Kender Solar Engine

[Mr Skeptic]

The only power consuming element in this engine is the two electromagnets (solenoids) controlling the movement of a very light weight displacer with almost no friction involved in its movement - that could conceivably run for hours on a flashlight battery.

...

The only other loss would be the friction of the turbine bearings and air to air friction or air producing friction against the pipe walls etc. But in this configuration, even much of this heat/friction is put to good use.

 

For simplicity, you can assume a frictionless mechanism and a 100% efficient motor. What you should be looking at is not the motor, it is the work done on the gas by the compressor, and the work done on the turbine by the gas. And anywhere else work is done or energy transferred. And make sure at all points where heat flows that it flows from warmer to cooler.

 

The same basic displacer set up works to power a piston in a heat engine, why not a turbine ?

 

This is incorrect, if I understand what you are saying. The displacer (or whatever you call the thing that pushes cold gas into the warm heat source) is pushing in a small volume, whereas after expanding the gas is a larger volume so it can do more work on the engine (the pressure being the same).

 

So for example push 1 liter at atmospheric pressure into the heat source, get 10 liters at 1 atmosphere out, get 9 liters*atmosphere of work overall, minus losses.

 

 

If what it comes down to is the math, I'm afraid that for me at the moment, it would be easier to just go ahead and build a small model engine and see if it works. That seems a lot less complicated and should be relatively easy to do.

 

If the concept works at all, it should work on any scale...

 

Then I can post the video on You Tube.

 

If you say so. We we could help you with the math if you need any help. Also, the integrator can do calculus for you, and google calculator can do arithmatic and keep track of units.

 

The maths for heat engines really isn't that complicated, especially with turbines as that way things are constant, unlike with pistons.

 

A pressure times a volume will give you units of energy, so if you keep track of the pressure of your gas and its volume, and any changes to those, you should have a pretty good idea what is going on.

[Tom Booth]

For simplicity, you can assume a frictionless mechanism and a 100% efficient motor. What you should be looking at is not the motor, it is the work done on the gas by the compressor, and the work done on the turbine by the gas. And anywhere else work is done or energy transferred. And make sure at all points where heat flows that it flows from warmer to cooler.

 

I think we've covered that. As far as I can see, any heat transfer that is going on is always from warmer to colder. But just for clarification, the "compressor" isn't really a compressor exactly, and it isn't doing any work on the gas directly. By utilizing the temperature differential, the gas is being made to do work against itself.

 

By being heated inside a closed chamber the gas expands and escapes through a check valve - something like steam escaping from a pressure cooker. Then, (continuing with the pressure cooker metaphor), the gas in the "pressure cooker" is then cooled, creating a partial vacuum inside the "pressure cooker" that draws more fresh air in. This fresh air is then heated and made to expand and escape... etc. etc.

 

The check valves keep the air that has already escaped from being drawn back in when the "pressure cooker" cools.

 

There is no "work" as such, being done by the "compressor". The "compressor" is just a closed chamber like an empty pressure cooker with some check valves added on to it. It functions LIKE a pump or a compressor but it doesn't actually do any "work", any more than a pressure cooker does "work". What is doing the work to expand the air and keep it moving is HEAT. Ultimately the "ambient" heat of the air itself which has been concentrated in one area by the air cycle "heat exchanger" into which the "pressure cooker" is "pumping" the air.

 

This is incorrect, if I understand what you are saying. The displacer (or whatever you call the thing that pushes cold gas into the warm heat source) is pushing in a small volume, whereas after expanding the gas is a larger volume so it can do more work on the engine (the pressure being the same).

 

So for example push 1 liter at atmospheric pressure into the heat source, get 10 liters at 1 atmosphere out, get 9 liters*atmosphere of work overall, minus losses.

 

Let me try to continue with the pressure cooker idea so as to hopefully make this clear.

 

The "displacer chamber" is just that. a CHAMBER. Lets call it a pressure cooker just for illustrative purposes.

 

There is a volume of air inside the "pressure cooker".

 

If we heat up the pressure cooker, the air inside will try to expand creating "pressure" if it has nowhere to go. We give it a place to go by drilling a hole in the side of the pressure cooker and installing a check valve so that the air can escape but not get back in.

 

After heating the pressure cooker and allowing the gas to escape, we now plunge the pressure cooker into some ice water. The air inside cools rapidly and contracts creating a vacuum inside the pressure cooker. To utilize that vacuum we drill another hole and install another check valve that allows the air in but won't let it back out - So the pressure cooker sucks in some fresh air. Now we heat it up again - again the air escapes through the first check valve. Then cool it down - more fresh air being drawn in through the second check valve.

 

In other words, the "pressure cooker" doesn't do any "work". The temperature differential is doing the work of pumping the air through the pressure cooker. There really is no compressor, but the "pressure cooker" for all practical purposes is functioning as an air pump or compressor without doing any work. The temperature differential is doing the work.

 

If you say so. We we could help you with the math if you need any help. Also, the integrator can do calculus for you, and google calculator can do arithmatic and keep track of units.

 

The maths for heat engines really isn't that complicated, especially with turbines as that way things are constant, unlike with pistons.

 

A pressure times a volume will give you units of energy, so if you keep track of the pressure of your gas and its volume, and any changes to those, you should have a pretty good idea what is going on.

 

Thanks, I'll check those out.

 

I'm pretty sure I could figure out the math if I just knew what variables to insert into the equations.

 

The main question is, to begin with, can a "pressure cooker" work as a "compressor" or air pump as I've just tried to describe ?

 

If it can, how many CFM at what initial temperature differential ?

 

I'm imagining that if the outlet to this "pressure cooker" were connected to a tank rather than the open air it would be able to build up pressure in the tank which would be limited to some point below the pressure that could be developed within the pressure cooker itself if it had no outlet.

 

We start out with the "pressure cooker" full of air at ambient temperature and normal atmospheric pressure. We alternately heat and cool it (or just the air inside it) with the temperature differential provided by the air cycle heat exchanger system. The air being "pumped" by the "pressure cooker" is being used to provide the air flow for the air cycle heat exchanger which is in turn providing the temperature differential needed for the operation of the "pressure cooker".

 

There are a few additional tricks being played on the air along the way to increase the temperature differential.

