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Hi Troll, a simple note: "a desire to build air expansion engines": Air engines are simply steam engines with less power/psi...
Put simply, the air expands, usually from atmospheric temperature and cools, giving out a bit of energy to the piston, etc. Whereas steam expands from temperatures above 100deg.C. to give power and cool - maybe to cooler steam or to a mix of cooler steam and hot water. But the energy per cu.in. per psi of air isn't anywhere as great as the energy in steam per cu.in. per psi.
So a "steam engine" at 1 bar of air (Enthalpy = 30.184 kJ per kilogramme.) contains only about 1% of the same engine on Steam at 1 bar (Enthalpy = 2675.43 Kj/Kg). But the engine can't use all the Enthalpy, maybe only a relatively small fraction. (I just don't know).
So Steam engines on steam are much more powerful than when run on air. Especially as the steam can be superheated and hold even more energy for use by the engine.
As the cycle is the same, steam engines can all run on air (as far as I know) but air engines can be made from plastics, wood, etc. that cannot handle the heat and wet of steam.
Air may be thought of a simpler and safer than steam. But compressed air can be blown through the skin to form an air bubble in flesh and veins, that if if gets to the heart can cause a heart attack.... The same effect from steam would make you scream with pain while you rapidly move away, thus avoiding getting so much damage to your flesh, but it may cook the flesh so it never grows back. Yet the majority of people recognise the dangers of steam and run steam plant for a lifetime without injury. I don't know what air accidents are like to say "it is safer"?
Stuart Models make casting kits to make steam engines, and with a different configuration of valve gear some can be used to make compressors. (e.g. Sun Engine).
I hope to see the results of your model making in due course.
Enjoy the sight. There are many here who can give expert advice on most matters, particularly machining.
WELCOME!
K2
 
Steamchick said:
Hi Troll, a simple note: "a desire to build air expansion engines": Air engines are simply steam engines with less power/psi...
Put simply, the air expands, usually from atmospheric temperature and cools, giving out a bit of energy to the piston, etc. Whereas steam expands from temperatures above 100deg.C. to give power and cool - maybe to cooler steam or to a mix of cooler steam and hot water. But the energy per cu.in. per psi of air isn't anywhere as great as the energy in steam per cu.in. per psi.
So a "steam engine" at 1 bar of air (Enthalpy = 30.184 kJ per kilogramme.) contains only about 1% of the same engine on Steam at 1 bar (Enthalpy = 2675.43 Kj/Kg). But the engine can't use all the Enthalpy, maybe only a relatively small fraction. (I just don't know).
So Steam engines on steam are much more powerful than when run on air. Especially as the steam can be superheated and hold even more energy for use by the engine.
As the cycle is the same, steam engines can all run on air (as far as I know) but air engines can be made from plastics, wood, etc. that cannot handle the heat and wet of steam.
Air may be thought of a simpler and safer than steam. But compressed air can be blown through the skin to form an air bubble in flesh and veins, that if if gets to the heart can cause a heart attack.... The same effect from steam would make you scream with pain while you rapidly move away, thus avoiding getting so much damage to your flesh, but it may cook the flesh so it never grows back. Yet the majority of people recognise the dangers of steam and run steam plant for a lifetime without injury. I don't know what air accidents are like to say "it is safer"?
Stuart Models make casting kits to make steam engines, and with a different configuration of valve gear some can be used to make compressors. (e.g. Sun Engine).
I hope to see the results of your model making in due course.
Enjoy the sight. There are many here who can give expert advice on most matters, particularly machining.
WELCOME!
K2
Click to expand...

Thank you for such a thoughtful reply.

The goal of CAES is to find ways to store compressed air by either compressing the air with no temperature increase or a tempurature increase and storage of both heat and air. The energy sources are typically things like wind or hydro.

So CAES is an air battery, in essence.


The goal is then that the air be expanded with maximum entropic shift, in an engine, so that work is done.

A drop in tempurature and efficiencies in the low 90's are possible in current turbo expanders, as well as discharge air in the -30C to -40°C range from air admitted at ambient Tempurature or hotter.

While steam engines will run on compressed air, like you said, they are designed to convert energy from very different working fluids, again as you said.

I'm more interested in the storage/generation side so any air engine would be demonstrational of the ability of the compressor to gain efficiency from the engine.

Currently I have a couple gast vane pump heads and an air motor that are "on the table" as possible expanders, but I also really wonder about the degree in air temperature drop I can get with a piston engine designed for high expansion vs a steam engine running on air. Totally calculating piston size and cylinder bore to maximize expansion and produce the coldest air possible.

In hydraulics, piston pumps beat vane, gear and any variable displacement rotary pump for efficiency Hands down. That's what makes me want to try pistons.

Steam engines absolutely have more power capacity pound for pound due a far superior working fluid but compressed air has the edge on storage (just ask Fowler's ghost mwahaha [either one ha])


Thank you for the safety notes. The dangers of air embolism are very real and I actually do wear ppe when handling certain compressed air actuators as well as using a gast pump on a foot switch at a meager 10psi for clean up of myself and tooling, as well as a tool cooling and chip flushing set up when boring - all in the name of compressed air safety.

I also rigorously test components I make with a off the shelf hydrostatic tester and dual gauges.

Hopefully in a year or so I will have something to show.
 
