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So I'm writing a scifi/Fantasy story and the setting is a primitive steampowered era. No electricity, gun powder, etc. I was wondering how realistically storing steam power in canisters for mobile use would work. Can a steam engine store pressure like a CO2 cartridge? Would it be able to be used on the go as energy for a cyborg like arm instead of a battery like the person in the picture? How long would they last? What are the drawbacks? Thanks :penter image description here

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    $\begingroup$ A primitive steampowered era? Yet you want to have a steam-powered cyborg arm. This suggested a more advanced version of steam-powered era especially since it has to be powered by steam canisters. The canisters need extremely effective thermal insulation to maintain power. Insulation would need to be quite advanced in its own right. Perhaps, the setting should be an advanced steam-powered era? Just a suggestion. $\endgroup$ – a4android Jun 1 '17 at 7:13
  • $\begingroup$ I didn't explain in much detail. The few nations that are building steam powered inventions are very primitive and new to the idea. The main girl is a bit of a genious and progresses things much quicker so one of the ideas I had was her making an arm for someone. I appreciate the suggestion. $\endgroup$ – Steampunkery Jun 1 '17 at 8:08
  • $\begingroup$ magic? I just noticed that, and nobody else answered in a magic-based way either. I don't see how that tag fits. $\endgroup$ – JDługosz Jun 1 '17 at 23:54
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Letting steam cool in a sealed container is a good way to make a weak vacuum. It won't do much except make it hard to open the container.

You would do better to use a pump to just pressurize the air. That will be mostly immune to cool down. the air will heat up as it is being put under pressure and will cool down some later but not enough to make a noticeable difference if you have a good pump and a strong pressure vesicle.

On the bright side, you could use a steam powered pump to fill the pressure vesicle.

I think that pneumatic actuators ought to be acceptable steam punk tech.

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Steam relies on the phase change to expand the gas, creating pressure.

Water is very difficult to boil. It has an Anomalously large specific heat and then another huge chunk of energy is needed to make it vaporize.

Use a different fluid that will vaporize at, say, body temperature. Spent vapor can be recovered in a cool chamber using the typical London weather as a heat sink.

So he just needs to keep the flask of “top secret volatile alcohol” close to his skin to keep a head of pressure.

This is still handwaving, since the work done is being driven by his body heat, which is a limited power source. The same concept could use a small heater such as a limelight. Or, have two modes: body heat generates a pressure reservoir over time and allows for occasional movement including common actions. But lighting the burner gives him strength and speed, when demanded.

Note that advances in chemistry would allow propellants that simply work at normal temperature. Look at any modern aerosol can! It is a liquid in the can, stored at room temperature, but generates a fixed pressure. The same effect is seen in CO₂ and propane tanks. I don’t know if anything available would give enough pressure, and of course it’s not cycled but used up.

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There are fireless steam engines which work on this principle.

Problems for portable use will include:

  • Hot steam cools down. It must be used or reheated quickly.
  • Low energy capacity for the weight.

Advantages:

  • They use the "steam" buzzword and are hence suitable for steampunk. (Not much of a practical advantage, I admit.)
  • Providing hot steam refill stations may be easier than providing CO2 refill stations, especially at pre-20th-century technologies.
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  • $\begingroup$ @Steampunkery, yes, those are steam engines that store compressed steam which has been created in a stationary boiler. The same principle can work without wheels, in a smaller package, but it would be less efficient. $\endgroup$ – o.m. Jun 1 '17 at 5:46
  • $\begingroup$ So you're saying if a steam engine put steam into a canister as soon as that canister cools which id imagine would take very little time it would be useless as a form of power on the go? $\endgroup$ – Steampunkery Jun 1 '17 at 5:49
  • $\begingroup$ Steam as a source of power relies on the Ideal Gas Law, which holds that for a given amount of a gas at a given volume, the only way to increase the pressure is to raise the temperature. High-pressure steam expands through pistons or turbines to create mechanical work. Cool steam has less pressure and thus can do less (or no) work. $\endgroup$ – Chris M. Jun 1 '17 at 17:19
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I like steampunk tech so this should be a fun one.

