Again, it may work in a vacuum I an enclosed space where the vapour continues to be in contact with the liquid water. In open space the vapor would dissipate too quickly.
It's a vacuum in the video. The water vapor is being removed by the pump as fast as it boils. If it wasn't, it would stop being a vacuum.
Your skin and sweat are already the same temperature. Just as you say later on, thermal energy is used to change state to vapor. Because water and skin conduct heat, it will equalize and cool your skin.
Just plain circulating liquid cooling is a closed loop without a state change. Unless you are talking about refrigeration. Then compressed gas is hotter than ambient and then equalizes with surrounding air outside the radiator. And then when the refrigerant is depressurized, it has a lower thermal density than ambient air and can chill things.
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