Tesla's Ambient Heat Engine Theory - Right or Wrong ?

[Tom Booth]

Have a look at what he says at 2 :08 in the first video. He explains that the cold side does need a heat sink or the engine stops once it heats up.

He attributes this to friction, which makes sense, considering the relatively enormous amount of surface to surface contact between the inner glass tube (piston) and the outer (cylinder), but this is a secondary effect and has nothing directly to do with what is going on with the gas inside the cylinder.

Also, no doubt, despite glass being a poor conductor of heat, some heat is migrating through the glass. Again, this has no direct bearing on what is happening with the "working fluid", the air inside the cylinder which is the important thing to consider.

The heat of friction is a result of the gas expanding, pushing the piston and the piston dragging against the cylinder wall. There is energy conversion going on:

Flame > Gas Expands > Expanding gas pushes piston > Piston meets resistance dragging on cylinder wall creating friction > friction generates heat.

In other words, the transfer of energy is not a direct transfer of heat from the gas to the cylinder wall (effective heat sink). Even after the gas has given up its heat, which has been transferred or converted into the kinetic motion of the piston and the gas grows cold and contracts, pulling the piston with it, or perhaps more accurately; creates a vacuum which allows atmospheric pressure to push it back there is this heat generated due to friction on the cylinder walls on the return stroke.

At any rate, the question could be settled through experiment.

Free piston Stirlings have been built to such close tolerances that the piston forms an effective air tight seal without actually touching the cylinder walls virtually eliminating this source of friction. Materials even less heat conductive than glass could be used to prevent heat migration through the cylinder walls.

No heat is 'disappearing'. Its operating principle is no different to any heat engine other than it uses a resonance effect instead of energy in a flywheel to achieve the compression stroke.

The so-called "resonant effect" in this type of engine is pure speculation (and pure fiction IMO). This is not a thermoacoustic engine, though there are some superficial resemblances.

As far as the heat "disappearing"; When a gas expands and does work simultaneously it gives up its energy (heat) to do the work it then tries to get back that heat from its surroundings. i.e. it gets cold. The kinetic energy (heat) of the gas molecules is translated into kinetic energy of the piston or whatever the gas is working against or upon. As a result the temperature of the gas drops. There is no mystery about this  (well, maybe a little) and yes the same thing happens in any heat engine to one degree or another. The more efficient the engine; the greater the temperature drop. The more energy the gas transfers directly into mechanical motion; the greater the temperature drop.

This usually goes unnoticed because the gas, having expanded and done some work generally has plenty of heat around to replace the heat it lost. It seems, or might be said that the gas absorbs heat so it can expand and do work, but this is not really the case and is not really logical.

In a heat engine the gas absorbs heat, expands and does work - loosing heat and is then ready to absorb heat again and the cycle repeats all within a fraction of a second. It is difficult to follow exactly what is going on and in what order, but here IMO is what I think happens:

Heat is applied to the engine. The heat is transferred to the gas, the gas expands and does work against the piston, the energy is transferred to the piston. At this point the gas is expanded to its limit, has given up its energy and finds itself, in effect, "hungry". It can do one of two things, either absorb heat from its surroundings or contract. If there is not enough heat available in the immediate surroundings it will contract.

This is exploited in numerous ways in all kinds of applications.

Under such circumstances as just described, having expanded and done work simultaneously and not being able to find "replacement" heat immediately, the gas may contract to the extent of condensing into a liquid (liquefaction of gasses). The same principle or phenomenon is exploited in some refrigeration systems. etc.

I believe that what is happening in the engine in that youtube video is that in spite of all the heat from friction and conduction the expanded air still cannot find enough heat to replace what it lost and so contracts.

The heat has been transferred to the piston, converted into the mechanical energy or kinetic energy of the piston. The glass cylinder even if relatively hot from friction etc. does not give up its heat to the air readily. Momentarily, as far as the gas is concerned there is no heat readily available to replace what it lost so it contracts.

I think that if heat from friction were eliminated and heat from conduction were eliminated (as well as heat from ambient) one might actually be able to observe a real cooling or refrigeration effect in the cylinder.

That heat could produce a cooling reaction is not so ludicrous as it might sound.

This is, to some degree, speculative, but it is based on sound reasoning and observation, IMO and is backed up by an enormous history of scientific research and experimentation as well as real world applications. It would have to be confirmed by experiment in this specific instance.

