The phrase “warmth engine” would possibly set off some unhealthy reminiscences out of your introductory thermodynamics course. However don’t be concerned, I’m going to point out you the best warmth engine you possibly can presumably picture—the thermoelectric generator (TEG).
The essential thought behind a warmth engine is to attract some helpful power out of a temperature distinction. This output power could possibly be mechanical or electrical—and different bizarre stuff. However there is a very primary instance that you’ve got in all probability seen: the steam engine. You warmth up some water to make steam, which may develop and push one thing. Then it condenses to let one thing shrink.
For this steam engine to work in any respect, you want the skin 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 need a extra in-depth rationalization of the mechanics of a steam engine, try this video.
Now for the only warmth engine you’ll ever see—you possibly can even make this your self. You simply want a paperclip and naked copper wire (or any two completely different metallic wires). I am assuming this can be a metal paperclip. Minimize 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.
Significantly, this setup alone goes to be a thermoelectric generator. How cool is that?! With a purpose to get this to work, simply put one finish of the copper-steel junction into one thing scorching 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 gadget, I’m simply going to attach the output to a voltmeter. For my scorching finish, I’m going to make use of a scorching 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 possibly can 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, when you have been questioning.)
What you might be seeing right here is the Seebeck Effect (named after Thomas Seebeck). Two completely different metals collectively at two completely different temperatures can create an electrical present. The impact is extra pronounced with a bigger temperature distinction and a few metallic combos work higher than others—however there it’s, your thermoelectric generator.
Truly, you may make a greater generator through the use of a semiconductor as a substitute of two completely different metals—however the two metallic model is means simpler to construct. Here’s a demo with a semiconductor. The gadget is sandwiched between two aluminum legs, with one leg in scorching water and the opposite in chilly water. The output from the gadget 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 may take means too lengthy. However right here is my tremendous quick reply: An electrical conductor has free fees that may transfer about (considerably). Once you apply an electrical subject, these fees transfer and create an electrical present. Usually, we consider these fees as electrons—but it surely could possibly be one thing else. For those who take a metallic and make one finish scorching and the opposite finish chilly, the electrons on the recent aspect could have extra power and transfer about extra. These hotter electrons unfold out and on the chilly finish the electrons have much less power. The quantity of cost separation will depend on the actual metallic.
Now take one other metallic with two ends at completely different temperatures. However since this metallic is completely different than the primary one, it’ll have a distinct cost separation on the cold and warm ends. When these completely different metals are put collectively, they are going to kind a kind of battery—not an excellent battery, however nonetheless it is like a battery. And increase—there’s your thermoelectric generator.
In case you are fascinated with constructing a thermoelectric generator to energy your home, I’ve some unhealthy information. These items are very inefficient. You want fairly large temperature variations to get one thing helpful out of them. Nevertheless, there’s additionally some excellent news. These thermoelectric mills haven’t any transferring components. No transferring components means they’re small and fairly dependable. And that is why they’re utilized in some spacecraft (like Voyager, Cassini, and others). With a purpose to make a temperature distinction, the spacecraft will use a radioactive supply that stays extremely popular—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 means higher.
However wait! There’s extra. You are able to do one thing else with two completely different metals. What if I exploit the identical two metals, however as a substitute of placing the ends at completely 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 just a little bit simpler to measure the temperature. With a purpose to get a measurable impact, I made two modifications: 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 perform of time. I ought to see one beaker of water enhance in temperature and the opposite lower, but it surely does not fairly work. I must 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 might really feel it together with your palms, 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 is not very environment friendly in cooling issues, however you may make an excellent small gadget that may lower the temperature of one thing with none transferring components. The Peltier coolers are very helpful in cameras which are very delicate to thermal noise. They’re additionally helpful for holding your drink chilly when you are driving in your automotive. They even make thermoelectric wine coolers (the opposite title for a Peltier cooler).
OK, there’s one very last thing you are able to do with two completely different metals (simply in case you do not need to construct a radioactive thermoelectric generator). You need to use the 2 completely different metals to measure temperature. Sure, that sensor I positioned within the beaker of water labored by measuring the voltage produced by two completely different metals with a temperature distinction.
If you are able to do all of this with simply two items of metallic, simply think about what you possibly can with three.