# Scientist Wanted. (Los Angeles)

So, I've come up with what I think is a pretty darn neat idea for my Burningman project, but the technical implementation thereof is what I'm getting hung up on.

The reason?
...It involves things I conceptually understand, but have never implemented on an applied basis- like thermodynamics, isolating nitrogen through fractional distillation of supercooled air, precision machining, the compression/expansion of gases, a variety of mathematical formulas, and so on.

The idea?
Well, I can't go into too much detail here (shhh- its top secret!!), but basically I'm trying to build something like a lightweight Adiabatic Carnot engine to power sub-atmospheric flight from my backyard.

No, really. Trust me. I'm actually serious.

...Its completely steampunk; the plan is so elegant and simple, I can't see why its been this overlooked for this long.
In fact, the technology has been around since the late 1700's, its just that nobody seems to have bothered to put it all together in this particular way- which is what makes it both elegant art and great science.

Plus, it also looks like you can't order what I want off the Internet- (um, anybody got a spare minature turboexpander??) we're going to have to make make it all ourselves.
But- the good news is, I think you can get *most* of the required parts at Home Depot.

Oh- it might also help if you had access to a machine shop, and lived in or near Los Angeles.
Hell- even if you just have a machine shop and aren't a scientist, we should probably chat.
And yes- unfortunately, I don't have a grip of cash to implement it- but that's also kind of the point. ...Much in the same spirit that the UNIX operating system was developed, we'd be doing this just for the fun of doing it- to see if it actually can be done.

So- if you're interested and have a few weekends to spare, why not drop me (Steve) a line??

No disrespect, but I think this forum does not allow solicitations.
However, if you want to actually discuss the physics of your project...

No- I totally understand. No disrespect to the Forum intended.

...But where the heck else can you find a Physicist?? I mean, its not like you can just go get one out of the Yellow Pages.
Plus, all the folks I know over at JPL are busy with the Mars Moon Rover project right now...

This *is* a collaborative project- its not for profit, so while it may not be to the letter of the forum, I think it certainly embodies the spirit of the forum, que no?

Also, you could just ask specific questions. At least until you can get help from the jet propulsion lab.

Ok, well- I'm somewhat reluctant to discuss it in great detail, because I want to be the first person to actually do it, but basically, the general idea is:

1). Use fractional distillation to remove the oxygen from the surrounding air, leaving only nitrogen. This will be our "fuel".
The advantage of this is that there's already plenty of it (so you won't run out), and it goes allllll the way up through the atmosphere...
...No expensive helium to purchase, no explosive hydrogen to kill you with, and provided you can make the engine described below lightweight, (say, lighter than the two propane tanks you'd have in a normal hot air balloon) it should be more efficient than just plain old hot air, because it's less heavy. So- you won't have to displace several metric tons of plain vanilla air just to get off the ground.

2). Compress the aforementioned nitrogen through a counterflow heat exchanger, and into a lightweight tank. The compression activity generates heat. The nitrogen becomes more dense, and eventually liquifies. (So, its lightweight- and in a small container. Very nice.)

3). Release the compressed nitrogen out of the tank, through an expansion valve and a counterflow heat exchanger. The expansion activity causes cooling. The nitrogen becomes less dense, and eventually becomes gaseous.

4). Allow the now cool, yet expanded nitrogen to be superheated by the aforementioned compression cycle (via crossover to the other side of the couterflow heat exchanger), thereby causing it to be lighter than air.

5). Fill a balloon with the superheated, expanded nitrogen.

6). Pump the superheated nitrogen back out of the balloon, cool it using the expansion cycle (via counterflow heat exchanger), and then compress it back into the nitrogen tank mentioned in step 2.

7). Rinse. Repeat.
(Save of course for step 1, because eventually you'll get to a point where you have enough supercooled/superheated nitrogen flowing through the system that you wont need any more. But guess what- if you *do* need more- it's already around you! ...Just distill more!)

So, in essence, the compression/heating cycle drives the expansion/cooling cycle, and vice versa.
And, what would be at the heart of it all is a Stirling engine which uses the temperature differences between the two to drive the pumping of the nitrogen through the system.
So- that way, it becomes like an Adiabatic Carnot engine. (But not a perpetual engine because, duh- you're going to lose energy through friction- but hopefully not much.)

