Air Temp Nitinol

[gadgetmall]

Hi  thanks for the response . Good info . When i say HOT i mean hotter than 98.6 . i have not measured it as this Nitinol is only 0.20 mm .. I do have 0.45 in a flat wire also . It is not enough heat to boil anything:) I can see your point though , why not make a big stranded blanket out  of these and possibly stay warm in the winter ..

[Tom Booth]

What I mean is; An LTD Stirling Engine will run on the heat from your hand. If the Nitinol stays hot enough to FEEL hot to the touch it should be hot enough to run a Stirling Engine, but what this sounds like to me is a refrigeration cycle.

In a refrigerator a gas is compressed to force it to change phase (condense into a liquid). At that point it gives up a lot of heat which is released to the room through the condenser coils on the back of the refrigerator by convection. Then when the refrigerant is released and allowed to expand it reclaims the heat it lost while under pressure (gets cold) producing the refrigerating effect inside the freezer.

Generally phase change takes place gradually at a constant temperature, like ice melting at 32 F. It can take a long time but eventually all the ice melts (or all the water freezes).

So what I'm thinking is that the bending of the nitinol is more or less equivalent to the compression phase in refrigeration where the refrigerant changes phase from a gas to a liquid under pressure. When the Nitinol is released it tries to reclaim the heat it lost like a refrigerant when it is released from pressure and allowed to change phase back into a gas.

So what I'm imagining is that the Nitinol when bent is going through some kind of gradual phase change similar to water freezing. It will continue to give off heat at a constant temperature for a long time until the phase change is complete, but my guess is that it will cool off eventually. Like a block of ice melting, that could take hours or even days.

The fact that the Nitinol gets cold when released from stress indicates to me that it has given up heat that it then wants to reclaim when released from being bent. I'm guessing that as in any phase change, this takes place gradually over time at a constant temperature. Like a pot of boiling water will stay at 212 F until all the water changes phase no mater that you keep adding more heat or a block of ice will stay at 32 F until it all melts.

In other words, I think the bent or stressed Nitinol may give up heat gradually at a constant temperature, say a little above body temperature, but in a normal phase change this cannot continue indefinitely, though I don't discount the possibility that with Nitinol, perhaps something abnormal is going on and the phase change never completes due to some sort of quantum mechanical brownian motion or cashmere effect or something. If that is the case that would be really remarkable but my guess is that eventually the bent Nitinol will cool down completely.

I wonder if anyone has ever done this (bent nitinol to get it hot) to see what happens using an infrared camera. That might be interesting.

Anyway I need to send away for some of this stuff ASAP I think.

[Tom Booth]

BTW, after posting, I see advertisement links appearing in the text of my post that I didn't put there. Is that normal for this site or have I picked up some kind of adware on my computer ? 

[Paul-R]

BTW, after posting, I see advertisement links appearing in the text of my post that I didn't put there. Is that normal for this site or have I picked up some kind of adware on my computer ?

I think that is pretty normal. The site drips with advertising which is why every page
is so data bulky.

[gadgetmall]

Hi Tom . Very nice explanation but i am not a physicist and all i know is what i see and do . That is a good suggestion . I will try and find that information i was reading where scientist  put the color changing thermal liquid crystal on it . they see what i see but  infrared imagery would be real proof  .

This only works if the Nitinol is in its austinite stage or it's parent state . As long as the wire is in that stage where it is stiff as steel wire and has a strain put on it it crys heat . Now i got several pieces i keep in my pocket for demos on the go . Springs and stuff i made with it and i can bend the stiffest piece i annealed for temp range above 100f  and it does stay warm even in my cool house / I tried this unscientific by bending it on my lip and feeling the heat and waiting ,then place the unstrained wire on my lip it feels cool like the air temperature in here now 73f it really don't conduct heat from my body and stays kind of cool.You would think it would conduct my body heat and transfer it to the metal . it don't do it very well  . I also tried bending it off my lip then wait a min and put it on my lip and it is very warm . just as soon as i start to release  some of the strain pressure it starts to get colder than the room temp then it seems to return to ambient temperature or just a bit under . The cold is really quite cold .and the heat is an amazing plus considering it looks just like wire . i also tried this with guitar string . nada..

I hope i am not loosing my mind here and i know someone else has some Nitinol in my thread so if you do please speak up and verify this this if you can.

Tom i recommend that 40 foot roll to everyone as i have tested all of the ones available including Magic wire and Dental brace wires. I Do like the 0.025X0.045 thermal dental brace wire from China. it is flat and Strong as hell and comes pre conditioned in a U shape and holds it's shape if you bend it in 50 degrees It transforms fast and super strong . and these  can be tuned easy with just some small batteries or ultra caps like i use . I tried the others as well much thinner brace wire (11cents a pack of 10) and has to be annealed first . The key to getting it close as possible to martinsite with no elasticity at room temperature is the key reason this wire is the right mixture of Ni Ti . i understand from reading that just 1 thousandth more or less will make inferior Nitinol for the purpose i  am using it for . 

Gadget