Stirling Cycle, Can it be a Continuous as Well as Batch Process

I guess I am not certain of the implication of "batch" in this use. Stirling is "closed." The working fluid is contained, with no loss or gain. But, in reall implementation it is externally fueled and heated. So fuel, in some form, is supplied which provides heat. Through whatever means, the engine must have ahot node and a cold node to function. They relate through the regenerator, which is perhaps the most unique aspect and key to funtionality. The process defines a continuous cycle, though. Nothing "batch" about it that I see. Look at the illustrated discussion at:

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

r/

Sam

"I have looked at the Stirling cycle and believe it is quite possible to convert the batch process into a continuous process from which you could extract the energy say from an included turbine, but I have not come across anything in the literature."

The Stirling cycle is the one utilized in a Stirling engine. It is NOT a process. It has an input of thermal energy at a temperature Tsub.H and waste heat rejected at Tsub.L work is output as mechanical energy.

The Stirling cycle and Stirling engine has no analogy to batch and / or processes.

What are you trying to accomplish by muddying the waters and confusing the uninitiated ???

Looks like a batch process, a defined volume [batch] is being moved by a piston. There is a beginning & end to each cycle [batch]. The velocity of the gas raises or lowers depending on the position of the piston. It is certainly a closed system.

I think this is what duikerbok was trying to express.

You could be right, but as the motor runs as long as sufficient heat is available, that is continuous or is he scamming us for an idea for a perpetual motion Stirling engine? Once running, no more heat required???

No scam. You obviously input the heat, external source, (solar,fire) but the idea is to do away with the reciprocating element. You extract mechanical energy with a turbine (say) inside the enclosure but with external coupling of whatever means, but use some of the energy to process the working gas back to the heating chamber. I guess it would be similar to closed systems using phase change materials but without their complications, and with lower efficiencies.

I cannot believe that a Turbine would do anything that you require, nor can a Turbine be built by any Tom, Dick or Harry as you almost can with reciprocating steam and Stirling engines....

Turbines, except at one specific design speed, are usually wasteful of energy.....but do not let me put down a Turbine expert, I have some experience of gas and steam Turbines , but not exceptional amounts or knowledge...... I am prepared to learn some more, so let us know what you have in mind!!

Are you a Turbine expert yourself? What is your back ground in such things if I may ask?

Hi andy,

I started a thread that's vaguely related

http://cr4.globalspec.com/thread/18674/Pellet-Powered-Tranportation-conversion

there is a pseudo continuous turbine machine here, scroll to bottom

http://www.ent.ohiou.edu/~urieli/stirling/engines/engines.html

http://www.ent.ohiou.edu/~urieli/stirling/me422.html

http://www.sunpower.com/index.php?pg=15

The Stirling is a reciprocating heat engine that utilizes the Carnot Cycle. There are a number of Stirling configurations that also induce the Carnot Cycle. And there are other Carnot Cycle engines besides the Stirling.

Because Dr Stirling invented the engine before Carnot defined the cycle, many refer to any Carnot Cycle device as "Stirling" cycle.

Without conjecture, I am not sure what you mean by "batch."

"The Stirling cycle is essentially a batch process like the Otto cycle."

No. Not so. It is just a little bit more complex. There is heating of a part of the gasseous fluid (air) in one portion of the machine, cooling in another part simultaneously and there is the ~ 90 deg. crank offset between the two processes. Hence it is the net difference is pressure that affects the movement of the piston. Don't try to make a sow's ear out of a Silk Purse!

Sterling Stan,

Right on -- I had to read down all the comments to find you and your comments. I have given your comment Right On.

That there other Carnot Cycles than Sterling's. You have explained the displacement cylinder to cylinder requirement very succinctly.

soaralone1

an electric motor is a continuous motor. An otto diesel is a pseudo-continuous motor, since it is made of repeated batch transactions. Remember the old one lunger motors, with large flywheels to create a continuous rotary power source from the 1 bang per every other turn. We now have gas/oto engines that are de-facto continuous processes as the contribution of each bath is subsumed into the totality.

Similarly you can make a Stirling do this with more pistons etc.

It will not be truly continuous like an electric motor or a turbine.

they might be able to make a continuous Stirling some day with rotary regenerators etc??

Thank you Aurizon.

You have given a clue as to the next stage i.e. the rotary regenerator.

However,the problem of fluid (gas) carry over would have to be addressed.

So we now have a closed loop as follows : Shaped vaguely like a figure of 8 with the bar of the 8 enclosing the disk regenerator.

Imagine the top of the 8 as the heat input area and the gas circulating in an anti-clockwise direction.

The gas passes through the regenerator which transfers some heat to the right hand side.

It then passes down to the energy extractor (some form of fan/turbine) maybe mechanically or magnetically coupled to the outside to do useable work, which reduces the temp and pressure of the gas. vol. esentially constant.

Possibly add in an expansion valve to reduce temp and pressure further, with vol increase.

So at the bottom of the 8 we have the cold end.

The cold gas passes up the narrower right hand side column through the regenerator ( temp rises,pressure rises, volume stays same)

and into the widening column bending over at the top of the 8.(volume increasing, pressure maybe decreasing slightly, temp. rising), and then repeats the cycle.

I am not totally convinced that the regenerator is not an add-on that was introduced in the original design to make the concept work ie as a fine tuner for a bizarre concept that worked .

Also this design as originally conceived might require a small pump (displacer) using part of the energy generated earlier in the cycle to push the gas back into the hot end, again as a fine tuner for different conditions.

This thread is a good time to vet the notion of the external combustion engine.

