Stirlingengineforum.com

Some interesting posts here have led me down a rabbit hole for the last hour or so. Sharkskin, owl feathers, golfball dimples, vortex cannons... Don’t reckon I’m any smarter than when I started, but some random thoughts: The sharkskin is directional and lowers resistance by keeping the flow more attached, so it might well make a better heat exchanger, but only in one direction, and I’m not sure air would behave the same as water. That’s why I looked into owl feathers, but I think I left that topic more ignorant than when I started. At any rate I’m not sure if the silence of owl feathers comes from flow management or sound dampening. If it’s flow then there might be some lessons there to apply to exchangers, though again any benefits would likely be directional. Thinking about answers in nature reminds me how I’ve always thought that for low-temp engines, lambs wool would probably make a better regenerater than steel wool. Which that reminds me I've mentioned before how I think a blanket regenerater could also serve as the heater and cooler in a Beta short-stroke pancake-type engine, by radiantly exchanging heat with the ends of the chamber, and passing the exchange to the air convectively as the blanket moves through the chamber alternately blanketing the hot and cold ends. The air doesn't move, the blanket moves. Or I could be wrong about all of that, that’s the problem with reading more than doing.

Bumpkin

As soon as I find time, I will do a numerical modeling of the exchanger with openfoam. Now with 3d printers, we can make complex shapes with conductive materials.

I would imagine, to facilitate flow in a regenerator, the fluid diode would have to have alternating channels with the convolutions facing in opposite directions.

Kind of interesting; flexible straws:
Close to the right "wave" but the ratio between wave height and tube diameter is off. (Tube too big, wavelets too small.

Anyway, using the flex straws, I'm trying to illustrate what a regenerator might look like. A kind of honeycomb of tubes with alternating wave patterns.

The wave patterns could nearly fit together so the wall thickness could be minimized.

I'm not sure this is anything like what Sadi had in mind, but his comments got me thinking.

Edit: It just occurs to me, the internal pattern of the toroidal valvular conduit could be turned on a lathe.

I don't know why I did not realize that before now. I have both wood and metal lathes. Then, from that pattern a conduit could be cast out of resin or something.

On a different note, looking at the drawings; for example:
Would it be possible to use diaphragms in place of the opposed cylinders? Something akin to TK motors engine:

viewtopic.php?f=1&t=5180

The top of the opposed pistons move, virtually in unison, so the effect would, I think, be the same as the whole connecting rod and crank apparatus, but less weight, bulk and friction.

Or perhaps some form of scotch yoke.

I haven't really thought through how the diaphragms might be arranged or connected to effect some mechanical power output, but if one piston moves right or left while the other also moves in the same direction simultaneously, then it seems it might be possible to have just one barrier, like a diaphragm, or single piston, separating the paired cylinders.

For now, I'm going to model an exchanger like Tom drew in the post above. With 3d printers, we can make complex shapes.

@Tom - I assume from that diagram that each of the pistons is linked together via a crankshaft, so diaphragms wouldn't work, but I may be wrong.

Jumping back several steps, I thought that sharkskin worked similarly to the 'step' on a flying boat hull, but sounds like I'm wrong, or at least over-simplifying?

I was not familiar with what the step on the hull of a flying boat is for, but from what I can find, there is little, if any, correlation.

Apparently the "step" is only useful at takeoff, to help keep the tail of the plane from going under water and break "suction".

A vortex generating shark skin, is, I would say, something altogether different.

normandajc wrote: ↑Tue Aug 18, 2020 3:52 am I removed the regenerator and replaced it with a heat exchanger.

First off: I'm excited you are developing your engine design!

A note on terminology: I understood the regenerator is what differentiates the Stirling Engine from other hot air engines? Wouldn't removing the regenerator mean this is a new type of hot air engine?

Keep up the good work!

Jess

"I removed the regenerator and replaced it with a heat exchanger."

I missed that little gem the first time - what does it mean, since the whole point of a regenerator is that it is a specific type of heat exchanger already?

MikeB wrote: ↑Wed Apr 14, 2021 1:55 am "I removed the regenerator and replaced it with a heat exchanger."

I missed that little gem the first time - what does it mean, since the whole point of a regenerator is that it is a specific type of heat exchanger already?

True. It looks like the heat exchanger is a counter current type rather than reverse flow.

I'm interested in seeing the results of the modeling of the two way toroidal fluid diode heat exchanger.

Thinking about it, and looking at the results of the previous modeling of the two way flow type toroidal fluid diode, it looks as though it could act as the long sought after Maxwell's demon. Similar to how a vortex tube works, perhaps, but without the high resistance to air flow or need for high air pressure.

