Big Beta Stirling 1kw, 100degC to 400degC

[Bumpkin]

Vamoose, your post is a very important subject to some of us - maybe you could start a new thread or add it to Soeren's "DIY rubber bellow as power piston" if he wouldn't mind, so we could expand on it. I'd love to see a collection of the many ideas for home-built diaphragms, bellows, roll-socks, etc. I'm even currently messing with a bicycle tire for a rim-type bellow of a pancake Beta. (Partly inspired by your comments of radiant transfer to the displacer.) Bumpkin

[zhivko]

Sealing fixed. You can see video at:
Big beta stirling engine (sealing fixed)

Fix one thing broke another :) That weird noice you can here is displacer touching hot cylinder. This is because the displacer rod is welded at slight angle to the base of the displacer.

[zhivko]

Talked to the guy who do wire electric discharge machine (EDM) and found out, that price for slicing such big cylinder with edm would be enormous - cca. 8000€ for all 3 parts.
This is for sure price overkill for the engine I am aiming - such machine would take a lot of years of running for it to pay off.

[Ian S C]

What you need is a shaper, with a narrow (similar to a lathe parting tool), tool. Some form of indexing, and a lot of time. The more expensive methods of manufacture can be justified when you start production in large numbers. Shapers can be bought secondhand (I don't think they are made now), and do not cost too much, nothing like the price of a milling machine. Although I don't have one myself, it's one of my favourite machines, and although its slow compared with other machines, its good for prototype production. This will form the narrow slots you require. You do of course stand a chance of borrowing a machine (you can't take it home to use, it will be at least 1/2 a ton). Ian S C

[zhivko]

Thanks Ian for idea,

also shaper would be expensive operation (or renting it) if I compare it to idea that I mentioned earlier in my post:
http://stirlingengineforum.com/viewtopi ... t=30#p4992

For that exchanger I would need to cut rectangular pieces of stainless steel (can be cutted with ordinary metal saw, although cutting 260 piececes would take long - but surely not as long as EDM would require it) and fix them in equal spacing by a ring that would be laser cutted.
The issue with this exchanger is that must fit tightly to inner cylinder wall.

I have an idea that if I make laser cutted ring (opened in one side) a little bit wider than cylinder inner diameter, and also ex-centric regarding cylinder inner diameter, this would cause tight contact with cylinder wall when exchanger is inserted into cylinder (it would act like a kind of spring).

[Bumpkin]

Here's a notion possibly only of entertainment value: For a big low pressure slotted chamber; form a length of sheet into continuous facing folds, then pull it around and weld the seam so the finished chamber looks sorta like a pleated round air filter. Bend for parallel air-slot sides facing in, and "V" shaped slots facing out. The bore could be fine-tuned by the size of external reinforcing rings - nothing need be welded until it's right.
It'd take some fiddling and you'd have to figure how to make accurate short folds, though accuracy wouldn't be so critical if you fit it around the displacer with an appropriate shim before welding the external rings on. Dunno how to make those bends though.
Bumpkin

[zhivko]

Thanks bumpkin - had my brain in red area last few days and that is what it came out :)

Heat exchanger acting as spring will hopefully push lameles (rectangles 25mm x 3mm x 250mm for hot exchanger) to the cylinder wall. Lamels would be welded only in two endpoints of each lamel to the stainles steel 2mm pipe. Place between exchangers would be filled with steel wool.

Hot heat exchange area: 1,70 m^2
Cold heat exchange area: 1,39 m^2

dead volume of heat exchanger: 1,80 lit
dead volume of cold exchanger: 1,44 lit
dead volume of regenerator: 2,38 lit

Whole volume of air inside engine is 9 lit.

Mass of whole part is 43 kg.

1) Maybe sombody more experienced with little better filling for those numbers (dead volume to air volume ratio) could tell if numbers are reasonable?
2) Also another question - what do you think of idea to use corrugated plate instead of flat stainless steel for lamellas? See picture of corrugated plate in attachment (corrugated_sheet.jpg) - I think I can use half of lamelas in that way since corrugation causes better heat transfer.

Comments - critics - improvements - anybody? :)

c:\Work\Klemen\Stirling2.1\HeatExchangerAss_dwg.png

HeatExchanger.jpg (193.7 KiB) Viewed 6631 times

[zhivko]

Hey guys,

I've been playing around with silicone bulbs and have been using them in a double acting alpha configuration (so far with limited success. But am getting some positive momentum (and hoping for some more)).



The right kind of silicone compound can tolerate some decent temperatures up to and above 300 deg C. Also they have very low friction with certain textured materials and/or smooth surfaces, and seem very flexible.

