60L drum medium temp Gamma build

[matt brown]

Golly Matt you sure have tons of goodies up your sleeve.

long sleeves...

At least this drum build will be relatively easy to change/modify.

Indeed, this config is very flexible AND low tech. I've always subscribed to the KISS theory and clueless why so many guys chase pie-in-the-sky 'solutions' that offer little beyond different.

My continued beef is that the more ideal the cycle gets, the less ideal the implementation gets.

The challenge is to integrate a thermal cycle with the appropriate mech and avoid the typical nonsense common to nearly all ECE designs (typical SE and PTO crap).

My current realization is just how damn fickle the gas is, especially at these low temperatures. Although I guess the reservoirs do well at keeping larger volumes of gas at the right temperature.

The gas is only fickle when it doesn't do what we want, like slow heat transfer rates and low dP that limits cycle rate. Reservoirs have pros and cons that require careful consideration. Yep, these buggers are in a league of their own and most guys are oblivious to their issues.

Maintaining gas temperature throughout the cycle is like trying to steer butterflies down a path, when they can barely fly straight on their own.

But then Chuang Tzu asked himself the following question: "was I Chuang Tzu dreaming I was a butterfly or am I now really a butterfly dreaming that I am Chuang Tzu?"

single DP res.png (8.58 KiB) Viewed 2128 times

I don't think that THIS reservoir scheme will work and that the HP res will quickly 'drain down' to LP res. The problem is the variable reservoir volumes during the DP 'valve' action vs previous low profile 'tin can' version. If this double DP res scheme did work, then a single DP would simplify scheme (albeit less eff) and converge on the more familiar...

res w valves.png (3.24 KiB) Viewed 2128 times

where displacers have evolved into distinct valves.

[VincentG]

I am making significant changes to the chamber. The drum lid is unfortunately not flat enough to seal well against the displacer, so instead of just reinforcing it, it will be replaced with a plasma cut 3/16" steel plate and then bolted down to a flat flange instead of the v-band connection. A flange ring will then need welding to the chamber.

A recent test has shown that only 1 inch of XPS foam is more than sufficient to serve as a displacer. After 20 minutes, the top surface of the displacer only increased 5 degrees F. This will allow 7 inches of height to be removed from the chamber walls and displacer sides, drastically reducing unheated/cooled surface area.

Starting temperature was 80F.

60l drum 1 inch displacer test.jpg (215.49 KiB) Viewed 2030 times

[matt brown]

Each configuration is a mixed bag of pros and cons. The drum style tends to favor a simple LTD style displacer. Your scheme raises the bar with

(1) displacer nearly abutting at least one end of case
(2) driving means providing at least one dwell
(3) spring might solve common inertia work loss of displacer
(4) displacer likely requires counter balance (did Koichi use such???)

Basically, this design uses the displacer as a valve, whereby a more regulated cycle is achieved. Xlnt idea, but tricky to implement practically. I think the biggest downside to this scheme is the massive displacer relative the output potential. I think you're on the right track to shrink your displacer size, mass and 'stroke' (or whatever geometry) while increasing the working volume ratio (aka compression ratio).