General questions from a new guy.

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mcfish2004
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Joined: Tue Mar 19, 2002 3:03 pm
First Name: Mike
Last Name: Stuart

General questions from a new guy.

Post by mcfish2004 »

1.Is there any limit to the size a Stirling Engine can be built?
2.Does the temperature difference matter in total output power?
3.Does the type of metal used to construct the engine matter?

I would appreciate any responses to the questions anyone could give.
I'm just getting started in my new hobby and could use all the info
I can get.
info74
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Response to General questions from a new guy.

Post by info74 »

1. I don't think there is a theoretical upper limit on power in a Stirling engine. 2. The bigger the temperature difference the easier it is to get power out of a small engine. In other words to put out any significant amount of power an engine running on small temperature differences would have to be physically very large. 3. The place where metals are critical is in the hot side of the engine. If you are going to build an engine that puts out a significant amount of power you will probably want to build the heater head out of at least a good grade of stainless steel and perhaps a more exotic metal like Inconnel or Hasteloy.

If you're interested in building models, where the main function is beauty and "does it run" then high-temperature metals are probably not required

If you're interested in power producing engines you really should read The Philips Stirling Engine. Unfortunately this book is incredibly expensive and also hard to find. I think it still is technically "In Print" but the publisher doesn't try very hard to sell them.
ijgordon
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Response to General questions from a new guy.

Post by ijgordon »


I'm interested in a related question. If the Stirling engine works on a temperature differential then if the cold end was 'really' cold then the hot end wouldn't need to be that hot in order for it to generate power, would it?
atc
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Response to General questions from a new guy.

Post by atc »

In response to the second question, it is the temperature differential that is critical to producing power, not the actual temperature itself.
fvanicek
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Response to General questions from a new guy.

Post by fvanicek »

Hi everyone, just a very stupid question of mine: Is there some simple mathematical rule of thumb that would predict mechanical output power of a given engine and it's optimal geometry? /// Imagine a simple gama type low-delta engine that would work with a displacer chamber with footprint X square metres (cold side X m2 and hot side X m2), running on temperature difference Y degrees Kelvin. //// For given engine then there should be some simple approximate formulas that would give these answers: 1. What will then be the theoretical output power? /// 2. What should be the height of the displacer chamber? /// 3. What should be the ideal height of the displacer if a-non regenerative (e.g. styrofoam) b-regenerative (yellow foam) /// 4. What shoud be the volume (bore and stroke) of the power cylinder?
the_wildman_richard
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Response to General questions from a new guy.

Post by the_wildman_richard »

im new also. when you talk about temp. differences to make power in a small to medium sized engine, what kind of difference (in deg F) are we talking about? im interested in electrical power and possible water pumping for a house
privacy.lover
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First Name: Inventus
Last Name: Privaticus

Response to Richards questions.

Post by privacy.lover »

Richard:

Some, although rather extreme (read: difficult and expensive to construct), LTD (Low-Temperature-Difference) Stirling engines can run on temperature differences as low as 10 deg. C. (~ 20 deg. F.) Some, typically small model-engines, will even run on just 4-7 deg. C. (which is to say, the heat from your hand in relation to the air in your living room will make such engines run when you hold them - That is, unless it is very hot outside and your AC has broken down ;-))

However, LTD engines tend to be BIG in relation to their power-output, so you would probably want to use a HTD (High-Temperature-Difference), or at least something in between (which is to say: A LTD design, running on as high a difference as you can provide, say 100-300 deg. F.)

Unless you plan to use a HTD design (and a VERY high temp-diff), you should probably forget using a very small engine, if you want to produce significant power.

I know of one commercial Stirling "co-generator" (which is to say it produces electricty AND use the waste-heat to make hot water), which produces about 6 KW of electricity (and 10 or 20 KW, I forget which, of hot water) from a small diesel/gas/propane burner. This engine (including the generator and water heat-exchanger) is about two feet on each side (or thereabouts).

Hope this helps?

Regards,

Inventus.

P.S. In case I've made a mistake, converting between C. and F. Please forgive me - I am one of those freaks of nature, born with just ten fingers, instead of the usual twelve and feet that aren't a foot long. To make matters even worse, I live in this strange place where water boils at 100 degrees and freeze at zero. Very stange, I know, but you'll have to blame my parents... (or, possibly, nature?)
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