The phrase “warmth engine” would possibly set off some dangerous recollections out of your introductory thermodynamics course. However don’t be concerned, I’m going to point out you the good warmth engine you would probably picture—the thermoelectric generator (TEG).
The essential thought behind a warmth engine is to attract some helpful vitality out of a temperature distinction. This output vitality might be mechanical or electrical—and different bizarre stuff. However there is a very primary instance that you have most likely seen: the steam engine. You warmth up some water to make steam, which may broaden and push one thing. Then it condenses to let one thing shrink.
For this steam engine to work in any respect, you want the surface temperature decrease than the temperature of steam—or the steam would by no means condense. And in reality, all warmth engines depend upon a distinction in temperature. If you’d like a extra in-depth rationalization of the mechanics of a steam engine, do that video.
Now for the only warmth engine you’ll ever see—you may even make this your self. You simply want a paperclip and naked copper wire (or any two totally different steel wires). I am assuming this can be a metal paperclip. Lower the paperclip into two components after which join every half to 1 finish of the copper wire. It ought to look one thing like this.
Severely, this setup alone goes to be a thermoelectric generator. How cool is that?! With the intention to get this to work, simply put one finish of the copper-steel junction into one thing sizzling and the opposite copper-steel junction into one thing chilly The 2 free ends of the paperclip would be the output of this generator. Since this is not a really environment friendly thermoelectric system, I’m simply going to attach the output to a voltmeter. For my sizzling finish, I’m going to make use of a sizzling plate and the chilly finish goes to be salt and ice (which is colder than simply plain ice). This is what it seems like.
As you may see from the voltmeter, I get 1.2 milliVolts. That is not a lot, however it’s one thing. (The mass on the recent plate is simply there to push the copper-steel junction down for good contact, should you had been questioning.)
What you might be seeing right here is the Seebeck Impact (named after Thomas Seebeck). Two totally different metals collectively at two totally different temperatures can create an electrical present. The impact is extra pronounced with a bigger temperature distinction and a few steel combos work higher than others—however there it’s, your thermoelectric generator.
Truly, you can also make a greater generator by utilizing a semiconductor as a substitute of two totally different metals—however the two steel model is manner simpler to construct. Here’s a demo with a semiconductor. The system is sandwiched between two aluminum legs, with one leg in sizzling water and the opposite in chilly water. The output from the system goes right into a small electrical motor on high.
So, how does this work? Why does a distinction in temperature (for various metals) produce an electrical present? I am not going into the full story, since that might take manner too lengthy. However right here is my tremendous brief reply: An electrical conductor has free prices that may transfer about (considerably). If you apply an electrical discipline, these prices transfer and create an electrical present. Usually, we consider these prices as electrons—however it might be one thing else. Should you take a steel and make one finish sizzling and the opposite finish chilly, the electrons on the recent aspect could have extra vitality and transfer about extra. These hotter electrons unfold out and on the chilly finish the electrons have much less vitality. The quantity of cost separation is determined by the actual steel.
Now take one other steel with two ends at totally different temperatures. However since this steel is totally different than the primary one, it’s going to have a special cost separation on the cold and hot ends. When these totally different metals are put collectively, they’ll type a kind of battery—not an excellent battery, however nonetheless it is like a battery. And increase—there’s your thermoelectric generator.
If you’re interested by constructing a thermoelectric generator to energy your own home, I’ve some dangerous information. This stuff are very inefficient. You want fairly massive temperature variations to get one thing helpful out of them. Nevertheless, there’s additionally some excellent news. These thermoelectric turbines haven’t any shifting components. No shifting components means they’re small and fairly dependable. And for this reason they’re utilized in some spacecraft (like Voyager, Cassini, and others). With the intention to make a temperature distinction, the spacecraft will use a radioactive supply that stays highly regarded—and actually that is it. That is how your radioisotope thermoelectric generator (RTG) works. It is identical to the paperclip and copper wire generator—besides that it is manner higher.
However wait! There’s extra. You are able to do one thing else with two totally different metals. What if I take advantage of the identical two metals, however as a substitute of placing the ends at totally different temperatures and getting a voltage, I join them to a battery? Additionally, I’ll put the 2 ends in water simply to make it a bit of bit simpler to measure the temperature. With the intention to get a measurable impact, I made two adjustments: I am utilizing nichrome wire as a substitute of metal and I made a number of junctions in collection. This is what it seems like.
Each beakers of water begin off at room temperature. There are some further wires you see—these are to measure the temperatures of the 2 quantities of water similar quantity. Now once I hook up a D-cell battery, I can measure the temperature as a operate of time. I ought to see one beaker of water enhance in temperature and the opposite lower, however it does not fairly work. I have to maybe enhance my setup, however one thing like this could work. That is referred to as the Peltier impact (when it really works). It is the alternative of the Seebeck impact.
Here’s a higher demonstration. If I take the electrical motor off the thermoelectric generator, I can apply a voltage. On this case, one aspect will get heat and the opposite aspect will get chilly. You can really feel it together with your arms, however that does not work over the web. As a substitute, I can present you this infrared picture.
Sure, that is principally a fridge. It isn’t very environment friendly in cooling issues, however you can also make a brilliant small system that may lower the temperature of one thing with none shifting components. The Peltier coolers are very helpful in cameras which can be very delicate to thermal noise. They’re additionally helpful for protecting your drink chilly while you’re driving in your automotive. They even make thermoelectric wine coolers (the opposite title for a Peltier cooler).
OK, there’s one last item you are able to do with two totally different metals (simply in case you do not wish to construct a radioactive thermoelectric generator). You should use the 2 totally different metals to measure temperature. Sure, that sensor I positioned within the beaker of water labored by measuring the voltage produced by two totally different metals with a temperature distinction.
If you are able to do all of this with simply two items of steel, simply think about what you would with three.