Imagine that a robot disguised as a child walks into an airport to board a plane. Because of the pandemic there are many IR scanners stationed at every entrances/exits within the premises.

This android is state owned and its first real world assignment is to cross an ocean without exposing its identity, so far the state of the art AI has managed to fool everybody.

It is powered by a sophisticated hydrogen cell reactor which produces 67,000 Watts for normal operation, how does it cool or vent the excess heat without raising alarms at the checkpoint?

Assume 1 million btu if you must ;D

  • 1
    $\begingroup$ i think 67000 watts will be fairly hard to manage, as in impossible hard $\endgroup$
    – Topcode
    Jan 11, 2021 at 6:17
  • 3
    $\begingroup$ How did it fool everybody while melting the world around them? 67kw coming from the body of a child is going to cook food within several meters. $\endgroup$
    – Ash
    Jan 11, 2021 at 6:19
  • $\begingroup$ Good thing she's flying and not traveling by boat. 67kw of heat at sea will create moist updrafts, forming thunderclouds. I haven't done the maths on this but I suspect your child may be a cyclone machine. $\endgroup$
    – Ash
    Jan 11, 2021 at 7:23
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    $\begingroup$ @Ash: 67 kW is very very much less than the exhaust of any half-decent marine engine. I don't read about container ship does not create thunderclouds above them, and they exhaust a hundred times more heat. But anyway, that child will glowing red hot... $\endgroup$
    – AlexP
    Jan 11, 2021 at 8:24
  • $\begingroup$ I wonder any material can absorbs >90% IR? ;P $\endgroup$
    – user6760
    Jan 11, 2021 at 14:25

7 Answers 7


I think that when you made the back of the envelope calculation to size your kid you must have spilled some beverage on the envelope and messed up with the numbers.

First of all, 67 kW is a lot. If it was a car engine it would be about 90 horse power. In a single kid body!

A human kid can already be annoying enough when on sugar burst, I don't dare imagine how would it be traveling with such a kid next to my seat!

Then you say that 67 kW is the power for normal operation. Assuming that this kid doesn't juggle boulders or some similar heavy physical work in normal operations, and that normal operation is indeed just running the AI systems and whatsoever controls it, it means it is spitting out all that whole energy as waste heat, because that energy is not leaving the body under any other form than heat.

But look at the bright side: this kid would be so hot that airport security wouldn't catch them for the simple reason that the airport would be burning way before they could walk in the security check.

  • 1
    $\begingroup$ 67,000 Watts, not 67000 kW, 67kw. Still massive. 90 horsepower. Still lighting fires as she walks. $\endgroup$
    – Ash
    Jan 11, 2021 at 6:50
  • $\begingroup$ @Ash, thanks. Corrected $\endgroup$
    – L.Dutch
    Jan 11, 2021 at 6:56

Temperature is the Least of Your Problems

Modern Airports utilize full body x-rays machines to detect for hidden weapons and contraband. By posing as a child who is under 13 years old, your robot might be exempt from a full body xray scanner... but that airport has the right to perform whatever alternative screening policy they want. In many cases, the "alternative screening policy" is that the child is still required to go through an xray scanner as long as they are physically and mentally able. So, if your robot is just a pluckly little pre-teen, it will still usually get xrayed and it's lack of human internal structures will be revealed.

However, let's say your robot is posing as a crippled or mentally handicapped child, the robot would still have to be carried through a metal detector as a bare minimum precaution to make sure that the "guardian" is not using the child to smuggle a weapon onto the plane. But, building a robot without any metal in it is pretty much impossible; so, your robot will raise some serious alarms.

This means that your guardian will need some forged documents saying that the child has all sorts of metal implants. At this point, TSA may still require a strip search or require a full body x-ray since the metal detector scan would be so inconclusive. Designing a robot that can pass for human through the whole strip search process without falling into the realm of uncanny valley would be especially difficult. This means your robot has to not just look human, but feel human too. Human skin releases sweat and oils, it is warm to the touch, and has a certain platistity that is VERY hard to replicate because it is a layered composite of different materials with different physical properties. Also, your robot will need scars all over its body to explain the metal implants; so, if you need your child robot to perk up and look like a normal human child once it gets to the other side, your odds of getting past TSA are very low.

Lastly, there is also a good chance that your robot will spook drug dogs for not smelling human which could also lead to a full body search or compulsory x-ray.

