3
$\begingroup$

So in my story the protagonist is a genetically enhanced vigilante that uses a full bulletproof jumpsuit in her activities.

But because of her accelerated metabolism, dealing with the heat of getting inside a closed suit would be undoable without a cooling suit, and i envisioned some sort of smart fabric full-body compression sleeve with embedded structural batteries that collect energy both from the movement and the heat of the body, effectively absorbing the heat and cooling her down even if it's a closed system.

The energy collected could be used for heating when it gets cold or drying in case of getting wet.

Does this concept make sense?

Edit: I guess i didn't made exactly clear what "closed system" means in the question, i meant that is an impermeable jumpsuit so there's not much ventilation, i though about it being coated in some futuristic waterproof coating like aerogel of some kind that would also fireproof the suit and provide electric insulation, but I don't think that the air would circulate anyway.

"jdunlop" made a good job of summarizing the question:

"can I cool an environment by capturing the heat as electrical energy?" to which the answer is "no"

If not by convection, it can still be by conduction and/or irradiation I suppose, and there are some very interesting suggestions in this answers, thank you.

Like the suit that conducts heat away from the skin, that would probably create a pocket of hot air between the sleeve and the jumpsuit, and I don't know if this is a good or a bad thing...

But there's also the irradiating coating option that could be applied to the jumpsuit, but i would rather it to have infrared camouflage and i think this would be more of a deterrence...

Maybe the jumpsuit could have some exhaust openings, in an angle where rain wouldn't enter anyway, how did i not though about this before?

$\endgroup$
11
  • $\begingroup$ Why is this a problem? $\endgroup$
    – Daron
    Jul 28 at 18:47
  • 3
    $\begingroup$ May want to edit the "closed system" part. I think I know what you mean but some take certain phrases literally and are biting at the bit to get mileage from their degrees. $\endgroup$
    – Gillgamesh
    Jul 28 at 18:54
  • 2
    $\begingroup$ @gillgamesh certainly true! It's one of those loaded terms that you cannot quite discern if they are using it in a strict sense or a broader sense. I wonder if we can have a buzzword warning when submitting questions... $\endgroup$
    – PipperChip
    Jul 28 at 19:13
  • $\begingroup$ @PipperChip not a bad idea! I await the coming of our AI overlords! I can't fault anyone for pointing out these phrases. And Had the Hard Science tag been applied I would have a completely different take. $\endgroup$
    – Gillgamesh
    Jul 28 at 19:21
  • $\begingroup$ Need to circulate cooled fluid (water works), to some sort of unit on the back. That's where heat exchange occurs. Probably not alot of energy can be harvested from it, possibly none. There have been a few experimental systems, increased athletic potential is hinted at, if not outright shouted. $\endgroup$
    – John O
    Jul 28 at 19:34

7 Answers 7

3
$\begingroup$

In principle, I'd say it's POSSIBLE. At least almost.

If the suit absorbs her body heat, where does the heat go? You say it's a "closed system" which I take to mean that the heat is not radiated to the outside air. So you must be storing the heat energy somewhere, some kind of battery. In principle, you could have a thermoelectric generator that converts the heat differential between the person's body and some lining in the suit into electricity and uses that to charge a battery. I'm not aware of anyone having built a device quite like this, but it sounds plausible to me.

There's no such thing as 100% efficiency so trying to build a suit that will absorb heat on hot days or when you're burning calories and then release it back when you're cold, even if the thermodynamics was doable it won't be 100% efficient so you'd have to dump heat at some points and have a power source to produce more heat at other times.

$\endgroup$
8
$\begingroup$

Not If It's a Closed System

The Second Law of thermodynamics says no. Transformation of energy results in wasted energy. Wasted energy is released as heat. You cannot generate energy from heat without a gradient, as specified by @PipperChip.

So if a system is closed, if you don't have an entropy sink (eg. something very cold that will be exhausted), the heat energy cannot be captured as a means of reducing entropy, because the entropy of the system must always increase.

