Stirlingengineforum.com

Here is another idea I've been working on.

I've been fooling around for a long time trying to design a kind of Stirling Turbine.

What I finally came up with is what appears to be a kind of "perpetual motion machine" or "free energy" device.

It combines a Stirling Type displacer or "inturbulator" (as I prefer to call it now) to expand and contract air in a chamber but instead of a piston or diaphragm it has ports or check valves to simply draw in and compress the air,

This is combined with a "simple air cycle" heat exchanger.

Relatively warm air is drawn in from the atmosphere and compressed into a narrow tube inside the "displacer" chamber. The compressed air is thus forced to give off heat. Next the compressed air, having lost some of its heat energy is decompressed through a turbine.

As the air molecules impact with the turbine blades and expand they give up much of their energy which is converted into electricity by the turbo-generator.

Due to having lost much of its energy and due to being allowed to expand the air leaving the turbine is VERY VERY VERY cold.

The cold air is used to create your temperature differential at the other side of the chamber.

This is like the hot and cold coils in a typical refrigeration system but with a much greater temperature differential.

In other words - warm air is drawn in from the atmosphere and its energy is "wrung out" by the heat exchanger, some of the energy is used for the displacer chamber and the rest is converted into electricity by the turbo-generator.

Warm air is drawn in - the energy is extracted and cold air is ejected as a "waste" product.

This is not really "perpetual motion" - the energy is ultimately coming from the sun. The Earths atmosphere itself is being used as a giant warm-air solar collector.

The air cycle system is able to create extreme temperature differentials - much more so than a typical refrigeration system. Air leaving the turbine of an air-cycle system can be extremely cold.

Like most Stirling Systems this would probably need to be started by some outside source - like an auxiliary air compressor, but once started, as long as the turbo-generator keeps drawing off energy to maintain the temperature differential - it should keep going.

That this COULD work (or in fact DOES work) in theory, is illustrated I think, by the novelty "dippy bird" that is really a kind of tiny refrigeration system or heat exchanger that draws its energy from the ambient heat energy in the air to keep the bird moving.

Here is an illustration of the basic system.

[url]http://prc_projects.tripod.com/stirling_air_turbine.html[/url]

Tom,

Interesting. I'm not sure I understand your idea completely.

"Relatively warm air is drawn in from the atmosphere and compressed into a narrow tube inside the "displacer" chamber. The compressed air is thus forced to give off heat."

Why is this? And what it is the consequence? I am pretty new to this and have limited engineering/thermodynamic understanding. I think I understand the cooling side - using the turbine in the process of decompressing the air, but how the compression and "displacement" occur is not obvious to me.

Dale.

dalekh wrote:Tom,

Interesting. I'm not sure I understand your idea completely.

That probably makes at least two of us.

It started out that I was just trying to design a solar powered Stirling engine and trying to maximize efficiency and use some kind of refrigeration system to keep the thing cool. I read somewhere that turbines are supposed to be more efficient than a regular piston engine and that an "air cycle" refrigeration or heat exchanger produced the widest temperature differentials of any cooling system.

Apparently, the main reason an Air Cycle refrigeration system isn't more commonly used is just that the temperatures produced are too extreme. But I figured, for a Stirling engine... extreme temperature differentials are what you want.

You have probably seen small model Stirling engines running on ice.

This is basically the same idea. Mostly to run the Stirling engine on the extreme cold produced from the air cycle heat exchanger and using the ambient heat in the air for the expansion phase and possibly getting a little extra heat due to the compression of the air in the coil behind the turbine.

The only problems I see are that in most air-cycle systems the air volume being sent through the system is very large without a whole lot of compression and this whole idea of using a displacer chamber as a kind of heat exchanger compressor directly with leaf valves or check valves directing the flow of air is something that, as far as I know, hasn't been tried yet either.

There are a lot of "Ifs" and Maybes there.

In a refrigeration system, generally, some form of gas is compressed through a narrow coil and the coil cooled with a fan or by convection to drive off the heat (when a gas is compressed it heats up. Like the hot coils on the back of a conventional refrigerator which are cooled by convection). Then the gas is allowed to expand again through a set of larger coils - becoming very cold (This is the equivalent of the refrigerator or freezer coils inside a conventional refrigerator)

In an air cycle system, the air is expanded through a turbine which takes away even more energy than a conventional freezer producing extremely cold temperatures on the expansion side.

The idea is basically to put the compression and expansion coils of the air cycle system right inside the displacer chamber to get your hot and cold temperature differential.

"Relatively warm air is drawn in from the atmosphere and compressed into a narrow tube inside the "displacer" chamber. The compressed air is thus forced to give off heat."

Why is this? And what it is the consequence? I am pretty new to this and have limited engineering/thermodynamic understanding.

As to the "Why" exactly ? I don't really know either. That's just what I read as far as how a "simple" Air-Cycle cooling system is supposed to work, and basically how any refrigeration system works. Compress a "refrigerant" into a narrow coil and for whatever reason, the molecules being forced close together I suppose, give up some of their energy in the form of heat, the heat is driven off somehow, by a fan or by convection, then when the molecules are allowed to expand again they try to get that energy back. With most refrigeration systems there is a "change of state" involved, but apparently in an air cycle system change of state is not necessary.

