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I didn't even get to put on my tie...

March 22, 2007 11:44 AM

Not that I’m all that enamored of ties in the first place but having one machine down when you walk in the door and another go down while you’re working on the first makes for a busy morning.

I hate when things happen like that but if you recall I did say that my plate needed to be more full. I guess I just didn’t mean in this direction. :-/

Still pondering Stirling engines. I’ve figured out some things and really want to build one. Since the tin-can version is fairly simple and cheap I might try that first. Though I could probably make an effective one from copper plumbing parts if I shaved things down and was careful about weight.

Here’s another weird thought. Why can’t you make a completely ceramic Stirling engine that you could put in the magma of a volcano. I wonder what material it would take to be able to withstand the heat of the molten rock. Once one of those is constructed I can’t see it not being cost-effective to run. I mean you’re running off the internal heat of the planet at that point which is for our current purposes almost endless.

Got some cheap copies of the “miser” style Stirling engines on the way from a guy off E-Bay. That’s the model that runs off a differential as low as the heat from your hand or a cup of coffee or sunlight. I think that’s got some potential for a sunlight based charger for batteries. Actually you could likely charge batteries using the differential between the inside and outside of your house and get something running that way.

There are a lot of options with this technology. Victorian era technology is may have been but it’s being updated at a rapid pace and is quite good at what it does and can be made from locally available materials pretty cheaply. And unlike solar cells it requires nothing but some good metalworking skills to create and sometimes not even that depending on the design.

Lots of opportunities...




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Comments

( 2 comments — Leave a comment )
(Anonymous)
Mar. 23rd, 2007 01:02 pm (UTC)
"miser" stirlings
Stirlings are awesome and have a lot of potential for low tech, locally produced power, as well as larger scale applications.

A couple of notes:

According to thermodynamics, the maximum theoretical efficiency of any device producing power from a heat differential is given by:

1 - [(temperature of cold side, in Kelvins) divided by (temperature of hot side, in Kelvins)]

or an easier to read version,

1 - (Tc/Th)

For example, taking 300K as room temperature and 310K as body temperature, a stirling engine running of the heat of your hand can, at most, be 3.2% efficient.

This means that "miser" models will only ever be viable as models, because their maximum efficiency is dismal. In order to get maximum usable power from a solar powered stirling, one objective is to concentrate the sunlight as much as possible in order to increase the temperature, and thereby the amount of power that can be extracted from a given amount of sunlight.

Also, if you were to run a Stirling off of the temperature differential between the inside and outside of a house, it will tend to equalize the temperature difference. If that temperature difference were created by a powered device, then the load on the powered device will increase and there will be no net gain.
nimitzbrood
Mar. 23rd, 2007 01:23 pm (UTC)
Re: "miser" stirlings

This means that "miser" models will only ever be viable as models, because their maximum efficiency is dismal. In order to get maximum usable power from a solar powered stirling, one objective is to concentrate the sunlight as much as possible in order to increase the temperature, and thereby the amount of power that can be extracted from a given amount of sunlight.


I actually know this already but thanks. I was planning on putting one of the stick-on fresnel lenses on the window then setting up the stirling/charger at the focal point just to see how much I could get out of it. This is all theorhetical anyway as I don't have the misers yet. (The post is mis-typed, I ordered plans not the $29 Gakken misers that abound on E-Bay.)

Also, if you were to run a Stirling off of the temperature differential between the inside and outside of a house, it will tend to equalize the temperature difference. If that temperature difference were created by a powered device, then the load on the powered device will increase and there will be no net gain.

Some of us have a fair amount of computers that generate surplus heat. ;-) And like I said this was only theoretical at this point. If it were used with the surplus heat of the systems in the winter to charge UPS batteries that would be ideal. But I'm a long way off from doing anything like that.
( 2 comments — Leave a comment )

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