There is also the added advantage that, unlike a conventional helium balloon, you don't have to worry about this balloon ever expanding to the point of bursting as it goes up through the atmosphere. So, as long as there is nitrogen around, you're golden. ...If the balloon expands too much, you'd just pump a bit back into the tank. Or likewise, pump more out of the tank and into the balloon on the way back down.
And heck- the atmospheric/temperature differences between high-aloft and sea level could even further be used to lift or brake the aircraft.
So- in theory, you should be able to go higher aloft than say, Joe Kittinger did with his helium balloon?

And yes- granted, you'll need some initial energy to get the whole reaction started, but once the nitrogen is fully flowing through the system- getting superheated then supercooled- the idea is that you would be able to stay aloft longer than anything else.
So- that's why I was thinking about using a turboexpander which would initially use the pressure of the nitrogen to kick-start the reaction? Then, once its all working you could shut it off, and work on thermodynamics vs. pressure differences to drive the reaction.

Make sense?

Alternately, I'd tinkered with the idea of using supercooled/superheated helium as the gas- meaning while you'd give up the advantage of having lots of available "fuel", you'd need to fill the balloon with even less helium than one filled at room temperature at sea level, so- smaller balloon, even more lift...

Now, I just need somebody to help me build it...

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It's gonna take a while to grasp all you have said but the first thing I thought was that it would be funny if you turned it on and asphyxiated immediately.

But that's also the other thing I hadn't mentioned- the oxygen waste product from the fractional distillation could then be used for breathing while aloft.
In essence, nothing in the system is wasted, because it recycles all of the waste products to do what needs to be done.

Ok, so we have as general composition of air:

Nitrogen: 78%
Oxygen: <21%
Argon: <1%

And a myriad other much smaller percentages(trace) of other gases(14 or so) to equal 100%

I'm sure these percentages differ with altitude and such, but maybe a good start to see what we're dealing with.

Exactly.
So- let's assume you remove ~22% of the stuff that's making the air we breathe heavy in weight...
That leaves us with just the ~78% nitrogen.
Heat the nitrogen. Fill the balloon with that nitrogen.
That *should* mean you get at least 22% more efficiency than a 1970's Remax hot air balloon filled with regular air (which is inefficient and clumsy to begin with).

So- that means, less volume of surrounding air must be displaced to get aloft.
So- that means smaller balloon.
...Less trucking it around.
...Less clumsy.
...Less worry about the surrounding air temperature, making daytime Burningman playa flights in warm air possible.

But then the question is- how to make something that is lightweight- say lighter than the 2 propane tanks in your 1970's Remax balloon, and which will be able to continuously heat or cool the nitrogen to ascend or descend the balloon?

So- the answer is: Stirling engine and thermodynamics.

Compress a gas, and it heats up.
Expand a gas, and it cools.

Only problem is- we want hot expanded gas. So, that's why we run the gas through two cycles on the way to/from the balloon, for ascent or descent. Like this:

1). Expansion of gas. <-- This causes cooling.
2). Heating of gas. <-- This drives the expansion cycle (which makes cooling).
3). Cooling of gas. <-- This drives the compression cycle (which makes heat).
4). Compression of gas. <-- This causes heating.

See? Everything in the system is being used to power everything else in the system.

Actually, using the word "gas" is something of a misnomer.
Keep in mind its just a gas because of what surrounds it. In theory, you could even have gas made up of any element.
Heat up gold high enough, and it becomes a gas. Heat up uranium enough, and it becomes a gas.
Cool down nitrogen enough, and it liquifies, and eventually becomes solid.

Keep in mind, nitrogen is commonly found as a gas because it boils at around -400F.
If we lived in a world where the air temperature was on average, -410F, there would be little pebbles of nitrogen laying about everywhere.
Oddly enough, +400F is the temperature at which most hot air balloons operate.

So- cool the nitrogen to -400F, heat the nitrogen to +400F... cool the nitrogen to -400F, heat the nitrogen to +400F...

The difference between those two temperatures is what would drive the stirling engine to pump the gas through the system.

Take that liquid/solid nitrogen aloft with you- the weight of it doesn't change.
The weight of compressed nitrogen in a little genie bottle is just the same as it is inside the expanded volume of the balloon. But what's different is that the balloon is displacing the surrounding air, causing lift, while the nitro tank is just sitting there, displacing nothing.

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Further info... sorry for the long post:
http://www.chem.hawaii.edu/uham/lift.html

"Any gas with a molecular weight less than air will generate lift. If you remember your high school chemistry you can easily figure the molecular weight of a gas based on its formula and check it against the approximately 28 grams per mole for air.

For instance, it is easy to make acetylene gas by the reaction of water on Calcium Carbide. It is C2H2 as a formula. It is (2*12) + (2 * 1) = 26 grams. True that is a bit lighter than air, but not a practical amount.