My theory is that enough of a temperature differential will be made available inside the displacer chamber to expand and contract air - as in a conventional Stirling engine.

In my drawing, a solenoid is used to drive the displacer as there isn't any conventional drive mechanism to attach it to.

There would also need to be some sort of electronic "brain" or perhaps just a small motor with some make-or-break circuit to control the solenoid (or solenoids - it might be necessary to use more than one)- or a small independent motor with a connecting rod to move the displacer up and down could be used.

I don't really know how much, or even IF air could actually be compressed in this way... If so, I imagine that some form of two stage compressor, (two displacer chambers side by side) might work more smoothly and keep the air flowing at a greater volume.

I think it is pretty obvious that this is all theoretical at this point, but as far as I can see, it shouldn't be too difficult to build some sort of small prototype to see if it works.

At first I had the expanding/contracting air in the chamber driving a more conventional piston or diaphragm which then drove a compressor for the air cycle... but then I thought... why use compressed air to drive a piston to drive a compressor to compress air ? Just eliminated all that and put in a couple check valves.

Somehow I've become convinced that this, or something like it could actually work, on more or less the same principle that allows a Stirling engine to run "on ice" (actually it is running on the ambient heat in the air) or that allows a "dippy bird" novelty to run on evaporative cooling (again actually running on the ambient heat in the air) With the "dippy bird" energy is actually being drawn away through evaporative cooling and being replaced by the heat in the air. With this "Stirling turbine" the energy is being drawn away by the turbo-generator.

It seems counter intuitive that more energy is made available to run a mechanism by taking away energy but apparently that can work.

By taking energy out of the system with the turbo-generator you are left with a cold heat sink so as to have your temperature differential which then makes the ambient heat in the air available for utilization. As the heat in the compressed air tries to flow toward the heat sink energy can be extracted to compress more air - theoretically at least.

I think I understand the cooling side - using the turbine in the process of decompressing the air, but how the compression and "displacement" occur is not obvious to me.

Dale.

Like in any conventional Stirling engine. The displacer moves up and down or back and forth forcing the air to move alternatively to the hot and then to the cold ends (in this case top and bottom) of the chamber - every time the air hits the cold end (cold coils) it contracts - creating a partial vacuum, then when it is forced to the hot end the air expands - creating pressure.

Normally a cylinder with a piston would be attached that would be driven by the expanding and contracting air - but in this case there are just some check valves. When the air contracts at the cold end it creates a partial vacuum and more air is drawn in and trapped inside the chamber, then this air is forced to the hot end where it expands and creates enough pressure to drive some of the air out through the other valve where it is again trapped under pressure and can only escape by passing through the coils and the turbine.

I was planning on making an animation of this to make it all clearer, but haven't gotten around to it yet.

Does any of this help at all ?

I would love for someone to at least see if it is possible to compress air directly from a displacer chamber through some leaf valves - using some more conventional heat source - just to see if this would work.

If not, possibly some similar but more conventional Stirling engine/heat exchanger hybrid would work.

Tom,

That helps. I am an HVAC guy and actually found out about stirling engines when researching cooling systems. Now I'll have to think through your idea so the cycle makes sense. The concept of getting a larger TD by giving up more heat as opposed to adding more heat is interesting. The mechanics seem feasible but I'm not yet at a point in modeling this stuff to try it. So far I have one tin can stirling to my credit - but at least it runs!

Keep thinking,

Dale.

Oh,...

One other problem I became aware of...

That is, if this thing ever ran long enough to actually begin functioning as intended...

As the air expands through the turbine and looses its energy and becomes extremely cold, the cold produced is REALLY extreme - according to what I've read on the subject...

Like - potentially near cryogenic / absolute zero type negative hundred(s) of degrees below zero...

I don't imagine a simple prototype would ever get quite that cold, but it may certainly reach below freezing temperatures easily - if it works at all - which makes ice formation on the turbine blades a common problem in an air-cycle system.

Either some means of removing the moisture from the air might be needed, or I was thinking that a closed system might just simplify things, though a closed system would need some sort of additional heat exchanger to re-warm the air/refrigerant at some point.

One possible advantage, I think, of operating the displacer independently of the turbine is that the driving mechanism (motor or solenoid) would be driven electrically, which means the need for seals to prevent leakage (around any kind of mechanically driven displacer shaft) could be eliminated by encapsulating the motor/solenoid. And, in theory at least, it could be electronically controlled so that the timing/displacer movement could be tweaked for maximum efficiency.

I suppose I'm thinking too far ahead though.

I thought I might also mention that the reason I had the hot end of the displacer chamber at top is, not only that hot air rises, which might make it easier to keep the heat where it belongs so to speak but also because the cooler, presumably denser air entering the "compressor" area would tend to stay at the bottom.

Somehow I don't think you would want to compress hot - already expanded air, that would be additional work - just the cooler "fresh" air at the bottom.

My thinking may be wrong on this.