$\endgroup$
7
  • $\begingroup$ To my updated answer's point, a true thermally closed system is very rare, approaching impossible. Most IRL situations are not closed systems, although sometimes we can use this idea to make predicting behavior easier! $\endgroup$
    – PipperChip
    Jul 28 at 18:34
  • $\begingroup$ @PipperChip - this is true, but a heavily insulated outer suit would make it effectively closed. Ultimately, it seems (to me) like the OP's question boils down to "can I cool an environment by capturing the heat as electrical energy?" to which the answer is "no". $\endgroup$
    – jdunlop
    Jul 28 at 18:38
  • $\begingroup$ Closed system, yes, but for how long? Imagine a "thermal battery" of some sort which is incredibly small and has enormous storage capacities. Yes, it will have to be replaced from time to time, but if lasts for long enough, then for the purposes it's used for, is essentially "infinite". $\endgroup$
    – vsz
    Jul 29 at 17:44
  • $\begingroup$ @vsz - A "thermal battery" is an icepack. You need an entropy sink. And it sounds like unlimited duration. You cannot transform heat into more useful energy as a means of cooling something without somewhere to radiate/dump the heat. $\endgroup$
    – jdunlop
    Jul 29 at 18:27
  • $\begingroup$ @jdunlop why unlimited duration? Will that suit be used without maintenance until the heat death of the universe? Or at least for millions of years? No, likely it will be used for a few hours at a time, at most a few days. So you can have a heat pump, storing the heat somewhere, which you later dump. It will be a closed system until the vigilante goes back to her home base to recharge the suit and dump/replace the hot part. $\endgroup$
    – vsz
    Jul 30 at 1:10
6
$\begingroup$

Possible, With Caveats

This is an interesting series of thermodynamic problems. As people have already stated, you need a cold reservoir (e.g. the environment) to extract any usable work from a temperature gradient. I'm going to assume that by "closed system" you mean "no external usable power inputs" and not a thermodynamically closed system. The upper efficiency limit on a heat engine operating between two reservoirs is the Carnot efficiency: 1-Th/Tc. From this discussion on Physics SE, the baseline thermal output of the human body is probably around 100-120W. If your enhanced vigilante is 10x that, you could expect to have 1200W of body heat. Extracting energy from this gradient is possible, but a perfect heat engine will only generate 60W from 1200W in at room temperature and less if it's warmer. You'll see this is a bit of a problem since as the environment gets hotter, the thermal gradient is less so you are less able to passively reject heat and your available power for a cooling system is also lessened.

As for cooling systems, the number you need is called the Coefficient of Performance or COP, which is the ratio of how much heat can be transferred from the area being cooled to the environment per unit of work put into the system. It's usually around 4 or 5. Since heat will only naturally flow from a hotter area to a colder one, your heat pump needs to dump heat at a higher temperature than the environment and your vigilante would need to have some sort of radiator on her suit. The energy to power the heat pump would be more than what could be harvested from thermal means so you need a bit of extra energy from somewhere.

You could possibly make up the difference from kinetic energy harvesting. This article gives a figure of 10-11W from leg-powered systems. Make that a round 50W if you extend that to the whole body and multiply it by your vigilante's enhanced strength and you might be getting somewhere. You could add in the detail that her baseline metabolic rate isn't too much higher than normal (a few x) and that the real problem is only when she's engaged in physical activities. It would also throw in the odd twist that above a certain temperature, she needs to be constantly moving in order to not overheat.

I've also not dived deep into the specifics behind it but electroactive polymers are a possible way to harvest energy that could be somewhat more efficient than existing kinetic systems. They also have the interesting ability to act as muscles when power is applied to them, making the cooling suit a strength suit when necessary. It could also explain the bulletproof nature of the suit by having a patch stiffen on an electrical command if it is impacted by a bullet or some other projectile. I think they actually used that device in the original Deus Ex.

$\endgroup$
2
$\begingroup$

Thermoelectric Generators

Yes, we can harvest heat from a gradient (like from a warm person to cooler air) to yield electricity. This could power some sort of further cooling system or other electrical gadgetry. There is a simpler solution

Increase Surface Area and Conductivity

You could simply weave very cheap, flexible metal threads into the suit. These metal threads will conduct heat away more quickly than air, allowing the person to cool themselves more quickly. It can be something cheap, like annealed aluminum. It is passive, so no active effort is required to keep the system cooling. This effectively raises the surface area the skin has to remove heat, a practice we see in cooling towers and heat sinks.

Radiative Cooling

Okay, nothing is really a closed system. Even in the vacuum of space, which denies conductive and convective cooling, you can radiate heat. In fact, this is exactly what modern satellites do.

This means you need something that radiates infrared heat easily. Enter the cutting-edge world of radiative cooling paints. Place these into the outside surface of the suit, and it will cool in most situations. Once again, this technology doesn't require any fancy electronics or anything, so it just is "always on" and working.