On the other hand, I find no support whatsoever, in my research on the question, for the idea that the piston returns due to some "resonant effect". This is IMO a "red herring". Many, however, seem to have latched on to this explanation and you will find many YouTube videos of "Thermoacoustic" Stirling Engines which are IMO, nothing of the sort.

A couple random references:

"when a gas expands and does work on its surroundings, its temperature decreases" - http://www.howeverythingworks.org/page1.php?QNum=1257 (second paragraph)

"Isothermal and Adiabatic Expansion.

When a gas expands and does work, as by pushing a piston in a cylinder, we see from the first law of thermodynamics that the equivalent in the form of heat must be supplied from somewhere. If the temperature of the gas is to be kept constant, heat must be supplied to it from the outside, in exact equivalent to the work done. In such cases the expansion is said to be isothermal, ... But if no heat be allowed to enter the gas, as would be the case if the cylinder and piston were perfect non-conductors of heat, the work done in expansion will be at the expense of the heat energy in the gas itself, and its temperature will therefore fall during the expansion. We have seen that the pressure is less as the temperature falls, other things being equal; hence under the conditions the pressure p will fall faster than if the temperature were kept up by the addition of heat from outside.
...
Both isothermal and adiabatic curves are of great importance in thermodynamic studies, but they represent conditions that are only imperfectly realized in practice. "

Cyclopedia of engineering; a manual of steam boilers, steam pumps, steam engines, gas and oil engines, marine and locomotive work"  - http://books.google.com/books?id=JWNGAAAAMAAJ&lpg=PA34&ots=TqYj87FgAI&dq=%22a%20gas%20expands%20and%20does%20work%20as%20by%20pushing%20a%20piston%22&pg=PA34#v=onepage&q=%22a%20gas%20expands%20and%20does%20work%20as%20by%20pushing%20a%20piston%22&f=false


http://youtu.be/OXIZhqypNUI (about 4:00 - 5:30)

[Tom Booth]

Consider the following scenario, might clear it up.
If you had a flow of heat, you can extract a certain portion as work.

Just curious; from an engineering standpoint, how exactly would you do that ?

What exactly is a "flow of heat" to begin with. Heat is not like a river you could just stick a paddle wheel into.

If that heat is at 'ambient' temperature then for you to be able to extract any work some portion of it must end up at a lower temperature.

"end up" at a lower temperature or already BE at a lower temperature ?

If that heat is Ambient, the temperature is more or less uniform. So there is no "flow" to extract energy from. Right ?

Also, heat only flows from a higher to lower temperature. (Zero'th law of thermodynamics and is in fact the definition of temperature).

So where is the "lower temperature" in the ambient ? It doesn't exist initially. First, as Tesla stated, you have to dig your "cold hole".

Combine those two facts  together and then try to devise a device that would extract all the energy from a flow of heat as work before reaching the cold sink (presumably the 4 Kelvin ambient temperature of the universe at heat death ) and you'll realise it is logically impossible.

Nobody is talking about extracting "all the energy" in the absolute sense.

Just all the heat energy supplied to the engine at any given interval or cycle.

If any engine ever was capable of extracting "all the energy" - literally, in the absolute sense, the engine itself would likely implode shrinking into a virtual nothingness beyond detection.

It is more than a "logical impossibility" it is also another straw man argument and a red herring.

[Tom Booth]

No confusion here. I was merely making the comment that the you-tube  video showed a device that is entirely consistent with the laws of thermodynamics and not doing anything remarkable from an energy standpoint.

Tom Booth made the comment that more heat than expected is 'disappearing' (or as you point out is being converted to work). I  am simply pointing out that it is not.

Your diagram is entirely correct. Along with the knowledge that the PROPORTION of energy as work that can be extracted from a flow of heat from one reservoir to another is dependent on the temperature difference between them explains why the device as envisaged by Tesla is at best, simply a heat engine that obeys the 2nd Law. Nothing new in that.

Ummm... now I'm confused. I was under the impression that your stance was that the device as envisioned by Tesla was "impossible".

Is the engine in the video violating the second law ?

If the engine runs but no heat is transferred from the heat source to the heat sink then I think yes. That would be a violation of the second law of thermodynamics.

Obviously, as you pointed out, heat IS being transferred.

The question is, how?

If we eliminate friction in the cylinder and eliminate conduction through the cylinder walls, that is, if we assume that this is possible, we are left with heat transfer by the "working fluid", the air or gas in the cylinder.