I started out with a diaphragm between the displacer chamber and the "compressor" thinking that the air would need to be kept separated, but then I thought - if the cooler / denser air just settles or stays at the bottom naturally - there would not be any need for a diaphragm, the denser incoming air would just stay where it belongs by itself, at the bottom where it can be compressed.

Maybe.

I'm glad you are an HVAC guy. This thing is really more like an air conditioning unit than a Stirling engine... It is just utilizing the more efficient Stirling principle to drive the compressor.

P.S.

I do have a design on paper where the cold "exhaust" is routed back through the air intake. That is, another cold air coil inside the intake duct. The idea being that moisture in the incoming air would condense onto the coil before entering the system and drain off - like a dehumidifier.

This would (theoretically) also make the incoming air more dense and easier to compress. After compression (probably on the side where the compressed air is traveling upward before the "heating coils" ) there could be a kind of heat exchanger exposed to the outside air to reclaim the heat that may have been lost in the dehumidification process if necessary.

On the other hand, if ambient air temperatures are already below freezing... the incoming air may already be dry enough to forgo all that. Then insulating this pipe or heat exchanger against heat loss might be more appropriate...(?)

I have several thoughts so far. As I study your design it appears that achieving the TD you will need is going to be difficult. You did state that a "starter" will be needed and I think it will need to be substantial. I'll have to do some study on this type of refrigeration but I believe velocity is required (it is a turbine) and substantial TD's will be needed to produce the pressure differential required to produce high velocity. The same is true in respect to having enough compression to make your warm end warm. Just thinking here. As a "Perpetual motion" machine, it appears it is going to need a really good running start.

Your other concerns about freezing and humidity control raise a point. If you have to remove moisture from the air, you are going to be removing heat (latent or otherwise) and you need that heat (energy) on the warm side. But as you say, we're getting ahead of ourselves on that.

This is an intriguing idea. I am just having trouble envisioning sufficient energies to properly operate the turbine. Maybe someone with more knowledge there can chime in?

Dale.

dalekh wrote:I have several thoughts so far. As I study your design it appears that achieving the TD you will need is going to be difficult. You did state that a "starter" will be needed and I think it will need to be substantial. I'll have to do some study on this type of refrigeration but I believe velocity is required (it is a turbine) and substantial TD's will be needed to produce the pressure differential required to produce high velocity. The same is true in respect to having enough compression to make your warm end warm. Just thinking here. As a "Perpetual motion" machine, it appears it is going to need a really good running start.

LOL...

Probably all too true,

I've already considered most of these points and thought there might be some work arounds. 1. I think high velocity may not be necessary. There are some air-cycle freezers that as far as I can see use higher pressure with relatively low velocity. I think that high velocity is possibly just a convenience in some applications (cabin cooling on jets) because it's available. I was thinking larger capacity displacer chamber with a relatively small turbo-generator - or multiple displacer chambers feeding a single turbine if necessary. (hmmm... but of course... a smaller turbine might not produce enough cold air to feed all those big displacer chambers ?)

My theory being that a displacer takes very little energy to move. Using bigger, or multiple displacers would require a relatively small additional energy input whereas the potential energy gain (the reservoir of solar heat in the atmosphere - miles deep and the size of the entire earth...) seems virtually unlimited... and is constantly renewing itself.

Your other concerns about freezing and humidity control raise a point. If you have to remove moisture from the air, you are going to be removing heat (latent or otherwise) and you need that heat (energy) on the warm side. But as you say, we're getting ahead of ourselves on that.

Right, but getting it back might not involve any additional loss, since your heat source is the atmosphere - just expose some air coils to the air where they can warm back up (?)

This is an intriguing idea. I am just having trouble envisioning sufficient energies to properly operate the turbine. Maybe someone with more knowledge there can chime in?

Dale.

Well, that has been a problem for me.

Applicable information on air-cycle refrigeration seems hard to come by. I've found very little online regarding the "simple" air cycle system, which I've only seen in print (in an encyclopedia, that didn't go into much detail). Other air cycle systems seem unduly large and complicated.

Also I can find ZERO information regarding using a displacer type "compressor". Just how much air could something like that actually move or compress ?

As far as I know, this is a new idea that has never been tried. Perhaps it could all be determined mathematically on paper, but I'm not a mathematician and I don't know the applicable formulas.

I have heard, however, in relation to heat exchangers, that they are very efficient due to the fact that it takes LESS energy to simply MOVE heat than it does to produce heat.

Here, with this "turbine" you are ONLY moving the heat already available in the atmosphere so that it can be utilized, theoretically extracting more heat-energy than would be required to move more.

I was encouraged at one point when I was thinking about "change of state" and wondering if, with enough cooling/compression, the air might actually liquefy.

I put "liquid air engine" into Google and found this interesting old article:

Mclures Magazine

A Mr Tripler invented such an engine - it was basically just a steam engine but used liquid air as a fuel, and he claimed that he could produce MORE liquid air with this machine than it took to run it.

The article reads:

------------clip
"That is perpetual motion," you object.

