Greetings and a few Q's

[Corey872]

Greetings all -

Been lurking for a bit and gathering tons of info. Thought I'd finally sign up in hopes of kicking off my new project. I'd like to drive my wood stove blower off a stirling engine. This will be the actual blower moving air through a shroud and out into the room - not the typical stove top fan. Seems like a natural fit...hotter stove means faster fan, colder stove, lower fan...stove burns out, fan stops.

My main concern is a) getting enough power and b) noise. I think power should be OK. The blower right now is ~80 watts, so that is the rough stirling design power. The stove top typically runs 400-500F an sometimes up to 800-900F. I don't have a problem cutting a hole in the stove top and fitting the bottom section of the displacer cylinder so it can actually be 'licked' by flames inside the stove. I can also braze a set of fins to the cold side to really move the heat out. So 800F hot side, room temp cold side should be a fair dT.

The big concern is noise. Every post I see talks about how quite a stirling engine is. Every video I see...clack!...clack!...clack!...clack! One video the guy even remarks the stirling sounds like a 2-stroke gas engine! This will be pretty much unacceptable for an engine on the stove in the living room. I intend to run nice bearings, bushings, balanced flywheels, watch the displacer clearance, etc. Plus, I'm looking at some low speed / high torque designs which should run pretty slow and hopefully quiet. But then I'll be geared up to run a squirrel cage blower at a decent speed...maybe 250 at the stirling and 1000-1250 at the blower.

So the main question to those who dream stirling...can an 80-100 watt engine be built to run quiet given a 800F hot side and room temp cold side? Side question - if there is noise...where does it come from? Displacer hitting the cylinder? sloppy bearings on the pistons/con-rods?

Thanks for any additional insight!

Corey

[Ian S C]

Cory, have a look at the thread called "woodburning Stove-Top school project", its on the same subject, more or less. Ian S C

[Corey872]

Thanks - I've been watching that thread closely. Though I think that design will be a little different. Seems like he is wanting something to set on the stove top and run relatively fast to spin fan blades. But will be interesting to see the projects come together.

[fullofhotair]

If you use the squirrel cage fan I think that will be a first. I have at least never seen a centrifual fan being powered by a stirling engine. Are you making the fan or are you using one off the shelf? if you get it up and running I sure hope you make a video or at least take pics.Id sure love to see it.

[Corey872]

I will probably buy one or maybe find on at the scrap yard and clean it up if possible. The main issue is the hottest part of the stove being nearly front and center of the top steel sheet. But the cold air needs to be pumped into the back, circulate forward to be blown out into the room. I guess I should clarify this is actually a 'fireplace insert' which is basically a wood stove enclosed in a second steel box.

I can build the stirling engine to be nice and pretty...stainless steel, brass, shiny flywheels, etc - and really like watching all the linkages, rods an flywheels work. But not much I can do with a blower! Plus putting it somewhere near the back side will cut down some of the noise.

[Ian S C]

On the 2.5 cc motor in my album I fitted a centrifugal blower on the crankshaft, with a shroud made of heavy cardboard, directing the air over the cold end of the displacer cylinder, I took the water hopper off, and got more power with that, than with the water cooling, it kept the temp to about half of what it is when water cooled.
For an effective stove top fan, 2watts works OK, 5 watts, and it will be an annoyance, creating too much air movement. As an experiment I fitted a disc behind the fan, with magnets, and mounted two coils next to them , and generated about 4 volts, and was able to charge a pair of Nicad batteries, while still having a fan. Ian S C
ps;most of the noise comes from the connecting rod bearings, the clearance for our size bearingsshould be around .0005" for anything less that 1/2", and that would be most motors on this site.