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Tom Booth

Stirling Turbine

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(continued from previous thread)


I'm starting to make some progress with the mathematics. At least I finally think I figured out what "p" in pV=nRT means in terms I can understand.


Please correct me if I'm wrong.


p is absolute pressure. The scale of absolute pressure begins at a total vacuum. This is very different from what I had supposed earlier.


Putting this in units that are more familiar I came up with this table:


(figures are rounded out)


1 psi = 6895 p (absolute) = .06 atm = .0689 bar

5 psi = 34475 p = .34 atm = .34 bar

10 psi = 68950 p = .68 atm = .69 bar

14.7 psi = 101317 p = 1 atm = 1.01 bar

15 psi = 103425 p = 1.02 atm = 1.03 bar

20 psi = 137900 p = 1.36 atm = 1.38 bar

25 psi = 172375 p = 1.7 atm = 1.72 bar

30 psi = 206843 p = 2.04 atm = 2.07 bar

35 psi = 241325 p = 2.38 atm = 2.41 bar

40 psi = 275800 p = 2.72 atm = 2.76 bar

45 psi = 310275 p = 3.06 atm = 3.1 bar

50 psi = 344750 p= 3.4 atm = 3.45 bar



I'm most familiar with psi as that is the common measure for blowing up tires and what not, it is easily read on a gage - such as a common household compressor which I've used frequently etc.


I put absolute pressure second (and bold-ed) as those are the numbers we need for our calculations. It is also nice to be able to relate all this to atmospheric pressure, which we all experience, so I've included that. Bar I just threw in for the hell of it.


T - Absolute temperature I'm OK with (Kelvin). n - moles aren't a problem, that can be easily calculated. V - volume, I'm still not sure what measure is supposed to be used and R - the gas constant, I'm still fuzzy on. But I am making some progress I think.


What I want to figure out to begin with is what happens if we start off with a temperature "x" (above ambient) for the hot end and "y" (below ambient) for the cold end.... (achieved by artificial means, such as applying heat and cold from a torch flame on one end and ice on the other)


First we drive the air (at ambient/atmospheric temperature and pressure) in the chamber to the cold end where it contracts by whatever amount - drawing in more air, (which might also contract some once it enters the chamber). Then we drive that combined air to the hot end where it expands or tries to, increasing the pressure.


What I want to figure out to begin with is if the exhaust port were blocked so that the air could not expand or escape the chamber what pressure would have developed by the above procedure ?


I think this would represent about the maximum pressure that could be achieved at the given (x,y above) temperature differential.


The air is not yet escaping and flowing through any tubes or turbines or anything so this should be relatively easy to figure.

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The P is for pressure, which has units of force per area. You can use any of the pressure measures (they mean the same, with different units), although if you use the ones that match your measure of area they cancel easier. If you use google calculator, it can do both the math and unit cancellation for you.


An important distinction is between total pressure and a pressure difference -- the gas law tells you the total (absolute) pressure, but it is a pressure difference that is used to do work.

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The P is for pressure, which has units of force per area. You can use any of the pressure measures (they mean the same, with different units), although if you use the ones that match your measure of area they cancel easier. If you use google calculator, it can do both the math and unit cancellation for you.


An important distinction is between total pressure and a pressure difference -- the gas law tells you the total (absolute) pressure, but it is a pressure difference that is used to do work.


OK, Thanks.


I'm not entirely sure what you mean by "unit cancellation" yet, but maybe I'll figure it out when I get further along.


At this point, no real work is being done. I'm just trying to calculate what maximum theoretical pressure could be built up in the chamber at any given temperature differential if the chamber only had an inlet valve but no outlet to the piping or the turbine. (i.e. starting at 1 atm, the volume of air in the chamber is cooled and contracts, more air is drawn in, the total air is heated in the now sealed up chamber - what would be the new pressure.)


If the air were released, it would be back to 1 atmosphere at this point.


I don't think a second cycle could result in any further pressure increase as there would now be more air in the chamber and until the air was released the pressure in the chamber would probably remain above 1 atmosphere even if cooled back down again (the greater inside pressure holding the inlet valve closed).

Merged post follows:

Consecutive posts merged



I'm a little confused by your statement:


You can use any of the pressure measures (they mean the same, with different units)


I was going by the statement here:


The modern form of the equation is: pV=nRT where p is the absolute pressure of the gas




I assumed that if p represents absolute pressure as stated there, would it not then be necessary to convert to those units before doing any calculations ?

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"Absolute pressure" isn't a unit but rather a specification of how you use the units you choose. You can still work in atmospheres, psi, torr, Pascals, or whatever, as long as you use absolute (not gauge) pressure and you use the appropriate R for your units.

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The units are what you use to measure. You can measure distance in inches, miles, km, meters, lightyears, cubits, standardized-blue-whale-lengths, or anything you like. You can convert from one unit to any other, so long as you know the conversion factor. When multiplying or dividing stuff, you can get units of the same type on both the numerator and denominator; these can cancel. 1 foot / 1 inch = 12 is a conversion factor.


Try these:



Play with it a little.


Now, for the absolute pressure. Consider inflating a party balloon. It will have just over 1 atmosphere of total (absolute) pressure. However, it is contained in the atmosphere, which cancels out 1 atmosphere of pressure on the rubber. If your balloon were in space there is no way it could hold air at even close to 1 atmosphere.

