I feel like these are not as common/popular as they were back in the day. Now it's all water cooling with those all-in-one setups. I always thought the Peltier coolers were cool (pun not originally intended, but now it is).

I was very young, probably as a teenager back in the 90s, when I discovered the existence of Peltier elements for the first time, and that one had been part of one of my former CPU coolers for all the time.

After an upgrade, I had this now unused CPU fan on my desk, and took it apart for whatever reason (because it and the screwdriver were there, I guess). And there I noticed that as part of the assembly there had been... another thin plate sandwiched between cooler and fan, separate and just held in place with the screws, and I now saw that it also had two wires for power that were spliced into the fan's power cable? Optically, this was clearly just a thin, static slate of something, maybe ceramic. Definitely no moving parts, why in the world does that need power.

I curiously applied some voltage, and was amazed that it turned cold! I played around with it a bit, and unwittingly touched the other side of it. Hot, surprisingly hot! It wasn't touching anything, that was just from the air around it!

I was mesmerized, good times.

It would have been far less interesting had you accidentally touched the hot side first. :)

Would it though? I guess I'd have been extremely confused, "why is there a thing that generates heat on my cooler", and hopefully I'd have also touched the cold side at some point, and I'd still have been mesmerized... I think?

My university surplus store was selling a huge batch of peltier elements that were used in cloud chamber research for very cheap. I bought them and connected some to a homemade water cooler loop circa 2006. I could generate temperatures around -20f in my dorm room IIRC. Condensation, and then frost would start to form quickly. It was an interesting project, for sure!

Sadly they’re extremely inefficient when compared to radiators and fans, whether directly on the heat source or across a water loop.

In the olden days of Pentium 3 (or Pentium!!! if you prefer), one guy graphed his Peltier element's performance vs. voltage and found a 115% efficient point (with assistance of his fan, ofc.)

Limiting voltage and coupling it with a very efficient cooler for its time, he overclocked his CPU a great deal.

Looked for the article, but it's possibly gone down with the downfall of old internet, because it was a personal webpage.

The real issue with Peltier junctions is that unless you shed the heat away from the "hot" side very effectively, the "cold" side will heat up even faster. That makes them kind of a non-starter.

See, I don't understand why there aren't strange shaped Peltier cells in order to increase the surface area on the hot side vs. cool side. Then it might be worth it...