Stirling engines need large temperature differentials, but...

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Response to Stirling engines need large temperature differentials, but...

Postby stan.hornbaker » Wed Dec 17, 2008 9:46 am

Jim Boyle: To answer your question you would attempt to use the largest temperature difference that the materials of construction for the hot end could withstand over a long period of operation. You will also have to account for the rate at which that heat is applied.

Attempting to build a Stirling engine for your application is best left to those in the business such as Kockums who has been building them for submarines for a number of years. The build a Stirling powered section which can be 'cut-in' to a conventional submarine hull or used as the basis for a complete build up around it.

IIRC the Kockums uses hydrogen and oxygen as the heat source. Chlorine is deadly in enclosed quarters and is a real problem for battery operated subs if and when sea water... Sodium is also a hazardous material to handle under the best of circumstances, let alone in confined and close quarters.
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Response to Stirling engines need large temperature differentials, but...

Postby vimnjicki » Thu Dec 18, 2008 2:18 pm

I have been in contact with Kockums and have received some very valuable information, as I have received from William. I have also received both ridicule and disdain from many in response to my queries. I appreciate honest, contructive advice and criticism in their proper places. I have long considered this project a long shot, with Stirling engines the most resonable solution. Thank you for your answer to my original question. Kockums started small. Thank you for your information, advice and attention.
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Response to Stirling engines need large temperature differentials, but...

Postby bptdude___2569 » Fri Dec 19, 2008 1:27 pm

How much heat is required for your Stirling engine?
That is almost impossible to ask, of course.
I am glad you were helped by the first sub maker to field an AIP.
They are suddenly quite popular, with various designs coming out.

But, a "personal sub" ?

And you are talking to a miltary sub maker and to bypass diesel/electric?

The premise is a bit fishy.
What would the personal sub do:
go deep to explore or treasure hunt?
do oil platform repair?
scuba rescue?
skim coral reefs at shallow depths for tourism?

A personal sub you would think is something you would lower over the side of your yacht like a dighy?

If you had a supply of hydrogen and oxygen, wouldn't you use a fuel cell to just power the electric motor? Burning it any other way would use at least twice the fuel. And for a sub, a fuel cell is silent and small, as well as safe and easy to use.

Do you need stealth, like a military, but do not want to say?

Do you care if you can just refuel easity at standard yacht club docks, or are we talking about you getting support from your own fleet of ships?

Can it look like a large science experiment, because you want it propelled through the water for long periods of time without fuel?

You are funny, like so many business men. You are trying to find the magic number for temperature difference without stating what you are trying to accomplish.

Explain your businss need for a vessel, and try the inquiry again.

Why you are even looking at a Stirling is a wonder.

The needs of a military sub and a personal sub are just so far different. A small diesel electric is probably the best answer for a personal sub.

If I were a billionare really and want to live like Caption Nemo?
The sub would be large, light, very slow, and run forever with no extermal power. I would bore you with how, but it would not be a Stirling, but yes a unique engine taking advantage of ocean water. It just would not be a good weapon system or spy platform.

Good luck.

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Response to Stirling engines need large temperature differentials, but...

Postby bptdude___2569 » Mon Jan 05, 2009 6:06 pm

This thread is just too much fun not to add one more.
I had to think for a bit, though.

As far as I'm concerned, here on this board, we have made the case why subs should long distances by burning hydrogen, and not building or hold silly amounts of new battery technology.

So, what about Stirlings. It would also be a good argument that the ultimate Stirling would be replacing the steam turbin plant with a dry Stirling. Key to this would be a dry nuclear process, which now exists.

I have also found an interesting potential project at one of my favorite govennent labs, for a portable, no maintanance, international security monitored nuclear reactor. It was about 60 feet tall, shaped like a cigar, and about 1o feet in diameter. The output was electric power. I kid you not, and these folks were serious that if they had market, this thing could be built.

Would you believe me if I told you this design was not too different from what be a Dish Stiring engine? It was not a Stirling, but I would like to add to the suggestion box of that project.

But, then I had one of those brainstorms. A sea vessal of the future, and probably not too distant future. Something to run silent, run deep and be what prowls the oceans endlessly the sentinel. And due to its nature, I can only think of a Stirling to get the job done.

Somebody tell me they want to hear it, and I will post.
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Response to Stirling engines need large temperature differentials, but...