 

The air being "pumped" out of the "pressure cooker" is being redirected back through some tubes inside the "pressure cooker" so that the heat is recirculated and concentrated inside the "pressure cooker" then when it leaves the coils inside the "pressure cooker" it is cooled by sending it through another set of coils which are exposed to ambient air temperature. This second set of coils is used to drive of any excess heat and get the temperature of the air back down to ambient. It is then, possibly, cooled some more in another set of coils utilizing the cold exhaust from the turbine, bringing the air temperature down below ambient while it is still somewhat compressed. Finally it is released into a well insulated turbine where it expands and does some work turning the turbine against some load on the turbine, upon which its temperature drops precipitously well below ambient temperatures.

 

As the cold gas leaves the turbine it is directed back to the "pressure cooker" to be utilized for cooling the pressure cooker to draw in a new supply of air.

 

The only thing I've left out here, in this "pressure cooker" explanation is how do you apply the heating and cooling to the "pressure cooker".

 

Well, you don't actually heat and then cool the "pressure cooker" at different times. You heat and cool it simultaneously. Heat the top and cool the bottom.

 

Here is where the "displacer" comes in.

 

All the displacer does is move up and down inside the "pressure cooker" displacing the air.

 

As the displacer moves up, the air is displaced and moves down against the cold side of the "pressure cooker" causing the air to contract and creating a vacuum inside the "pressure cooker" that sucks air in through one of the check valves. Then when the displacer moves down it displaces the cold air forcing it up against the hot top of the "pressure cooker" where it expands and escapes out the other check valve.

 

The resulting flow of pressurized air out of the "pressure cooker" is sent through your air-cycle heat exchanger.

 

The only power input needed for this entire system (other than the heat in ambient air) is whatever energy it takes to move the displacer up and down inside the "pressure cooker".) The "pressure cooker" acts as a compressor for your air-cycle heat exchanger.

[Mr Skeptic]

I suggest you familiarize yourself with the following:

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

This has all the important equations for gases other than heat transfer.

 

http://en.wikipedia.org/wiki/Specific_heat#The_simple_case_of_the_monatomic_gas

This is so you know how much thermal energy it takes to increase the temperature 1 degree.

 

I think we've covered that. As far as I can see, any heat transfer that is going on is always from warmer to colder. But just for clarification, the "compressor" isn't really a compressor exactly, and it isn't doing any work on the gas directly. By utilizing the temperature differential, the gas is being made to do work against itself.

 

By being heated inside a closed chamber the gas expands and escapes through a check valve - something like steam escaping from a pressure cooker. Then, (continuing with the pressure cooker metaphor), the gas in the "pressure cooker" is then cooled, creating a partial vacuum inside the "pressure cooker" that draws more fresh air in. This fresh air is then heated and made to expand and escape... etc. etc.

 

The check valves keep the air that has already escaped from being drawn back in when the "pressure cooker" cools.

 

There is no "work" as such, being done by the "compressor". The "compressor" is just a closed chamber like an empty pressure cooker with some check valves added on to it. It functions LIKE a pump or a compressor but it doesn't actually do any "work", any more than a pressure cooker does "work". What is doing the work to expand the air and keep it moving is HEAT. Ultimately the "ambient" heat of the air itself which has been concentrated in one area by the air cycle "heat exchanger" into which the "pressure cooker" is "pumping" the air.

 

Ah, I see. This makes more sense.

 

Your power source is the temperature differential. Your compressor does do work, but only on the gas so it is not so obvious. This compressor looks to be extremely inefficient, due largely to the fact that the walls of the compressor will eat a lot of your heat energy. We can assume for simplicity that the walls magically have zero heat capacity, and it should still be rather inefficient.

 

So, lets see. Let's have chambers A and B, where A is before B, both the same size, volume V. Room temp gas input at A. Let's call room temp 300 K, a little warmer than normal but a very convenient number. Now, are we using heating, cooling, or both? Pick convenient numbers for that. Heat capacity of your gas is C.

Steps:

1: A full of gas at 300 K at 1 atmosphere. B full of gas at 300 K and 1 atmosphere.

2: heating or cooling? Must keep track of heat transfer energy.

[insane_alien]

perhaps tom should draw a diagram clearly showing the flows of gas and energy flows.

[npts2020]

Tom Booth; I am a little surprised that you can't see why this won't work.

 

I think we've covered that. As far as I can see, any heat transfer that is going on is always from warmer to colder. But just for clarification, the "compressor" isn't really a compressor exactly, and it isn't doing any work on the gas directly. By utilizing the temperature differential, the gas is being made to do work against itself.

 

By being heated inside a closed chamber the gas expands and escapes through a check valve - something like steam escaping from a pressure cooker. Then, (continuing with the pressure cooker metaphor), the gas in the "pressure cooker" is then cooled, creating a partial vacuum inside the "pressure cooker" that draws more fresh air in. This fresh air is then heated and made to expand and escape... etc. etc.

 

The check valves keep the air that has already escaped from being drawn back in when the "pressure cooker" cools.

 

There is no "work" as such, being done by the "compressor". The "compressor" is just a closed chamber like an empty pressure cooker with some check valves added on to it. It functions LIKE a pump or a compressor but it doesn't actually do any "work", any more than a pressure cooker does "work". What is doing the work to expand the air and keep it moving is HEAT. Ultimately the "ambient" heat of the air itself which has been concentrated in one area by the air cycle "heat exchanger" into which the "pressure cooker" is "pumping" the air.

 

The pressure cooker does no work but you have a stove or some other heat source that does a *lot* of work on the system.

 

Let me try to continue with the pressure cooker idea so as to hopefully make this clear.

 

The "displacer chamber" is just that. a CHAMBER. Lets call it a pressure cooker just for illustrative purposes.

 

There is a volume of air inside the "pressure cooker".

 

If we heat up the pressure cooker, the air inside will try to expand creating "pressure" if it has nowhere to go. We give it a place to go by drilling a hole in the side of the pressure cooker and installing a check valve so that the air can escape but not get back in.

 

After heating the pressure cooker and allowing the gas to escape, we now plunge the pressure cooker into some ice water. The air inside cools rapidly and contracts creating a vacuum inside the pressure cooker. To utilize that vacuum we drill another hole and install another check valve that allows the air in but won't let it back out - So the pressure cooker sucks in some fresh air. Now we heat it up again - again the air escapes through the first check valve. Then cool it down - more fresh air being drawn in through the second check valve.

