Regenerator for a Stirling Engine

[dave27]

http://ipdl.wipo.int/cgi-bin/ifetch5?ENG+PCT-402002+6+1049922-REVERSE+0+0+1264+BASICHTML-ENG+2+4+1+25+SEP-0/HITNUM,B,NULL+sunstein

REGENERATOR FOR A STIRLING ENGINE

NEW POWER CONCEPTS/Dean Kamen Patent Application

A regenerator for a thermal cycle engine and methods for its manufacture. One method for manufacturing a regenerator has steps of providing a length of knitted metal tape and wrapping a plurality of layers of the tape in an annular spiral. Another method for manufacturing a regenerator has steps of providing a length of metal tube having a tube axis and axially compressing the tube along the tube axis thereby generating a bellows.




-dave

[dave27]

quote:Originally posted by dave27

http://ipdl.wipo.int/cgi-bin/ifetch5?ENG+PCT-402002+6+1049922-REVERSE+0+0+1264+BASICHTML-ENG+2+4+1+25+SEP-0/HITNUM,B,NULL+sunstein

REGENERATOR FOR A STIRLING ENGINE

NEW POWER CONCEPTS/Dean Kamen Patent Application

A regenerator for a thermal cycle engine and methods for its manufacture. One method for manufacturing a regenerator has steps of providing a length of knitted metal tape and wrapping a plurality of layers of the tape in an annular spiral. Another method for manufacturing a regenerator has steps of providing a length of metal tube having a tube axis and axially compressing the tube along the tube axis thereby generating a bellows.




-dave


Anyone make anything of this?? Seems significant to me

-dave

[Blinky]

<<http://ipdl.wipo.int/cgi-bin/ifetch5?ENG+PCT-402002+6+1049922-REVERSE+0+0+1264+BASICHTML-ENG+2+4+1+25+SEP-0/HITNUM,B,NULL+sunstein>>

This link required a user name and password, or there might be something wrong with my system.

Either one is correct :)

[Casey]

quote:Originally posted by Blinky


<<http://ipdl.wipo.int/cgi-bin/ifetch5?ENG+PCT-402002+6+1049922-REVERSE+0+0+1264+BASICHTML-ENG+2+4+1+25+SEP-0/HITNUM,B,NULL+sunstein>>

This link required a user name and password, or there might be something wrong with my system.

Either one is correct :)


User Name - guest
Password - guest

[n/a]

The fact that patent applications for the stirling are still popping up tells us that the stirling is not ready for a reveal.

I hope some expert explains to us the significance this particular patent application.

[dave27]

quote:Originally posted by Lawrence

The fact that patent applications for the stirling are still popping up tells us that the stirling is not ready for a reveal.

I hope some expert explains to us the significance this particular patent application.


not an expert - but here is some info on exactly what the regenerator's function is in the stirling cycle engine...


Stirling cycle
The Stirling cycle is a thermodynamic idealization of an external combustion heat cycle in which the working fluid inside the engine is contained within a closed-loop system. The heating and cooling of the working fluid is achieved through metal heat exchangers, with the fluid never coming in direct contact with the heat source. Key advantages are that none of the internal parts become fouled by the combustion process and that practically any fuel source can be used. An ingenious regenerator helps to capture and use some of the waste heat from a previous cycle to heat the current cycle, making it one of the most efficient engines in use today. The idealized cycle consists of four stages: isothermal expansion and heat addition, constant volume heat rejection into the regenerator, isothermal compression and heat rejection, and constant volume heat recovery from the regenerator.


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http://www.howstuffworks.com/stirling-engine3.htm
The regenerator is a device that can temporarily store heat -- it might be a mesh of wire that the heated gasses pass through. The large surface area of the wire mesh quickly absorbs most of the heat. This leaves less heat to be removed by the cooling fins.

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An important feature of the Stirling is the regenerator to store energy from the gas as it passes through on the way to the cooler (low temp. heat exchanger) and gives energy to the gas as the gas flows back through the regenerator going to the heater (high temp. heat exchanger). It is the regenerator that makes the Stirling Engine.

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An essential feature of the engine patented by Robert Stirling in 1817 was the careful description of the idea of regeneration. In the standard thermodynamic cycle representation of the engine, regeneration is the storing and the reusing of the thermal energy released in the constant volume cooling part of the cycle

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This regenerator can, like the name already says, "regenerate" the air. If the piston goes upward, it is flowed through by warm air and takes up a part of the energy of the air then - it stores it. If the piston goes downward, it is flowed through by cold air now and delivers its stored energy to it. At the same time the wire mesh cools down. The piston helps so to avoid losses of energy. Also because of the regenerator, stirling engines reach excellent efficiencies.

