Author Topic: Electronic Stirling (Read 7068 times)

iFred · « **on:** October 15, 2004, 11:22:44 PM »

Many times I think of things in a strange but particular and interesting way, I find it opens up other pathways of thinking outside the box. When I meet a challenge from a mechanical viewpoint I sometimes will convert this viewpoint to an electrical or electronic viewpoint which I can then understand the problem better. It's nothing new to make electronic circuits that will imitate mechanical devices. However I have stumbled into something which I am having trouble with and am in a sort of do loop and need some assistance.

The challenge was to produce an electronic equivalent circuit to imitate a Stirling motor.

At first I approached the problem from a refrigeration or heat pump device. Whereby a compressor; would by way of pressure changes a fluidic or gaseous movement produce both a hot coil and a cold coils thereby moving heat from one point to another most efficiently.

I immediately thought of several electrical equivalent electronic circuits of a mechanical device which would imitate such a simple process. But to my surprise, I could not come up with an equivalent component of the common "expansion valve", and it became difficult to figure out what could be used to create a cold side of such a circuit. The secret component was a "thermal Peltier device or junction" for the cold side, but an expansion valve is something else.

In Fig A, I began working out the problem rapidly for the hot side, easy, a resistor solved this. X-device is the expansion valve still in question. Y-device was the question which turned out to be a thermal Peltier device. But then I ran into a new problem. The Peltier device produces both hot and cold in the same device, in essence it is a self contained refrigeration/heat pump all it's own from an electronic standpoint. Opp's back to the drawing board on that one.

Anyway; as I was mentioning. The idea is to create an electronic equivalent circuit to imitate a Sterling motor.

I figure it's a basic oscillator with regeneration. Any idea's?

Why do it, because if a mechanical device such as Stirling Motor has such a high efficiency ratio can you imagine what an equivalent electronic circuit could be??

I'm open to thoughts....

windstuffnow · « **Reply #1 on:** October 16, 2004, 01:06:35 PM »

It seems to me, and my knowlege in the electronics area is limited, that with the available technology it really wouldn't come out that efficient in the end. You'd probably be better off buying solar panels. If there were better ways to convert heat directly into electric then, depending on the process, it might be a viable and more efficient.

The conversion process of turning heat into mechanical motion is a fairly simple technology although not real efficient. The gas engine is one of many heat engines tried and proven to work but not very efficiently....

% goes out the exhaust
% goes into and out of the cooling system
% goes into friction, compressing springs, and overcomming crankshaft inefficienies.
% goes into driving the vehicle down the road and powering accessories.

If you think about how the stirling works, its simplicity alone allows it to reach higher shaft output power by utilizing the power more efficiently. A standard non pressurized stirling will create about 13psi in the displacer chamber. If you have a 1.125" piston this means there will be 13lbs of force on the crankshaft. The same engine with a 5" piston would have 255 lbs of force on the crank and a 10" piston would yield 1021 lbs of force. The difference between the steam engine and the stirling engine is the volumn of heated air used. The steam engine uses alot of volumn and wastes the balance, the stirling uses it's own swept volumn over and over. The gas, diesel, and steam amoung others waste a great portion of the initial heat input through the exhaust which could be recaptured and used again... and again at a lower level until.

The presurized stirling engine creates a much higher output but only because there is more volume of gas to be expanded. Unfortunately that pressure must be on both sides of the power piston in order for it to work properly. So you really haven't gained it's actual potential. Some stirling engines running upward to the 2000psi range... some have gone higher. Sounds like a bomb ready to blow to me...! Of course the 700 hp torpedo engines were going to blow up anyway... they didn't have to worry about any longevity or safty as long as it made it to their destination. GM's stirling auto engine worked out very well but was scrapped because you couldn't get into it, start it and drive away within 7 seconds... it took 2 or 3 minutes to get enough heat in it to move the car sluggishly then came up to full power within 5-10 minutes. It achieved 45 mpg with a V8 style engine... pretty good for a prototype... I thought (back in the 70's).

What if you took a standard gas engine... say a 4 cylinder, and only used 2 of the cylinders to run on gas. Convert the other 2 cylinders to utilize the waste ( stirling base ). The exhaust gasses are from 800 to 1300 degrees as they go on their merry way out the tail pipe. If you could capture 50% of the waste from the 2 gas driven cylinders. Lets say the engine originally is 90hp and the two will make 45hp. This means your using a total input of 180hp equivilant of fuel. So your getting 45 hp from the gas portion, while wasting 135 hp... Now we simply dump the waste into the second portion of the engine. The cooling system will use up 30hp so there is still 105 hp going out the exhaust. Lets say we can reclaim 40% of that... thats 42hp... we almost have our 90 hp engine back and instead of 30mpg we get 60... kind of makes you wonder...

Have Fun..

Windstuff Ed

JW · « **Reply #2 on:** October 16, 2004, 06:03:32 PM »

Huh, pretty sweet posting iFred,

For an extremely detailed explaination of the Stirling Crank-Shaft Motion, refer to this book.

