Air that rotates around an axis (like a tornado) is called a vortex. A vortex tube creates cold air and hot air by forcing compressed air through a generation chamber, which spins the air at a high rate of speed (1,000,000 rpm) into a vortex. The high speed air heats up as it spins along the inner walls of the tube toward the control valve. A percentage of the hot, high speed air is permitted to exit at the valve. The remainder of the (now slower) air stream is forced to counterflow up through the center of the high speed air stream in a second vortex. The slower moving air gives up energy in the form of heat and becomes cooled as it spins up the tube. The inside counterflow vortex exits the opposite end as extremely cold air. Vortex tubes generate temperatures as much as 100 deg F (56 deg C) below the inlet air temperature. The fraction of hot air exhausted can be varied to change the outlet cold air temperature, with more exhaust resulting in a colder cold air stream (with lower flow rate), and less exhaust resulting in a warmer cold air stream (and higher flow rate).