Stirlingengineforum.com

Tom Booth wrote: ↑Sat Mar 23, 2024 9:32 am

matt brown wrote: ↑Tue Mar 19, 2024 11:27 pm If this was LTD model, then PP would be on hot plate. I've found various studies on "hot end" gammas like this (fig. b)


hot vs cold.jpg


Everything else equal (always a risky premise) hot end displacer connection has same efficiency as cold end displacer connection, but a lot more output...

Could you say where that image is from, and/or what you mean by "efficiency" in that context.

I'm trying to get some context for your statement:

"Same efficiency.... but a lot more power"

Does the actual heat input change?

Or in what sense, or in what way can you have "a lot more power" but "everything else equal" yet the same efficiency?

Tom, hot PP vs cold PP is interesting. On my "why Stirling engines have low power and efficiency" thread (or whatever I titled it) I speculate that cold PP gamma is bogus and less efficient than hot PP gamma. But I was way too hasty (behind another similar post for Vincent). Here's the original graphic and later conclusion


Returning to my previous graphic, it all became clear...consider each 100cc DP is comprised of 2x 50 cc volumes. The hot PP model will have two 600k 50cc volumes become two 600k 100cc volumes, but the cold PP model will have one 600k 50cc volume become one 600k 100cc volume while the other 50cc 600k volume becomes a 50cc 300k volume via the regenerator. In this manner, the hot PP model does indeed use twice the heat input of the cold PP model to produce twice the work output.

So, the hot PP model has greater output (and torque) than the cold PP model, but both have substantially the same efficiency (varies slightly depending upon charge vs buffer pressure).

Tom, here's the summary of the 1992 paper by Kentfield that 'started' the hot PP gamma stuff. Many hot PP studies reference this paper, but I can't find it online:


Kinda funny that someone had to due a study on this when some simple graphics would suffice (no doubt, a grantmeister at 'work').