"P.W. Atkims"

"The Second(2nd)Law"

Energy, Chaos, and Form

ISBN 0-7167-6006-1

JW

iFred · « **Reply #3 on:** October 17, 2004, 05:22:21 AM »

When a problem bug's me enough I know I'm onto something major.

Today I hunted down the principle of the expansion valve.

Evaporator; A device in which refrigerant changes from a liquid to a gas and absorbs heat from its surroundings.

The expansion valve is the replacement for the old manual or automatic governor. The expansion valve of today measures flow of gas or liquid entering the evaporator at a rate that matches the amount of liquid or gas that is being boiled off in the evaporator, it also provides a pressure drop in the system by separating the high pressure from the low pressure; Thus allowing the low pressure liquid or gas to absorb heat onto itself.

An electronic equivalent to this would be a couple transistors, a load and a couple sensors to control current flow and temperature to adjust output/input and load accordingly. So, no big deal here. Once I understood this I could now build a block diagram of the circuit. That I beleive was the hangup or do loop I was missing.

So here it is ... what I believe it basically looks like...An electronic equivalent of the mechanical version of a Stirling Engine. The Peltier device creates voltage from being hot and cold, the cap acts as a flywheel, the Oscillator output would behave in the same manner as the output of the flywheel in a sine wave output fashion, the temperature sensor provides feedback control and adjusts the driver/load control which adjusts the load according to the amount of temperature that there is and thus determines the amount of power to deliver to the load without being overpower or underpowered. Load/power compensated.

inode buddha · « **Reply #4 on:** October 17, 2004, 05:49:21 AM »

Fred, that's fascinating! For the electronic equivalent of your expansion valve, have you considered "Avalanch" diodes? IIRC from my old TV repair training, they exhibit a so-called "negative" resistance when they break over, with large current flows. (This being what they are intended for). I have seen similat techniques used with neon bulbs to make simple "oscillators": a cap charges at a given rate through a resistor, until the neon flashes over (about 90 volts IIRC).

Hehehe, you really got my creative juices going, thanks for a great post!

JW · « **Reply #5 on:** October 17, 2004, 12:08:46 PM »

iFred,

Ah-ha, I see what your doing. The problem of the "regenerator" in stirling engines is a serious issue. Quite interesting approache to hybredizing an electronic circuit, with pelter juctions, and a working fluid. In reference to "expansion valves" take a look in "Mark's" its a reference book for mechanical enineering. In Marks check,-the definition of what is called "wire-drawing"... Also have you ever heard of what is called "thermo-acustic cooling"? Seems to me it was on the cover of physics today(magazine) in the early 90's. Would be iteresting to incorperate some moving parts in reference to the regenerator, and your electronic hybridization ideas. Keep at it, Nice work...

JW

iFred · « **Reply #6 on:** October 17, 2004, 05:06:07 PM »

AHHHH! YES! That may do it... Check out this info I found..

http://www.st-andrews.ac.uk/~www_pa/Scots_Guide/RadCom/part5/page1.html

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

http://home.earthlink.net/~lenyr/ntype-nr.htm

The last link is very cool!

Spark, Bang, Buzz and Other Good Stuff

http://home.earthlink.net/~lenyr/index.html

iFred · « **Reply #7 on:** October 17, 2004, 05:10:29 PM »

Yes, I remember reading about the acoustic heating and cooling experiments that where going on, something that started in a test tube and went to Nasa and some other Labs, they are doing some heavy reseach on it.

>> The problem of the "regenerator" in stirling engines is a serious issue

Yes, you got it! keep going.... Your almost there...

JW · « **Reply #8 on:** October 17, 2004, 05:32:52 PM »

Ya, thats some pretty cool stuff iFred.

Soooooo, basically your saying that a standard oil-filled automotive style spark-ignition coil's, ALWAY's get warm over-time(in operation) regardless of the DC pulse-train being fed-and-collapsed into it, (again)regardless of secondary high-voltage induction, resistance heat-losses in the electrical-circuit... Let alone the best layered anti-hysteris techniques, that may be applied in the reluctor-core (attempt to reduce induction-heating in flux medium). And... It "is" interesting that simular DC pulse-trains may in-fact produce a "cooling effect" with relation to 'thermo-acustics devices'.

Brought to you by your local thermodynamics police

JW

iFred · « **Reply #9 on:** October 17, 2004, 05:51:59 PM »

ED...Any mechanical device converted over to an electronic equivalent will be like 99.9% more efficient then any mechanical device could hope to be. There are no real losses suffered as there are in mechanical devices. If you want efficiency then you want to convert everything mechanical to electronic control. This is why solar and wind is so efficient, because it is as direct as possible the route to control, transfer and final usage of energy. You even agreed with me on this and the energy transfer concept remember...(conversion chart)

iFred · « **Reply #10 on:** October 17, 2004, 06:23:14 PM »

There will always be a 1% loss no matter what or how you define it or how it is produced, however it will be a lot less then any mechanical device could hope to be. Minimalization of losses due to conversion of mechanical to electronic control is far better then suffering losses induced by the analog equivalent of mechanical devices. If you have a transformer just sitting there and powered but without an connection to the secondary you will still have heat due to the magnetic field that touch's any surface that is magnetic and the production of eddy currents, can't get around that, no matter what you do or how you slice it- pun intended. a wall wort is a perfect example.