Postby cpallandro » Tue Jan 13, 2009 12:30 am

First, your original question concerned temperature differential. I've been conducting my own limited research in Stirling cycle engines. This is what I've found: The few companies building industrial Stirling cycle engines/dynamos for solar operation use parabolic mirrors to concentrate solar heat for the hot end of their engines. The figure of 600'C (somewhere around 1100'F) pops up as the amount of heat one of these concentraters can gather on a fair day. I think the cylinder gas pressures at that temperature are about 150 psi. The engines turn over at 1500 rpm +30 rpm and the 10kwe dynamos were 200 v 3ph (European). Eurodish has a 10kwe unit that uses helium. SES has a 25kwe unit that uses hydrogen. Sunmachine has a 3kwe unit for 30k euro. Google Eurodish, Stirling Energy Systems (SES), Econology...

Secondly, water as a working fluid? No. Water doesn't compress; the engine could lock hydrostatically. Steam as a working fluid? No. Air engines and steam engines seem similar, but steam is an altogether different animal#Stirling doesn't condense a gas back to a liquid. Besides that, friction is the bane of the Stirling. Resistance comes from sliding surfaces, bearing surfaces, and the working fluid (hence hydrogen and helium as working fluids since their small molicules would cause the least impedence as opposed to a heavy fluid like steam) and from the mass of moving engine parts. Small size and high output of the engines/dynamos were major design parameters for the solar companies. That is the reason for the high temperature differential and the elemental gasses#high output yield in a small package that can hang in the focal point of a 38' parabolic dish which automatically tracks the sun.

For your application and the afore mentioned industrial engines: Is 10 kw enough to charge your batteries? Too much? A solar concentrater on a big Navy sub is not impossible, but can your personal sub accomodate a 38 foot diameter solar dish? Weather permitting? There would be the engineering problems of making a dish and its support/tracking structure underwaterproof at speed, or providing a deployment plan and storage facility for it belowdecks while submerged. Or another possability would be reconfiguring a concentrator that would not be circular but would still concentrate/track the required amount of light. Or you could just tow one behind you, like a tender for a locomotive...

If you are not using solar as a heat source, and I suppose you don't have a handy nuclear pile to generate heat, then you have to burn something. In that case, go conventional generator set(s) and forget the Stirling.

Now, about the smaller temperature differentials. The smaller the differential, the larger the Stirling has to be made to output the same kwe#to a point. The larger the engine is made, the heavier the moving parts become, the larger the bearing surfaces become, and the more inefficiency is introduced in terms of friction from bearing/sliding surfaces and impedence from the rotating mass and motion of the mass of gas. In other words, a hobby Stirling engine couldn't be scaled up to make a 10 kw work engine, just like you couldn't scale up a small model airplane engine to use in a full size airplane.

I hope this clears up your question about "non-oxygen compounds." Free air is primarily nitrogen, not oxygen. However, the oxygen in free air plus heat plus lubricant vapors would equal an explosive mixture in a hot Stirling (crank)case, so oxygen is to be avoided in the presence of any substancial heat plus lubricant vapors.

And so you have the sum total of my research on Stirling engines. I hope this helps as I have no other information to impart. I do wish you well with your submarine endeavor.
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Response to Stirling engines need large temperature differentials, but...

Postby stan.hornbaker » Tue Jan 13, 2009 7:24 am

Jim S:
The Kockums Stirling engine for submarine application burns hydrogen and oxygen to power the submarine when on the bottom conducting surveillance of the surface. The same engine or a modification of it has/is/proposed for use in a solar dish power project in the Mojave Dessert according to an article in Popular Mechanics late in 2008. Similar projects have been proposed in the past but never came to fruition due to lack of significant progress and/or R&D support.

The company that succeeds in producing a line of power producing Stirling engine/generators at competitive prices will make a significant contribution to the energy problem particularly if waste heat from kilns, and similar heat sources can be utilized.
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Response to Stirling engines need large temperature differentials, but...

Postby craig___4888 » Mon Jan 19, 2009 5:11 pm

Hi all,
I have a similar question for this thread on temperature differential.

I have an idea, to build a Stirling engine that uses the heat from a decomposing organic waste.
Temperature differential of probably no more than 20-30 d Celcius.
What sort of power is likely to come from this? A few watts only from the sounds of it. Considering 600 d C is powering 25Kw on the Sunpower machines.

I am interested to see some facts on Temperature/ power ratio of the Stirling Engine.
Can anyone provide some references.

Craig Lambie
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Response to Stirling engines need large temperature differentials, but...

Postby joewein » Thu Feb 19, 2009 11:49 pm


it takes about 5 times more energy to turn water already at the boiling point into steam of the same temperature than to heat that water from 0C (just about freezing) to 100C (boiling point at standard atmospheric pressure).

It takes about 4.2 kilojoules (kJ) to heat 1 kg of water by 1 degree centigrade. Make that 420 kJ to heat it from 0 to 100 degree C. It takes 2.27 megajoules or 2270 kJ to turn 1 kg of 100 degree C water into 100 degree C of steam at standard atmospheric pressure (it's more at higher pressure).

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