A Way Easier Alternative: Travel by Mail Instead

Just ship it like the piece of hardware that it is. We humans pay a premium to fly in air-conditioned, breathable, commercial flights, but robots don't need all that comfort. Just put your android in a crate, label it as a sex doll (hopefully you were just wanting it to look like a child to get past TSA...), and ship it. Worst case scenario is that someone xrays the package, finds something that looks a lot like a robot, and ships it anyway since shipping robots is not illegal.

This also means your robot does not need to be on to get where it is going; so, there is no heat output to worry about but you do need to be careful about its power source. It can not have any radioactive fuel in it, or you will have a VERY big problem trying to go by airport or frieght.


Lots of insulation, and heat sinks.

This is only going to work for a limited time, 67kw is just too much to hide for more than a few minutes. So you use heat pumps to push your waste heat into a heat sink, hidden somewhere deep inside the android within a lot of insulation. This heat sink is going to get unbelievably hot, like "center of a blast furnace" hot. But it's hidden deep in an insulation cocoon and so doesn't show up on IR scanners. Once you're away from any pesky scanners, turn off that heat pump and pop out the heat sink.

This is in addition to Ash's suggestions. Just to be clear, you're never going to be able to hide 67kw for long.

  • $\begingroup$ A heatsink made of 5kg of steel, absorbing that heat for 6 minutes (The best airport security wait time I've ever had), will reach 10,351 degrees. That's enough to liquify it. That's hotter than surface of sun. Equivalent to about 100 meters from the Little Boy nuke. Good luck popping that out discretely inside an airport terminal. $\endgroup$
    – Ash
    Jan 11, 2021 at 7:38

Reduce the power.

A (massive enough) CPU core burns about 400W, and normal human operations require about 200 W. So let's start by reducing the waste heat to just one kW.

Thermal sump.

One kilogram of ice at -40 °C can harmlessly become one liter of water at 95 °C; that absorbs about 2 kilojoules per K to go from -40 to 0, and that's eighty kJ. Then a whopping 334 kJ is needed to liquefy the ice. Finally the remaining 95 K eat up 4.186 kJ each, for a total of 397 kJ. All told, that's around 810 kJ, or 810 kW*s.

You can hide your 67 kW of power for twelve seconds, or a more reasonable 1 kW for thirteen minutes.

If you can store five kilograms of ice inside the body, that's five time the endurance; but thirteen minutes ought to be plenty.

To be really picky, the child's body can and should already radiate about 80 W away to maintain a believable temperature.


You don't need to maintain a human temperature, you just need to fool a thermal imager. Thermal imagers usually ignore temperatures below 25 or 30 degrees (even if they are capable of detect the range, which not all do) to reduce visual clutter. For example, there's no way that the floor here is all at the same temperature. It can't be. But it's shown as black because it's below 24 °C.

enter image description here

So if you know this, and if the ambient temperature is, say, 20 °C, you can blow out air at a controlled 23 °C provided you're far enough from anyone else that they won't notice. The quantity of air you need to vent will be huge: at 0.55 kJ/K per cubic meter, and having only (23-20) = 3 K of deltaT, you can get rid of 1.66 kJ every thousand litres of air. Eliminating one kW requires 600 liters per second, or 21 cubic feet, which is a bit much.

Another possibility is to radiate the energy in some direction it won't be intercepted. Imagine the head containing a hollow cylinder, open at the top of the head, covered in IR-transparent fake hair and the bottom heated until it radiates in the near infrared. The cylinder also needs to suck air from the outside to prevent a heat plume becoming visible on the thermal imager. With a three square cm aperture you should be able to eliminate one kilowatt without problems, even if the ceiling will heat perceptibly. Moving around and looking all around, as children are wont to do, should be enough to spread the "heat ray" and avoid this; even if your android will need sensors to be sure never to "illuminate" anyone, since at close range the IR discharge would be enough to ignite paper and permanently blind.

Air cooling plus radiant heat discharge plus internal heat sump ought to be enough against the average scanner.

Frankly, I'd be much more worried of the metal detectors (due to the way they work, they will detect electromagnetics and non-ferrous circuits, and the only shielding possible - iron yoke or magnacloth - will both be readily detected).

(Also, terahertz-flash imaging detectors and facial scanners would probably react to the android's skin, but that can be prevented using a suitably complex covering for the android - same goes for skin texture etc. (NSFW link)).


