dye request - spriggan black

[Gemina]

An olympic size swimming pool is 50 by 25 metres, so it has an area of about 1250 square metres. If painted a perfect black and with sun shining from directly overhead, it would absorb around 1.3 megawatts of power. Examples of things with the same magnitude of power: a small locomotive, a medium-sized data center or about three 18-wheelers.


There's actually a limit to how hot it can get. The hotter it is, the more heat will be radiated into the air (and eventually space) as well as conducted into the ground. I did some calculations and it looks like it could reach around 100 °C over typical ambient temperature, but not much more than that. A higher ambient temperature makes the gap somewhat narrower because thermal radiation follows a quartic law. Still, you'd have an easier time frying things in California than Greenland.


Assuming you built this in a magical place with the sun permanently overhead and an ambient temperature of 50 °C, it could reach a temperature of around 130 °C. Not quite enough for Leidenfrost effect, which in the case of water requires temperatures closer to 200 °C. If the pool has one metre of concrete on all sides, the total volume of concrete is about 2000 cubic metres. Structural concrete has a specific heat capacity of 1 kJ/kg°C and a density of 2400 kg/m³. After it drops below 100 °C it's no longer able to boil water so we're interested in how much heat it can give off in the span of those 30 degrees. Multiplying the relevant values together gives an impressive 144 GJ. Since we're in a pretty hot environment it takes 2.5 GJ to heat up and boil a cubic metre of water, so the pool's stored heat would be able to boil the first 50-odd cubic metres poured into it before cooling down below the boiling point of water.

Most of the incoming power is in visible light wavelengths, but the pool will radiate in far infrared. A cover made of a material which lets visible light pass in but prevents the infrared from getting out would trap the heat inside, significantly increasing the temperature. Even so, there's only enough power input to boil about two cubic metres per hour. To fill a pool of that size you'll certainly want more flow than that. As a point of comparison, a firehose can spew out more than 30 cubic metres of water per hour. A 500 °C pool would be able to boil away the water from a firehose for about 26 hours (taking into account the extra heat from the sun during that time), but eventually it would cool down and water would be able to stay liquid.

Science and math are really interesting. I wish I had the aptitude to wrap my head around it more, but the more I tried, it was like trying to learn an instrument; which if I was to even perform with it somewhat decently, it would require hours upon hours of practice, and well longer than someone better attuned to it.

Still though, that is really hot and a lot of energy just with some paint. I wonder now if the pool was made of steel opposed to concrete, as metal is a far better conductor of heat. Not asking you to science more numbers, I'm just thinking out loud as I know this would increase the temperature of the pool and the energy it releases substantially. Plus we're getting a bit away from the blackness of Spriggy caps xD

[tdb]

Still though, that is really hot and a lot of energy just with some paint. I wonder now if the pool was made of steel opposed to concrete, as metal is a far better conductor of heat. Not asking you to science more numbers, I'm just thinking out loud as I know this would increase the temperature of the pool and the energy it releases substantially. Plus we're getting a bit away from the blackness of Spriggy caps xD

It wouldn't affect the balance of incoming and outgoing thermal radiation. Steel is a better conductor of heat than concrete though, which means the heat accumulated at the inner surface would be transferred to the surrounding earth faster, and the equilibrium temperature would actually be lower. At the same time it would also feel hotter to the touch because heat would be transferred to your skin faster.

Did you know that space shuttle thermal shielding elements are so poor conductors of heat that you can hold a 1500 °C element in your hand without getting burnt? This allows them to keep the inside temperature of the shuttle tolerable even as the friction of re-entry heats up the outside to immense temperatures.

Edit: As for the spriggan black dye, I think it's clear to everyone what's being requested and most people are just picking nits now. So might as well throw some fun science into the mix.

[Gemina]

It wouldn't affect the balance of incoming and outgoing thermal radiation. Steel is a better conductor of heat than concrete though, which means the heat accumulated at the inner surface would be transferred to the surrounding earth faster, and the equilibrium temperature would actually be lower. At the same time it would also feel hotter to the touch because heat would be transferred to your skin faster.

Did you know that space shuttle thermal shielding elements are so poor conductors of heat that you can hold a 1500 °C element in your hand without getting burnt? This allows them to keep the inside temperature of the shuttle tolerable even as the friction of re-entry heats up the outside to immense temperatures.

Edit: As for the spriggan black dye, I think it's clear to everyone what's being requested and most people are just picking nits now. So might as well throw some fun science into the mix.

I knew that space shuttle thermal shielding, as the name implies, shields our astronauts and the shuttle from the immense heat of reentry. That is one of those curious random thoughts that has me google "why don't astronauts incinerate upon reentry of Earth's orbit?" while in a waiting line at the store. However, I did not know you could hold a heat blasted rod of the stuff without getting burned though, or that it would take such a huge amount of heat and energy to get to the point that it does. I would imagine that is also the stuff put on probes sent to Venus so it can withstand the hostile environment there. If only we were higher on the Kardashev scale in this lifetime.

I watch a lot of Kyle Hill on youtube. He has fun and neat ways of explaining how Superman would actually kill everyone and everything when Lois dies in the first movie, turning Jupiter into a star, or all the ways super heroes would mangle themselves with their powers. Also helps a little that he's the Hemsworth who got the brains instead of the brawn.

I couldn't help but nitpick the blackness of the Spriggan cap. I suppose we could get a dye that is more black than jet, but part of the reason why the cap is so black is due to lack of visual textures to reflect anything. It just has two beady yellow eyes, and that's about it. Even when I tried dying the event Spriggan gear jet black, is wasn't even close.

[Iscah]

To throw a little more science on this very non-sciencey claim about the pool, the size of the pool wouldn't really be relevant, just the depth (as each square metre of the floor needs to boil the column of water directly above it, regardless of the overall size).

The amount of energy reaching the bottom of the pool would also be lessened by some of the sunlight being reflected off the water rather than ever reaching the bottom.