Can Polystyrene Withstand the Heat in a Stirling Engine Displacer?

[UnitedMi]

Hey Guys,
I'm working on a Stirling engine to show my nephew. I have made one before that runs off off coffee water but now I'm planning on making a system which will use a heat source around 90-125°C and I do not know if polystyrene will melt or not. So if you guys have any suggestions for a displacer please let me know.

 

[jambaugh]

You haven't given much info to narrow down the possibilities. You could use aluminum, diamond, carbon composite, teflon, depleted uranium, glass, ivory, ... Is cost an issue? Is weight? (of course they always are but to what degree?) What's your design, what's your primary concern?

My first instinct was to suggest aluminum. Indeed you might be able to make a pretty good displacement piston by tightly compressing wadded aluminum foil with a bit of epoxy to bind it together. You could lighten solid aluminum by drilling out holes along the shaft and filling with brass or copper wool.. (to act as regenerator).

 

[Sanky123]

One thing

why stirling engine is not replay as domestic engine for automobile

 

[jambaugh]

I do recall pictures of Stirling automobile prototypes from back in the 70's however the big issue is power output for size. Stirling engines, though efficient with regard to converting heat to work, are notoriously low powered devices for a given size. It is a matter of the pressure differences involved which are inherently low give the nature of the engine.

 

[Sanky123]

I do recall pictures of Stirling automobile prototypes from back in the 70's however the big issue is power output for size. Stirling engines, though efficient with regard to converting heat to work, are notoriously low powered devices for a given size. It is a matter of the pressure differences involved which are inherently low give the nature of the engine.

Ok...?,
issue is only power output for size.

can we overcome that problem and use this for domestic purpose ?

 

[jambaugh]

The short answer is "No". The "problem" is inherent in the method. You are using hot gas's pressure difference. You can design a pressurized version with better working gas but it still is not going to reach pressures comparable to IC or steam engines. With that low pressure you need a larger cross section for the work piston and/or more speed. Speed though is limited by the rate of heat flow into the work gas. To increase area you will increase the size of the engine. Ultimately "fixing" the problem will be a matter of designing something that is no longer a Stirling engine or one of its hot air cousins. It will be something qualitatively different like a gas turbine, quasiturbine or DynaKinetic(tm) engine. But in each case there would be a choice of Stirling mode and internal combustion mode with the latter being inherently more powerful. At some stage the Stirling type engines must rely on diffusion of external heat into (and out of) the working fluid, an inherently slow process.

Internal combustion (or other form of heat generation) is exactly the magic solution to this. Generate the heat at the place where you want it. Even if you're using say nuclear power, you would be better off (in terms of power per size) with gaseous nuclear fuel in say a gas turbine or rocket than using heat exchangers and a separate turbine or Stirling engine.

However there were very early very successful uses of Stirling engines were for pumps in remote locations. See for example http://en.wikipedia.org/wiki/Rider-Ericsson_Engine_Company.

Finally I would assert that for a revolutionary new improvement you should look to better electric generation. Something like the liquid metal anode, solid electrolyte fuel cells (http://www.netl.doe.gov/file%20library/events/2008/seca/posters/Thijssen.pdf) that can burn any reducing fuel (coal, scrap lumber, biofuel, lawn trimmings...) and can potentially be more efficient than a perfect heat engine given they are directly converting chemical energy to electricity. Major corporations are already using them (http://www.datacenterdynamics.com/focus/archive/2012/06/ebay-goes-second-bloom-box-installation) and we should see household units in the next couple of decades (imnsho).

 

[Sanky123]

The short answer is "No". The "problem" is inherent in the method. You are using hot gas's pressure difference. You can design a pressurized version with better working gas but it still is not going to reach pressures comparable to IC or steam engines. With that low pressure you need a larger cross section for the work piston and/or more speed. Speed though is limited by the rate of heat flow into the work gas. To increase area you will increase the size of the engine. Ultimately "fixing" the problem will be a matter of designing something that is no longer a Stirling engine or one of its hot air cousins. It will be something qualitatively different like a gas turbine, quasiturbine or DynaKinetic(tm) engine. But in each case there would be a choice of Stirling mode and internal combustion mode with the latter being inherently more powerful. At some stage the Stirling type engines must rely on diffusion of external heat into (and out of) the working fluid, an inherently slow process.

Internal combustion (or other form of heat generation) is exactly the magic solution to this. Generate the heat at the place where you want it. Even if you're using say nuclear power, you would be better off (in terms of power per size) with gaseous nuclear fuel in say a gas turbine or rocket than using heat exchangers and a separate turbine or Stirling engine.

However there were very early very successful uses of Stirling engines were for pumps in remote locations. See for example http://en.wikipedia.org/wiki/Rider-Ericsson_Engine_Company.

Finally I would assert that for a revolutionary new improvement you should look to better electric generation. Something like the liquid metal anode, solid electrolyte fuel cells (http://www.netl.doe.gov/file%20library/events/2008/seca/posters/Thijssen.pdf) that can burn any reducing fuel (coal, scrap lumber, biofuel, lawn trimmings...) and can potentially be more efficient than a perfect heat engine given they are directly converting chemical energy to electricity. Major corporations are already using them (http://www.datacenterdynamics.com/focus/archive/2012/06/ebay-goes-second-bloom-box-installation) and we should see household units in the next couple of decades (imnsho).

Ok ,
so,
stirling engine can not work efficiently as compared to IC engines

so what can u say about solar operated stirling engine generator which is widely use in japan?