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A heat engine invented by Robert Stirling (1790-1878), a Scottish Presbyterian minister, and his brother in 1816. It is an external combustion engine consisting of a hot cylinder and a cold cylinder separated by a regenerator that functions as a heat exchanger. The cylinders enclose oscillating linked pistons. Heat applied externally to the hot cylinder causes the working fluid in it to expand and drive the piston. The fluid then passes to the regenerator, where it gives up its heat before passing to the cold cylinder to be compressed by its piston. The fluid is then heated in the regenerator before starting the cycle again in the hot cylinder. Although expensive to make, these engines are quiet and efficient. They had a modest success in the 1890s and were revived in the 1960s, using helium as a working fluid. They have not, however, found a practical use.
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important to note also...this patent application says it is specifically for the manufacture of a regenerator for a stirling engine.

-dave

[n/a]

Thanks for the info Dave. Another question I have is: Will the patent application protect the Stirling if they are to put it on the market? I would think that they would have to wait for patent approval before they put it on the market. That could take anothe year or more?

[Casey]

I think "Patent Pending" protects the patent application while it is being approved.

quote: PROVISIONAL PATENT APPLICATION

It is important to get "patent pending" protection for your invention at the earliest possible time to lock in your ownership of the invention. While this once required hiring a patent attorney and spending many thousands of dollars, it now costs $80 – the government filing-fee for filing your own provisional patent application.

The provisional patent application includes a technical disclosure of the invention, informal drawings, and a provisional cover sheet. While some legal guidance is often required to avoid common pitfalls (such as who should be listed as an inventor, how to handle assignments of patent rights, various patent and tax issues, etc.), it is usually possible to obtain this initial protection without hiring an attorney. It also does not require "claims" – the legal language required in an ordinary utility patent application. Since claims are not required, you can prepare the application yourself -- without an attorney.


http://www.inventor-at-work.com/PatentInfo.htm#PROVISIONAL%20PATENT%20APPLICATION

[ftropea]

Again, this is yet another DEKA/NPC Stirling patent that seeks to lock down manufacturing methods for their Stirling engine. It's one thing to create a prototype, benchtop Stirling which is very efficient - however it's a totally other thing to develop practical manfucaturing processes which would allow the mass production of that Stirling for the consumer market. Doing it in mass quantities and at low cost makes something which "would be nice, but it costs too much" and turns it into "everyone 'needs' one of these." "Need" isn't always defined by "life or death" standards, as you know :)

Regards,

Frank A. Tropea

[don c.]

".. a length of knitted (braided?) metal tape and wrapping a plurality of layers of the tape in an annular spiral. Another method for manufacturing a regenerator has steps of providing a length of metal tube having a tube axis and axially compressing the tube along the tube axis thereby generating a bellows."

Along with patent# 6,381,958 from May 7: "The heat exchanger has a set of heat transfer pins each having an axis directed away from the cylindrical wall of the expansion cylinder, or, alternatively, a set of fins substantially aligned with the axis of the expansion cylinder", we have 3 distinctly different heat exchanger concepts. Kamen the engineer is aware that good electrical conductors are also good heat energy conductors. Braided copper cables are commonly used as electrical grounding straps because they have very low resistance to electrical current; they may also work pretty well in heat regenerator applications.

Question: Do three widely different heat exchanger patents equal great flexibility for DEKA in determining their final Stirling design, or do they indicate that they may not be close to a final design decision, let alone a production unit?

[n/a]

quote:Question: Do three widely different heat exchanger patents equal great flexibility for DEKA in determining their final Stirling design, or do they indicate that they may not be close to a final design decision, let alone a production unit?

They are designing the stirlings to be able to use what ever fuel is most widely available. Might that also apply with regard to the materials being used to manufacture the stirlings?

[no1]

Heat exchanger isn't the same as regenerator, in this usage.

The regenerator is a heat exhanger, but the one they're talking about in patent 6,381,958 is the one that exchanges the heat from the fuel source into the interior of the cylinder. The regenerator collects heat from the hot side as the fluid is pushed into the other side of the cylinder, or the other cylinder, depending on configuration.

[dave27]

More info now available on this patent application. Looks like it addresses efficiencies in manufacturing the regenerator.


....


"Stirling Cycle engines have not generally been used in practical applications due to such practical considerations as efficiency, lifetime, and cost, which are addressed by the instant invention."

