Hey all. A question has come up regarding the rapid cooling of air, and if that cooled air is "denser" as result. On the surface, this seems trivial to me, but it quickly exceeded my ability to answer (not a physicist, just a hobbyist question asker and answerer at best). I've tried to draw a picture that summarizes the situation: http://i193.photobucket.com/albums/z260/JasonWilliamPics/Misc Pics/Junk Drawer/density_question.jpg (This application is in regards to using water/meth to cool incoming air to an engine, to thus make the engine produce more power on a hot day). On the right of the intake tube is ambient "air". For simplicity sake, lets say we're at sea level on a typical summer day. Track temps are 120degrees (not uncommon) and humidity is low at around 40%. On the left of the intake tube is the engine. Its sucking air thru the tube. Some folks have introduced a delivery system into the middle of that tube that sprays a fine mist of 50% water and 50% methanol. They report they see the 120deg air cooled to around 70deg at the exit of the tube. Typically, that's a very good thing. But... it being a very good thing is based on the assumption that cold air = dense air. So my question is, is that cold air really dense air too? Or is it that the pressure in the tube has changed and the air is no more dense than it was at 120deg? Keep in mind the air thru the tube is being sucked at a (guessing here) speed of 40mph. So its moving very quickly during this cooling process. I can make guesses at this all day long. For example: No, the air is no more dense than it was before. The pressure in the tube dropped. Yes, the air is denser. But the process of cooling sucked air at an accelerated rate from both down and upstream sources, creating a vacuum. Ect ect ect... I just don't have the background or knowledge needed to answer. Do any of you? Thank you for your time!