60L drum medium temp Gamma build

[Fool]

Excellent.

[Tom Booth]

Any further progression this project?

[VincentG]

Yes, though I didn't think it was worth a new post yet. I have started making the displacer and working out the displacer rod connection into the drum.

60l gamma displacer 1.jpg (231.71 KiB) Viewed 6758 times

The displacer connecting rod will pass through the top of the drum using a big block Chevy valve guide, which has an ID of 3/8". This will allow the use of a valve guide seal and readily available 3/8" rotary shaft. I think I will machine a nice holder for the valve guide but it could easily be affixed with 2 part epoxy.

[Tom Booth]

That one enormous displacer!

What kind of heat do you intend putting to this?

I'm kind of worried about using pink foam board though. That stuff burns like gasoline and melts into a black goo that can be hard to put out of it catches fire, and it catches fire pretty easy.

[VincentG]

That's a good point, I'll be careful. Luckily I think the fire would run out of oxygen in the chamber and self extinguish.

The displacer is not even as big as it will need to be yet lol.

I plan on running it off the waste heat of a small engine exhaust so figure around 600F. The bottom of the displacer will be made from a more heat resistant material and there will be ample radiant heat shielding. If need be, I can add some simple active cooling of the displacer from the cold side.

I'm lagging this project a bit behind the LTD development so I can implement what I learn from that.

[VincentG]

Finally got around to ordering a type 36 air chamber. This engine will now be built around a low temperature diffential to make use of the large volume of the displacer chamber and foam displacer. At first I'll see if I can mimic my early long stroke LTD specs of a 1:9 power piston to displacer ratio. In this case it will be roughly 2 liters to 18 liters.

The little LTD was easily able to reach the zero point on boiling water so we'll see what applied temperature diffential it takes to get the big one there.

Based on my current theory of operation, with a 30k-100k cycle, the engine will only contain about 8.8 liters worth of standard atmospheric air. So theoretically when cooled down it will have quite a vacuum inside if there is no manual valve installed. In practice a manual valve will be needed, assuming the diaphragm based design can remain 100% air tight.

[VincentG]

Total blunder on my part as I was running Celsius numbers but in Kelvin lol! That's what I get for rushing during my break. Ill update later with the real numbers.

[VincentG]

Ok with the correct 300-373k cycle the starting volume is closer to 16.5 liters. So still a vacuum.

These engines never stop with the surprises however. Using a 1 to 2 pp to dp volume ratio closer to the Koichi LTD, things get even better. Even more pressure gain available and far far less gas to heat and cool. Displacer stroke is reduced from near 6 inches to only .5 inches, keeping the heat exchangers much closer to the gas. He was really on to something back then. Just a bit lacking in heat exchanger layout IMO.

[VincentG]

Quick update on the new dimensions of the LTD 60l drum engine. The whole middle section has been removed and only 3 foam discs will make up the displacer now. Displacer swept volume will start at 4 liters and be reduced from there based on testing. The displacer in this picture is positioned as it will sit on the hot plate, with the area below that filled in with concrete. I'd make the drum even shorter and use less concrete but it's much easier to weld a lap joint from rib to rib than the straight section of drum. The 13" diameter displacer will sweep 2"(yea made another mistake in the last post) to displace 4 liters. The displacer will have either aluminum or copper foil both top and bottom to double heat exchanger area.

Although I gamed a 300-375k cycle, actual external temperatures will be closer to 285-395k. Thats 50f to 250f.
Estimated heater and cooler dead volume is zero. Estimated neutral space dead volume is .32 liters.

ltd 60l gama.jpg (199.65 KiB) Viewed 4904 times

[skyofcolorado]

Marvelous progress, I bet it feels good to have some parts coming together. It's certainly motivational for me to see it progressing.

Looks like a steel drum, but aluminum cooling fins? How did you weld those?

Does that seem like enough cooling, or will you be adding more fins?

How will you concentrate and isolate the applied heat to the hot end so as to avoid heating the cold end?

[skyofcolorado]

I'm kind of worried about using pink foam board though. That stuff burns like gasoline and melts into a black goo that can be hard to put out of it catches fire, and it catches fire pretty easy.

There are different kinds of foam board, some that burn, others not so much. Could be additives to meet fire code or something.

I have a painful memory of using some foam board to mold the inside of a cast rocket stove with a somewhat complex path of inlet air and combustion products. I figured that I could just burn it out after the refactory material cured. I ended up busting it apart and starting over because even a mapp gas torch wouldn't degrade the foam, nor would any of the solvents like acetone, mek, or xylene.

That stuff would have made a pretty robust displacer. I think it was a yellow color, not the pink or blue stuff.

