Stirling Engine Question - Glass displacer cylinder

[Steamchick]

Daryl: I suggest the bottom plate (that "sees" the heat source) should be BLACK, or Matt finish, to readily accept the radiant heat from the heat source. (Shiny silver rejects 95% of the radiant heat!).
The Top plate, which is the cool end of the Displacer, should be black as well, but probably insignificant compared to the surface cooling that occurs.
I "hear comments about end plates "as thin as possible", but the difference of conductivity of a 0.6mm plate compared to a 1mm plate of whatever metal is barely worth considering, in terms of heat flow. I doubt if you could measure even a 1 degree difference in surface temperature on a 3mm thick steel sheet in this application....
But a black coating on the bottom of the displacer chamber (that sits on the boiler top) is REALLY worthwhile.
To check it out:
Hold your hand a few inches from the boiler top. Feel the RADIANT heat.
Use a sheet of aluminium foil to make your skin Shiny, I.E. Touch the foil, (stick to your hand with some glue?) and hold it in the same place, and it will not be so hot.
You will then "feel" the difference of a shiny surface compared to another non-shiny colour (skin).
Welders often use a shiny foil thimble on their welders' gloves to reflect the radiant heat away from their digits.
K2

 

[Bazzer]

This one has both cylinders as glass. It runs a treat.

 

[Steamchick]

My engine looks to be about as free running as the Jeroen Jonkman engine video... yet is doesn't run.. Must be something really obvious I am missing.
K2

 

[Bazzer]

 

[Daryl_bee]

Daryl: I suggest the bottom plate (that "sees" the heat source) should be BLACK, or Matt finish, to readily accept the radiant heat from the heat source. (Shiny silver rejects 95% of the radiant heat!).
The Top plate, which is the cool end of the Displacer, should be black as well, but probably insignificant compared to the surface cooling that occurs.
I "hear comments about end plates "as thin as possible", but the difference of conductivity of a 0.6mm plate compared to a 1mm plate of whatever metal is barely worth considering, in terms of heat flow. I doubt if you could measure even a 1 degree difference in surface temperature on a 3mm thick steel sheet in this application....
But a black coating on the bottom of the displacer chamber (that sits on the boiler top) is REALLY worthwhile.
To check it out:
Hold your hand a few inches from the boiler top. Feel the RADIANT heat.
Use a sheet of aluminium foil to make your skin Shiny, I.E. Touch the foil, (stick to your hand with some glue?) and hold it in the same place, and it will not be so hot.
You will then "feel" the difference of a shiny surface compared to another non-shiny colour (skin).
Welders often use a shiny foil thimble on their welders' gloves to reflect the radiant heat away from their digits.
K2

When I say "silver" I mean the metal. It's the 2nd best heat conductor (429 W/m K) after diamond (2200 W/m K - wow!). Copper is only (398 W/m K). Silver will transfer heat to/from the internal air better than any other practical material. I don't think the stove plate (input) needs to be black as the primary means of heat transfer is conduction (maybe on it's inner surface to additionally radiate to the air) however the top plate would be ideally black as it is truly radiating. The displacer itself, of course, should be a non-conductive insulator like, say, grill brick (0.2W/m k).

I finally got an answer from the manufacturer and the issue with glass as the outer cylinder while great in theory is a practical one. With higher performance and the resultant need for higher bolting torque on the retaining screws reliability can be an issue when using glass cylinders as they can crack.

Until then I guess we'll just have to wait for "transparent aluminum" to be invented. ;-D

FWIW I remember 30 years ago SIL-Fosing up a copper still and oxy-welding the steel base for the propane heater. I got more burns doing that project. With steel you could weld a joint and pick it up 6" away from the weld. With copper you'd braze (SIL-FOS) it on one side ( a lower heat process) and just touch it way over on the other side of it's 2ft diameter and you'd have a burn. It was nasty working with two totally different thermally conductive materials. I found I ended up saying to myself "this is copper, this is copper, remember - don't touch, this is copper" every time I worked on it. If in a busy moment you forgot - the lesson was burned into you again as a reminder.