So here are the requirements that I'm gonna work with for this:

  • Portable

  • Steam-related

First point is that if you've got a society that is a 'steampunk' society, they're gonna have to have a way of heating water to produce steam. Duh. So this would likely be coal, oil or gunpowder, and this kind of stuff wasn't used in 'primitive' times (as in like caveman times). Also, gunpowder isn't a new invention, it's been around since the 9th century, so if you are talking pre-9th century, steampunk ain't gonna happen, sorry. So I'm going to assume the setting is a Victorian style era with no gunpowder (for whatever reason).

Well I've had 2 ideas.

  • Furnace

If the person was using a cyborg arm, perhaps with some support for the legs also, they could carry a small furnace on their back, which could be powered by a reserve of coal or some other flammable substance (oil, coal, etc) and this would evaporate water, which would be pressurised and that would power the arm. This would be VERY heavy, and would get VERY warm, so not a likely option. It would last as long as you could top up the water and fill it with fuels, however it would be pretty slow and cumbersome.

  • Canister

Another idea could be have a tank (similar to a scuba tank) and have a reservoir of water in it, with some sort of combustible fuel in the bottom, so when you need some pressure you use some of the fuel to heat some of the water to produce steam and force that into the piston. This would be expensive, as you may be able to refill these however producing the system in the first place would be difficult. But it would provide fast, small amounts of steam if necessary.

Just as a post-options note, steam is a really bad way of powering pistons, as pneumatics (the use of pressurised air or steam in order to apply pressure) cannot provide massive forces unless you have massive pressures (stuff that you need a lot of reinforced materials to deal with) so that front is difficult. Also, pneumatics generally are an out or in thing, especially with pistons, there's very little halfway with pneumatics, they're for quick high-force movements that don't stop halfway. So yeah, steam is a really bad idea.

I have designed plans for hydraulic packs used to provide pressure to hydraulic pistons, however that isn't what you asked for so I shan't say here, let me know if you want me to show you the plans.

Tl:dr - steam is a pain in the ass to work with and pre-gunpowder 'primitive' times it would be nigh-on impossible to produce this technology.

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  • $\begingroup$ I have a nail gun that is essentially a primitive form of internal combustion. A small canister of something like butane or propane is connected, and a spark makes the piston drive the nail with a single blow. That same piston could compress a stiff spring, to provide for more gradual application of the stored energy. $\endgroup$ – JDługosz Sep 9 '20 at 16:01
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You could retain the pressure in an accumulator - which is essentially just a sealed, pressurized bottle - and using whatever control system you've got port pressurized steam / oil / whatever you're using from the accumulator through a manifold to valves, and finally into the appropriate pistons. You're limited to the max pressure the accumulator can store, which depends on things like what its made out of, how it is sealed etc... I imagine welded copper. Overpressurize it and the accumulator could burst - or the valves, hoses, pistol seals etc might burst. Any break in the hydraulic circuit and you'll lose pressure. Probably enough charge for a few simple movements before you need to recharge it.

Pistons, valves, seals, manifold, accumulator.. these are all pretty simple parts to make now but would be considered high-tech even 100 years ago. Getting the valves tuned precise enough for a prosthetic would be artificer level skill.

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    $\begingroup$ The accumulator would probably use air (or another gas); steam depends too much on temperature, while oil is basically incompressible. At that point you're working with pneumatics. As for the amount of energy that can be stored, scuba diving tanks are about 200 atmospheres, while pneumatic working pressure might be 5-7 atm; you can work out how long it'll last based on length of movement and how much force is required. $\endgroup$ – sabik Sep 4 '20 at 2:33
  • $\begingroup$ For added drama, using up air cools down the valve, especially where it leaves the accumulator; if the air has moisture, it can potentially freeze in the valve, leading to a malfunction... $\endgroup$ – sabik Sep 4 '20 at 2:41
  • $\begingroup$ I think a pneumatic system would be ideal. If for no other reason a leak in a steam system will cause scalding burns $\endgroup$ – Adam Coville Sep 5 '20 at 4:26
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A small stirling engine

enter image description here

A small stirling engine could be hooked to a clockwork spring and be continuously winding it. It runs on alcohol and is fairly cool so doesn't have to boil water and build pressure.

The arm uses power from the spring for movements and might be good for 20 minutes heavy use whilst the stirling engine rewinds the spring more slowly.

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