For example- the compound mix they use for oven trays.
Not sure how much more they will tolerate above 300C, but some may, and seem to remain stable??



There are a lot of different type and size oven (silicone) trays available. Maybe it might be worth a try to scrapyard and cut some of them up, to experiment around with, for a loose fitting seal??
Just a school-yard suggestion, don’t take it too seriously.

vamoose

p.s. i don't recommend the Pink ones specifically, i just happened across them, ......'honest'..

What's the friction of silicone on stainless steel 1.4301?
Which silicon is 300degC resistant? Compound name? Mixture? Product name?

[vamoose]

Hey zhivko,

I can tell by your 'very stunted' questioning that i should leave your thread alone.
Good luck with your project!

vamoose

[zhivko]

Hey zhivko,

I can tell by your 'very stunted' questioning that i should leave your thread alone.
Good luck with your project!

vamoose

Sory, but I don't quite understand you. How do you mean stunted ?

[Geoff V]

Zhivko

From what I have seen so far of the #14 engine by Peter Lynn, my best advice to you would be to recommend you delay spending money on fancy heat exchangers and develop the engine you already have.

From your video, I suspect your engine is suffering from too much friction and would benefit from more careful assembly, the air cooling is probably quite inadequate and I'm sure there is room for significant improvements to the heater. Because your displacer is rubbing on the casing, the gap must be zero on one side and twice as big on the opposite side which will reduce the heat transfer within the engine.

I have also recently learnt, from a friends engine, that departing from a true sinusoidal piston/displacer motion can be very detremental to the performance, may I suggest you look carefully at the CAD plot of your kinematics.

GeoffV

[zhivko]

Zhivko

From what I have seen so far of the #14 engine by Peter Lynn, my best advice to you would be to recommend you delay spending money on fancy heat exchangers and develop the engine you already have.

From your video, I suspect your engine is suffering from too much friction and would benefit from more careful assembly, the air cooling is probably quite inadequate and I'm sure there is room for significant improvements to the heater. Because your displacer is rubbing on the casing, the gap must be zero on one side and twice as big on the opposite side which will reduce the heat transfer within the engine.

I have also recently learnt, from a friends engine, that departing from a true sinusoidal piston/displacer motion can be very detremental to the performance, may I suggest you look carefully at the CAD plot of your kinematics.

GeoffV

GeofV,

surely you have right about that improvement can be done by preventing rubbing against cylinder wall, but regarding cooling I have doubts - If I could steel hold the bottom of cylinder with my bear hand - I don't think I need to increase heat drain.
To drain something you firstly need to put in "something". That "something" being heat in case of SE.

Thanks,
Zhivko

[Geoff V]

Zhivko

I agree with your comments regarding the cooler, at the moment, but with improvements to the heater and a concentric displacer to aid the heat transfer the next problem is likely to be the lack of water cooling.

I understand that Peter realised a significant power increase (170 to 260w) on one of his engines by simply changing the gas jet to a smaller size which achieved better combustion and therefore a hotter flame!, he also realised a similar increase with another engine by just insulating the combustion chamber.

With these engines the 'devil is in the detail', carefull assembly, good sealing with minimal friction are essential.

GeoffV

[zhivko]

I plan to add water cooling later as soon as it would be obvious that bottom part is overheating.

I think I am ready for next iteration. If somebody knows what material should I put for regenerator - the SE should operate from 80-400degC. Should it be fine steel wool, or more this like SS mesh? If yes which thicknes/granularity?
When I would stretch open exchanger sleeve in hot cylinder (hopefully with kind of wedge) - I don't want to change regenerator to often. Therefore I hope to guess right regenerator material from my first try.

I additionally placed another ptfe sealing in displacer - that one should be OK below 250 degC.

Another thing that I have in my mind is - how to prevent heat to penetrate through displacer to the cold side. Maybe with a kind of ventricles? What do you think?

Here is what I have:

Stirling2_1.png (176.06 KiB) Viewed 6546 times

[zhivko]

Made some progress, if somebody is interested - I am doing my best to implement so called "low cost slotted heat exchangers".

The inner pipe of exchanger came to have "only" 0,5mm difference in roundness. After grinding I expect to be even lower.

Here are some pictures:

New displacer

IMG_20130323_122959.jpg (27.67 KiB) Viewed 6511 times

Regenerator

IMG_20130401_183915.jpg (16.12 KiB) Viewed 6511 times

Heat exchanger ribs

IMG_20130401_204945.jpg (17.39 KiB) Viewed 6511 times

I'll keep you informed in difference in efficiency.

Regards,
zhivko