Another one I saw was a copper pipe.. the key is a heated wire mesh screen about 1/5th to 1/4 of the way up the pipe. The note is a resonance of the column of air in the pipe length.
The "thermodynamics" are as follows:
Warmth in the pipe expands the air and it rises - convection currents then draw air through the pipe. As the air transitions through the wire mesh screen, it is heated, expands rapidly, and causes a tiny reverse shock wave to pass back through the screen. So some of the hot air is then cooled when it gets to the cold side of the screen, contracting, and causing a low pressure zone, but this is immediately forced back through the screen by the convection current and heated again, so the high pressure shock wave passes back through the screen, cools, etc.
Note how a pipe held horizontally does not resonate? = no flow by convection. Like a flute when no-one is blowing. but - like a flute - when the air flow is above a threshold value, the oscillations begin and the pipe resonates at the natural frequency of the quarter-length of the wave being the distance from the hot mesh to the "long" end.... - I think?
The wire mesh needs to be a substantial wire thickness to hold the heat for the time he uses the Rijke's tube. Possibly his pipe is plastic - ABS, or something? - as it is cold enough to hold. Copper, steel, etc. gets hot.
Note: There is a very small amount of heat powering the tube when removed from the flame. Mostly creating the convection current, but a small proportion making the sound. Yet is is VERY LOUD, and Health and Safety recommend less than 1 minute exposure to such loud sounds before ear damage can occur! (I once had a table of something like 85dBA limit for a week's average industrial exposure, 90dBA continuous sound for hearing protection to be required, or max 10 mins exposure, 100 dBA for max 1 minute exposure, 110dBA for 0.1 minute exposure (6 seconds!), and a whole concert for Megadeath music!!).
I was testing a large air motor (single 10in dia piston powered by 28Bar air and when the valve opened to release the air the meter recorded 137 DB at 1 metre - with me holding the meter...). The "bang" (single pulse) caused permanent damage to me. (max 10 in a week) - It left my head ringing for hours, I have permanent tinnitus now. NOT NICE. So PLEASE wear ear defenders when playing with a Rijke's tube. (Over 100dBA!).
K2
The "thermodynamics" are as follows:
Warmth in the pipe expands the air and it rises - convection currents then draw air through the pipe. As the air transitions through the wire mesh screen, it is heated, expands rapidly, and causes a tiny reverse shock wave to pass back through the screen. So some of the hot air is then cooled when it gets to the cold side of the screen, contracting, and causing a low pressure zone, but this is immediately forced back through the screen by the convection current and heated again, so the high pressure shock wave passes back through the screen, cools, etc.
Note how a pipe held horizontally does not resonate? = no flow by convection. Like a flute when no-one is blowing. but - like a flute - when the air flow is above a threshold value, the oscillations begin and the pipe resonates at the natural frequency of the quarter-length of the wave being the distance from the hot mesh to the "long" end.... - I think?
The wire mesh needs to be a substantial wire thickness to hold the heat for the time he uses the Rijke's tube. Possibly his pipe is plastic - ABS, or something? - as it is cold enough to hold. Copper, steel, etc. gets hot.
Note: There is a very small amount of heat powering the tube when removed from the flame. Mostly creating the convection current, but a small proportion making the sound. Yet is is VERY LOUD, and Health and Safety recommend less than 1 minute exposure to such loud sounds before ear damage can occur! (I once had a table of something like 85dBA limit for a week's average industrial exposure, 90dBA continuous sound for hearing protection to be required, or max 10 mins exposure, 100 dBA for max 1 minute exposure, 110dBA for 0.1 minute exposure (6 seconds!), and a whole concert for Megadeath music!!).
I was testing a large air motor (single 10in dia piston powered by 28Bar air and when the valve opened to release the air the meter recorded 137 DB at 1 metre - with me holding the meter...). The "bang" (single pulse) caused permanent damage to me. (max 10 in a week) - It left my head ringing for hours, I have permanent tinnitus now. NOT NICE. So PLEASE wear ear defenders when playing with a Rijke's tube. (Over 100dBA!).
K2