Air Temp Nitinol

[Reiyuki]

A friction heater using that force could easily achieve.

What about using the movement of one nitinol spring to create friction on the next nitniol spring, creating a kind of cascade-activation?  Lots of outputs from a single input.

Or put it on the spring so the friction aids its own constriction.  That might lower the required thermal gradient.

[sm0ky2]

The point6 for me is that Nitinol engines produce very little power for their cost and size. There are far better heat engines out there.

Most of this has to do with the particular designs
Not the alloys themselves.


When properly applied, these engines can convert heat to work at rates
quite frankly unheard of in the world of heat engines.


While something like a Sterling Engine can easily outperform Nitinol in terms
of overall efficiency, when waste heat is used and system losses are irrelevant
Nitinol can convert more heat into work per unit time.


Cooling the metal seems to be the major hitch in most designs.
Because of the slow rate of cooling, energy is often dumped into
these systems on the cold side in an attempt to increase cyclical rate.


Which brings up another point - generally the alloys used in robotics have a low temp
operation point. This places them close to their super elastic state after current is stopped.
Inherently this decreases the available force over distance of the actuators.
Therefore current limiting or pulsed current should be employed. To keep from overheating
the alloys. In other words, care should be taken to prevent entering into the superelastic state.


Alloys advertised as "superelastic" have heat activation temperatures lower than ambient.
60F is not uncommon.
A heat engine made from these will run on "cold" rather than heat.
As heating would occur naturally and the cold side would require cooling.
We want alloys with a little less nickel composition.


All of these are (roughly) equal molar mass.
Ti55% and Ti60% are two commonly sold alloys.
In general the more nickel, the lower the heat activation temperature
We don't want our heat engine to use too high of a heat
Nor too cold of a cold.


But rather, the alloy we select should have a near ambient cold temp
and as low of a hot temp as possible.


I will try to compile a list of which NiTi alloys fall into this category.
So we have a baseline to source from.


But i must stress the point:
Training techniques can have as much to do with the functionality of
Nitinol as the composition of the alloy itself.

[sm0ky2]

What about using the movement of one nitinol spring to create friction on the next nitniol spring, creating a kind of cascade-activation?  Lots of outputs from a single input.

Or put it on the spring so the friction aids its own constriction.  That might lower the required thermal gradient.

I like that line of thinking
Use one actuator in the hot stage ,to apply friction to another actuator in the cold stage
Both deforming the metal and partially heating it, so less heat is needed to finish the process.


Unfortunately his metal has no problem absorbing heat. It's a natural heat sink.
The problem is getting the heat to leave the metal.


Maybe connect the actuator to a heat pump to separate temperatures
that cause the engine to run.
Not the air-conditioner type of refrigeration heat pump
I'm thinking more along the lines of a Venturi vortex heat pump
That used airflow from a portion of the actuators motion while leaving
some room for mechanical output.


If I remember correctly we needed 150psi to create 100 degree differential
from ambient air.
Compare that to 55tons per sq in

[sm0ky2]

To understand how this metal works in terms of force
You look at the cross sectional area in the direction of
the working force.


The length of the metal is a factor of the distance this force
is applied over, and is therefore proportional to the work.
The length has no effective value in the equation that determines
the magnitude of that force.


This is distinctly a property of the alloy and its' training.
In a wire - the cross sectional area is the area of a slice
of the wire of infinite thinness.
That is to say: Pi R ^2
R is half of the wire's diameter.

[sm0ky2]

The information in this video contains the inventor of Nitinol
And some of the most basic discoveries.
Including the information provided to McDonald-Douglas
When they began their research.


https://m.youtube.com/watch?v=oKmYqUSDch8


Time stamp: 1:34-2:15
This (I believe) is the basic structural approach
to a Nitinol replacement of the combustion chamber.
When attached as linear piston actuators linked to a
crankshaft, rotary motion will be attained.
The combustion chambers, the intake and exhaust systems,
and the fueling system of an ICE can be removed and replaced
with a temperature differential system which contains a heating
system and a cooling system.


The heating system could consist of a trough of warm water
when the piston is compressed, or bent (stressed) by the crankshaft
it curves downward and dips into the warm water ( or fluid) thus
providing a driving force to the crankshaft.
When the metal is "straightened" by the Nitinol action, the cooling
system blasts it with a cooling fan (or circulated fluid, etc).


That's kinda where I'm leaning towards.


I think it is important to analyze each approach in its' own right.
Spring mechanics provides for a wide array of shapes and the work
has already been done for us. However there lies an infinity of
non-conventional spring geometry that was never researched due to
the conservative nature of springs. So for those we are faced with the
raw differential equations and a segment by segment analysis that
rivals each design against the next in a quest for time and resources.
Such time and resources is better spent on the workbench than in the
calculator and notepad. ( for this particular scenario).


Known (common and uncommon) spring designs that have been analyzed
we can simply insert the Nitinol specs into the spring characteristics variables
and see exactly how it will perform. This (I believe) is the basis for almost every
Nitinol mathematical analysis available to us publicly.
I don't think it's because they're lazy, it's  just too much for most to try and do
on their own. I'm still recovering from the gyroscope thing and I only did a dozen
or so. I couldn't imagine the mind boggling task of a full Nitinol mechanical work-up
to relate the metal into our mechanics textbooks.


I don't mind helping out if someone posts an "out of the box" spring design.
But as far as calculating every possibility we have in front of us
You guys are on your own on that one.


Real world tests are probably easier to deal with.


That being said I will discuss over the next few days:
The known Nitinol contraptions, their cons and pros, etc.
As well as several possible Nitinol contraptions, based on
known spring designs. Of which there are enough of, to
recreate every contraption on earth in Nitinol form.
How we get the heat in and out of each system will be a major
determining factor of whether or not someone chooses one design
over another.
It's not just the function of the Nitinol, but our realistic means of
providing the scenario upon which it functions.




Time stamp (in the video at the beginning):
2:50 - 3:50


This horizontal wheel is the worlds first solid-state heat engine.
When the springs contract in the water they push against the water.
Like when the Jesus lizard runs really fast. Except it's  not just surface
tension, its water pressure and gravity and the whole of what keeps
the water in the container. Namely Archemedes Displacement and
water's natural resistance to movement through it, combine to provide
a constant force on the driveshaft as long as the temperature difference
is maintained between the two reservoirs.


More later when I have time to type.