 

In other words, the "pressure cooker" doesn't do any "work". The temperature differential is doing the work of pumping the air through the pressure cooker. There really is no compressor, but the "pressure cooker" for all practical purposes is functioning as an air pump or compressor without doing any work. The temperature differential is doing the work.

 

Once again the pressure cooker did no work but your heat source has. In addition, you have done even more work to get your heat sink by moving the pressure cooker or pumping coolant (ice water in this case or air in your engine) around it. Even if it were possible to get a temperature differential in the manner you have been describing (IMO it is not) it would be a tiny fraction of the differential in the pressure cooker analogy you are using.

 

Thanks, I'll check those out.

 

I'm pretty sure I could figure out the math if I just knew what variables to insert into the equations.

 

The main question is, to begin with, can a "pressure cooker" work as a "compressor" or air pump as I've just tried to describe ?

 

It can compress air in the manner you describe it would be rather inefficient and very difficult to get high pressures from.

 

If it can, how many CFM at what initial temperature differential ?

 

I'm imagining that if the outlet to this "pressure cooker" were connected to a tank rather than the open air it would be able to build up pressure in the tank which would be limited to some point below the pressure that could be developed within the pressure cooker itself if it had no outlet.

 

We start out with the "pressure cooker" full of air at ambient temperature and normal atmospheric pressure. We alternately heat and cool it (or just the air inside it) with the temperature differential provided by the air cycle heat exchanger system. The air being "pumped" by the "pressure cooker" is being used to provide the air flow for the air cycle heat exchanger which is in turn providing the temperature differential needed for the operation of the "pressure cooker".

 

You are trying to pull yourself up by your own bootstraps here. Even if you start out with a higher pressure/temperature differential in the system, you will lose more than you gain at every step you have described.

 

There are a few additional tricks being played on the air along the way to increase the temperature differential.

 

The air being "pumped" out of the "pressure cooker" is being redirected back through some tubes inside the "pressure cooker" so that the heat is recirculated and concentrated inside the "pressure cooker" then when it leaves the coils inside the "pressure cooker" it is cooled by sending it through another set of coils which are exposed to ambient air temperature. This second set of coils is used to drive of any excess heat and get the temperature of the air back down to ambient. It is then, possibly, cooled some more in another set of coils utilizing the cold exhaust from the turbine, bringing the air temperature down below ambient while it is still somewhat compressed. Finally it is released into a well insulated turbine where it expands and does some work turning the turbine against some load on the turbine, upon which its temperature drops precipitously well below ambient temperatures.

 

Again you are going to lose more energy than you gain at every step described.

 

As the cold gas leaves the turbine it is directed back to the "pressure cooker" to be utilized for cooling the pressure cooker to draw in a new supply of air.

 

The only thing I've left out here, in this "pressure cooker" explanation is how do you apply the heating and cooling to the "pressure cooker".

 

Well, you don't actually heat and then cool the "pressure cooker" at different times. You heat and cool it simultaneously. Heat the top and cool the bottom.

 

Here is where the "displacer" comes in.

 

All the displacer does is move up and down inside the "pressure cooker" displacing the air.

 

As the displacer moves up, the air is displaced and moves down against the cold side of the "pressure cooker" causing the air to contract and creating a vacuum inside the "pressure cooker" that sucks air in through one of the check valves. Then when the displacer moves down it displaces the cold air forcing it up against the hot top of the "pressure cooker" where it expands and escapes out the other check valve.

 

The resulting flow of pressurized air out of the "pressure cooker" is sent through your air-cycle heat exchanger.

 

The only power input needed for this entire system (other than the heat in ambient air) is whatever energy it takes to move the displacer up and down inside the "pressure cooker".) The "pressure cooker" acts as a compressor for your air-cycle heat exchanger.

 

Exactly!!! You will find that whatever means you are using to move your "displacer" requires more energy than can be extracted from the system.

[Tom Booth]

I suggest you familiarize yourself with the following:...

 

Thanks for the tips. I'll see if I can wrap my brain around this and figure something out.

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Merged post follows:

Consecutive posts merged

perhaps tom should draw a diagram clearly showing the flows of gas and energy flows.

 

Hi,

 

There is a diagram I posted earlier:

 

http://prc_projects.tripod.com/stirling_air_turbine_2.html

 

There are a few details missing.

 

For example: the displacer (What I've labeled "inturbulator") would probably also need to be a "regenerator".

 

That is, it would be comprised of a top and bottom plate with slots or fins to help swirl the air as it passes through the thing with some stainless steel-wool or mesh sandwiched in between. The regenerator is a common component in many Stirling Engine displacers, but I've heard from some Stirling Engine model builders that they found that their engines run just as well or even better without it. For this engine though, after trying to visualize the heat flow in this thing, I think the displacer would need to have some regenerative capacity.

 

Here is a You Tube video animation illustrating how the displacer's movement creates alternating pressure and vacuum to drive the piston in a conventional "Gamma" type Stirling Engine (without a regenerator), which is the same basic design I've used except that I'm using check valves so that the expanding gas escapes rather than pushing a piston and the vacuum draws in fresh air through a second check valve rather than sucking a piston back in:

 

http://www.youtube.com/watch?v=CDntL4GZh0E

 

I've been trying to find the time to make this simple diagram into a gif animation showing air and heat flows, pressure changes etc. but I still haven't had the time. I'd have to draw the images by hand frame by frame. For now, I can say that the air goes in the intake and pretty much keeps going the same way (flowing through the tubes) until it exits through the exhaust. I've tried to illustrate heat changes in the gas with color (red=hot, orange=warm, blue=cold).

 

I have also neglected to show insulation. There would need to be a lot of it.

 

Basically you can assume that anywhere the gas traveling through the system where the pipes or other things the gas is passing through are not intentionally exposed to ambient air for heat exchange would need to be well insulated.

 

I can add some arrows and insulation to the diagram....

 

Maybe it won't be too difficult to make this animated, as there are not too many moving parts.

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Merged post follows:

Consecutive posts merged

Tom Booth; I am a little surprised that you can't see why this won't work.

 

The only power input needed for this entire system (other than the heat in ambient air) is whatever energy it takes to move the displacer up and down inside the "pressure cooker".) The "pressure cooker" acts as a compressor for your air-cycle heat exchanger.