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"Absolute pressure" isn't a unit but rather a specification of how you use the units you choose. You can still work in atmospheres, psi, torr, Pascals, or whatever, as long as you use absolute (not gauge) pressure and you use the appropriate R for your units.


OK. I think I follow you.


What I referred to as "absolute" above (second column) is Pascals.


But as I understand it, if you use pascals you are automatically using a measure of absolute pressure, since pascal units start at zero pressure or a vacuum rather than at 1 atm or anything else. Similar to how absolute temperature measured in Kelvin... Or am I just lost in the woods ?


Never-mind, I think I've got the picture.


I was thinking in terms of the "atmosphere" scale starting at 1 atm. It just clicked. All the scales start at zero. so 0 atm is the same thing as 0 Pascal or zero anything else.

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Pascals aren't automatically absolute. You can say "0 atm" and mean absolutely 0 pressure if you're working in absolute pressures.


Think of it like Celsius and Kelvin. A degree of difference is the same in each; if the temperature rises one degree Celsius, it also rises by one Kelvin. But one starts at 0 and the other doesn't. That's like the difference between absolute and gauge pressure, and you can use any unit of pressure either way.

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Now, for the absolute pressure. Consider inflating a party balloon. It will have just over 1 atmosphere of total (absolute) pressure. However, it is contained in the atmosphere, which cancels out 1 atmosphere of pressure on the rubber. If your balloon were in space there is no way it could hold air at even close to 1 atmosphere.


OK, I get what you mean by ""cancel" now.


This is rather obvious, I just wasn't familiar with the usage of the term.


Thanks, I think I'm almost out of the woods.

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I am currently working on building a model of the proposed "Stirling Turbine" discussed here. While doing some research I came across a description of the theoretical working principles of this engine written by Nikola Tesla and published in Century Illustrated Magazine, June 1900.


I find it very interesting that Tesla believed this principle possible and for some time worked on some such engine himself though due to various circumstances - such as his workshop burning down - never completed it and/or moved on to what he considered projects more of a priority.


Here are some extracts of the article:





by Nikola Tesla



... The windmill, the solar engine, the engine driven by terrestrial heat, had their limitations in the amount of power obtainable. Some new way had to be discovered which would enable us to get more energy. There was enough heat-energy in the medium (The Air, Earths Atmosphere), but only a small part of it was available for the operation of an engine in the ways then known. Besides, the energy was obtainable only at a very slow rate. Clearly, then, the problem was to discover some new method which would make it possible both to utilize more of the heat-energy of the medium and also to draw it away from the same at a more rapid rate.


I was vainly endeavoring to form an idea of how this might be accomplished, when I read some statements from Carnot and Lord Kelvin (then Sir William Thomson) which meant virtually that it is impossible for an inanimate mechanism or self-acting machine to cool a portion of the medium below the temperature of the surrounding, and operate by the heat abstracted. These statements interested me intensely. (...)






Conceive, for the sake of illustration, [a cylindrical] enclosure T, as illustrated in diagram b, such that energy could not be transferred across it except through a channel or path O, and that, by some means or other, in this enclosure a medium were maintained which would have little energy, and that on the outer side of the same there would be the ordinary ambient medium with much energy. Under these assumptions the energy would flow through the path O, as indicated by the arrow, and might then be converted on its passage into some other form of energy. The question was, Could such a condition be attained? Could we produce artificially such a "sink" for the energy of the ambient medium to flow in?


Suppose that an extremely low temperature could be maintained by some process in a given space; the surrounding medium would then be compelled to give off heat, which could be converted into mechanical or other form of energy, and utilized. By realizing such a plan, we should be enabled to get at any point of the globe a continuous supply of energy, day and night. More than this, reasoning in the abstract, it would seem possible to cause a quick circulation of the medium, and thus draw the energy at a very rapid rate.


Here, then, was an idea which, if realizable, afforded a happy solution of the problem of getting energy from the medium. But was it realizable? I convinced myself that it was so in a number of ways, of which one is the following.


As regards heat, we are at a high level, which may be represented by the surface of a mountain lake considerably above the sea, the level of which may mark the absolute zero of temperature existing in the interstellar space. (...) Heat, like water, can perform work in flowing down,(...) But can we produce cold in a given portion of the space and cause the heat to flow in continually?


To create such a "sink," or "cold hole," as we might say, in the medium, would be equivalent to producing in the lake a space either empty or filled with something much lighter than water. This we could do by placing in the lake a tank, and pumping all the water out of the latter. We know, then, that the water, if allowed to flow back into the tank, would, theoretically, be able to perform exactly the same amount of work which was used in pumping it out, but not a bit more. Consequently nothing could be gained in this double operation of first raising the water and then letting it fall down.


This would mean that it is impossible to create such a sink in the medium. But let us reflect a moment. Heat, though following certain general laws of mechanics, like a fluid, is not such; it is energy which may be converted into other forms of energy as it passes from a high to a low level. To make our mechanical analogy complete and true, we must, therefore, assume that the water, in its passage into the tank, is converted into something else, which may be taken out of it without using any, or by using very little, power. For example, if heat be represented in this analogue by the water of the lake, the oxygen and hydrogen composing the water may illustrate other forms of energy into which the heat is transformed in passing from hot to cold. If the process of heat transformation were absolutely perfect, no heat at all would arrive at the low level, since all of it would be converted into other forms of energy.