Propane is C3H8, (3*12) + (8*1) = 44 grams, as heavy as CO2, and a balloon filled with either would drop like a basketball. Butane is even worse C4H10 or 58 grams, more than twice as heavy as air. Ethane is C2H6 or 30 grams, several grams too heavy. Oxygen is 32 grams and four grams per mole too heavy. Nitrogen is 28 grams, not surprising since most of the density of air is due to nitrogen. A balloon filled with Neon would float, if you could afford the high price of inflating one with this rare inert gas. As mentioned before Carbon Dioxide is 44 grams and much too heavy.

The practical possibilities rapidly narrow down gas selection to Hydrogen, Helium and [marginally] Methane. Plus, of course, Hot Air, something not yet explored for lofting antennas as near as I can determine, but practical in theory. Helium would the the number one choice given its combination of lift and safety."

russ_watters
Mentor
So, in essence, the compression/heating cycle drives the expansion/cooling cycle, and vice versa.
And, what would be at the heart of it all is a Stirling engine which uses the temperature differences between the two to drive the pumping of the nitrogen through the system.
So- that way, it becomes like an Adiabatic Carnot engine. (But not a perpetual engine because, duh- you're going to lose energy through friction- but hopefully not much.)
You described in the beginning using oxygen as fuel, but then never mention it again. That's ok because oxygen isn't a fuel anyway, it is an oxidizer. You still need fuel to burn to generate energy...

...otherwise, what you are describing is a perpetual motion machine. You can't generate enough energy to drive a compressor with the energy you gain by expanding the same gas through a turbine. The best you can hope for is to generate about 1/3 of the energy you need to keep this cycle going.

Also, a "sub-atmospheric" craft would either be a submarine or subway train.

No goofball, I said: "Use fractional distillation to remove the oxygen from the surrounding air, leaving only nitrogen. This will be our "fuel". "
I then went on to talk extensively about nitrogen.
Besides, I'm not trying to generate energy, I'm trying to generate lift.

Anyway- here's the other thing: The atmosphere is progressively less dense as you go up, and progressively more dense as you go down.
Likewise its colder as you go up, and warmer as you go down.
The difference between those two densities/temperatures could be used to add or remove action from one side of the equation to the other, or vice versa. Because after all, we're dealing with thermodynamics- which is what is inherently in the surrounding air...

So, yeah- I totally get that there is no such thing as a perpetual motion machine, but 30% theoretical efficiency sounds pretty darn good to me.

What I'm really trying to build is an Adiabatic Carnot engine.

But mostly, what I'm trying to find is somebody to help me *do* it vs. just talk about doing it...

Oh- sorry Palladin: I had already read that. In fact, that's why I'd chosen nitrogen. Its an inert, nonflammable gas that is as common as air, but is also lighter. And, when super-heated, super-lighter.

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SO- with all that said, why don't we get on to some pragmatic questions?
After all, that's what this forum is for, right?

For example:

If I am using superheated nitrogen to lift the balloon:
1). How big does the balloon need to be, what should it be made of, and what is the ideal shape for it? Assume I want it to lift the weight of itself, and up to ~4000lbs (like, me and a ladyfriend- plus some scientific equipment).

2). Is it possible to build this Carnot engine so that it will do what needs to be done, but also be super lightweight? I don't really know that much about what would be best to use. ...Copper tubing? Brass tubing? ...What happens as the air density increases or decreases? Will the tubing expand/contract and possibly crack/break?
Plus, if its super heavy, and you have to use a super big balloon to lift it, then it doesn't really make sense to build. We want to have a small balloon that does a lot of lifting, because its efficient.

3). How much entropy can I expect in the system? ...What will happen over time? ...Will it all eventually reach the temperature of the external air, and then crash?

vanesch
Staff Emeritus
Gold Member
What energy source are you going to use to drive the compressor ?

In as far as I picture the thing, you're making a "hot nitrogen gas" balloon, heated with a compressor...

Right. We're wanting to use a lightweight Stirling engine.
See here:
http://en.wikipedia.org/wiki/Stirling_engine

Note that one side of the Stirling engine is hot, and one is not (like a McDLT)?
Note that as a gas is compressed, it generates heat, relative to its surroundings.
Note that as a gas expands, it generates cooling, relative to its surroundings.

Now, if you've ever used a counterflow heat exchanger,
(see here: http://en.wikipedia.org/wiki/Countercurrent_exchange) you'll know that what is put in on one side gets the opposite on the other, and vice versa?
So, as you have hot nitrogen coming in, it comes out cold, and on the other side, as you have cold nitrogen coming in, it comes out hot...