 

Exactly!!! You will find that whatever means you are using to move your "displacer" requires more energy than can be extracted from the system.

 

I think that if this were true, a Stirling Engine wouldn't work either, the theory and operation of which is based in part on the principle that it takes less energy to move the displacer than what can be recovered from the force of the resulting expanding and contracting volume of air. I don't see how converting the expansion and contracting force into a linear flow making it possible to use a more efficient turbine instead of a piston would alter that equation.

 

In a conventional Stirling Engine, ultimately everything (all the moving parts of the engine) is driven by the temperature differential. The temperature differential can be above or below ambient. If above ambient, then ambient is used as the heat sink and heat has to be added. If below ambient then ambient is used as a heat source so heat has to be subtracted.

 

The problem is how to subtract enough heat from the system to maintain the cold side of your temperature differential. This thing is basically a long condenser coil throwing off heat. By keeping the turbine insulated, more heat is extracted to do work rather than added in the expansion phase.

 

Theoretically, an enormous amount of heat/energy is being extracted from the air creating a huge temperature differential.

 

The displacer is relatively light weight and encounters very little resistance as it does not expend much energy in moving the air. It is not directly expanding or compressing the air, the air just goes right around it or through it.

 

The turbine should be able to extract more energy than would be needed to move the displacer, just as the piston in a conventional Stirling Engine can extract more energy than needed to move the displacer.

Edited February 8, 2010 by Tom Booth
Consecutive posts merged.

[dalekh]

Tom,

 

You have stated, I think correctly, that you have two energy inputs: the electrical energy that drives the displacer, and the "heat" in the ambient air. The energy in the air is only available if you have a temperature difference. (I do not believe there is any way around this fact).

 

In your engine, you are creating a temperature difference (by doing work via the turbine) using the energy that results from that same temperature difference. Does this analysis make sense? I lack the education of others posting here, but I believe this is the crux of the matter.

 

Dale.

[Tom Booth]

Tom,

 

You have stated, I think correctly, that you have two energy inputs: the electrical energy that drives the displacer, and the "heat" in the ambient air. The energy in the air is only available if you have a temperature difference. (I do not believe there is any way around this fact).

 

In your engine, you are creating a temperature difference (by doing work via the turbine) using the energy that results from that same temperature difference. Does this analysis make sense? I lack the education of others posting here, but I believe this is the crux of the matter.

 

Dale.

 

No, it doesn't make sense.

 

The process, if it can or could work at all, would have to be given an initial boost, like most anything. A regular Stirling engine for example has to be given a push to get it started. Your car needs a starter motor etc.

 

This thing would also have a bit of difficulty getting started I think. At least some external source of compressed air to get it charged up and get air flowing through it.

 

This "charging" would have to continue for some time until the turbine started putting out some cold air to establish a temperature differential in the displacer chamber.

 

Once the turbine starts, it would need to be put under a load. The energy drain should, theoretically, make the air coming from the turbine extra cold. Once the turbine starts generating some cold and electricity then the electric power output from the turbine can start delivering the current to the solenoids and the controller motor to actuate the displacer movement.

 

So now everything has come full circle and you should be able to remove the external source of compressed air.

 

I've been working on that animation today and finally got something done with it.

 

It doesn't show every detail.

 

Like I didn't bother showing the cold air exhaust or the turbine turning - but there is not much action to see there anyway.

 

I made some captions, but they probably go by too fast for anybody to read.

 

I also don't show the full cycling... mostly just the air being driven down to cause the air to contract the cooling coils is sort of missing - the displacer just kind of snaps back - but I think it is pretty good to illustrate what is supposed to happen.

 

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

 

This shows the engine running after it has been started. Admittedly, it might take some doing to get it going, but once the full cycle has been initiated, it looks to me like it might just continue on its own - as long as the load is maintained on the turbine, i.e. IT HAS TO DO WORK TO OPERATE.

 

The turbine doing work is where you get that little bit of extra cold to compensate for any inadvertent heat infiltration.

 

Originally this thing had about a 15 foot diameter parabolic solar dish focusing heat on it...

 

Originally I was just trying to use the Air Cycle to keep the Stirling Engine from overheating...

 

But once I came up with this configuration it seemed like adding any additional heat would be TOO MUCH HEAT. It seemed to be running fine without the direct solar input. It seemed to be getting enough indirect solar heat right from the air...

 

Of course, a little extra solar heat on a cold day probably wouldn't hurt.

 

Here it is again:

 

Stirling Turbine Animation

[dalekh]

Good job showing how the "compressor" actually works.

 

Have you made any progress with the numbers yet? I was hoping there might be someone on this site that could give insight into actual performance of a turbine - I think that is where we most lack in accurate knowledge. My son-in-law is a jet engine mechanic for the Air Force so I asked him about this cycle. Unfortunately they are pretty specialized and he didn't know much more than I.

 

I'll hold on my evaluation of the energies but it still seems to me that regardless of the jump start, a net gain in energy is required to actually create a temp. difference. I think a little solar (at least minimally focused) would be required on any day.

[npts2020]

TomBooth; Nice animation. Unfortunately the two things that will keep it from working in real life are; 1) you will require more energy than you can extract to raise your displacer piston. 2) if you are heating your exhaust from the turbogenerator, it will create a backflow from losing your vacuum as it heats up causing the turbine to stop.

If you actually build one of these machines, you will see the truth of this, the laws of thermodynamics are very stubborn, I dare say even more stubborn than you are. If you can improve efficiency of an engine through this, it will still be worthwhile to build it but I am skeptical of even that. One thing I am absolutely certain of, is that it will not work the way you describe.

[Tom Booth]

Good job showing how the "compressor" actually works.

 

Have you made any progress with the numbers yet?

 

No, not yet. I spent most of yesterday on that animation. (And most of today working on making it a little more realistic. In particular the pressure gauge. There should be a lot more pressure drop during the intake phase as air would still be decompressing through the turbine at that point, I also got the turbine turning, but there are a few more doodads I need to work on, like the temperature changes in the regenerator -- that mesh in the center of the displacer)

 

I was hoping there might be someone on this site that could give insight into actual performance of a turbine - I think that is where we most lack in accurate knowledge. My son-in-law is a jet engine mechanic for the Air Force so I asked him about this cycle. Unfortunately they are pretty specialized and he didn't know much more than I.

