Low delta T : Light materials ?

[Bill-W]

Hello,

Am trying to understand some basic stuff.

Would it be more appropriate to use very thin light materials to build the 8" diameter main cylinder for a low delta T engine such as aluminium plate 0.060" for top and base and thin plastic soft drink bottle plastic for the cylinder walls 0.030"(estimate I know its much thinner than the plate)

The way I see it : heavier materials would simply absorb heat and the engine would never run but just get slightly warmer by sitting on the palm of my hand ?

Am I being a bit simplistic here ?

Bill

[Ian S C]

I presume you mean the displacer cylinder, yes to the aluminium top and bottom, but the side/the cylindrical bit in between needs to be quite ridged, my motor has a bit of 6" plastic water pipe, with a wall thickness of about 3/16" thick. The top and bottom plates are joined with twelve 5 mm nylon bolts, use non metallic means of attachment to reduce heat conduction bottom to top. The aluminium discs that I used are the bottoms of a couple of frying pans I found in a skip. 0.060" on a 8" disc would probably be too flexable.
Ian S C

[Bill-W]

Ian,

Thanks for the reply.

The way I visualise it as long as there are some sturdy screws holding the top and bottom plates then the cylinder wall need not be too rigid all it has to do is enclose the space that the displacer occupies whilst it is moving up and down.

Why does it need to be rigid ?

I appreciate your point about the material that the screws are made of - thanks - I would not have thought of that. I may try some very thin wooden dowels (size of 3-4 matchsticks) and glue.

Am fascinated by this and looking forward to having a go when I understand things a bit better.

Regards

Bill

[Aviator168]

Bill, it is important for the cylinder wall to be a bit rigid since you need to hold the plates down AIR TIGHT. Even though it's a low temperature engine. If the pressure differential is 0.1 lb/in^2, the pulling and compression forces of the plates might be significant. Would be up to a lb depending on temperature differences, and the pulling and compressing happens a few time per second.

[Ian S C]

To hold it together, you could use wooden blocks/bits of dowel, or plastic rods and small screws.
Ian S C

[Bill-W]

Ian S C

Bill, it is important for the cylinder wall to be a bit rigid since you need to hold the plates down AIR TIGHT. Even though it's a low temperature engine. If the pressure differential is 0.1 lb/in^2, the pulling and compression forces of the plates might be significant. Would be up to a lb depending on temperature differences, and the pulling and compressing happens a few time per second.

[/quote]To hold it together, you could use wooden blocks/bits of dowel, or plastic rods and small screws.
Ian S C[/quote]

Thanks for the advice will proceed beariung these things in mind.

Bill

[Ian S C]

Just a little note; if you don't feel like making a foam plastic displacer, there's nothing wrong with making it from Balsa wood, it's grain needs to be sealed, and the interior divided up with ribs to stiffen it.
Ian S C