"No," says Mr. Tripler sharply. "no perpetual motion about it. The heat of the atmosphere is boiling the liquid air in my engine and producing power just exactly as the heat of coal boils water and drives off steam. I simply use another form of heat. I get my power from the heat of the sun; so does every other producer of power. Coal, as I said before, is only a form of the sun's energy stored up. The perpetual motion crank tries to utilize the attraction of gravitation, not the heat of the sun."
(...)
"But I actually find that I can produce, for every two gallons of liquid air that I pour into my engine, a larger quantity of liquid air from my liquefier."
--------------

I'm afraid though that Mr. Tripler was failing to take into account that his liquefier was using the cold water in a nearby river to take away heat.

This would be difficult to do otherwise. He could dump an unlimited amount of energy into the river next to his liquid air factory... Then use the liquid air produced to run his steam engine. (actually running on the ambient solar heat in the air which boiled the liquid air) but you can't take a river with you... to drive a car for example.

But could a turbo-generator, which converts heat energy in the air into electricity act as your "river".

Theoretically, the more energy you draw off with the turbo generator, the better this should work.

That is, as the turbine "strains" to produce power it slows down and the air pressure builds up behind it... The more power you draw away, the sharper the temperature differential...

For this to work, you would have to have the turbo generator feeding a lot of energy to something to prevent it from "free wheeling" and loosing compression.

Again, this seems counter-intuitive. But like the dippy-bird, or the Stirling engine running on ice, or Mr. Tripler's liquid air engine - you need to get rid of, or "throw off" vast quantities of heat energy - AND KEEP THROWING IT OFF to maintain your heat sink.

What better way to get rid of energy than by generating useful electricity ? Theoretically, the more energy you can draw off with your turbo-generator, the greater the temp differential - or the colder the heat sink left behind - the colder the heat sink, the more the latent heat in the air becomes available.

Also, the harder your turbo-generator has to work, the more pressure will build up behind it - producing more heat for the other side of the temp differential.

So, in terms of "getting a running start" you would also, and possibly more importantly, have to have the turbo-generator actually doing some work - like charging batteries or feeding the electrical grid or powering a toaster - so as to get rid of excess heat. Otherwise your turbine will freewheel and the system will deflate (lose pressure) - and you wont "throw away" enough energy to produce any cold for your temp-differential.

What I'm trying to say above is difficult. But I've noticed this in regard to air-cycle systems and how they are considered "inefficient".

An Air cycle system generally, has to have the turbo generator DO REDUNDANT WORK.

Without doing work, the turbine won't produce the desired cold.

Usually, in an air cycle system they just have the Turbine do some "dummy" job - like run some redundant fans or something, just to convert the heat energy into another form so that the cold is left behind. But then the cold is TOO COLD and so they have to add some heat back to the cold air produced - as in air conditioning or refrigeration. Nobody needs minus 200 degree temperatures to air condition a room or refrigerate food. So this all gets very complicated and inefficient.

But anyway, once the cycle is started,... say, by pumping in air with an external compressor, which should begin generating some heat in the top coils... and then get the turbine moving...

Once the turbine is moving - it would have to be given some work to do...

Theoretically, (short of coming to a stop) the more work the better.

You need to have the air "back up" behind the turbo generator - make it do work to start drawing off excess energy.

Then you can maintain the pressure more easily as the turbine is running slower and not freewheeling and the energy being drawn off is necessary for producing the cold. You have to begin converting the heat to electricity - which leaves the air cold. Now you are starting to get your temperature differential and can turn on your displacer motor to utilize it to compress more air.

After that - it might just keep going without the external compressor - BUT YOU HAVE TO KEEP DRAWING OFF ENERGY.

If you were charging batteries... Once the batteries were charged the energy would have nowhere to go,... the turbine would begin to freewheel, you loose the compression and your temp differential and the system would grinds to a halt.

You need the "river" (in the form of a load on the turbo-generator) to throw off the EXCESS energy so as to maintain the temp differential (cold heat sink) that is then allowing energy to be drawn from the atmosphere.

It seems to me that we have at least three examples of this working, not just in principle but in fact...

The "Dippy Bird"

The Stirling Engine running on ice and

Mr Tripler's liquid air engine.

In each case, ambient heat in the atmosphere is utilized and EXCESS ENERGY is THROWN AWAY to maintain a temperature differential.

The only difference here, it seems, is that instead of just throwing the excess energy away by dumping it into a river or some other heat sink, like ice, or the dippy birds cold nose, it is being converted into usable electricity.

P.S.

In other words...

The sun has heated up the Earth's atmosphere something like 4 or 5 hundred degrees above where it would be without the sun (-450 F or so) That is a huge reservoir of (heat) energy.

The problem with this idea isn't finding enough heat but getting rid of the heat fast and efficiently enough to prevent your cold spot from warming back up again and loosing the temperature differential.

(Of course, some insulation would probably be a good idea - especially at the COLD end of the displacer chamber - to prevent the surrounding air from warming it back up.)