 

I've referred to this as an "Air Cycle" and I guess it is, but I think it has more in common with gas liquefaction methods. The Air Cycle used on aircraft generally uses ram in flight. High velocity, large duct-work, low pressure differential. Liquefaction is basically the same principle but higher pressure, smaller pipes, lower velocities. I figure there is a relation between velocity and pressure, similar to amps x volts = watts. Pressure x velocity = ?

 

I'll hold on my evaluation of the energies but it still seems to me that regardless of the jump start, a net gain in energy is required to actually create a temp. difference.

 

Yeah, more than likely the "jump start" would have to continue indefinitely - LOL...

 

I think a little solar (at least minimally focused) would be required on any day.

 

Originally I was just working on trying to design a more efficient engine so as to be able to reduce the size of the parabolic dish that would be needed for a Stirling solar generator. Something more suited for a residential application.

 

I was told that the engines used on those big Stirling solar farms in the desert require a refrigeration system to keep the engine cool and throw off the excess heat. Sounded very inefficient. I thought if I could find a way to improve the efficiency of the Stirling Engine then the size of the dish required could be reduced.

 

Well,... It seemed I reduced it alright. Reduced it right out of existence.

I spent a lot of time yesterday also boning up on Thermodynamics. There were some points I found interesting. Like, the way these Laws a written. i.e. "in an isolated system...", "in a closed system..."

 

Well, this is an open system. So are these laws that apply to an isolated system actually applicable to this engine ? How is the entropy of the atmosphere effected when this thing starts drawing in warm air and ejecting cold air, or when it starts simultaneously powering various remote loads ?

 

You know I'm looking for a loophole.

 

I'm also wondering about how "change of state" works into these laws.

 

Does some of the air change state in an air-cycle system ? Maybe condensing into a kind of vapor cloud temporarily.

 

I hate to get into this on a "classical science" forum, but aren't these laws also based on the assumption that heat IS NOT a particle ? Yet isn't infrared light supposed to be the same thing as heat, and isn't a "photon" a particle ?

 

I'm referring to what I read here:

 

clip----------

"Perpetual motion of the second kind

 

"Before 1850, heat was regarded as an indestructible particle of matter. This was called the “material hypothesis”, as based principally on the purported views of Sir Isaac Newton. It was on these views, partially, that in 1824 Sadi Carnot formulated the initial version of the second law. It soon was realized, however, that if the heat particle was conserved, and as such not changed in the cycle of an engine, that it would be possible to send the heat particle cyclically through the working fluid of the engine and use it to push the piston and then return the particle, unchanged, to its original state. In this manner perpetual motion could be created and used as an unlimited energy source."

-------------

 

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

 

Isn't this recycling of heat what is behind the idea of the Stirling Engine "regenerator".

 

It is also (apparently) an element in this engine in another way. i.e. the heat used to expand the gas in the displacer chamber one time is then reused as the same gas just heated and expanded is compressed to provide heat to compress the next batch of air, which next batch of air is then compressed to extract the same? heat again in order to compress more air etc. etc. etc.

 

My thought was that the "kinetic" energy or movement of the air, being forced through the narrow tube was being converted into heat due to a kind of friction - giving off infrared radiation that gets transmitted to the incoming air.

 

Particle or radiation, It seems it would amount to the same thing. The "heat" whatever it is is in effect being transferred and reused over and over again.

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TomBooth; Nice animation. Unfortunately the two things that will keep it from working in real life are; 1) you will require more energy than you can extract to raise your displacer piston.

 

Probably true, especially if for some reason the so-called "compressor" doesn't compress, then there will be NO energy. But if there is ANY, the displacer is very easy to move.

 

2) if you are heating your exhaust from the turbogenerator, it will create a backflow from losing your vacuum

 

I'm not sure what "vacuum" you are referring to. The turbine, theoretically, will run on compressed air and/or expanding air not a vacuum. I guess, relatively speaking, one atmosphere is a partial vacuum as compared with air in a compressor tank, but somehow I don't see this happening.

 

If I take a compressor hose from an ordinary compressor tank and direct the nozzle through a heated tube, the heat on or in the tube is not going to cause the air to stop coming out of the nozzle - no matter how hot the tube gets.

 

 

as it heats up causing the turbine to stop.

If you actually build one of these machines, you will see the truth of this, the laws of thermodynamics are very stubborn, I dare say even more stubborn than you are. If you can improve efficiency of an engine through this, it will still be worthwhile to build it but I am skeptical of even that. One thing I am absolutely certain of, is that it will not work the way you describe.

 

Well, the only real innovation here, as far as I can see, is using a temperature differential to operate a "compressor" with very little energy input, other than heat.

 

If such a compressor works, I should think it would have numerous applications besides acting as the compressor for an air-cycle heat exchanger or refrigerator.

 

An air compressor that runs, instead of on 20 Amps of household current - a flashlight battery and a heat source... It think that in itself would be something.

 

But if that DOES work. Then the compressor output should be comparable to a regular compressor running on 110v or any other energy source.

 

How could something with that kind of power output NOT be able to power something that could otherwise run on a flashlight battery, even if that other "something" is itself ?

 

I don't know. But I'm not yet convinced that this couldn't work.

Edited February 9, 2010 by Tom Booth
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[npts2020]

TomBooth; As the coils running through the outlet (vacuum or not) of your turbine heat the exhaust up, it has to increase the pressure as well. At some point the pressure will become such that there is no longer enough pressure differential across the turbine to enable it to work. Exhaust from a turbine is always cooled and not heated for good reason. I wish you luck in building this since it will be a great learning exercise and who knows, you may even come up with a more efficient engine. I do believe that it is impossible for it to work in the manner you describe, however, and would caution against raising your expectations too highly.

[Tom Booth]

TomBooth; As the coils running through the outlet (vacuum or not) of your turbine heat the exhaust up, it has to increase the pressure as well. At some point the pressure will become such that there is no longer enough pressure differential across the turbine to enable it to work. Exhaust from a turbine is always cooled and not heated for good reason.

 

I imagine what you say here is true in a closed system. But this is vented to the atmosphere. How could it possibly build up much pressure ?

 

This is like saying that if I hold a blow torch to my cars tail pipe, the heat will create back pressure inside the tailpipe and the car will stall.

