Rijke tube

A Rijke tube is a thermo- acoustic resonator. It is named after Pieter Rijke Leonard, who described the underlying effect first in 1859.

The Rijke tube ( dimensions in order of magnitude: length: 1 m, diameter 0.1 m) is open at both ends of pipe, a heating grid is in its lower half., The tube is held vertically, the air rises through the heating to the heater grid, there is formed a vertical flow. Since the heat output of the heater grid is dependent on the flow rate of the air varies this, when the flow rate varies, which always passes through the smallest interference. When the heater grid as described in the lower half of the tube ( about 1 /4 of the length ) is arranged, so heat release fluctuations and acoustic pressure fluctuations ( associated with the speed fluctuations, but are phase-shifted ) in phase, the Rayleigh criterion thermoacoustics met and the resonance frequencies of the air column in the pipe to be excited. This is noticeable by clearly audible whistling. The effect is mainly due to the fact that the heat release fluctuation in the heating grid of the velocity fluctuation slightly lags ( phase delay ) so that pressure and heat release fluctuation ( approximately ) can be in phase.

As the flow is generated in the tube, is irrelevant for the effect. The pipe can thus also be arranged horizontally, if a flow is generated by some kind of pump.