I doubt anyone could ever get rid of the heat fast enough with a conventional heat exchanger to produce much energy, maybe just enough to run itself - like the dippy bird, which would be pretty useless as a power generator - but the turbo-generator gets rid of the heat very fast and efficiently by CONVERTING IT into another form of usable energy: electricity.

Again, I think this seems odd or counter intuitive, but I think that anyone who is familiar with Stirling Engines knows that one of the main problems is not the heat source, but rather how to throw off excess heat fast enough to maintain the temperature differential.

If you are trying to keep the engine cool with air at ambient temperatures.... you will have to get the other end very hot. But if you are using ambient air to heat the hot end, then you have to get the other end very cold, and you can make cold by converting the heat into another form of usable energy. You don't really have to MAKE cold. Cold is what's left when you take away (or convert) the heat.

This all seems to make sense to me THEORETICALLY... but I have a hard time believing it could actually work, though I can't figure out why it wouldn't... and there seems to be some real examples that demonstrate that it can work.

LOL...

Even one of these might generate a little power...

Giant Dippy Bird Video

This guy has got the idea... sort of LOL...

Dippy Bird Generating electricity Video

dalekh wrote:... If you have to remove moisture from the air, you are going to be removing heat (latent or otherwise) and you need that heat (energy) on the warm side.

Dale.

About this.

I've been reading about the use of Desiccants (Drying agents, like silica gel etc.) to dehumidify air (instead of condensation).

What I found interesting is that apparently -- the reaction that takes place as the desiccant absorbs moisture from the air is kind of the opposite of evaporative cooling, and the air, instead of getting cooler actually gets a little warmer (though the low humidity air feels "cooler" or more comfortable)

Perhaps a "desiccant wheel" of some sort at the inlet duct would do the trick - and instead of loosing heat there would actually be a slight heat increase (?).

I've been thinking about the other thing too... That is, the turbine... and do you really need high volumes of air traveling at high velocity...

You get the heat from compressing the air and the cold from expanding the air.

In actuality, this would work to some degree without a turbine.

Force the air into and through a narrow coil to get it to give up heat and then let it expand so that it tries to get the heat back - producing cold. This would happen even if there was virtually no air flow at all - such as compressing and expanding air in a cylinder.

Expansion through a turbine increases the temperature differential even more as you are not only making the air colder by expanding it but you are making it doubly cold by making it do work simultaneously...

So what all that adds up to in my mind is that a relatively high volume "compressor" with a relatively small turbine might actually still do the trick... On the theory that you are getting some cooling from the air expansion even without a turbine.

I was thinking when I envisioned this thing that what would really be needed is a pressure relief valve somewhere!

LOL...

I mean, If an LTD Stirling engine can run on the heat from the palm of your hand - or a cup of coffee - or some other very low temperature difference of just a few degrees...

Let's say that you have ambient air at around 75° F. If you compress it, say to 35 PSI you end up with something like what ? 250° F maybe ? As it passes through the displacer chamber it looses some heat and cools back down quite a bit before reaching the turbine (It could be cooled more if necessary, while still under pressure in another open air coil (radiator/heat exchanger) before reaching the turbine, to bring the temperature back down to near ambient temperatures) - now expand it through the turbine - and lets say you only get it down to somewhere around freezing as it leaves the turbine.

You have a temperature difference of over 200° and I'm thinking that this is a very conservative estimate from what I've been able to find out in regard to actual air cycle system temperatures. (close to 500° F on the hot side and well below 0° F on the cold - possibly MUCH MUCH colder)

I mean, if a dippy bird can produce a few micro volts... I'm having a hard time imagining that something couldn't be finagled around to get at least that much out of this setup...

I mean a turbine doesn't necessarily have to spin like a jet engine.

Even lackadaisical water wheels or slow moving Dutch windmills are types of turbines. I can't imagine that really high air velocities are an absolute necessity - especially not just for a proof of concept.

If it can so much as turn a pin wheel it could be made to produce some power, if only a microvolt or something.

I'm pretty well convinced something more than that might be possible.

Tom,

Not ignoring you. You are covering a lot of ground and I'm a bit behind you on on all this. I will see what I can come up with about using turbines for cooling - principles as opposed to "how it's done on airliners, etc.". Your idea is starting to make some sense to me. I looked in an old HVAC/R book and found a "vortex tube" which uses a similar principle but different mode. It does, however, require large (relativley) amounts of compressed air. This was my concern with the turbine. Hopefully you are right and it can operate with smaller energies.

Speaking of the practical aspect of trying to prove the concept - how complicated is the machining on a turbine? For us "tin-can" modelers, that is important. I'm sure there are some people on this forum with superior skills and equipment - I'm not one of them. I have a cheap drill press and decent modelling skills. I have no idea where one might come up with a "model" turbine to play with this idea. The other aspects seem "build-able".

Well, I'm teaching an Air Conditioning class tomorrow evening and have to work tomorrow so I better move on to other things - you know, the ones that pay the bills so we can play with this stuff!

Dale.

dalekh wrote:Tom,

...Your idea is starting to make some sense to me. ...Hopefully you are right and it can operate with smaller energies.

Speaking of the practical aspect of trying to prove the concept - how complicated is the machining on a turbine?