 

Probably this would also be some problem with a reaction type turbine, as a reaction turbine is in the flow right inside the pipe or duct-work and relies on the pressure head in the line directly.

 

I'm using an impulse turbine not a reaction turbine. The power for an impulse turbine comes from the high velocity jet of air coming out of the nozzle. It doesn't care about some pressure fluctuations in the exhaust.

 

I wish you luck in building this since it will be a great learning exercise and who knows, you may even come up with a more efficient engine. I do believe that it is impossible for it to work in the manner you describe, however, and would caution against raising your expectations too highly.

 

Thanks, I have no expectations.

 

I more or less stumbled upon this particular arrangement by accident. I was not out to create any "perpetual motion machine".

[Tom Booth]

I don't have you guys stumped do I ?

 

I had a few ideas about possible ways to increase the efficiency of the turbine:

 

First of all, thinking some more about this entropy thing and the fact that the application for this turbine is power production rather than liquefaction or JUST cooling alone, It crossed my mind that it didn't make sense to pre-cool the gas in the line as this would rob the gas of some of its energy before reaching the turbine - wouldn't it be better and make more sense to pre-cool just the turbine housing ?

 

The gas would still have to draw on its own internal energy to do the expanding - more so, I should think, but would have more internal energy to work with and therefore could deliver additional power to the turbine rather than having that power extracted before reaching the turbine.

 

So I came up with this idea for using the turbines cold exhaust gases to pre-cool the turbine housing itself instead of pre-cooling the gas before it enters the turbine:

 

Turbine Details

 

On the same page (scroll down) I've included another idea for increasing the efficiency of the Tesla Turbine (theoretically).

 

I was thinking that in the Tesla Turbine, perfectly smooth and uniform flat plates are used. Normally this would probably be OK as the gas would be picking up heat from the turbine as it spirals towards the center. But in this application, the gas would be loosing internal energy and cooling and presumably contracting as it spirals towards the center of the turbine, which I think would tend to create some degree of turbulence or drag on the turbine disks as in effect, the contracting gas would have too much room between the disks and so would loose cohesion with the sides of the disks - slow down and create turbulence - reducing the power output of the turbine.

 

So my idea was to TAPER the disks.

 

In this way, the passage the gas is using as it spirals inward would become narrower and narrower as the gas simultaneously cools and contracts. Theoretically, the narrowing of the passage would result in the gas maintaining speed as it spirals in and cohesion with the turbine disks.

 

wadayathink?

 

By the way, I'm starting to get somewhere with those equations.

 

Mostly I'm just having some trouble with the terminology.

 

Like "the gas constant".

 

What is the "absolute pressure of the gas". How is this different from regular pressure ?

 

The equation for an isentropic process in an open system (the turbine):

 

W = m(h1 - h2) = mcp(T1 - T2)

 

W = Power Output; T = Temperatures; m = mass; mcp = specific heat at constant pressure (?)

 

h1 and h2 represent entropies. How do you determine the before and after entropy ? The idea of entropy seems rather abstract to me at this point and I'm wondering how this can be reduced to numerical values. Or is that what we are supposed to be solving for ?

 

Anyway, without some actual values to plug in to the equations, it would all be guesswork anyway. What I need to know is how much actual pressure can the "compressor" really deliver - and since this is only a theoretical compressor that hasn't been built yet, who knows ? It might not work. It seems that the only way to find out would be to build one.

 

If it does work, then the actual pressure it can develop can be measured and then that can be plugged into these various equations and formulas to arrive at some guestimate about potential power output (or lack thereof).

 

But if it is 60 F out and the "compressor" can maintain about 30 PSI (absolute i.e. 2 atm or about 15.5 PSI above 1 atmosphere) then from what I've figured so far, the "heating coils" might be able to develop a temperature of around 550 F. If 60 PSI 1,500 F, if 100 PSI 3,000 F

 

I think that just refers to the temperature reached from pressure alone. I'm not sure if this applies to passage through the coils. It also doesn't account for any regenerative effect.

 

Worst case, the lowest pressure that could turn a Tesla turbine is about 3 PSI (above 1 atmosphere = about 17.5 PSI absolute (?)) which might generate 140 F (?)

 

Given a "heat pump" averaging 300% efficiency and a "Stirling Engine" averaging 20% efficiency, combining the two in one engine should produce a 60% overall efficiency (20% x 3 ?).

[insane_alien]

no, you don't have us stumped, it is just that nobody can be bothered arguing with you anymore as you don't seem to understand what is being said.

[npts2020]

TomBooth; I will second what InsaneAlien said. From what you just said it is obvious to me that you do not have a thorough understanding of how turbines work. Every multistaged turbine in the world has tapered disks. The thing is that they are tapered from small to big, opposite of the way you describe. The reason for this is to allow the gas to expand while passing through. That is how a turbine works. It is this expansion that work is extracted from. The whole idea of greater temperature differences (like in say superheated steam) is to allow even more expansion and thereby greater ability to do work. It is not possible to use the same source (atmosphere in your case) as both a heat source and heat sink with no other inputs. It is those other inputs that prevent any engine from being 100% or greater in efficiency.

[Tom Booth]

TomBooth; I will second what InsaneAlien said. From what you just said it is obvious to me that you do not have a thorough understanding of how turbines work...

 

Well, I certainly don't claim to be any turbine expert. I'm talking specifically about a Tesla Turbine, which, as far as what I've read about it and seen from You Tube videos and such, it has closely spaced perfectly smooth parallel disks with no tapering one way or the other.

 

This is also a different application. Most turbines are not insulated so as to prevent the gas entering in from picking up heat to do the expanding. Here the idea is to keep the turbine cold so that the gas would have to draw on its own internal energy to expand. and yes, I did say expand, but I'm thinking that this expansion might be limited and before the gas finished spiraling to the center of the turbine (as it does in a Tesla turbine - delivering power all the way, as it spirals inward, loosing energy), I would imagine that this expansion would be reversed. In liquefaction processes using the same method (pre-cooling the gas and insulating the turbine) the gas liquefies, condensing on the inside of the turbine housing.

 

Prior to condensing into a liquid, it seems reasonable to assume that the gas contracts before it condenses - before leaving the turbine.

 

Anyway, that idea was just a thought on a possible way to tweak the power output of a working engine. We don't have a working engine as yet so the point is mote either way.