Corresponding to this ideal case, all the water flowing into the tank would be decomposed into oxygen and hydrogen before reaching the bottom, and the result would be that water would continually flow in, and yet the tank would remain entirely empty, the gases formed escaping. We would thus produce, by expending initially a certain amount of work to create a sink for the heat or, respectively, the water to flow in, a condition enabling us to get any amount of energy without further effort. This would be an ideal way of obtaining motive power.


We do not know of any such absolutely perfect process of heat-conversion, and consequently some heat will generally reach the low level, which means to say, in our mechanical analogue, that some water will arrive at the bottom of the tank, and a gradual and slow filling of the latter will take place, necessitating continuous pumping out. But evidently there will be less to pump out than flows in, or, in other words, less energy will be needed to maintain the initial condition than is developed by the fall, and this is to say that some energy will be gained from the medium. What is not converted in flowing down can just be raised up with its own energy, and what is converted is clear gain. Thus the virtue of the principle I have discovered resides wholly in the conversion of the energy on the downward flow.





Having recognized this truth, I began to devise means for carrying out my idea, and, after long thought, I finally conceived a combination of apparatus which should make possible the obtaining of power from the medium by a process of continuous cooling of atmospheric air. This apparatus, by continually transforming heat into mechanical work, tended to become colder and colder, and if it only were practicable to reach a very low temperature in this manner, then a sink for the heat could be produced, and energy could be derived from the medium.


This seemed to be contrary to the statements of Carnot and Lord Kelvin before referred to, but I concluded from the theory of the process that such a result could be attained. This conclusion I reached, I think, in the latter part of 1883, when I was in Paris,(...)


This work was continued until early in 1892, when I went to London, where I saw Professor Dewar's admirable experiments with liquefied gases. Others had liquefied gases before, and notably Ozlewski and Pictet had performed creditable early experiments in this line, but there was such a vigor about the work of Dewar that even the old appeared new. His experiments showed, though in a way different from that I had imagined, that it was possible to reach a very low temperature by transforming heat into mechanical work, and I returned, deeply impressed with what I had seen, and more than ever convinced that my plan was practicable. (...)


Full Article can be found here: http://www.tfcbooks.com/tesla/1900-06-00.htm



Tesla's idea of creating a "sink" or "Cold Hole" for heat energy to run towards affording a flow from which some energy could be extracted and that; by converting the heat flow into some other form of energy so that the "Hole" is never filled "By transforming heat into mechanical work" thus maintaining the "Cold Hole" or "Sink" in the process all describes in a nutshell what is accomplished by the "stirling Turbine".


"The conversion of the energy on the downward flow" so described by Tesla is, I think, something accomplished on a rather routine basis today by means of an "expansion turbine" or "turbo-expander" used for liquifying gases, cryogenics and other cold temperature processes.


As a compressed gas passes through the turbine the Heat-Energy within the gas is converted into mechanical energy - leaving the system. This is the point of conversion. Like Teslas decription of an underwater tank that is never filled because the water entering is converted to a gas which is allowed to escape.


In a Turbo-expander the gas itself is left at an extremely low temperature. In the Stirling Turbine, (this cold gas the energy from which has been spent to produce electricity) is then utilized to "scavange" whatever heat "leaks" through or into the system without being converted.


Again, here is a "working" illustration of the engine, though I've made a few design changes since this drawing was made it does illustrate the basic idea or principle that I'm working on:




I don't know as the configuration shown will work exactly as illustrated, but basically the flow of compressed air from the Stirling type "displacer chamber" will give off heat while compressed and become very cold when expanded through a turbine. The turbine generates more power than it takes to raise the displacer therefor producing an excess of energy while maintaining its own temperature differential. This is essentially. IMO, identical to how the "dippy bird" toy works in principle. Both are types of heat engine that produce enough excess power to operate their own heat exchanger so as to maintain a temperature difference.


A slightly more elaborate design here:




And animated: http://prc_projects.tripod.com/stirling_air_turbine_anim.html


BTW. I misspelled "Insulation" but I'm not going to go through the hundreds of frames of animation to fix it.

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In viewing the first illustration (above) It might be noted that the so-called "compressor" consists of nothing more than a chamber with two check valves, one check valve for admitting ambient air and the other for "exhausting" the same air or rather compressing it into a narrow tube.


The mechanism for "pumping" air through this chamber is almost identical to that of a hydraulic jack. All a hydraulic jack consists of, basically is a means of drawing in and pushing out a fluid - a plunger raised and lowered by the jack handle between two check valves so that the fluid is "pumped" from a reservoir into the hydraulic cylinder.


The "plunger" in this case, however is not the "displacer" illustrated, but rather the air itself which in the process of expanding and contracting acts as a kind of pneumatic ram or piston to "pump" additional ambient air into the system. The thing that looks like a piston to pump the air is actually just a "displacer" to move the air from hot end to cold end of the chamber. The pumping action is accomplished by the resulting expansion and contraction (heating and cooling) of the air in the chamber not by the "displacer" which only serves to direct or "cycle" the air towards the hot or cold end of the chamber as is accomplished in a regular Stirling engine.


The ambient air contains heat which, given a volume of compressed air can be extracted by more or less ordinary methods such as is commonly used in refrigeration, heat pumps, air conditioning etc.