We will assume that there are no leaks. No transfer of matter is taking place.

Here is the scenario I described earlier which is what I already stated is what I THINK is going on in this engine.

I said first of all that GLASS is a poor heat conductor.

I know this from experience. You could put your hand on one side of a pane of glass and a blowtorch on the other and you would not feel the heat from the blowtorch immediately. It would take some time for the heat to penetrate the glass. The thermal conductivity of glass is about 1. Just a little better than air (.024) but not as good as many substances considered Heat Insulators like Asbestos-cement - 2, Firebrick - 1.4, Porcelain - 1.5 etc. Just for comparison, copper, a good heat conductor is around 400

Reference: http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html

So logically, IMO, heat transfer from the air inside the test tube (engine cylinder) to the air outside the test tube can be all but discounted, at least in consideration of the apparent rapidity of the heat transfer taking place, judging by the speed of the engine.

This is a "free piston" engine, so there is nothing attached to it to restrict its motion (discounting friction), therefore the only thing controlling its motion is pressure changes.

In a Gas, Pressure is related to Temperature and Volume. These three might be thought of as a triangle. When one rises, the other two tend to rise with it, when one falls the other two tend to fall with it unless something is constrained.

If volume is constrained and temperature rises then pressure will rise. If temperature rises and pressure remains the same then volume will increase, etc.

So heat is added to the engine. The piston is free to move so pressure remains relatively steady. Volume increases freely. Temperature may begin to increase but as the volume increases rapidly temperature may remain relatively constant.

As the gas continues to expand rapidly kinetic energy is stored up in the free moving piston. Once the gas has expanded enough to compensate for the temperature increase it stops expanding. Equilibrium has been restored, except that the piston still carries MOMENTUM. As the piston continues down the cylinder the volume continues to increase. As a result, the gas is further expanded, but has now gone beyond the point of equilibrium. The pressure begins to drop and finally falls below the atmospheric pressure outside the cylinder. As the pressure drops but the volume continues to increase the temperature also drops sharply. The net result is an "implosion" as sharp and violent as the heat "explosion" that originally propelled the piston outward, so it is now propelled inward.

In all of this it seems to me that there is no time for heat transfer to the "Heat Sink", nor does there seem to be any necessity that such a heat transfer take place so as to fully explain the motion of the piston.

As a matter of fact, it seems to me that at the extent of the pistons travel down the cylinder its momentum and the expansion of the gas that results from it would of necessity, result not only in a pressure drop below atmosphere but also a corresponding temperature drop below ambient.

The engine, or rather the "working gas" within it, not only does not transfer heat to the sink, it probably absorbs heat from the sink.

When the internal pressure drops, outside atmospheric pressure works upon the piston to push it back inward and in turn the piston works upon the air in the chamber. This results in a transfer of energy from the outside ambient air to the air in the chamber. When dealing with a gas, Energy translates into heat. Kinetic energy transfers from the outside air, to the piston, to the inside air. The temperature of the air being worked upon rises. The air now being compressed meets with the heat being added to the engine and another "explosion" takes place driving the piston outward and the cycle repeats.

This engine is apparently not only not transferring heat to the sink but logically it is in fact taking energy from the sink. It is in effect using the heat added on the "power stroke" to put kinetic energy (and momentum) into the piston which energy is then used to effect refrigeration at the end of the power stroke. The refrigerating effect causes a drop in pressure and temperature which allows heat to be transferred out of the heat sink in the manner of a "heat pump". It is this transfer of energy FROM THE SINK (ambient) that drives the piston in its return stroke.

This, IMO, if true, would constitute a clear contradiction of the second law of thermodynamics. At least according to Wikipedia which states: 

Heat engine

In classical thermodynamics, a commonly considered model is the heat engine. It consists of four bodies: the working body, the hot reservoir, the cold reservoir, and the work reservoir. A cyclic process leaves the working body in an unchanged state, and is envisaged as being repeated indefinitely often. Work transfers between the working body and the work reservoir are envisaged as reversible, and thus only one work reservoir is needed. But two thermal reservoirs are needed, because transfer of energy as heat is irreversible. A single cycle sees energy taken by the working body from the hot reservoir and sent to the two other reservoirs, the work reservoir and the cold reservoir. The hot reservoir always and only supplies energy and the cold reservoir always and only receives energy. The second law of thermodynamics requires that no cycle can occur in which no energy is received by the cold reservoir.