Use the hot side of that compression to drive the hot side of the Stirling engine, use the cold side of the expansion cycle to drive the cold side of the Stirling engine...

Now use atmospheric/temperature differences on the way up or the way down to add to or to take away from one side or the other...

But what I'm really looking for now is some kind of mathematical calculation which will tell you what will happen in the system- but that seems to be a function of what the system is made of.
Like, brass tubing is different in thermodynamic conductivity than copper, and there may some limitations on what you can use with nitrogen... And you'd have to have the system be completely air-tight...

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vanesch
Staff Emeritus
Gold Member
Yes, but any system, be it a Stirling engine or anything else, will be able to compress LESS gas than it can win energy from expansion.... otherwise you'd have an over-unity device...

So I was thinking that you were going to use some or other kind of combustion engine to drive your compressor which heats the nitrogen which you put in your balloon, which is in that case nothing else but a complicated way to make a kind of hot-air balloon.

You don't need a scientist. You need a scientologist and a screenplay and a lot of insulation. I hear that Tom Cruise lives down your way.

You don't need a scientist. You need a scientologist and a screenplay and a lot of insulation. I hear that Tom Cruise lives down your way.
Come on Phrak. I'm an idea man myself. I've got this invention: It's a self-starter for an automobile! It works like this: You turn the key and the car starts! THERE! That's the idea now I just need to find some scientist to build the thing for me now that I've given everybody the idea!

[With appropriate credit to Rod Serling]

Staff Emeritus
That leaves us with just the ~78% nitrogen.
Heat the nitrogen. Fill the balloon with that nitrogen.
That *should* mean you get at least 22% more efficiency than a 1970's Remax hot air balloon filled with regular air (which is inefficient and clumsy to begin with).
How do you get that? The mean molecular weight of air is around 28.8 (that's an 80-20 mix of N2 and O2, close enough), whereas for pure nitrogen it's 28. So it's just under 3%.

You only get your 22% if you fill your balloon 78% full of nitrogen and 22% full of vacuum!

A balloon filled with Neon would float, if you could afford the high price of inflating one with this rare inert gas.
I wonder why neon is so expensive. It's running about $2/liter, which is about 100x as much as helium. A very good deal on xenon is$8/liter, and there is only 1/200 as much of it in the atmosphere.

jack action
Gold Member
Make sense?
Sorry, but no.

You're trying to heat a gas with its own stored energy with a very complex refrigeration cycle that makes no sense thermodynamically speaking. A refrigeration cycle is a "heat pump" that takes heat from one place (say the outside air) and adds it to another one (say inside your balloon).

In your process, you're just heating and cooling back the fluid back and forth, without releasing or adding any mechanical energy.

If you heat your gas, you have to add, somehow, some energy somewhere in the process (by heating). If you take your heat from another source, you need mechanical work somewhere (i.e. a pump).

Since methane would work - maybe you could just have a cow on-board and exhaust the methane into the balloon.
And since methane is linked to global warming, maybe it might also heat the balloon.

But something tell me this approach might be flawed.

Since methane would work - maybe you could just have a cow on-board and exhaust the methane into the balloon.
And since methane is linked to global warming, maybe it might also heat the balloon.

But something tell me this approach might be flawed.
No need for a cow. Just the pilot with a good supply of beans for food.

Seriously, though, I don't think a "hot nitrogen" balloon would have any significant advantage over a "hot air" balloon. And, the total infrastructure of a nitrogen balloon would be much more expensive to maintain correctly.

You guys are hilarious.

A bit of backstory: In essence, its an art project for Burningman (see here: http://burningman.com), and no, I'm not trying to build a perpetual motion machine. Please, for God's sake, don't tell me I can't build a perpetual motion machine. I already know that.

So- if it sounds a little nuts, its *supposed* to sound a little nuts. That's the idea.

The title is "Montgolfier's Folly In The Battle For Los Angeles".

The idea for it came about largely because of a bad breakup with an ex-girlfriend.
It's kind of about how difficult it has been to win the hearts of Los Angeles back- about the folly of how I'd been internalizing everything- almost supercompressing it to get things to cool off, then spewing it all back out as all this angry hot air, but nobody was listening anyway.

...But what is little known is that even back in WWII, there actually *was* a real battle for Los Angeles, which was quietly won by the people who plotted it.
Los Angeles devolved into sheer chaos at it was mysteriously attacked by UFO's, and at the end of it, everyone was fascinated, but nobody could figure out who'd plotted it. (See here: http://en.wikipedia.org/wiki/Battle_of_Los_Angeles).