The compressed air being forced through a narrow coil or tube is made to give up its heat. The heat thus obtained being utilized to "pump" additional air. After the "pumping" has been accomplished the air is allowed to decompress through a turbine where it becomes very cold by two means simultaneously. First by ordinary expansion as in common refrigeration and secondly by being expanded THROUGH a turbine as it expands where it is made to give up additional "internal" heat/energy - the heat being converted into mechanical "work" -> the "work" used to produce electricity by the action of the turbo-generator. This is the point at which the heat is converted to a different form as described by Tesla. The heat - converted into electricity, leaves the system as a different form of energy so that the heat does not ever reach the "Sink" and so does not accumulate.


The resulting very cold air is then used in the Stirling type "displacer chamber" for the contraction of air in the pneumatic compressor which contraction or temporary vacuum draws in additional heat laden air from the atmosphere and in the process the same cold air also scavenges out any excess heat that passes through the system..


I see a few possible problems with this very simple design such as there not being enough pressure generated by the pneumatic compressor to give much of a rise in temperature; The placement of the "intake" and "exhaust" ports or check valves may be critical so as to retain the most incoming heat for extraction and use, not enough heat converted into mechanical energy by the turbine so that there is not sufficient "cold" to scavenge out excess heat passing through the chamber, The diameter and length of the various heating and cooling tubes or coils would no doubt be critical just as in any other heat pump or refrigeration system, but these various incidental problems do not appear to me to be insurmountable. They are design problems rather than any actual flaw in the theory of operation.


Having stumbled upon Tesla's description of his own theoretical "Ambient heat engine" has given me some renewed ambition to go ahead with building a small prototype engine.


I recently paid a visit to the local scrap metal yard and have gathered what materials I felt would be needed; old refrigeration tubing, gas canisters and so forth.


In reading what I could find regarding refrigeration, heat pumps etc. trying to get a clue as regards lengths of tubing needed and such, what I discovered is that even in the construction of a conventional refrigerator or heat pump the mathematics involved is just too complicated. Even a computer would only be able to arrive at an approximation. In practice it seem that most refrigeration systems, heat pumps ect. are actually built more by trial and error than by any kind of accurate mathematical calculations.

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I'd like to address a few issues regarding this design:


1. Earlier someone expressed that a turbine does not or can not be used to remove heat in the manner described.


I will take one reference regarding this, there are many others like it that I've read in studying Air-cycle refrigeration:



Refrigeration and Air-Conditioning Hundy, Trott and Welch


Page 28:


"Air cycle refrigeration works on a reverse Brayton or Joule cycle. Air is compressed and then heat removed; this air is then expanded to a lower temperature than before it was compressed. Heat can then be extracted to provide useful cooling, returning the air to its original state (see Figure 2.14).


"Work is taken out of the air during the expansion by an expansion turbine, which removes energy as the blades are driven round by the expanding air. This work can be usefully employed to run other devices, such as generators or fans..."



There is no doubt whatsoever that in expanding through the turbine the Air releases its internal kinetic/heat energy to drive the turbine and simultaneously the air becomes very cold as a result. It seems too good to be true but the reality is that not only does this provide very cold temperature air for cooling purposes but simultaneously produces usable energy, in fact, it MUST produce energy or rather convert the heat into usable energy in another form in order to produce the cooling effect. In other words it is a requirement in an air cycle cooling system that the turbine used for effecting such cooling be attached to some form of load - such as driving an electrical generator so that the energy is converted and so removed. The resulting cold is a result of the removal or conversion of the heat energy in the air driving the turbine.


A second issue I've run across is the assertion that an Air-Cycle system is inefficient.


The reason for such inefficiency however must be kept in mind. The air cycle system is not practical for most refrigeration purposes in that the temperatures produced are too extreme for most purposes. An Air cycle system produces cold as well as a great deal of heat which is usually wasted as there is no use for heat in most air-conditioning applications, however the following should be noted:


From: Frozen Food Science and Technology By Judith A. Evans Pg 119:



"The established public opinion is that the air-cycle is inefficient as it has a low COP. It is fairly mentioned in almost every manual, that air-cycle possesses low thermodynamic efficiency when using it solely for cooling within a temperature range common for the commercial food refrigeration. Nevertheless, thermodynamic evidence shows (Kulakov et al., 1999) that air-cycle refrigeration may reach or exceed the performance of vapor-compression systems in two practically valuable cases:


(i) at low refrigerating temperatures (approaching or falling within the cryogenic range), and


(ii) when using the air-cycle for both cooling and heating, i.e. as a heat pump."




This "Stirling Turbine" utilizes both the extreme cold produced by the air-cycle system as well as the "waste" heat which are both utilized in driving the Stirling-Type "compressor". In this application, therefore, the Air-Cycle System should be about as efficient as any closed cycle heat pump using conventional refrigerants.

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It might be said or observed that this system basically - very much resembles a simple "bootstrap" air-cycle cooling system where the energy produced by the expansion turbine helps reduce the load on the compressor which compresses the air to run the turbine.


In such a "bootstrap" Air-Cycle system, however, the turbine can only REDUCE the load on the compressor by some relatively small percentage.