With all the interest in green or sustainable forms of energy, the Carnot Cycle (Stirling), when combined with concentrated solar energy generation, fills the bill. Using the high heat of solar troughs, parabolic dishes and power towers can power heat engines without burning anything! Zero pollution.

Those of us working with this technology are somewhat secretive because of the legal gyrations necessary to protect intellectual property. But I think the gentlemen who submitted the question should be encouraged to pursue his hypothesis with experimentation, perhaps somehow splicing an addendum within the closed cycle of the Stirling. I wish him luck; it sounds difficult.

After several years of research into the Stirling I have noted the following: The Stirling had a few years to develop before Faraday brought us induction and the electric motor and it destroyed the economic viability of the Stirling. Today there is a resurgent interest in the Carnot Cycle engine.

The Stirling has two serious problems that need to be addressed:

• piston compression of the fluid (gas) is limited because the chamber is extended
• Heat conduction between the hot and cold ends reduces the efficiency.

A good engineer can solve these problems - Infinia is one). http://www.infiniacorp.com/applications/Prod_Spec.pdf

So much is available on line about the Stirling (as liberally noted and linked above by others who have studied it) that I am jumping off here, not with data and textbook instruction, but with observations from studying the machine, so others may be able to invent the engine that may warm and power posterity without pollution. If one becomes interested in the device the opportunities are manifest.

The financial rewards for success in giving us power when we need it cannot be exaggerated. Net zero energy homes or even net producing homes are the answer to oil dependency and pollution associated with burning things. There are limitless investor resources for those who can demonstrate viability empowering the individual house in an inconspicuous manner.

Googled easily, one can see that there is much research going on in back yards, private laboratories, utility size corporations and government research facility such as NASA and Sandia research centers.

I believe that, right now, one of the biggest problems is the lack of information sharing (because of patent realities) among the nation's inventors. Ranging from toys to simple household gadgets, the Stirling is making money and power in America today. The new Johnson Stirling is turning heat directly into electricity.

The fact that the reciprocating Stirling will run with just one power piston as, colleagues above have noted, is amazing when you compare it to the Otto. Multiple cylinders increase power dramatically but then convection as well as conduction become critical. The real engineering trick is in making the Stirling power to weight efficient.

The Stirling, unlike the violent explosion and heat of the internal combustion engine, runs quietly and with less stress than the Otto cycle, therefore other materials besides metal can be considered as cylinder/piston, E.G. Armature reinforced polished and engineered concrete. To reduce friction, O-rings can be substituted for steel.

Just like all engines, the Stirling is a heat pump; it's closed loop may be opened, but then the Carnot Cycle can be compromised. Still, a work around may be possible if the value of it surpasses effciency.

My experience with stirling engines relates to cryocoolers and the boats in the picture. So I am asking questions as much as exposing ideas.

The phase change in the boat application is what provides the phase angle difference necessary for the cycle to work.

I suspect a closed loop system could be worked out to work using this principle.

Then again, at high speed flows, would a proper venturi design be workeable, stationary waves providing the ''sealing'' of two chambers, or phase angle difference?

Gigaconcepts,

What is the application with the boats? What are the components? Very little seems apparent from the picture and your statements. Presumably some sort of propulsion system. Very curious...... What's the deal?

r/

Sam

Try these links:

http://www.sciencetoymaker.org/boat/JeffBindon.htm

http://www.mptl12.ifd.uni.wroc.pl/papers/36.pdf

http://www.jburroughs.org/science/eknispel/studentpic04/boatmovie.html

I did not find a java applet animation of this type of engine, but I hope it answers your curiosity.

I should have looked further before responding. It seems you are using the cryogenically cooled material as a solid to fuel an open system to convert the expansion of the material (due to change of phase, either evaporation or sublimation or both) to mechanical work. It is and open ended process and not a "cycle" of any type in the Carnot sense of the word. The expanding material makes one pass through the machine and then it is dispersed in the environment.

It is a cute toy (for adults only), or demonstration, but of very limited practical application.

To make it a true cycle a cryogenic refrigeration leg (returning the working medium to its original state) would be incorporated. With existing technolgy this would kill any efficiency the cycle might possess, almost certainly making it negative - requiring more energy input than produced.

Thanks for the demonstration.

I am still curious: what is the engine?

r/

Sam

This is purely an intellectual and speculative concept, and probably not very practical in real life, for now. It may on the other hand help find an answer to the continuous Carnot cycle question.

In a past life, I was able to reduce the power consumption of a mini cryogenic cooler production from 6W to 5W average for a 125mW heat load at 80K. There lies my interest.

Yes, the energy efficiency would be less than 100%, I am not an advocate of any magic energy solutions. Energy sources are abundant for this type of machine.

The expanding material does not need to be at cryogenic temperatures i.e. water, amonia, CFC's ().

If the environnement is small ennough, would it not be considered a closed loop cycle?

Do you mean how to get mechanical work out of the cycle, if it were possible to have continuous gas flow? I hope a way would exist without using pistons and valves... Perhaps a heat pump is enough of an engine.

For the sake of discussion, at micro or nano scale a gas may be viscous enough to replace water in the putt putt boat engine concept.

'The expanding material makes one pass through the machine and then it is dispersed in the environment"

Yes this is true. And I believe that new enthusiasts of the external sourced heat engine ( I don't use the term "external" combustion because of the solar application) should consider opening the fluid loop. Perhaps not to exhaust but to be recycled partially as heat through a regenerator, or as a circulating force. And of course, when there is pressure it can be modified by venturi.