I would like to get an explanations of an observed physical phenomena.
When a metal tube is placed vertically and heated and the air inside rises, the speed of the air moving through the tube continues to increase greatly when the tube reaches a certain temperature, despite no further increase in temperature.
I would like to understand why.
A little background:
Many years ago I was working on a construction project in the Kalahari Desert when I saw something unusual. In the works yard. There was a length of straight galvanised thin wall steel pipe standing vertically, about 15 cm dia and about 2.4 m long, that was making a very unusual noise like a jet engine. I went closer and saw that the bottom of the pipe rested on the corner of a tin box and was in the shade but the rest of the pipe was in the hot sun (45 degrees in the shade) and I was unable to touch it due to its high temperature. The noise was being generated by air that was being drawn up into the bottom of the pipe and then pushed out of the top at extremely high speed.
The only reason that I could see for this was that I was observing some sort of ram or standing wave effect and the air rising up the inside of the pipe had accelerated due to this. As the sun went down and the temperature dropped the phenomenon got less and less until it stopped. The same thing happened each day when the pipe got hot.