Dale.

I'm thinking something of a relatively large diameter, like a rather heavy metal disk with small groves cut around the edge, and an air nozzle - like an old oil burner or paint sprayer nozzle to provide the jet of air. A simple pelton wheel type turbine.

This would not require a tight enclosure and I'm thinking making it relatively heavy and large diameter would slow down the RPM and make it less noisy - that dentist drill sound

Heavy, and large diameter - as this would be easier to balance and hopefully slow down the RPM.

This is the least efficient type of turbine, I think, but as the function of the turbine in this case, is to get rid of energy (cool down the air) by making the air do work... I don't think efficiency is that much of an issue here. Though the more efficient, the colder the air gets I imagine.

I worked in a lawn mower repair shop where we used air tools of various sorts and I noticed that often frost would form at the air outlet when the torque wrench or whatever was used to do some heavy work, like torquing down head bolts.

Possibly any kind of air motor would do (vane or piston type).

I was reading somewhere that air or gas, can only carry energy as HEAT and so when it is made to do any kind of work it looses heat, so a piston type air motor might work just as well but it would still need some kind of load (actual work to do).

I found a small model turbine at the bottom of this website:

http://dynamicenergy.us/Impulse-Reaction-Turbine.html

They also say: "Dynamic Energy Corp. is planning to produce these models for hobbyists and other interested individuals who like tinkering with such toys."

The model pictured runs on just 3 psi.

As the turbine is at the air outlet or "exhaust", the enclosure would not have to be particularly air tight.

One of my biggest worries has been that with an enclosed displacer chamber with no piston or other air outlet... if the air nozzle at the turbine was too small (or clogged up) it could, theoretically, build up extreme pressure behind it very quickly, and if it did run, there would be no way to slow it down or turn it off...

I made one small Stirling engine and put it on a stove burner. It kept running for a long time after I took it off the stove.

The problem here would be - you aren't just expanding and contracting a static air mass - but continually adding air with each stroke of the displacer - so theoretically, it could build up a lot of pressure.

Maybe a throttle or choke of some kind at the air inlet would work - or increasing the load on the turbine, or cut the power to the displacer motor.

At least some sort of safety valve or plug might be a good idea.

I'm also thinking that what you don't want is a high volume or rapid air flow. You want the air to hang around in the pipes or tubes long enough to exchange heat. So a very small smaller-than-a-pinhole air nozzle at the turbine to hold back the pressure.

Also, turbines, even a small model - could build up incredibly high RPMs, especially without a load, which could be dangerous if a homemade turbine flies apart.

I may be worrying too much. It may not work at all, but just in case it did...

I just came across something interesting in relation to a relatively easy to build turbine.

The Tesla Turbine.

Instead of blades on the turbine, closely spaced disks are used. Some DIY's just use old CD's or old hard drive platters. A jet of air is directed between the disks which turn just due to the air drag between the plates.

Apparently it is good at removing heat. I read something on Wikipedia where Tesla was describing the advantages which included reducing the outlet temperature when steam is used to power the turbine.

You Tube video of DIY Tesla Turbine:

http://www.youtube.com/watch?v=yk-_IGd4 ... re=related

Building a Tesla Turbine from hard drive platters:

http://www.phys.washington.edu/users/sb ... rbine.html

It also seems MUCH quieter than a conventional turbine. The one in that You Tube video seemed almost silent. I couldn't tell if it was running by just listening.

Unfortunately, it seems it stalls at low speed and has some difficulty starting compared with a conventional turbine where the air impacts the blades directly.

Once it gets going however, it is apparently very efficient at high speeds.

At least it appears relatively easy to build and balancing shouldn't be a problem...

I was thinking, for a small prototype; possibly some small hard drive platters from an old laptop, though I've never taken one apart. The drive itself is less than 1/2 the diameter of a regular desktop hard drive.

Looks like here's are lots of exciting Tesla CD Turbine videos on You Tube

I like this one LOL:

http://www.youtube.com/watch?v=Dn6MR0Ws ... feature=iv

dalekh wrote:Tom,

... You are covering a lot of ground and I'm a bit behind you on on all this...

...Well, I'm teaching an Air Conditioning class tomorrow evening and have to work tomorrow so I better move on to other things - you know, the ones that pay the bills so we can play with this stuff!

Dale.

No problem,

I'm just trying to educate myself as I go along and posting what I find that seems applicable. Just to have it on record for anyone who might want to fool around with this idea.

I just found this today, reading the Wikipedia article more thoroughly:

"The efficiency of a conventional turbine is related to the difference in temperature between the intake and the exhaust."

So Turbine efficiency does matter (i.e. The more efficient the turbine, the greater the resulting temperature differential).

"Some of Tesla turbine's advantages lie in relatively low flow rate applications or when small applications are called for."

Good, in terms of building a small model.

http://en.wikipedia.org/wiki/Tesla_turbine

I'm also now reading about the "boundary layer effect", mostly in relation to how the Tesla Turbine works... but I think this is also applicable to the earlier question of why the air traveling through a very narrow tube gets hot. I think this is also due to the "boundary layer effect"...