 

It is not possible to use the same source (atmosphere in your case) as both a heat source and heat sink with no other inputs. It is those other inputs that prevent any engine from being 100% or greater in efficiency.

 

Well, technically, in this engine, (IMHO that is), the heat SINK is not the atmosphere, it is the kinetic/heat/energy being extracted by the turbine being fed to some remote electrical load. In a kind of convoluted way, the electrical load on the turbine is the heat sink.

 

At least as far as I can figure, in an expansion turbine of this sort, that is where the heat is "disappearing" to.

 

That is how a cryo-cooler using an expansion turbine works, from everything I've read on the subject, the heat is transferred to the load on the turbine. That load can be just a water cooled brake or an electrical generator.

 

Eventually the heat would get back to the atmosphere one way or another I suppose - through heat from incandescent lamps or heating elements or whatever - but maybe these will be far enough away so as not to cause any major concern - I don't know. How else do you explain the EXTRA cooling effect of an expansion turbine, above what would be expected from expansion alone if the HEAT in one form or another is not being transferred to the break on the turbine ? Where is it going then ?

 

This is what the literature on these things says quite plainly - i.e. the heat being extracted by the turbine "re-emerges" at the braking system and is carried of by the water used to cool the braking system on the expansion turbine.

 

Sounds kind of like one of those "spooky action at a distance" things in quantum physics that Einstein couldn't get used to - but as far as I can see, that's the way these things (expansion turbines or turbo-expanders) work.

 

That looks like a "heat sink" to me, for all practical purposes.

 

But we've already been through all that.

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no, you don't have us stumped, it is just that nobody can be bothered arguing with you anymore as you don't seem to understand what is being said.

 

I think that for the most part, I understand most of what is being said. I'm just thinking that most of what is being said doesn't seem to apply to this engine - other than it can't work because it would be "perpetual motion" or that it would violate "the second law of thermodynamics".

 

Those reasons in particular look to me like beliefs or prejudices rather than specific scientific explanations as to why some aspect or detail of this engine just won't work.

 

clip-----------------

Even though they fully respect the laws of thermodynamics, there are a few conceptual or real devices that appear to be in "perpetual motion." Closer analysis reveals that they actually "consume" some sort of natural resource or latent energy, such as the phase changes of water or other fluids or small natural temperature gradients. In general, extracting large amounts of work using these devices is difficult to impossible.

 

wiki - Perpetual motion

 

The drinking bird is given as one example of this apparent "perpetual motion".

 

As far as I can figure, this engine takes advantage of the same principles as this toy bird. i.e. converting a temperature differential into a pressure differential so as to extract work from the pressure differential.

 

clip-----------

"The drinking bird is a heat engine that exploits a temperature differential to convert heat energy to a pressure differential within the device, and perform mechanical work. Like all heat engines, the drinking bird works through a thermodynamic cycle"

 

wiki Drinking bird

 

I'm not saying that this bird proves that this engine will work. but I think it does prove that it is not impossible for something like this to work.

 

About the only difference in principle is that the bird uses a very inefficient cooling system to establish the initial temperature differential. Instead of evaporative cooling, this engine uses a turbo-expander.

 

Do you suppose the engine would work if it used evaporative cooling instead ?

 

IMO the "latent energy" being "consumed" (as described above) is the extra energy being extracted by the turbo-expander. In a sense it (this extra heat/energy) is being "consumed" as it leaves the system to power some remote load.

[Sayonara]

Sounds kind of like one of those "spooky action at a distance" things in quantum physics that Einstein couldn't get used to - but as far as I can see, that's the way these things (expansion turbines or turbo-expanders) work.

Yes, except it's not operating at the quantum level. It needs a physical mechanism or it can't have a physical explanation. I don't think you get to point at energy use away from the turbine and claim with a bit of a hand wave that there lies the heat sink.

 

If you can't draw an energy transfer diagram for the turbine, with 100% of the input energy being accounted for in the outputs, then the turbine goes into the box labelled "Magic", not the one labelled "Technology".

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IMO the "latent energy" being "consumed" (as described above) is the extra energy being extracted by the turbo-expander. In a sense it (this extra heat/energy) is being "consumed" as it leaves the system to power some remote load.

There has to be a differential within the turbine apparatus, or there is nothing to drive it. You can't just have a nebulous cloud of ad hoc numbers floating around outside the apparatus to balance out the utter lack of a working physical solution.

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The drinking bird is given as one example of this apparent "perpetual motion".

 

As far as I can figure, this engine takes advantage of the same principles as this toy bird. i.e. converting a temperature differential into a pressure differential so as to extract work from the pressure differential.

And yet the drinking bird is emphatically not an example of perpetual motion, apparent or otherwise. The system is driven by either the lower bulb being heated or the top bulb being cooled - in each case there is an energy source and an energy sink.

Edited February 14, 2010 by Sayonara³
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[npts2020]

Two things to add to what Sayonara said about the drinking bird.

1) As soon as you take away the water (heat sink) the bird will stop working.

2) It is doubtful that you can extract the extremely miniscule amount of energy the bird requires for operation to do any useful work.

 

Using the same source for heat and sink will not give you more energy than that required to be able to do so. Somewhere you have to add energy to give a differential in pressure/temperature. This addition of energy will always make efficiency >100%.

[Tom Booth]

If you can't draw an energy transfer diagram for the turbine, with 100% of the input energy being accounted for in the outputs, then the turbine goes into the box labelled "Magic", not the one labelled "Technology".

 

Just the turbine ?

 

You mean something like this:

 

Diagram

 

There has to be a differential within the turbine apparatus, or there is nothing to drive it.

 

You have a mass of compressed air, leaving the nozzle at high velocity driving the turbine - regardless of the air temperature or any temperature changes. The turbine is driven by a pressure differential not a temperature differential. A temperature differential results from the air doing work against the load on the turbine.

 

The temperature differential does not power the turbine. The pressure differential powers the turbine.

 

I don't really understand the problem, or why the focus on the turbine. The turbine is the last thing I thought there would be any debate about. These things are IN USE and have been for many years by industries all over the world for cooling and refrigeration. In transferring energy to the turbine, the gas looses energy and gets cold. Simple.

 

And yet the drinking bird is emphatically not an example of perpetual motion, apparent or otherwise. The system is driven by either the lower bulb being heated or the top bulb being cooled - in each case there is an energy source and an energy sink.

