Hi. I just read an article where following cooling method is described. Apparently it's very common, but I don't know what it's called: A gas under pressure is released into a vacuum through a small hole. The average particle speed in this beam of gas is the same as before, but the distribution is much narrower, and also all particles move in about the same direction. Although the energy didn't change, the temperature of the gas is much lower than before, because an observer flying next to the beam with the average particle speed would only see slowly moving particles. In short, thermal energy has been converted into kinetic energy. Now this seems a lot like the entropy of the gas decreased. The process looks irreversible though, so there surely must be a bigger entropy increase somewhere, but where? I suspect it's probably the increase in volume, but in the illustrations in the article the particle beam looks very narrow and the particles pretty localized.