In this case, though, the energy to run the "compressor" is derived from atmospheric or ambient heat. The "compressor" itself is a kind of hybrid heat-engine-heat-exchanger that requires no or very little assistance from the output from the turbo-generator. The "small percentage" that the bootstrap system normally would use to reduce the load on the compressor can instead be used for some other purpose remote from the system or as Tesla would say, this output from the expansion-turbine is "clear gain".


The energy required to move a "displacer" in a conventional Stirling Engine is negligible.


Of course, to get this thing started one would first need to "dig the hole" so to speak. That is, to get the cycle started would involve creating an initial heat-sink and heat source within the system.


This might be accomplished by dropping some "dry-ice" down the exhaust shoot; applying some heat to the heating coils with a torch; adding an auxiliary compressor to get things started, or some combination of some such strategies. Once the cycle is started however, all that should be required to maintain it is to keep some form of external load on the turbo-generator to draw away the excess heat. This is where the energy is converted into a different form - from heat into electricity - so that the heat does not accumulate within the system - instead it goes out and re-emerges at some remote point far away from the system - such as, perhaps, the light and heat emitted from a light-bulb attached by some wires to the turbo-generator.


This remote load is the means of converting the heat-energy into a different form so that - as in Tesla's illustration, the incoming "water" does not accumulate in the bottom of the underwater "tank" so that the tank remains empty and the "Sink" is maintained.


Once set in operation, if the load on the turbine were removed then no conversion of heat-energy to a different form (electricity in this case) would take place and the "tank" would quickly fill up with "water". That is, the heat would accumulate in the system and the mechanism would loose its temperature differential which is its means of functioning. The "Stirling Engine" or "Heat-Engine" or "temperature differential engine" part of the system, without some electrical load, would "overheat".

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Earlier I posted this drawing of a simple Stirling-Type Air Pump:




Theoretically, I figure that if this crude model can blow up a balloon then it should be possible for such a device to power a turbine.


Anyway, I have finally gotten around to building a prototype of this component.




I'll be testing this shortly, within the next few days. If possible I'll make a video demonstrating the success or failure as the case may be.



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Well, I made a video.


It seems my attempt to capture the experiment "on film" was more successful than the experiment itself.



(7.19 MB .MPG video file)


It appears that my rather crude check valves are either sticking or not opening or are otherwise not functioning as intended. (They consist of some old roller skate ball bearings balanced on the end of some cut-off refrigerator tubing held more or less in place with some screen).


Considering the crudeness of the model - there does appear to be some action. - i.e. the balloon expanding and contracting, though the check valves are not capturing the air and holding it in the balloon as intended.


If I can find, or figure out a better way to fabricate some better check valves I may try building an "improved" model in the near future.


The experiment was rather disappointing but not entirely without hope, I think.


P.S. this experiment was conducted with the "pump" sitting in a bowl of crushed ice rather than over a candle flame. I tried with a candle also with about the same or not-quite-as-good results. The balloon blew up a little better, perhaps but tended to loose the gain from the extra heat - slowly shrinking rather than slowly expanding after each stroke of the displacer.


The reason being, apparently that the flame tends to heat the air above ambient which then cools back down to ambient after entering the balloon.


The ice, on the other hand cools the air in the can below ambient which then heats back up to ambient after entering the balloon causing the balloon to continue to slowly expand after being filled with colder than ambient air.


OR, in other-words, ICE works better than flame. Pumping or compressing cold air by this method appears to have a slight advantage over pumping hot air.

Edited by Tom Booth

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I made some modifications to the one check valve that is accessible:




I stretched a neoprene washer over the end of the pipe and also bent a spring from a ball point pen over it to maintain some tension on the ball-bearing holding it against the washer.


The new valve arrangement seems to be much more sensitive and responsive when using a tube to gently blow some air through the valves.


Once the "Goop" dries that I used to hold the washer in place, I can try again. I would like to see how much pressure can be built up in the balloon before the pump quits working - or how long it takes to actually burst the balloon or something if at all possible.


I'll post another video of the results.



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Here is a video of the latest test using the improved check valve arrangement:


Stirling Air Pump On Ice (6.49 MB mpg)


There was definitely some improvement in the operation of this model with what amounts to - probably just one rather crudely made, partially working check valve.


To fix the other valve I would have to drill it out and replace it.


I think though, that this test has shown that the problem is, or was, primarily due to the faulty - not very functional check valves and not due to any flaw in the theory of operation.


I cut the video short as not much happened afterwards other than that the balloon continued to expand slightly and then contract with each stroke of the displacer.


The displacer BTW was just a block of plywood being lifted up and down inside the can to "displace" the air, or move it from the cold end on the bottom to the "hot" ambient end of the can at top.


Some additional improvements could be made, such as: using some non-heat-conducting material for the body of the pump instead of a metal can which metal allows too much heat to be conducted through the can itself (rather than through the air inside the can). I noticed that after the can was placed into the ice, the top of the can grew cold to the touch rather quickly. Any heat conducted through the metal sides of the can is lost. The idea is to make the heat pass through the air inside the can so that it will expand and contract.


Anyway, rather than try and improve this tin-can model any further, this test has given me enough encouragement to go ahead and build a larger model and possibly even spend some money on some precision made check valves.


My goal at this point is to pump enough air to actually pop the balloon. So far though, the check valves are still leaking too much. The balloon, though, does continue to inflate - before deflating, due to the leaking check valves, so I believe it is still possible to get more pressure out of this thing if better check valves were used.

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Here is something else interesting.