Air (or a fluid) traveling through a pipe, (or along the side of any smooth surface) tends to adhere to the pipe walls or surface (such as the wing of an airplane. In other words, there is a lot of "drag" of the air against the inside wall of the pipe.

The area at or near the inside surface of the pipe where the drag is greatest and the air tends to adhere tightly to the wall of the pipe is the "boundary layer"

Reduce the size of the pipe enough... and the entire channel that the air must pass through is then within the "boundary layer". That is; the air adhering to the pipe walls effectively "clogs up" the pipe - so that as the air is forced along under pressure it encounters a great deal of friction or "resistance" - very much like electricity passing through a very thin wire or foil in a heating element or the filament in a light bulb.

As with electricity, where wattage equals Volts x Amps, the amount of heat generated by the air passing through a thin tubular coil would be pressure (roughly equivalent to volts) x flow rate (roughly equivalent to amps).

Before the "heating coil" the air is compressed into a relatively large pipe or chamber and "friction" on the walls as the air moves upward is minimal... then as the air passes into the thin tube at the top of the displacer chamber, the "resistance" increases - producing or giving off heat, due to the boundary layer effect or increased "resistance".

The thickness of the boundary layer will also be relative to pressure and velocity.

There are exact equations for all this stuff, apparently, but I don't, as yet, understand the math... but it looks basically like BIG pipes, as in an air cycle system for cabin cooling in a jet, could use high velocity air (like high amperage in electricity needs big wires) to produce the effect, though very thin pipes would need relatively little velocity/pressure to produce the heating effect (just as very thin wires can get hot and/or melt at relatively low amperage/voltage).

Basically we are back to, what volume of air (if any) could a displacer chamber actually move or pump out, and under what kind of pressure ? The size of the heating coil/pipe/tube thing could be adjusted accordingly - as well as the size of the turbine nozzle orifice and the turbine itself.

I'm thinking about just using a tin can displacer chamber fitted with some check valves and heated by a candle with a balloon fitted to the outlet and moving the displacer up and down by hand... just to see if it could blow up a balloon to begin with, but I'm currently staying in a camper and am very limited as far as what I can do at the moment... but perhaps I can solder something together from some old soup cans...

I can think of a few (other) reasons why this might not work.

Normally a Stirling Engine works by expanding air which is made to do work DIRECTLY by pushing against a piston so that the air is expanded and made to do some work within the displacer chamber itself... As the air expands and works against the piston the heat energy in the air is converted to kinetic energy and the air cools back down immediately which, I suppose, helps maintain the temperature differential.

If the air is simply evacuated through a port, this might not have the same effect.

I'm thinking, though, that once the air is compressed to some degree then the back pressure of the air in the pipe outside the port will count as a "piston" to work against.

Also if the temperature differential (or cold) produced by the turbine is extreme enough, it might not matter.

There may be another problem with having a separate "compressor" area attached to the displacer chamber. Perhaps the extra air volume will act as too much of a "cushion" preventing the air from being compressed enough to do any real "work".

In other words, without a piston, you might loose the ability to maintain a decent temperature differential.

The idea behind using the displacer chamber to compress air directly is just to increase efficiency by eliminating a lot of friction from the moving parts required to push a piston to turn a crank to turn a pulley or gear to drive a belt or something to drive a separate compressor to turn another crankshaft to drive another piston to push air through a check valve...

I figure, if some efficiency is lost without a piston,... the efficiency gained due to the elimination of all these moving parts should compensate for that.

But... theoretically, I think this might still work with a conventional Stirling engine driving a small compressor/heat exchanger and using the temperature differential from the heat exchanger coils to run the Stirling Engine.

I decided on an Air Cycle System because it is supposed to produce the most extreme temperature differentials of any kind of heat exchanger - but maybe this is really overkill and some other, more conventional refrigeration system would work... though I like the Air Cycle System for many other reasons (environmentally friendly, no need to "charge" the system, less concern about leakage of potentially hazardous or expensive refrigerants etc.) But it's primary advantage in my mind, is that the Air Cycle throws off energy at the turbine as a "waste product"... which could be used to generate usable electricity... Which would make this a power producing unit rather than just a "perpetual motion" machine.

I have an old air compressor. The small hand held type that you plug into a 12 volt automotive cigarette lighter for inflating tires. I was thinking of taking the pump out and driving it directly with a small Stirling engine. Add some coils and a Tesla turbine...

But as I say, I'm very limited here at the moment, as far as what I can do, which is why I'm posting the idea here, in hopes anyone in a better position to cobble something together might do so.

This will, no doubt take time. In the mean time I'm just trying to sell the idea - (to myself as much as anyone else).

edit: I was just reading an article about the Tesla Turbine. Apparently, it does not take a very big Turbine of this type to produce high horsepower. In the article Tesla demonstrates a Tesla turbine with just 9 inch diameter disks that was developing 110 horsepower !

Apparently, also, unlike a conventional turbine which only develops power for a fraction of time while the air is impacting the turbine blades as they pass the nozzle, the air in the Tesla turbine continues to deliver power as it spirals to the center of the disks creating a constant and continuous "drag" on the disks all the while.