[VincentG]

Marvelous progress, I bet it feels good to have some parts coming together. It's certainly motivational for me to see it progressing.

Looks like a steel drum, but aluminum cooling fins? How did you weld those?

Does that seem like enough cooling, or will you be adding more fins?

How will you concentrate and isolate the applied heat to the hot end so as to avoid heating the cold end?
Top

Thank you. Most of this I covered in the opening posts, the fins are steel and are only to secure the cold plate down with springs to apply even clamping force with no distortion, as well as a high pressure blow off if needed for some reason. The cooling will come from the aluminum top plate that I will make. I'll also have provisions for a fully insulated top plate to test some of Tom and Matt's theories on self-cooling.

The tubes welded through the bottom are to provide hot water to the heater exchanger that I will fabricate. The tubes are long enough to pass through the 5 or so inches of concrete that will be used to reinforce the bottom and provide a thermal break to the metal drum. The interior of the drum will be lined with insulation to avoid temperature transfer to the gas while it is moving past the displacer. The tubes and bottom of the heat exchanger will also be wrapped in insulation plus a radiant barrier to minimize heat leakage to the concrete.

I've been experimenting with heat shielding of the foam displacer at the hot end to raise the allowable temperature a bit over the melting temp of the base foam(whatever it may end up being). It seems effective so far.

[VincentG]

Running some quick and dirty numbers with PLAN/33,000. 2(psi)x12.56(L x A)x1300(650rpm x2) If I use the full displacement of 2.5 liters, can reach 650RPM, and a M.E.P. of only 2psi than this thing could make 1HP. That may not sound like much, but a continuous 1HP is a significant amount of power, and at that RPM we get an earth moving 8 lb.ft of torque(lol) compared to the average 1HP small engine's 1.5 lb.ft at 3600RPM.

[VincentG]

Made some progress on this build.

The chamber welded to its final size. Volume ratio is still to be determined after some displacer chamber testing.

welded chamber.jpg (173.2 KiB) Viewed 208 times

The concrete poured in the bottom, and the pipe flanges that will bolt to the heat sink. There was ample space left between the concrete and the heat pipes that will be filled with insulation.

concrete bottom.jpg (249.94 KiB) Viewed 208 times

The heat sink was cut from two sheets of 1/16th stainless steel. I then bent the edges around both and welded them together, leaving roughly a 3/8" gap for hot water to flow through. The center of the sheets has a bolt welded to prevent the plates from flexing. Then shop air was used to expand the plates outward a bit and create a slight convex shape that should keep it from deforming with oscillating chamber pressure. The plate will be bolted to the pipe flanges and sealed with silicone. The exchanger was pressure tested and should be leak free.

welded heat exchanger.jpg (171.92 KiB) Viewed 208 times

The heat sink mocked up in the chamber. There will be insulation on top of the concrete, allowing for a small air gap to the heat sink so both sides of the sink will effectively heat the air. The surrounding insulation will extend above the heat sink so the displacer will effectively seal off the heat supply when at the bottom of it's travel. There will then be a reservoir of hot air at the ready when the displacer lifts.

heat sink in chamber.jpg (157.27 KiB) Viewed 208 times

That's all for now. I'm pretty excited to see how far I can push this design after some chamber performance testing.

[matt brown]

Running some quick and dirty numbers with PLAN/33,000. 2(psi)x12.56(L x A)x1300(650rpm x2) If I use the full displacement of 2.5 liters, can reach 650RPM, and a M.E.P. of only 2psi than this thing could make 1HP. That may not sound like much, but a continuous 1HP is a significant amount of power, and at that RPM we get an earth moving 8 lb.ft of torque(lol) compared to the average 1HP small engine's 1.5 lb.ft at 3600RPM.

(1) wow, size does matter - lol

(2) indeed Koichi was onto something and I agree that his regen scheme was a very bad idea. His thinking was likely that regen was more important with a low thermal ratio despite increase in dead volume. At least he chose a DP/PP ratio that was more realistic than LTD model.

(3) various guys have tried this with full sized drums, but these larger drums are more sensitive to PVT values than your smaller drum due to Pmax rupture. Your approach with smaller drum is better and allows more gaming PVT values within same safety margin. Most guys don't grasp this volume issue until gaming PVT values, whereupon they usually shelf their drum scheme.

(4) kudos on your "high compression" LTD idea (like Koichi) since for any given thermal ratio, increasing the volume ratio simply increases the power output as if by magic (eyes roll).

(5) the conv'l snag with low compression SE (all types) has been what scheme is capable of more than 2:1 volume ratio ??? A dwell scheme allows much higher volume ratios AND clean phasing, not to mention a decrease in any/all regen issues.