Quite a long time ago, possibly living in Arizona or California or where exactly I cant remember but I saw what I believe was a local news broadcast of some guys in a garage who were blowing air through a T shaped tube with a shop air compressor. The thing appeared to be nothing more than some copper plumbing pipe but they were blowing air into the bottom of the T and naturally the air was coming out the other two legs of the T but the remarkable thing was that bitter cold freezing air was coming out one side and burning hot air was coming out the other.


It has been a long time since then but I have finally, very recently, (thanks to the internet which didn't exist back in those days) located information regarding what I saw in that brief newscast so many years ago.


One name for it is "Wirbelrohr" also "Hilsch Vortex Tube" and is sometimes also referred to by some as "Maxwell's demon".


There are quite a few DIY guides or instructions, diagrams etc. to build your own. Not very much to it really but apparently it works. Here is one site with rather detailed diagrams:




Of course, you need compressed air.


If you had an air compressor that could run from a temperature differential than here is another very simple way to get the temperature differential to run the air compressor with no additional moving parts!


According to some reports it seems that it is possible to get the heating and cooling effect by simply blowing through the thing by mouth, though you would need pretty good lungs apparently.


There are also commercial versions being sold.


I'm currently working on putting together a slightly bigger test model of the "Ice Powered" Air compressor.



Wooden Body to reduce heat loss by conduction



Lighter weight Styrofoam Displacer



Larger copper heat conducting plates.

Edited by Tom Booth

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Here is a website about the Vortex Tube that includes a couple videos demonstrating a small commercial unit freezing water in a test tube and also recording the temperature differential produced. Also in the second video one is disassembled to show (close up and in detail), the inner workings.


Vortex Tube Videos at http://www.machine-history.com/


One thought regarding the efficiency of the Vortex Tube. Some sites I have been reading suggest that the efficiency (For Refrigeration Purposes Alone) is Low compared to a conventional refrigerator.


I am wondering though, how much of that "inefficiency" is due to the bulky compressors that would normally supply air to the unit. In a conventional compressor a tremendous amount of energy is wasted. In fact a typical shop compressor has cooling fins to help dissipate the "waste heat". Some say that ALL the energy used to compress the air by a conventional compressor is lost and that the only reason you can extract any energy from compressed air is due to the latent "internal energy" not due to any energy added by the compressor. This is all lost as "waste heat".


I think if there were a "compressor" that ran on heat so that all of this "waste heat" could be utilized the overall efficiency of this, or any air-cycle type heat exchange system utilizing compressed air as a refrigerant would be greatly increased.

Edited by Tom Booth

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Well, I couldn't resist.


I had some extra time today so I tried my hand at knocking together a Vortex Tube.


I didn't follow any specific directions. They seem so simple and I've seen so many examples online I thought I'd have no trouble making one. I even made some modifications I thought might make the thing work better at lower pressures (added an extra set of groves in a metal slug to generate the vortex).




I hooked it up to the compressor and, forgot I only had it held together with duck tape for low pressure testing and the compressor was at 125 PSI or so and it blew all apart.


I found the pieces and put it back together and started out at very low presure and gradually increased the pressure.


Nothing much happened.


The air came out both sides of the tube but otherwise there was no difference in temperature though the lower portion of the T that I was using for a handle did seem to get a little bit cold.


Well, I did not follow any specific directions or make any accurate measurements as far as lengths of tubing and such, and it didn't work.


I guess I should try making one to specifications to start out with. Apparently it does matter because I got no temperature difference whatsoever up to about 50 PSI when the thing came apart again.






I might mention that as usual, after turning on the compressor the pipes leading from the compressor to the compressor tank got blistering hot.

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After reviewing the available information about the Vortex Tube; sketches, diagrams etc. there is one theory (among many others) that the tube acts as an acoustic device.


I also notice in some of the old sketches, such as on this page:




very precise dimensions are given and the length of the "Hot Pipe" in particular must be exactly 32 times the inside diameter.




From my recollection of the news broadcast I saw years ago, it seemed that the guys being interviewed were just some plumbers working in their garage who had put some pieces of pipe together after cutting it to length with a hack saw of something and were just using the air hose to blow out the metal filings or something. They, along with the newscaster appeared genuinely perplexed by the mysterious phenomenon. The pipe appeared to be nothing special, just ordinary copper tubing put together in the usual way with a T shaped connection.


If my recollection is correct, then these guys accidentally stumbled on some phenomenon by chance. They just happened to cut a length of pipe that turned out to be acoustically "Tuned" to the right pitch.


If this is true, then possibly the action of the so-called "Vortex Tube" has little or nothing at all to do with any alleged "tornado" inside the tube making a reversal upon itself. At any rate, my modifications based on that theory led to complete failure.


I picked up the length of my "Hot Pipe" and held it vertically between two fingers and taped on it with the handle of a jackknife as if it were a kind of wind chime.


It was a dud.


It apparently had no acoustic quality to it whatsoever. I tried again, holding the tube very gently between my fingers and tapping the tube with the knife handle while letting it slide down between my fingers slowly, like finding the right point on a guitar string by gently resting a finger on the middle of the string while plucking it to set up an acoustic standing wave. (The sound produced by this technique can be heard in the Led Zeppelin tune "Stairway to heaven". Sure enough, when I hit just the right point the tube rang out like a bell or a wind chime, but as soon as it slid down a bit further it turned back into a "Dud" and striking it with a knife handle just let out a dull thud.


I've done a little guitar playing and I knew that if you find just the right point on the string and rest your finger on it gently it is possible to create a rather unique sounding resonance due to the standing wave formed.


Note the proportional dimensions in this chart for the vortex tube:


(lower right corner)




It appears that the reason that the length of the "Hot Tube" must be in exact proportion to the inside diameter of the tube is that it is necessary in order to create a resonant cavity - like a musical instrument - drum, violin, guitar, bell, wind chime etc.


In other words, the thing has to be precisely tuned.


I'm thinking that the "Maxwell's Demon" effect of sorting molecules has nothing to do with any vortex, or at least not any vortex artificially created by some swirling device inside the tube, because, as far as I know or as far as I can recall, the guys in the garage on the newscast had not made nor had they inserted any such device at all. The phenomenon was a complete mystery, or so was the story.


So my current idea or theory is that by creating a resonant chamber "Standing waves" are created inside the chamber which serve to "sort" the air molecules just like sand particles are sorted at the nodal points in a Chiladni figure when a violin string is drawn across a metal plate with sand scattered across it.


Chladni Figure




(Photo by Marek Chmielewski, http://www.mif.pg.gda.pl/index.php?node=stareinstrumenty&jezyk=en Gdansk University of Technology website)


If this is all true then it should be possible, perhaps, at just the right pitch to easily sort hot and cold molecules with nothing more than a resonant chamber tuned to the right pitch, the rest of the elements going into the contraption being completely or almost completely redundant.


The molecules thus sorted into "nodal points" in a resonant chamber could then perhaps be easily separated with little or nothing beyond a bit of compressed air. Perhaps nothing more than a simple throttling device, such as a washer with a hole in the middle. If there is a "node" formed through the center of the tube for example. Then one would only need to provide an escape route one way or the other for the sorted molecules to pass out of the tube in a more or less orderly way along with a bit of compressed air to send them on their way through the opening.


It might also be noted that in my experiment as far as finding the right "nodal point" at which to hold my piece of pipe while tapping it with a knife handle, it may have been my imagination, I'm not quite sure, but it seemed that at the moment at which I found the right spot to hold the pipe between my fingers and the pipe began to ring out it suddenly and quite unexpectedly grew cold in my hand.


As this was not at all expected I did not take any temperature readings or anything of that sort this would have to be verified but the sudden chilling of the pipe while it rang out seemed to me to be quite unmistakable, though, of course, this was my subjective impression and would have to be verified by further experiment.


Theoretically though, if simply by hitting the right pitch or tone with the pipe at the right length the "hot" and "cold" air molecules could be effectively "sorted" into nodal points with the "Hot" molecules perhaps forming a node or LINE through the center of the tube, this would tend towards leaving the shell of the tube rather cold I should think. A different pitch or tone or length or diameter of pipe with a different Chiladni type formation might produce the opposite effect.




P.S. Part of the reason I think this might be the case, i.e. the resonant theory rather than the vortex theory, is that in researching this I have found nothing to verify that any such vortex is actually formed.


I would think that the formation of such a vortex would not require any particular length of tubing and I suppose, neither would it depend on an exact geometric relationship between length and diameter of tube. It would be a "forced vortex" created by the inrush of compressed air.


Also, some of these models appear to have no real means of controlling such a vortex if it did exist, such as precisely crafted nozzles and so forth. Of course some DO HAVE, but other don't, and yet they still work without it so long as the dimensions are correct and in proper ratio even though using some crude valve from Home Depot as a control nozzle, which in my mind could not possibly effect a separation of different temperature molecules in the way described unless they had already been separated by some other means before reaching the end of the tube and the valve.


As far as I know, no one has ever seen, analyzed, detected or otherwise provided any evidence that there is any kind of vortex at all involved. This seems to be nothing more than conjecture or theory, in spite of some elaborate drawings that have been presented to illustrate the theory, as far as I'm aware it remains a theory.


On the other hand, there have been actual studies of the acoustics and it has been found that when certain sounds produced by the "vortex tube" are dampened or muffled or otherwise eliminated in some way the separating effect disappears, regardless or even in spite of any other conditions that might be involved.


This information seems applicable:




And this:



Edited by Tom Booth

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Here is what looks to me like some additional confirmation of the acoustic theory:


I reviewed the various information available again paying closer attention to size and proportions.


An old graph gives a proportion of 1:32


Yes the newer working commercial model disassembled in one of the videos was measured to have an inside diameter of 10 millimeters and a length of only 80 millimeters. A ratio of 1:8


There is a common denominator here. These are octaves.


Do Re Me Fa So La Te Do

1 2 3 4 5 6 7 8


8 16 32 etc.


With this information I drew a graph with various possible waveforms thus:




It can be seen how a full octave, that is, a 1:8 ratio between ID and length creates what might be called "Supernodes".


That is, "standing waves" have nodal points but with a 1:8 ratio between inside diameter and length a resonant chamber is formed where all possible wavelength converge at the ends forming "supernodes".


My theory at this point is that these "supernodes" create points where air molecules are forced to gather along the lines of the Chhaladni figures.


One of these supernodes is located directly at the convergence point of the air inlet, the vortex "spinner" device which is supposed to create a vortex and the "diaphragm" that separates the Hot from the Cold chambers.