Closed System?

Closed systems are very rare, practically impossible, especially when it comes to heat flow. If your character is suddenly in a vaccum AND surrounded by perfectly reflective surfaces, they have bigger problems than overheating. This is usually an approximation we use to make thing easier.

$\endgroup$
3
  • 1
    $\begingroup$ The OP specifies that the system is closed, so no gradient is provided. $\endgroup$
    – jdunlop
    Jul 28 at 18:17
  • $\begingroup$ @jdunlop addressed the "closed system" issue! $\endgroup$
    – PipperChip
    Jul 28 at 18:29
  • $\begingroup$ @PipperChip That doesn't address the issue. The gradient of the body heating up the suit will effectively be useless at producing work. $\endgroup$
    – DKNguyen
    Jul 29 at 3:32
2
$\begingroup$

Prity much a Dune StillSuite. StillSuite Just add a bit of magic sci-fi dust to enhance the efficiency of real world thermocouples to extract some power from the heat differential of her body and the atmosphere, (Or just use some batteries), to circulate the suites water over radiative materials. If she is like really hot .. any excess electricity can be used for powered cooling using peltier devices..

$\endgroup$
1
  • 1
    $\begingroup$ I miss StillSuite. Microsoft Still or Google Distillation just aren't the same. $\endgroup$
    – jdunlop
    Jul 28 at 20:22
2
$\begingroup$

The laws of thermodynamics prevent this from working. One of the rules of thermal energy is that it cannot be used to produce usable work. In order to store the energy in batteries, it needs to be able to do work. If you try, you end up generating more heat in other places, in a never ending spiral that never wins.

What you really need is a radiator. You need something on the outside of the suit to dissipate the heat and a way to transfer that heat. Once you have that, the best tool for the job is a heat pump, which is what an air conditioner is. They are extremely efficient at moving large quantities of heat from one place to another (even into a sink that's warmer than the source). You could power this using whatever method you like (such as harvesting some energy from movements).

Your "cool suit" would be one half of a heat pump system. The heat pump would continuously pump heat out of the inside of the suit (perhaps via a water cooling jacket) and transfer it to a rather hot radiator on the outside which can then radiate that heat into the atmosphere.

This could also be used to provide temporary defense against thermal imaging. The radiator could be used to cool down a "cold store" inside of the suit, in addition to the wearer's body. When thermal camouflage is desired, heat can be sunk into that cold store instead of the radiator, allowing the radiator to remain cold. Otherwise, you just have to make sure the radiator isn't anywhere on the body the enemy can see.

I recommend Technology Connection's video on how heat pumps work. He goes into the details of what they actually do (with real life residential technology).

$\endgroup$
1
$\begingroup$

No Problem

In your universe you have already handwaved such things as the bulletproof jumpsuit. I presume you mean something like what Tuna Thurman wears in Batman and Robin:

enter image description here

Here is the thing. Bulletproof jumpsuits are not real. When I see Tuna Thurmann leap from building to crosswalk getting pelted by machinegun fire and the bullets go plink plink plink off her rock hard thighs, I don't get out my Science Hat and Cape and try to estimate the cross-sectional shear of the nylon kevlar polymer needed to deflect the shrapnel.

I simply suspend my disbelief and agree that for the next hour and a half this kind of super suit makes perfect sense.

And while I'm at it, I suspend my disbelief on a bunch of less ridiculous things. If bulletproof jumpsuits are real, many other things do not require explanation.

Like heat dissipation. Super heat dissipating materials are easier to believe than super bullet-reflecting ones. When her head comes off, that's a problem.

enter image description here

"Say Freeze!"

$\endgroup$
2
  • $\begingroup$ About the armor, it's not the type of armor that can stop any bullet, and it's not skintight collant either, it's set in the future so I allowed myself some handwaving, but it's made of soft armor like UHMW polyethilene embedded in liquid armour that turns into solid when hit to spread the impact across a larger area and damp concussive damage(this is a real thing look it up), there are also the gauntlets that cover the forearms and that can unfold into a ballistic shield, now these being is made of ballistic plates that can stop more penetrating rounds. $\endgroup$ Jul 29 at 0:15
  • $\begingroup$ The bulletproof cornstarch slurry armor is only slightly more believable than the spandex catsuit armor. My answer remains the same. Cooling is not an issue. $\endgroup$
    – Daron
    Jul 29 at 14:24

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .