Rijke tube

P. L. Rijke was a professor of physics at the Leiden University in the Netherlands when, in 1859, he discovered a way of using heat to sustain a sound in a cylindrical tube open at both ends.

It is safer in modern reproductions of this experiment to use a borosilicate glass tube or, better still, one made of metal.

Making the gauze with electrical resistance wire causes it to glow red when a sufficiently large current is passed.

Rijke seems to have received complaints from his university colleagues because he reports that the sound could be easily heard three rooms away from his laboratory.

Lord Rayleigh, who wrote the definitive textbook on sound in 1877, recommends this as a very effective lecture demonstration.

[4][5][6] The sound comes from a standing wave whose wavelength is about twice the length of the tube, giving the fundamental frequency.

For half the vibration cycle, the air flows into the tube from both ends until the pressure reaches a maximum.

In this case, the cool air brought in from the bottom by the convection current reaches the gauze towards the end of the outward vibration movement.

Placing the gauze midway between these two positions (one quarter of the way in from the bottom end) is a simple way to come close to the optimal placement.

The Rijke tube is considered to be a standing wave form of thermoacoustic devices known as "heat engines" or "prime movers".

[12][13] (In demonstration models, the tube can be heated externally and steel wool can serve as a stack.