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

This engine presents something of a mystery. Even the guy who built it, (as a result of an accidental discovery), doesn't quite know how to classify it and asks the question at the end of his video. What kind of engine is this?

Most certainly, attributing its behavior to "resonant effect" explains nothing.

A real thermoacoustic engine has no moving parts except perhaps a loudspeaker.

[Tom Booth]

This type of heat engine, whatever it might be called, traditionally it would be a "lamina flow Stirling" I think, with the exception that there is no flywheel - seems to be the simplest possible mechanical heat engine, and might be a good place to start as far as experimenting with or testing Tesla's concept.

Just a piston and cylinder,... and linear generator.

I was thinking something along these lines.

[Tom Booth]

This is basically the same engine as in the YouTube video except that it is partly enclosed inside of an insulated cold box.

Unlike how I drew it (rather thick) the diaphragm at top should probably be of some very thin flexible material like cellophane. It need not be taught but rather very loose. Its only purpose is to act as a barrier between the cold air in the box and Ambient air outside the box while still allowing the atmospheric pressure in. Necessary as it is atmospheric pressure that, in part, drives the engine (on the return stroke).

The air in the box should be DRY air, as the air temperature would likely need to be well below freezing. Simply placing a desiccant pack in the box might do.

The yellow is of course insulating material. The higher the R value the better. The white inside the yellow is possibly air space (like a thermos) The idea being to keep as much ambient heat as possible OUT of the box. The heat, therefore, in order to get in must do so THROUGH THE ENGINE and as far as possible, nowhere else.

The gray heat fins that perhaps might be mistaken as being intended for a heat sink or for heat dissipation are actually just the opposite. Air is not very good at transmitting heat so there should be as much surface area as possible. These fins are meant to DELIVER heat TO the engine. The check valve is intended for long term pressure equalization when there are pressure changes due to changing atmospheric conditions (this might not be necessary but well, why not?)

It would, of course, be necessary to pre-cool the box by some means to have any hope of getting the engine started, and, maybe even apply a little heat to the fins just for good measure, but if the theory of operation is correct then the engine should act something like a Stirling cryo-cooler on the one end (inside the box) and a regular heat engine at the other end (outside the box).

Although it appeared in the video that it would probably take quite a lot of heat to run such an engine, I'm not so sure.

Remember that Glass is a poor heat conductor. So probably 99% of the heat applied (by a flame) would be simply lost to the air, going around, rather than through the glass tube.

The HOT end, or Ambient end of this engine in a cold box, should probably be made of something other than glass. The whole heating unit might be cast out of aluminum including fins and regenerator or copper tubing or some such heat conducting material. The inner cylinder however should be as non-heat conducting as possible so as to prevent heat migration into the cold box.

Something like this should not be particularly difficult or expensive to put together.

Of course the piston should be frictionless as far as possible. Friction OUTSIDE the cold box, at the generator or at bearings or sleeves holding up the connecting rod should not pose a problem although the connecting rod itself, since it passes through and into the box should be non-heat conducting.

The diaphragm at top might also be double layered with a dead air space between to help reduce heat infiltration.

If something like this can be started by pre-chilling the interior of the box to establish a temperature differential, then theoretically it should continue to run as the engine itself would be drawing energy out of the box, while the piston is at the extremity driven by momentum and on its return driven by atmospheric pressure.

My over all theory on this is that heat is really Kinetic energy.

Therefore, what we want is not so much a FLOW OF HEAT but a flow of kinetic energy.

For there to be a flow, the energy has to have somewhere to go.

Somewhere other than into the cold box.

Ambient heat is the source, but it needs somewhere to go, therefore, the linear generator is probably a necessity. And it should have some kind of load. Lighting lights or charging batteries or perhaps powering a fan to blow air through the heating fins.

In other words the flow of energy needs to continue somewhere, it cannot dead end in the box, it needs to go out the wires to power some electrical load.

In actuality it would be the load on the generator that is drawing the energy. The heat, from the interior of the box is kinetic energy that can be transferred to the load.

In other words, there is not really any such thing as "heat". Heat is just a sensation. It is simply kinetic energy. So the idea is not to establish a flow of heat from heat source to heat sink but rather a flow of energy from source to destination. The destination being the load on the generator.

Perhaps this is nonsense, I don't know. But I don't think it would hurt to do some experimenting and see what happens.