"In further embodiments of the invention, a regenerator is provided for a thermal cycle engine. The regenerator has a random network of fibers formed to fill a specified volume and a material for cross-linking the fibers at points of close contact between fibers of the network. The fibers may be metal, or more particularly, steel wool. The material from cross-linking the fibers may be nickel. The fibers may also be silica glass and the material for cross-linking the fibers may be tetraethylorthosilicate.

In yet further embodiments of the invention, a regenerator is provided for a thermal cycle engine, where the regenerator has a volume defined by an inner sleeve and an outer sleeve, the inner and outer sleeves being substantially concentric, and two parallel planes, each substantially perpendicular to each of the inner and outer sleeves. The regenerator also has a random network of fibers contained within the volume, and two screens, each coupled to bothe the inner and outer sleeves and lying in one of the two parallel planes, such as to contain the random network of fibers within the volume."

"A regenerator for a thermal cycle engine may be manufactured, in accordance with other embodiments of the invention, by filling a form with a random network of electrically conducting fibers, immersing the form in an electroplating solution, and applying a current between the solution and the random network of fibers in such a manner as to deposit a material for cross-linking the electrically conducting fibers at points of close contact between fibers. Alternatively, a form may be filled with a random network of fibers, whereupon the random network of fibers is sintered in such a manner as to cross-link the fibers at points of close contact between fibers.

A further method for manufacturing a regenerator for a thermal cycle engine, in accordance with embodiments of the invention, includes the steps of forming a reticulated foam into a specified shape, depositing a ceramic slurry onto the reticulated foam, heat treating the slurry in such a manner as to burn off the foam, and sintering the ceramic."

.....

"In accordance with an embodiment of the invention, a three dimensional random fiber network, such as stainless steel wool or ceramic fiber, for example, may be used as the regenerator, as now described with reference to Fig. 3a. Stainless steel wool regenerator 200 advantageously provides a large surface area to volume ratio, thereby providing favorable heat transfer rates at low fluid friction in a compact form. Additionally, cumbersome manufacturing steps of cutting, cleaning and assembling large numbers of screens are advantageously eliminated. The low mechanical strength of steel wool and the tendancy of steel wool to spall may be overcome as now described. In accordance with an embodiment of the invention, the individual steel wires 202, 204 are "cross-linked" into a unitary 3D wire matrix."

There are several more methods of manufacture described in the application.

ANY STIRLING EXPERTS OUT THERE???

-dave

[ftropea]

Wouldn't that be the trick...

Years of tinkering with methods, designs and materials to perfect the regenerator... and the answer all along was right under our kitchen sink. Steel wool!

Regards,

Frank A. Tropea

[dave27]

quote:Originally posted by ftropea

Wouldn't that be the trick...

Years of tinkering with methods, designs and materials to perfect the regenerator... and the answer all along was right under our kitchen sink. Steel wool!

Regards,

Frank A. Tropea


I was thinking the same thing. It would be nice to get some feedback from any technical experts out there on the information provided in this patent application. Hasn't there been analysis done by Stirling experts before on one of these forums?

-dave

[don c.]

Not a stirling expert, but: The use of steel wool in a stirling regenerator isn't new. It may be that Kamen/DEKA have found a way of improving either the heat-transfer characteristics or the manufacturability, or both.

http://www.nasatech.com/Briefs/Jan99/LEW16581.html

http://www.sigmaxi.org/amsci/articles/00articles/garrettp2.html

http://starfire.ne.uiuc.edu/ne201/course/webpages/kieser2/details.htm

http://www.phys.unt.edu/~cordonez/IMECE01.pdf

http://www.qrmc.com/tbo.html

From Darryl Stewart of the Quiet Revolution Motor Company (you may remember him from the 'Stirling expert' thread at TIQ: " Figure 4 (http://www.qrmc.com/tbofig4.html) adds the concept of the regenerator. In his 1816 patent, Robert Stirling called it an "economizer". Regenerators today are made of stacked wire screens, or stainless steel wool, or foamed vitreous material. As the hot gas passes through the regenerator, it heats the regenerative matrix. That is, it leaves its thermal energy in the matrix. When the gas reaches the cold end of the engine it is already most of the way cool, and the cooler only has to finish the job. An instant later the gas passes back thru the regenerator, picking the same energy back up. When it arrives at the hot end of the engine, the gas is already most of the way hot, and the heater only needs to top it off. On each stroke, the thermal energy is traded back and forth between the regenerator and the gas. This greatly reduces the amount of fuel needed, and also reduces the amount of energy thrown away in the coolant."

[don c.]

Please read the entire article at: http://www.qrmc.com/tbo.html if you're interested in Stirlings, and like me, have an enthusiasm for finely crafted technical articles. Excellent reading!

Imagine ghostly quiet, Stirling powered Cessnas...