Assumption: Reactor power > heat generated

If your child is putting out 67kw she's glowing white - that will gain the attention of authorities. (Unless you can arrange some heavenly music to play so everyone thinks they're seeing an angel and just waves her through). I think we need to lower the figures a bit to make this managable.

Going from the statement

so far the state of the art AI has managed to fool everybody.

I'm assuming that your android isn't melting the world around them in its normal life. 67kw is a lot of power - your child can boil water at like 10 meters if that's what they're putting out, so I'm assuming that your reactor is so efficient that it leaks so little heat that it isn't destructive. 99% efficient will leak 670 watts of heat, everything else is used for movement or thoughts. That's still 6.7 times more than a human, and will show up very hot on IR sensors, but wont randomly start fires by walking near paper.

Your android will be selected for Covid19 testing but wont melt the airport. I feel this is the assumption we need to make to get a solvable case.

Now how do we get your hot android past airport security?

So what does your android do? One or more of these:

  • Strip down as far as socially appropriate to get maximum sweat evaporation surface area. Loose T-shirt and shorts if male, tank top and loose skirt if female. Crank your sweating up. Androids don't need to put pheromones in the sweat, so no smell.
  • Turn your reactor down to low power (or off) a few minutes before testing. Use residual battery power to manage the body in the queue. The brain and body is basically idle so not much power is needed.
  • Actual cooling vests made for cooling the body down.
  • Act like a dog (No seriously, they radiate heat through their paws). Radiate heat through your feet. In some places (USA?) you have to take your shoes off at these screening points. Nobody points the IR scanner at peoples feet. If your feet are covered with a long skirt then it wont show up with even a IR viewer.
  • $\begingroup$ even at 99% efficiency that energy is still going to end up as heat, efficiency does not tell you how much heat you put out just how much UNUSED heat you lose. She should be so hot she glows. $\endgroup$
    – John
    Jan 11, 2021 at 6:34

Bathroom break.

Before venturing past the scanners, kid robot visits the potty. And drinks, and drinks, and drinks. If this were for a show I would have the kid robot pull back its hair and plunge its face in the toilet and suck up all the water, over and over. Later in the show kid goes into gas station and buys 5 lb bag of ice, then goes around the corner and eats it.

Water has a huge thermal mass. It will keep things chilly for a while. And no-one will be surprised that nervous kid needs to visit the bathroom a lot. Kid uses toilet exclusively so no-one sees steam rising from bowl.

When there no water around but no scanners to worry about, there is still a lot of heat. Kid breathes hard and uses air to exchange heat, like a diesel truck engine. Engineers were creative at figuring out how to move a lot of air in and out of the robot body, utilizing every possible entry and exit point.


It only uses what it requires

Some electrician can correct me if I'm wrong.

WATT is volt(V) times ampere(A). The thing is that components run on the V that is on the line (example is 230V for where I live), but only use the A that is required for their operation. For example, I have an RGB led strip here. Each "pixel" on the strip has 3 lights in it, the Red, Green and Blue (hence RGB). Each uses at maximum brightness about 20 mA, so if I turn on all at max, a single pixel will use about 60 mA. But reducing brightness in one or more will also reduce the A used.

Are you saved? Not at all unfortunately. The example is good with batteries or the power grid. Batteries only let go enough energy to power the stuff and don't release more than required. The power grid can manage it due to the whole grid heating up slightly due from the excess and the excess is managed 24/7. If you would use 67000W in motors or such like in something as small as a child (or adult for that matter), due to inefficiency it would melt a lot of stuff. Imagine if the excess would be put fully to heat.

Now the solution is quite simple. Change one sentence in your question: It is powered by a sophisticated hydrogen cell reactor which is capable of producing 67,000 Watts for normal operation, how does it cool or vent the excess heat without raising alarms at the checkpoint?

The sophisticated hydrogen cell reactor can create energy to the requirements. As the AI is running the show, it can manage all energy requirements in advance, so the energy production is near perfect to the demand. That way you reduce the need for cooling and you reduce waste, allowing for the AI to run for longer.

Cooling is easy with hydrogen cells. The by-product is water. As water is used in sweat, you have a great way to disguise the venting of excess heat you still have. It has a great heat transport capacity and the evaporation of it is also used throughout nature for its relatively great way to cool down.


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