Maybe after seeing the results of the modeling, he's busy down at the patent office and has forgotten us . LOL
Or maybe not.

it is not only the exchanger that is an evolution. In order to present the interest of the Stirling engine type, I describe the current versions and the new version
There are mainly 3 types of Stirling engine (α, β, ɣ)
Theoretical schematic of these engines

In practice, Stirling engines do not respect this schematization.



Example Stirling engine of type α Practical schematic of the motor α Whether for a Stirling engine type α, β, ɣ, it is a volume of gas that the four operations of the Stirling cycle are made to undergo during one engine revolution. Depending on the type of engine , there are differences, but basically, each operation of the Stirling cycle takes place over a quarter of a revolution.
The reason for this is technical, for example, in the case of an alpha engine, in order to achieve isochore operation, it is used that the crankshaft
covers a very small distance when the connecting rod axis travels from point A to point B. The displacement piston and the driving piston are offset by 90°. Compression is not isothermal and the regenerator is a dead volume that is not compressed.
The expansion is not isothermal and the regenerator is a dead volume that is not expanded
For cooling, heat recovery takes place partially during the cooling operation and partially during the compression operation.
The reason for using the same gas volume to describe the Stirling cycle is that this volume is always more or less in contact with the hot and cold source.
One cannot use the simple models of thermodynamics.
This situation can be modeled simply by thermodynamics. For a Stirling engine of type α, the isochoric transformation becomes Because of this, it is used in the articles the Schmit model to describe these α, β, ɣ type engines
This handicap forces for example to use ceramic materials, to create much more important exchange surfaces. This makes the Stirling engine expensive and forces to increase the operating pressure in order to increase enormously the number of moles. The overpressure again leads to additional costs, since the structure of the Stirling engine has to be reinforced.
The regenerator is a dead volume that impairs the performance of the engine. Developments are made to overcome the lack of performance due to the regenerator. The regenerator is used to generate clean modes and to improve performance under certain conditions.

New Stirling engine

The big difference is that it is not one volume of gas that undergoes the four phases of the Stirling engine. It is four distinct volumes of gas that undergo the four phases of the Stirling cycle successively. The four phases of the cycle take place at the same time but with four distinct volumes of gas.
An important difference is that each operation of the Stirling cycle does not take place over a quarter of a revolution of the engine, but over half a revolution. This increases enormously the times of thermal exchanges.
An important difference is that a regenerator is not used, but a counter current heat exchanger. The heat transfer is immediate.
Schematic of the new theoretical or practical Stirling engine .
New Stirling engine in practice. The practical schematic of the new Stirling corresponds exactly to the theoretical schematic.

A major advantage is that the hot and cold sources are perfectly distinct.
One can use the classical equations of thermodynamics (isothermal transformation, isochore, energy balance, etc).
The pre-publication "Innovative new type of Stirling engine" uses the classical models of thermodynamics.
By isolating the hot sources and insulating the heat exchanger, it is impossible to make cogeneration. This is a major advantage for the performance of the engine, there is no thermal loss.

It is possible with this new type of Stirling engine to make economical engines without using complex technology materials.

Hello,

I have an industrialist who is willing to finance a prototype of the Stirling engine with my concept. I would like to have an idea of the price of manufacturing a Stirling engine. I am thinking of making pistons with diameters of about 2 to 3 cm and using self-lubricating rings for the pistons.

In all, I will have 8 pistons. The exchanger I will make with a 3d printer with aluminum.
Do you have an idea of price

normandajc wrote: ↑Mon Jun 14, 2021 11:05 pm Hello,

I have an industrialist who is willing to finance a prototype of the Stirling engine with my concept. I would like to have an idea of the price of manufacturing a Stirling engine. I am thinking of making pistons with diameters of about 2 to 3 cm and using self-lubricating rings for the pistons.

In all, I will have 8 pistons. The exchanger I will make with a 3d printer with aluminum.
Do you have an idea of price

That's great news.

However, a concept, is probably not enough to go on, I wouldn't imagine, to present to any kind of manufacturer to actually make or come up with a ballpark price.

If I had a fully equiped manufacturing facility, (which I don't of course) given what I know about your design concept, I really wouldn't know where to begin. I don't even have a completely clear idea of the concept or exactly how it is supposed to work and I think I've probably spent as much time as anyone studying it.

I do have some equipment and have access to several local machine shops, so I might be able to get you some idea on prices for some parts and such but would need, or the shop would need, more exact specifications.

If you can make a CAD drawing of a part, many machine shops can just put that into their system and the machine cuts the part, but you need more than just a concept.

Thanks Tom

I will prepare some CAO drawings