so in one of my old Encyclopedia Brittanica Science Book of the Year (maybe 87 or 88) there was an article on the science of toys. one of these toys was a loop of wire made of nickel-titanium alloy, strung around two pulleys. one pulley was small, one was big.
nitinol 's got shape-memory, and when the loop of wire is warmed, it attempts to regain its original shape (i.e., straight). so if you dipped this nitinol toy in a glass of warm water, the wire would start to spin the pulleys.
How would you use it for power generation? The pulleys will only spin until the Nitinol suceeds in regaining it’s original shape. Then you have to spend energy turning the pullies back to force the Nitinol back into it’s stressed shape, plus the energy you have to spend on cycling the temperature.
OTOH you say the wire tends to straighten? hmmm… maybe there’s a remedy for erectile disfunction in there somewhere. Who cares about free energy when you can get free hardons? let the research continue.
You can, but why? First, it takes power to bend the wire into its original shape, and to get it to bend back it takes power to keep the hot water heated. It tends to be terribly inefficient. Now, people have tried using solar system, combined with cold tap water to do this, but really…it just doesn’t look very promising.
Not yet but I do believe it is used in shunts to open arteries and stuff. I think it’s put in as one shape then it forms the desired shape as it warms up.
Sigene, i second you about the shunts. i remember reading about those a while back.
as to why one would use nitinol, i wanna say ‘no duh’, but i spose i haven’t explained myself very well to you all. to turn a normal turbine, you need steam. to turn one of these little pulley toys, all you need(ed) is warm water.
less-heated water equals cheaper power generation. not having to heat the water to give it that extra kick to turn it into steam (i can’t remember that damn term- specific heat? something potential? dammit!) equals cheaper power generation.
but obviously, we don’t have supercheap nitinol power nowadays. so while the last paragraph is true, there’s gotta be some confluence of factors that makes the whole idea of nitinol power generation equal more expensive (or more of a hassel).
what is up with those other confluating factors? is nitinol too expensive? does it lose it’s memory over a short period of time? would such a large-scale turbine of nitinol and pulleys rattle and shake like the devil with d.t.'s? is the power generated by the unwarping nitinol strong enough to rotate some fairly efficient and lubricated joints, but not nearly enough to turn a turbine?
Nitinol doesn’t generate power, it just stores it.
Notinol is normally in it’s relaxed state. If you take a piece of Nitinol and pull on it, it will stretch a little bit. Put it in warm water, and it will return to the non-streched shape. That’s it. It’s basically a temperature-triggered spring.
The little nitinol-powered pully will only run until all the nitinol wire has returned to it’s contracted state. Then you have to put energy back in by manually winding the pullies back, stretching the Nitinol back into it’s streched form.
I don’t know about this wire, if it is just storing energy or it is transfering heat from a hot source to a cold and doing work in the process - but do know about laws of thermodynamics. The work you get from heat is a function of the hot and cold tempatures you are working between. If you use warm water you will not get much work out of it. This is one of the reasons power plants use superheated steam - you want as much temp difference as practical.
Reading the link it does appear to be an engine, actually transferring heat to do work. It sounds interesting, I wish I had one of those little engines
from what i gathered from the brittanica article, this toy measures about six inches long. a six inch rod of plastic connects two pulleys, one bigger than the other, and a single piece of wire, in loop form, goes round the pulleys.
you dip one of the pulleys in hot water (maybe dip the other in cold, don’t really remember that part) and the wire spins around, pulling the pulleys.
the theory i ascribed to the phenomenon is that the hotter the wire gets, the more it wants to be in its original shape. this causes the part of the wire around the pulley in the hot water to try to straighten. this straightening, combined with the temperature fluxing effects on the wire segements adjoining the heated areas, somehow provides torque to spin the pulleys.
i do believe that this is an engine, transferring heat to cooler areas (air or cold dish of water).
Ok. I understnad how that works now. It sounds like it’s just a heat-engine - using the difference in heat between the warm water and the cooler outside air to cyclically expand and contract the nitinol. We don’t use this for power generation because the amount of power you get out is tiny for the cost of the Nitinol, which isn’t cheap. After all, you have to provide a heat source anyway, no different than any other heat engine.
but a question which springs to mind is, what with much cheaper memory-enabled materials, why doesn’t the savings of using only heated water (instead of steam) offset the price over boiling-water turbines?
Memory wire isn’t cheap. For the amount of output power you’ll get, the cost is a lot less for a turbine design. Nitinol is an expensive material. Remember that the toy only uses a tiny bit of it. To get significantly useable amount of power will cost a lot for plant construction. If you did have a free low temperature heat souce that you really wanted to generate power from, you’de probably be better off using a Stirling cycle or other generic heat-engine.
Secondly, and more importantly, the efficiency of any heat engine is limited by the temperature difference between the hot sink and the cold sink. The more temperature difference you have, the more efficient your heat-engine can be. Real power plants operate with a temperaure difference of hundreds of degrees between the steam and the cooling water. The Nitinol toy is only working off a temperature difference of a few dozen degrees, so it’s going to be a lot less efficient.
Oh my God, a thread on Nitinol! Back in 1985 or 86 as I recall, Popular Science magazine was raving about how this metal was the ‘next big thing’, and I actually owned a toy boat that had the Nitinol pulley system incorporated into it (damn, I think my parents threw it out years ago)
You put it in a heated swimming pool with an ice cube in the special holder and the little paddle wheel spun at an ANNOYINGLY slow rate and slowly propelled the boat forward. Seemed pretty cool at the time because it could go for quite a while on that ice cube…
I remember reading about nitinol in OMNI magazine (May 1986, apparently). They ran a contest for the best suggestions for how to use it, and one of them was to use the heat differential between deep and shallow seawater to generate energy, which sounds expensive with the added bonus of being hard to maintain.
Although as others have pointed out, higher efficiencies are gained with greater temperature differentials between hot and cold reservoirs, but one particular point you seem to be missing is that by converting liquid water to steam, you actually increase the ability of the fluid to do work, e.g. convert the random motion of heated fluid into a directed impulse in a piston or rotation in a turbine. Without this phase transition, water can do almost no actual work; heating water below boiling doesn’t make it move much, and the expansion is very minor. Converting it to steam–which is compressible–allows for it to perform a dramatic amount of work, and most of the energy in a steam cycle is extracted due to this compression and expansion. Some systems do use what is called “regeneration”–essentially, a heat pump–to reuse extra heat in some fashion, but this provides only a modest improvement in efficiency albeit essentially for free (in thermodynamic terms) and often functions as an elegant solution for pre-heating propellants or cooling combustion chambers.
Extracting small amounts of heat is subject to much greater relative losses in efficiency that can’t be regained by simply scaling the system up. However, on the microscopic level, even small thermal differences can be substantial, and one of the most promising sources for nano-scale systems is using thermal difference between, say, sun and shade. (It has been hypothesized that lifeforms could and may even have used thermosynthesis to supplement or replace photosynthesis or nutritional energy sources, although no clear candidates have been identified.) However, these machines work at very tiny power levels where the efficiency losses are outweighted by the value of free ambient sources of energy and again, are not practical to scale up to macro levels, though they could hypothetically be used to power some kind of low energy chemical reaction that creates a chemical fuel. Purely mechanical devices that rely on non-compression cycle thermal energy are limited to very low power, low efficiency devices–essentially, toys.