Stirlingengineforum.com

The Vuilleumier device is very similar to a Stirling engine, or Stirling cooler, except that it has two regenerative displacers.

Like a Stirling it has a hot end and a cold end but it is different in that it takes in heat or absorbs heat from BOTH the hot end, as well as the cold end.

So while it runs on heat input, it also acts as a heat pump, removing heat from the cold end, making it even colder. A heat powered refrigerator.

I think it is well worth the time to read the original patent. It can give some insight into what is going on inside a Stirling engine.

https://en.m.wikipedia.org/wiki/Vuilleumier_cycle

The full patent for the Vuilleumier "METHOD AND APPARATUS FOR INDUCING HEAT CHANGES" from the US patent office can be viewed or downloaded here:

https://pdfpiw.uspto.gov/.piw?PageNum=0 ... C275%2C507

The Google OCR version that is linked to the Wikipedia page is badly garbled and virtually or entirely unreadable.

I've been having some difficulty with engineering the connecting rods and trying to keep things balanced.

Having designed an LTD style version, to keep the displacers centered and balanced I decided to have one connecting rod slide inside the other. Both would slide through a sleve.

I found copper and brass rods in the hobby section of the local hardware store. Built an engine/heat pump, but the thin soft metal did not have the strength or the rigidity I would have liked. Today I was trying to modify the engine and accidently bent a connecting rod irreparably. It also has the displacer and other parts soldered onto it, so It would be more work than it would be worth to try and fix. So I'm starting over.

I stopped today at the machine shop, told him what I needed, he had tons of stock metal around, but nothing quite right he would have to order pieces from a specialty place, likely mill them down on the lathe then lap them in with grinding compound for a good fit.

He would need exact measurements for what I wanted. I told him I'd try to work out what I needed.

From there I went to Walmart to reload my debit card to pay for my website when I came across what may be the perfect solution.

The machinist estimated the job would cost me around $100. Mostly for the time he felt it would take, and the close tolerances. It would have to be as light as possible, rigid, fit together with as little friction as possible yet be as air tight as possible. A pretty tall order.

Then I found these:
Need I say more?
They cost like $3 each.

I really don't think for $100 I could have gotten anything custom made as lightweight, rigid and to such close tolerances.

Each one has more tubes within tubes within tubes within tubes etc. than I actually need. I bought extra anyway.

I suppose an old radio or TV antenna might work, but these, although they look like those old telescoping antennas, seem somewhat sturdier. They are made to extend quite a distance, and feel more rugged than a radio antenna though they look and function similarly.

This thread is actually a fork of another, being my Tesla "self acting engine" discussion, but that is no longer apparent.

The contraption I had been working on, showed some slight evidence of trying to work, but was basically a complete failure. I can't imagine why considering the precision engineering that went into it:
Anyway, in browsing the internet I just came across this paper that described a self driving Vuilleumier heat pump, which is essentially what I was working on.

This version however uses a different approach for driving the machine.

Rather than having two displacers and one power piston to drive them, this drive mechanism uses the pressure differential of the cold displacer's connecting rod in a manner similar to a Ringbom displacer. However the displacer is not "free". The connecting rod is attached to the crank and is used to drive the entire machine.

This type of heat pump has only displacers, so driving it takes very little mechanical power. How this heat pump operates is not readily apparent from the drawing:
The image is accompanied by this explanation:

From fig. 2.1 it can be seen that the piston rod in the cold acts as a small power piston as in a stirling engine. The produced power is approximately proportional to the area of the rod. By proper dimensioning of the piston rod diameter in the cold cylinder it is possible to produce adequate power at the desired rotational speed to compensate for the power losses due to frictional pressure drop through the heat exchangers and regenerators and the power losses caused by mechanical friction. An electric motor is therefore only necessary for starting

.

PDF download link:

https://orbit.dtu.dk/files/4485141/Carlsen.pdf

I may actually have seen images of this type of mechanically self driving, all heat driven heat pump previously but just didn't know what I was looking at, assuming it needed to be driven by some outside motor or other driver.