Hi Troll. Sounds good! Ambitious? Maybe but that is never a problem. Your explanation of what you are doing sounds reasonable. A long stroke piston engine with early cut-off doesn' t give as much power but does improve efficiency - whatever the gaseous fluid. Wet air (high humidity) should - I guess - increase efficiency as the gaseous water in the air condenses and gives up its latent heat. But possibly a problem if it them freezes? So does this work better with high or low humidity? I am interested to learn....
Glad to know you appreciate safety.
K2
 
Steamchick said:
Hi Troll. Sounds good! Ambitious? Maybe but that is never a problem. Your explanation of what you are doing sounds reasonable. A long stroke piston engine with early cut-off doesn' t give as much power but does improve efficiency - whatever the gaseous fluid. Wet air (high humidity) should - I guess - increase efficiency as the gaseous water in the air condenses and gives up its latent heat. But possibly a problem if it them freezes? So does this work better with high or low humidity? I am interested to learn....
Glad to know you appreciate safety.
K2
Click to expand...
Going for dry gas, I found a way to use the humidity to cool the air and draw out more humidity to 100 of Rh so I'm working from there.


Can I ask a forum question, what's the best way to search this forum so I don't post those annoying "how to" questions?

Is the forum search good or is this a site that's it's best to use the Google search site function?
 
Hi Troll,
I can't advise on "the best way..." for you, but you may find posting your Project - or "proposed project" - and within that you can ask questions, to which those interested in your project can reply?
I suspect that most readers are interested in other people's projects, as well as simple sub-topics - like "how to bore a cylinder", or "how to hold a thin walled cylinder for finish machining" - sort of thing within the context of their projects. That seems to extract answers - of varied quality (especially from me!) - so you can add to your knowledge.
Does that opinion help?

On your CAES project, I'd like to learn more....
I was pondering the bit about compressing gas without raising its temperature. I'm a bit thick on Thermodynamics, but it sounded like trying to push water uphill.... or something? Compressing gas is within the gas laws, and the raising of temperature seems to be a part of those laws...
PV = Rt and all that. So you are trying to change the ratio of P:V while keeping Rt constant. And R is a constant.
So "in my head" You increase the pressure by reducing the volume (e.g. by a piston in a cylinder) but that raises the temperature too, as cyclists know when pumping up tyres and the pump gets hot in their hand! But you want to push that heat back into the gas at the smaller volume to further raise the pressure? - Or rather do the whole thing of keeping the temperature constant and just changing the Pressure to volume ratio, simultaneously?? Isn't that just Adiabatic compression?
That's where my thermodynamic knowledge falls apart and I am just confused. So presenting your project may help us help you, or at least tell me it is in the realms beyond my knowledge so I should just shut up and listen to others.
In conclusion, just tell us about the project and ask questions "How do I...?" or "what is...?" within that project? - It is what seems to happen on other posts, I think?
K2
 
Steamchick said:
Hi Troll,
I can't advise on "the best way..." for you, but you may find posting your Project - or "proposed project" - and within that you can ask questions, to which those interested in your project can reply?
I suspect that most readers are interested in other people's projects, as well as simple sub-topics - like "how to bore a cylinder", or "how to hold a thin walled cylinder for finish machining" - sort of thing within the context of their projects. That seems to extract answers - of varied quality (especially from me!) - so you can add to your knowledge.
Does that opinion help?

On your CAES project, I'd like to learn more....
I was pondering the bit about compressing gas without raising its temperature. I'm a bit thick on Thermodynamics, but it sounded like trying to push water uphill.... or something? Compressing gas is within the gas laws, and the raising of temperature seems to be a part of those laws...
PV = Rt and all that. So you are trying to change the ratio of P:V while keeping Rt constant. And R is a constant.
So "in my head" You increase the pressure by reducing the volume (e.g. by a piston in a cylinder) but that raises the temperature too, as cyclists know when pumping up tyres and the pump gets hot in their hand! But you want to push that heat back into the gas at the smaller volume to further raise the pressure? - Or rather do the whole thing of keeping the temperature constant and just changing the Pressure to volume ratio, simultaneously?? Isn't that just Adiabatic compression?
That's where my thermodynamic knowledge falls apart and I am just confused. So presenting your project may help us help you, or at least tell me it is in the realms beyond my knowledge so I should just shut up and listen to others.
In conclusion, just tell us about the project and ask questions "How do I...?" or "what is...?" within that project? - It is what seems to happen on other posts, I think?
K2
Click to expand...

Everything you said is part of it. Where the wasted energy of compression is so vast, I want to scrape together some efficiency by using some of that energy/water output to increase overall efficiency.

It's a combo of liquid/solid piston with air/water venturi induction and an interrupted compression cycle.

I've also been experimenting with using the heat wasted compressing water vapour to use the captured water to cool and collect more water from the gas stream.

Swapping Reed valves for articulated valves is a big part, as well as the recycled water usage.


I'm in the middlele of a reno ATM so right now there is nothing to put up on a project page.

Once the move is done, I need to upgrade my mini lathe and plan this out, so that's when I'll get more active.

Right now I built a test version of the intended cooler/dyer that takes air from the compressor and blows it in a swirl up the sides of a modified (and hydrotested and safety valve equipped) tank. It gets the incoming air to rapidly drop in temp and the increased water drop out in the tank = more coolant.

The air filter right after the tank stays dry and the tank stays at room temp, so I know that the cooled exciting air is 100%Rh @ room temp vs over saturated and hot with an equivalent same Rh but higher water volume.

Saves on desiccant for the paint booth where I am painting reno stuff.


The eventual air engine will be just the reverse.
 
Steamchick said:
This thread is becoming a thread on your project.
I am sure others will join-in with questions (and answers?) as I think about what you are doing and understand it...
Thanks,
K2
Click to expand...
No worries. Once I get into it I will start a full thread and then you more clever folk can smack me around the ears over choices like rotary valves.
 
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