However, what I am suggesting is that there are devices and methods available today that where not available before, to reduce losses and produce a new device for power control that may not have been suggested before. It's how you look at it, this post is just a simple examination and experiment in thought, it has produced interesting results already, as you are aware, we are now putting to use in circuits things that have not been thought of being put together to produce a new device. With new technology perhaps it's time to look at some of those old devices that where efficient like the heat pump, refrigeration system and yes even the Stirling... BUt what I am doing is attempting to show how this could be done.

So has it accomplished a goal? I believe so, and should be looked at seriously for what that concept holds.

Your oppinion?

windstuffnow · « **Reply #11 on:** October 17, 2004, 07:50:12 PM »

I admit it looks very interesting and the concept quite intriging. I still think its a ways off from actually producing a reasonable amount of power. The Peltier devices, at this point, aren't very efficient as well as solar panels. Wind isn't really very efficient either with the exception its free to start with. It is, however, a more direct approach and there are less conversions being made to achieve the end product. I have a better understanding of mechanical design and realize the their shortcommings but fewer parts usually takes care of a good portion of the losses. I expect my engine will be 100% efficient... The energy being put into it for making electric production will power the house the heat lost from the mechanical portion will be used to heat the house and water. Since I heat the house anyway in the winter it basically provides another free source of this power. Which in turn makes my furnace more efficient also.

Keep going on your device, I'd like to see it work ! How soon will you have a working prototype?

Have Fun

Windstuff Ed

LEXX · « **Reply #12 on:** October 17, 2004, 10:30:27 PM »

100% efficient?? What about the energy that is wasted by the production of noise? Will the final exhaust be the exact temperature of the intake?

LEXX

iFred · « **Reply #13 on:** October 17, 2004, 10:40:27 PM »

As stated the problem was regeneration. Therefore I believe this is the fix.

Since the Stirling process is a variable thermal system, why not have the entire circuit variable based upon changes in load and production thus regenerate by collection of the resistive load heat? I think that even a sensor on the resistive load would help.

A regenerator connected to the resistive load means a variable efficiency regeneration system. Oppinions?

iFred · « **Reply #14 on:** October 18, 2004, 01:11:12 AM »

To anwser your question simply, yes on all counts.

Read the following link!

http://www.physics.utah.edu/~woolf/acoustics/acoustics.html

iFred · « **Reply #15 on:** October 18, 2004, 01:28:28 AM »

Download the Doc file and read it... SOOOO COOL!

http://www.acs.psu.edu/thermoacoustics/refrigeration/laserdemo.htm

iFred · « **Reply #16 on:** October 18, 2004, 12:45:32 PM »

It just keeps getting better!

iFred · « **Reply #17 on:** October 18, 2004, 12:50:18 PM »

Hi Ed. Not sure when the first prototype.. Still working out some of the bugs and building blocks. If I get all the building blocks built and in order and it looks sound then I can begin purchasing the peltier junctions and making up the rest of the stuff. I still am in theory as to what I can use at this point.

JW · « **Reply #18 on:** October 18, 2004, 01:20:01 PM »

Hmmm,

the configuration of the acoustic elements, that you have there looks different from what im thinking of. Try this link.

http://ehp.niehs.nih.gov/docs/1994/102-9/innovations.html

It should bring you directly to an artical called "rock and roll refridgerator"

JW

iFred · « **Reply #19 on:** October 18, 2004, 01:25:11 PM »

Version 1067... ummmm... NEXT!

JW.. Check out the above links.. You can make them any size or dimension. THey do not seem that complicated to build either. I think it is do-able.

joedupont · « **Reply #20 on:** February 15, 2007, 03:27:06 PM »

WHY NOT USE THE PELTIER UNITS TO TAKE WASTE HEAT FROM THE STIRLING ENGINE AND RUN A FAN TO COOL THE STIRLING ENGINE AND ITS SELF . IN THAT WAY ONE WOULD HAVE TO PICK UP

EFFICIENCY.. IF THE PELTIERS COULD HELP RUN THE DISPLACER WITHOUT SEALS ALL THE BETTER. SUCH A HYPRID STIRLING ENGINE MIGHT BE WORTH LOOKING INTO..

HAS ANYONE SEEN THE ROTARY DISPLACERS .. NO UP AND DOWN.. JUST A ROTARY DISPLACER SWEEPING THE AIR ON THE OPEN SIDE.

MAYBE PELTIERS COULD OPERATE ELECTRONIC STIRRERS..INSTEAD OF DISPLACER.

IF THE MOTORS ARE ALTERNATING STIRRING THE AIR IN THE THE HOT AND COLD SECTION OF THE DISPLACERS THEN YOU ARE NOT MOVING A MASSIVE UNIT. JUST A THOUGHT.

THE ELECTRONICS YOU GUYS SEEM TO HAVE A HANDLE ON.

PERHAPS TWO LOOPS WITH A SPACE IN COMMON. HUMM.

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Author Topic: Electronic Stirling (Read 7068 times)