 

Heat is being "consumed" by the water. The water needs the heat to liberate itself (evaporation/phase change). The evaporating water absorbs energy resulting in a drop in temperature (heat sink).

 

In the turbine, energy is ultimately being "consumed" or absorbed by the load on the turbo-generator - resulting in a drop in temperature (heat sink).

 

I don't see anything too vastly mysterious or "magical" about this.

[Mr Skeptic]

In the turbine, energy is ultimately being "consumed" or absorbed by the load on the turbo-generator - resulting in a drop in temperature (heat sink).

 

I don't see anything too vastly mysterious or "magical" about this.

 

And that is the problem. A turbine is not a heat sink, although it does draw some energy.

 

Anyhow, you don't really need to look at the turbine. Just keeping track of the work done on and by the gas, and heat flow, will suffice. Do this, and you will see that, barring a magical turbine, your idea won't work.

[Tom Booth]

Two things to add to what Sayonara said about the drinking bird.

1) As soon as you take away the water (heat sink) the bird will stop working.

 

This would be true of the turbine as well.

 

If you take away the load on the turbine then the turbine will just freewheel and the gas will pass through without doing any appreciable work and there would not be much cooling effect.

 

2) It is doubtful that you can extract the extremely miniscule amount of energy the bird requires for operation to do any useful work.

 

Using the same source for heat and sink will not give you more energy than that required to be able to do so. Somewhere you have to add energy to give a differential in pressure/temperature. This addition of energy will always make efficiency >100%.

 

I'm going to assume you meant: efficiency <100%

 

My supposition is that the evaporative cooling on the dippy birds head results in a minuscule temperature differential. The bird, functioning as a heat engine can't extract much energy from such a small temperature differential.

 

If you increase the temperature differential the bird will move faster. Replace the water with alcohol for instance. The more rapid evaporation of the alcohol will result in a greater temperature differential and therefore the heat engine can extract more energy.

 

An air cycle cooling system, or similar system using a turbine for refrigeration, creates the most extreme temperature differentials of any heat exchange system. Not the few degrees difference resulting from the evaporation of a few drops of water but potentially hundreds of degrees difference.

 

Wider temperature differential, greater potential for extracting energy with a heat engine.

 

I mean, this thing probably won't work. Granted. But it won't be because turbines or turbo-expanders or expansion turbines don't work. That aspect of it is proven IN USE technology all over the world.

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And that is the problem. A turbine is not a heat sink, although it does draw some energy.

 

The turbine itself doesn't draw much energy... a bit of friction on the shaft bearings. The real energy is being drawn by the ELECTRICAL LOAD on the generator coupled to the turbine.

 

The energy to turn the turbine and attached generator against the electromagnetic force created by the load on the generator is being taken from the air or gas driving the turbine. As a result, the gas looses internal energy (i.e. the temperature of the gas drops in proportion to the work performed)

 

"for an ideal gas Joule showed that internal energy is a function of temperature only"

 

http://www.ent.ohiou.edu/~thermo/property_tables/gas/specific_heat/Cp_Cv.html

 

Google results for: "the internal energy of an ideal gas is a function of temperature only"

 

Anyhow, you don't really need to look at the turbine. Just keeping track of the work done on and by the gas, and heat flow, will suffice. Do this, and you will see that, barring a magical turbine, your idea won't work.

 

There is nothing "magical" about the turbine. That a gas drops in temperature as a result of doing work, (in a turbine or otherwise), is basic thermodynamics.

[Mr Skeptic]

There is nothing "magical" about the turbine. That a gas drops in temperature as a result of doing work, (in a turbine or otherwise), is basic thermodynamics.

 

The magic happens when you pretend the turbine is a heat sink. Go on, figure how much energy is extracted by the turbine and what the change in temperature, pressure and volume will be. And please, assume the turbine is 100% efficient. Just look at the gas and forget the turbine. The turbine can't extract more energy than the gas does work.

[Tom Booth]

The magic happens when you pretend the turbine is a heat sink. Go on, figure how much energy is extracted by the turbine and what the change in temperature, pressure and volume will be. And please, assume the turbine is 100% efficient. Just look at the gas and forget the turbine. The turbine can't extract more energy than the gas does work.

 

I'm not saying that the turbine extracts more energy than the gas does work.

 

I'm saying basically that the heat/energy added to the system as a whole, by in-drawing fresh warm (ambient temp) air should be roughly equivalent to the work/energy (electrical) output of the turbo-generator.

 

You have taken the heat out of the air by making it do work as it expands through the turbine. The resulting cold air is then used as a heat sink (or heat scavenger) for the heat/engine/compressor.

 

The compressor draws in warm air (energy added to the system) and compresses the air. as energy is being added to the air it gets hotter. The heat is driven off in a heat exchanger (at the top of the heat/engine/compressor). The air then decompresses through the turbine extracting more heat/energy (energy leaving the system as electricity).

 

The air leaving the turbine is now very cold and is passed through another heat exchanger (where the cold air scavenges heat from the heat/engine/compressor on its way out) .

 

The heat/engine/compressor uses the temperature differential between the hot and cold heat exchangers to draw in and compress more air.

 

If there is some failure point in all this, I would suspect it would be at the compressor, or between the compressor and the turbine, as this is where you are trying to force compressed air into hot coils via the heat derived from the same hot coils and I can imagine that there would be some build up of back pressure there which might result in the compressor valves failing to open or the coils wouldn't generate enough heat to power the compressor or both.

 

However, if the pressure is relieved through the turbine, then the valve would be able to open again, the air would move through the coils generating heat...

 

I'm imagining that the displacer action could be controlled by a pressure switch. In any event, the "compressor" would have to have the potential to pump more air than the turbine needed. This seems a bit more questionable than whatever the alleged issue with the turbine is supposed to be, which I just don't seem to get.

 

Given a supply of compressed air, a turbine will output work and cold air.

[Sayonara]

Just the turbine ?

 

You mean something like this:

 

Diagram

No, I mean something quantitative.

 

 

You have a mass of compressed air, leaving the nozzle at high velocity driving the turbine - regardless of the air temperature or any temperature changes. The turbine is driven by a pressure differential not a temperature differential. A temperature differential results from the air doing work against the load on the turbine.

 

The temperature differential does not power the turbine. The pressure differential powers the turbine.

pV = nRT