Sterling engine made from scroll expander

[ceo___1402]

Has any one ever made a sterling engine from a scroll expander. It's
basically a scroll compressor that is run backwards. It only has one
moving part.
Second question is would this type of solar motor be as efficient as
other sterling engines?

[stan.hornbaker]

A Stirling engine is a closed system, heated on one side cooled on the other, filled with a gaseous fluid to transport thermal energy from the hot region or source to the cold region or sink, and producing mechanical energy by means of a piston. All being limited by the Second Law of Thermodynamics. I don't see how a scroll expander could be utilized in a Stirling engine. Can you explain your idea further?

[ceo___1402]

The scroll motor only has one moving part and it can be a closed loop system
just like a sterling engine. One difference being it doesn't have a defined
hot and cold side unless you would consider the in side the hot side the out
side the cold side. It's closer to one of the single piston sterling
designs. It can use an external heat source. It will also work with a
regenerator. It can work with a helium, ammonia or water but water seems to
be the least efficient from what I've read. Helium expands about 7 time
more that water when heated so you could do much more work with helium.
Some are using a 80/20 mix of water/ammonia. To be a closed loop system you
would have to cool the out line before reheating it just like in any
sterling engine. One thing I'm not sure about is most sterling engines have
a kind of push pull system with the two pistons. I haven't read how this
helps or hurts efficiency but I would think that it's a plus for the design.
What got me interested in it is a post by someone about a rotary sterling
engine(not a wankel engine) I thought the rotary motion had to be more
efficient because even though in a regular sterling engine is very efficient
you still have the pistons come to a complete stop before changing
direction. This has to take something away from the efficiency so the
rotary sterling engine caught my attention. Then while looking at it I came
across the information of the scroll expander/compressor which are basically
the same thing just run in different directions. So in search of the
perfect sterling engine I thought I would see if anyone had worked with the
scroll expander engine using the sterling principle. I'll attach some
pictures.
I'd appreciate any feedback you have on any of the designs.

Phil

[stan.hornbaker]

To qualify as a StIrling engine a scroll expander must be capable of acting as a refrigerator or cooling machine when driven by and external motor or other prime mover.

Question: Will a scroll expander do this? Please try and respond.

[stan.hornbaker]

There are currently two Rankine Cycle systems entering the market. One uses <400 deg.F with a Trochoidal expansion engine. The other uses a novel means to provide near continuous operation by means of two valves and operates at <200 deg.
Look for MatterandEnergy as well as Ener-G-Rotors, Inc. for details.

[scientificker]

a scroll expander run in reverse is known as a scroll compressor and is often used in heat pumps and air conditioners http://en.wikipedia.org/wiki/Scroll_compressor so it meets the cooling criterion

[stan.hornbaker]

Where are the designs of a Stirling engine incorporating a rotary compressor or expander if such is practical?

Heat pumps and refrigerators do not incorporate Stirling engines as components.

[jon___2625]

I have a Sanden scroll compressor from a car and after removing the valve, it works well in reverse. I want to produce a rankine engine that uses waste heat at 130F with 70F cooling. Goal is to produce 50 watts.

Any idea if this is feasible? I know it won't be efficient, but I am ok with that (effectively I have an infinite supply of the 130F and 70F sources).

I suppose it involves getting the right size heat exchangers, selecting a working fluid (maybe R-134A) and finding something to act as a condensate pump.

Has anyone done this or have details that would help?

[stan.hornbaker]

Since this is a Power Producing Stirling engine forum we limit discussions to Stirling engines. Since no one has shown a way to use a scroll expander/compressor as an integral component of a Stirling engine further discussion of these devices is no longer acceptable.

[a_hiddin]

Wait a minute William,

To answer his question the answer is yes it can be used but not without modifications.

I have been working on several designs trying to come up with the proper solution.

He is just confused about the operation of a stirling system because of the terminalogy.

you cant use r-22a or any other refigerant, because of the boiling point issue. It is a man made gas of several chemicals and a oil for lubrication. Although the term fluid or liquid is used when talking about stirlings they actually mean gas.

The scroll compressor in a refrigerain unit is actually a vapor pumper. The operating pressure for a refrigeration unit is around 250 psi. Some service men have made the mistake of trying to fill a system tooo fast and "slugged" the system. This means it locks up the compressor.

You cant use a gas that has oil in it in a stirling for two reasons. It will clogg up the regenerators and your sytem will lock up. Most importantly never ever put oil in a pressurized system that is under pressure . When oil is compressed it will explode. Ive already heard of one death due to this.

just use atmosperic pressure air till you see if your idea will work.You will have to add more heat but it is safer. If your system works ok then consider a gas to use.

dont use any liquid. If you are heating the hot end and liquid comes back to the heating chamber it will explode. It may not be a major explosion but it will be detenation. It is a form of thermal shock that will cause metal to break to pieces.

The stirling engine can be used as a refrigeration unit but it has to be driven backwards by an electric motor or an other stirling running in the opposite rotation.

The stirling cycle works on compression of gases. compression is heat and expansion is cooling. It may be easier to think of it in high pressure and low pressure.

THe principal is that once somethings heated it cant stay that way it is going to seek cold, without energy such as heat being added to keep it there at the same temperature.

This temperature change is used to create motion. What you are doing is bouncing the gas from one side to the other. If left unheated for a period of time the gases will try to balnce, and equalize , or the motion will stop in other words. A good designed machine will runn off the outside air temp, but its hard to do..

yes a scroll compressor can be used but not like you think. Once you have leniar motion you want to change it to rotary motion but there is a price to pay called friction.

Once you get the compresser turning it goes in only one direction. The gas you just heated up is going to be looking for a low to go to. And after that first big push there is a low at the front of the compresser. it stalls the rotor this is called dead heading. You have built up this pressure and heat and it has no where to go In a alpha.

You have to figure out a way to go around the compresser and get back infront of it, because after that big push now there is a low pressure low temp situation that that hot compressed gas is seeking.

If you use a beta you have to have a regenerator because, that heated gas may have some moisture in it from the compression, and you dont want thermal shock. So you leave some of that heat in the regenerator and burn off any moisture. Remember moisture lowers your temp. too.

You cant use the compressor in the case it is in. It has oil in it and to use it you have to build it inside the engine. Thats alot of machining and design. It is not bi directional , meaning once you have the shaft turning one way it will stop and then go back the opposite direction. All you will get is a rocking motion.

There are ways to make it work but if you try always pull a vaccum first and fill the system with helium. put fittings for a set of regrigeration guage to put the helium in . never use anything oil based on the fittings either.

Remember you are playing with a pressure vessel and chemicals. Consult professional craftsmen like, welders, machinist, millwrights, and fabricators and engineers.