So, I had to go *do* something to win this quiet war- to go *make* something, simply for the sake of making it- because I must.
That's what good art is about, even if it involves a good bit of folly- (and keep in mind, there is also a quiet duality in the word folly, because folly can also mean "fun").
But why can't good art also include a good bit of science? ...Why couldn't it be also functional as well, and demonstrate to people some basic (if not somewhat obscure) principles of thermodynamics?
...About how all things must eventually achieve balance, but at the same time devolve into entropy? Those are just the basic laws of Physics, right?
So- I don't care if its a little Rube-Goldberesque- that's what would make it awesome.
...It would be awesome to know whether or not it would have been possible to go super-high aloft using super-arcane technology (like me).

Seriously, go to any party and tell people you are working on building a "Thermodynamically Powered Adiabatic Carnot Engine." ...Once you say the words "Thermal Heat Exchanger" and "Supercooled Nitrogen", people get really interested.

But then too- I kind of have this idea that it *could* be possible to use such a balloon to go higher than Joe Kittenger. (See here: )
...He used Helium, and jumped from the edge of outer space, but the problem was that it could only go so high before the balloon would expand to the point of bursting. Plus, my God, how much expensive Helium do you think that guy had to use to get up there? ...Being able to compress a more common gas from the balloon into the tank, and vice versa would function in a way that would allow you to achieve higher altitudes on the way up, and greater braking on the way down. So in that sense, yes you do have a super-complicated hot air ballon, but it also has the added advantage of achieving super high altitudes. ...And that's what makes it completely new and unique.

...It would operate much like how a submarine works- only in the air.
See- from Wikipedia:
The atmosphere's density depends upon altitude. As an airship rises in the atmosphere, its buoyancy decreases as the density of the surrounding air decreases. As a submarine expels water from its buoyancy tanks (by pumping them full of air) it rises because its volume is constant (the volume of water it displaces if it is fully submerged) as its weight is decreased.
Moreover, it was recently demonstrated by an IT manager in England (an ordinary dude, like me), that for a few hundred bucks you could send up a balloon and take near-space photographs (see here: http://www.dailymail.co.uk/sciencet...raphs-using-helium-balloon-pocket-camera.html).
A conventional hot air balloon just can't achieve those kinds of altitudes, and there are a number of world records which still remain within reach, but completely untouched since the 1960's.
Richard Branson is currently spending millions on Virgin Galactic, and people are lining up in droves to pay \$200,000 a pop to get to the same altitude- but why??
You could get the same result for a lot less money with a well-designed hot air balloon. ...Its just so obvious.

Ok- so who's laughing at this folly now?

But anyway- enough on that soapbox.
Let me just ask these questions:

The mean molecular weight of air is around 28.8 (that's an 80-20 mix of N2 and O2, close enough), whereas for pure nitrogen it's 28. So it's just under 3%.

You only get your 22% if you fill your balloon 78% full of nitrogen and 22% full of vacuum!
But if you see here: http://en.wikipedia.org/wiki/Lifting_gas#Hydrogen_and_helium
In the section where it compares the difference in the bouyancy of hydrogen and helium, it goes on to say:

...helium is almost twice as dense as hydrogen. However, buoyancy depends upon the difference of the densities (ρgas) - (ρair) rather than upon their ratios. Thus the difference in buoyancies is about 8%, as seen from the buoyancy equation...
So- if that's the case, I don't think Vanadium's comment may be 100% accurate, because again, we aren't accounting for just weight, what we have to take into account is the difference in relative densities (which is partially a function of temperature), right?

I think to get a clear answer about the efficiency of superheated nitrogen (vs. plain hot air), you'd have to do the following comparison:

Take the density of nitrogen at a temperature of +400F at sea level, relative to the density of the surrounding plain air at say, +85F.
Once you have that, take the density of just plain air at +400F at sea level, relative to the density of the surrounding plain air at say, +85F.
One is a hot air balloon filled with hot air, and the other is a hot air balloon filled with hot nitrogen.
Now, compare the two, and the picture of how much more efficient superheated hydrogen is relative to plain old air will emerge.
Compare that to the effiency of say, helium, or superheated helium, and now a picture begins to emerge about how to build a smaller balloon to do more efficient lifting...

...Right?
So, can we start there?

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You guys are hilarious.
...
So, can we start there?
After the part about your girlfriend leaving, the post stopped making any sense.