# Question: Stirling Engines

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If the heating mechanism for a stirling engine is replaced with compressed air, does the efficiency decrease that it is below the conventional internal combustion engine?

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I expect the efficiency rating you have in mind is the thermodynamic efficiency, which might be expressed as

the amount of work I can extract divided by the amount of thermal energy I put in X100%

If you skip the thermal energy input then thermodynamic efficiency ceases to have meaning and you are left with some measure for mechanical efficiency which could be quite high I guess....

Brian Whatcott Altus OK

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The reason I asked is as follows:

If I have a resovoir of air in a tank and use this in place of heated gas for the power cycle, would this be less efficient than just using a conventional intake-exhaust cycle motor for compressed air?

What I am trying to decide is whether or not a WEC that compresss air and converts this reserved energy into electricity is more feasible than other methods. The tank would act as a temporay storage until it passes through what ever conversion process is in place to generate electricity

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Storage with compressed air becomes a problem because the amount of work required to pressurize the air as the tank pressure increases is not a linear relationship. You are fairly limited in how much pressure you can store in the tank and then extract without significant inefficiency.

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You must keep in mind that the ocean's waves have tremendous potential for energy but capturing that energy is a problem. What I am looking into is a closed system that recycles air (or another gas if need to be) through the system to generate electricity. The storage would be temporary and not a great amount since it would be replennished as long as waves are present and large enough to move the compressing system. When waves are small or not present then the system would have to shut down until the wind blows again.

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I believe there is a system exactly like this one in development. I can't remember where I read about it, but they use the ocean waves to compress the air and drive a turbine-powered generator.

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This one I'm working on would be a closed system which could use other gases if needed and would be coupled in with a wind mill and tidal generator all in in unit. The tidal/current unit would be a constant reliable source, wind turbine is proven technology but a wave energy convertor due to the sporadic nature of a wave storm is the big question.

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Gotcha....sounds interesting

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The tower for the wind and tidal mills would be a pipe sort of arrangement which could house the generater/turbine and compressed air storage tanks for the WEC. This is the crucial part of any WEC--storing the energy in a form it can be controled and converted into electricity. Since air has a small density, the weight of the stored air wouldn't be as big an issue if a liquid such as water is used. With a closed system, the problems with condensation and corrosion can be minimized. Anyone with input into this concept is welcome.

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wrote

If it's a closed system, you might as well use dry nitrogen. Cheap, readily available, and prevents any potential oxidation or moisture issues inside your system.

Tom.

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Dear Tom Sanderson:

The only downside is that you will have a space that is deadly, if someone accidentally enters it. So precautions and training will need to be an established rule.

David A. Smith

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Another problem is wave size. Ocean waves in the area I have in mind range from 0 to 30 feet or higher. Such a range would mean a very small mean of sizes from which any device could capture energy. In the lower range, a lack of energy is the problem while in the higher ranger, preventing the device from being smashed would be the problem. The solution I see is to have a floating system that could be moved and re-connected to an under sea grid so the WEC would be in the limited sizes of in which the device could work could be utilized at a higher rate and place the device on a leeward shore when wave heights are excessive.

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