Also, according to the description of the reporter writing the article, the little turbine did not have any trouble starting, on the contrary, he relates that the turbine accelerated to top speed almost instantaneously.

http://books.google.com/books?id=Vv--Pf ... q=&f=false

Here is another drawing with a few more details that I had left out of the other basic "concept" drawing.

[url]http://prc_projects.tripod.com/stirling_air_turbine_2.html[/url]

This is more like a potential working design with some of the elements I left out previously and a few new ones. Also this shows an alternative displacer chamber design and the ports and check valves have been moved.

This is actually more like an older design I had on paper - except for changing the generic turbine to a Tesla turbine.

I'll try to explain the rationale behind it - following the air flow...

The assumption made here is also that the system has already been started with an external compressor.

Also the location of various pipes and what not are for illustration purposes. (so you can see everything). Otherwise the system could be more compact.

OK..

First - fresh air flowing in through a duct passes by some coils which have exited the top (Hot end) of the displacer chamber. This cools the coils back down to ambient temperature and also reclaims some heat. This will also (theoretically) cool/contract and densify the air before it reaches the turbine. The theory here being, as far as I understand it - the denser the air can be made before the turbine, the more violently it will expand when it is finally released into the turbine through the turbine nozzle. Also - the denser and COLDER the air can become, BEFORE it hits the turbine, the colder it will become yet upon exiting the turbine.

Next, the incoming air enters or is drawn into the bottom of the displacer chamber - hitting the cooling coils directly this time.

As the air enters and cools it contracts - drawing in even more air - which also cools and contracts - until no more air can be drawn in.

Now the displacer moves down pushing this cold air that just entered the chamber up where it impacts the heating coils and expands rapidly - creating pressure which forces it out into some pipes or a tank where it is allowed to expand somewhat.

At this point I'm not sure if the air in the pipes or "holding tank" will be hotter or colder than ambient temperatures. If colder - the pipes could be exposed to the air to absorb more heat. If hotter the pipes could be insulated.

Next the air is compressed (by additional air being pumped in behind it) and forced to pass through the narrow heating coils where due to the increased "resistance" the air/coils give off heat.

Then the air exits the chamber and enters a coil inside the incoming air duct where it is cooled to ambient temperature. (The heat removed is reclaimed by the incoming air)

Next there is a second cooling coil which further cools and contracts the air before it reaches the turbine.

This additional cooling and contracting of the air also helps draw the air through the heating coils by creating a partial vacuum.

Now the air is released through a nozzle into the turbine - where it drives the turbine (under a load) producing usable power.

Some of the electricity generated by the turbine is used to drive the displacer.

Cold air exits the turbine, having become cold due to expansion and also due to having lost energy in driving the turbine.

The cold air exiting the turbine is sent through a tube into the bottom of the displacer chamber.

Next the air exits the system, passing by the cooling coils where it cools the air about to enter the turbine.

The air is finally exhausted to the atmosphere.

A few points:

The displacer design.

The "displacer" has been replaced by something else that I'm calling an "enturbulator" for the moment. It's intended purpose is to direct the air in the displacer chamber into a spiral or vortex.

The inlet and outlet ports would be situated at such angles as to assist this spinning or mixing motion of the air. This should help with the heat exchange within the displacer chamber.

Two solenoids are shown this time. One to move the displacer up, and one to move it down. This will (theoretically) allow the system to operate in any position and also give greater control over the displacer movement. In this illustration, the solenoids are activated alternately by a simple make or break mechanism attached to a small motor.

I think the advantage of the displacer chamber design and the location of the intake and outlet ports on the displacer chamber will allow the reclamation or "regeneration" of the heat used to compress air in the displacer chamber.

As can be seen, I think, As the air is expanded by the heating coils it not only pushes air out of the chamber where it then travels through the system, but the heat that it carries with it is immediately reused. That is, this heated air circulates back through the heating coils where the heat first came from to expand it.

My guess... for this reason (due to this regeneration) is that this pipe or tank (The thing with the pressure gauge) will need to be insulated so as to retain the heat as my assumption is that the air inside will be considerably warmer than ambient temperatures.

[url]http://prc_projects.tripod.com/stirling_air_turbine_2.html[/url]

Originally this thing was attached to a solar collector (parabolic dish) which added heat to the system (where the pipes with the pressure gauge are), but once I started running it in my head It seemed that the added direct solar heat might not be necessary as the system seemed to be extracting (solar) heat indirectly from the incoming air. i.e. I envisioned that it kept right on running even after the sun went down!

I just discovered a similar discussion on another forum. I Just posted a message there with a link to this forum.

Apparently there is a company working on and promoting an engine that appears to be based on the same concept but that uses a closed air-cycle refrigeration system.

Kender Solar Engine:

http://www.scienceforums.net/forum/show ... hp?t=43818

Apparently this Kender engine also uses some kind of Stirling/Turbine hybrid, but they are not releasing detailed information about it.

They claim to have a working prototype.