By controlling the flow of compressed air with the valve/regulator at the end of the Hot tube the flow of compressed air can be, in a sense, "tuned" to the same frequency.


That is as the molecules oscillate a corresponding volume of air is made to draw the accumulated molecules at the node through the hole in the diaphragm. Since the nodal accumulation, that is, since the wave form reverses continually, Once one accumulation of molecules passes through the diaphragm another node forms.


I suspect that the speed of the air passing through the orifice in the diaphragm should be "tuned" so as to be proportionately the same as the volume of one unit of air per oscillation for maximum efficiency. By unit I mean the air volume contained within one segment of the pipe or resonant chamber. By segment I mean a length of pipe with a 1:1 ratio to the ID of the pipe as illustrated above.


I may not be correct as to detail but I'm fairly certain that I'm on the right track.


I will make some modifications to my model based on this acoustic theory and let you know what happens.


BTW I measured the ID of my existing Hot Pipe and used this to mark off the length of the pipe using the ID of the pipe as a unit of measure.


It turned out to have a length of about 11 and 1/4 "units".


This is perhaps the worst possible ratio in terms of acoustics. Putting this into a graph similar to the one above, no wavelengths converged anywhere at all so that there was no possibility of any nodal points forming, except at the point that corresponded with the point where I was holding the tube and tapping it with a knife handle and it rang out, but very little. A few waves converged at that particular point when marked out graphically. I double checked this by marking the pipe according to the graph or measurements, that is, using the ID of the pipe as a unit of measure. Holding the pipe at that point it would make a ringing sound when struck. Otherwise it was a total dud.


If I simply cut off the equivalent of about 3 and 1/4 units of measure off the pipe that would give it a 1:8 ratio.

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Well I went ahead and made another "Vortex Tube" from scratch being as careful as possible to stick with the specifications given. I used the smallest of the three configurations which involved using some tubing from a scrap air conditioner as it had the right size tubing.


Here are some photos of the finished product:










I hooked it up to the air line and cautiously started cranking up the pressure.


There seemed to be a good steady flow of air. No leaks.


I tried allowing some of the air to blow across my hand from a distance, But there seemed no difference in temperature. The air from either end seemed perfectly even. About the same as room temperature.


I got the pressure all the way up to 125 PSI. As high as the compressor could go. I ended up actually putting the jets of air on my tongue to see if any difference in temperature at all could be detected. Not a thing.


I did various experiments like using objects to block or partially block one end or the other. Insulating the pipes on one side or the other. I even put some stainless steel turnings in the end of the Hot Pipe as a "regenerator". This made no change.


The tube made no particularly unusual sound. Just the sound of air flow.


Reportedly these things create some sort of loud sound when working properly.


I think this tends to rule out the idea that the vortex tube works by the air expansion alone. I think the air was certainly expanding through the tubes.


One thing I thought I might have done "wrong" is when I drilled the hole for the air inlet I was a little afraid of getting too close to the "diaphragm" and may have drilled the hole a hair or two further away from the diaphragm than I might have done otherwise.


So what difference would that make ?


My thought is, If I did everything to exact specifications, as far as possible with materials at hand, I think I kept very very close to specifications, within 1/2 a mm or so, and it still isn't performing in the slightest little bit My best guess at this point is:


There is some kind of necessity for some sound production.


I'm thinking that the orifice between the Hot and Cold chambers or "diaphragm" with the hole in it with the jet of air swirling around it is what is supposed to generate sound. Kind of like blowing across the top of a pop bottle.


If you have ever tried to do that it might be understood that this takes some finesse to get the air stream to cut across the bottle opening "just so" at just the right angle with the right pressure at just the right distance and so forth, It can be exceedingly difficult at times. It is easier to generate a tone with some bottles more than others, or, the effect may be something akin to rubbing a finger around the edge of a wine glass to cause it to sing. Or whistling. Some people just cant whistle for some reason. One of the names for this thing means "whistle" so perhaps that is accurate and perhaps the "diaphragm" is called a diaphragm as it is intended to be - like a loudspeaker, an actual sound producing, vibrating diaphragm and not just an orifice.


If this is the case than quite possibly the reason for the failure is that the jet of air is just not hitting or not spinning around the diaphragm opening at the right angle or distance of something, so no sound is being produced.


I imagine the diaphragm acting similar to a speaker in a thermalacoustic engine.


One thing seems certain. There is some "trick" to this thing and it seems it is necessary to get it just right to get any effect at all.


I was fairly certain when I decided to make a vortex tube that even if It was not perfect there would still be some detectable temperature difference.


So far with these first two vortex tubes, I cannot detect any temperature difference whatsoever at all. Just regular plain old lukewarm - normal compressor air from either end.


But so far neither one has produced any unusual sound either. Everyone who has ever had one of these things working has made mention of the loud sound produced.


This seems a bit of additional confirmation that with no sound, there is no cooling effect, on the other hand, it doesn't seem there is much of any "vortex" being generated either. I'm thinking that this may require sound as well. A kind of acoustically driven vortex - if such a thing is possible.

Edited by Tom Booth

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Moderator Note

Tom Booth, I've hidden your two previous posts. We don't allow advertising for anything, even fundraising. Also, this isn't the place to air your gripes about other science discussion forums, or how you were treated elsewhere. 


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