High-amplitude thermoacoustic effects in a single pore

Nonlinear effects on thermoacoustic gain in a single pore are investigated experimentally. By creating a sharp temperature gradient in a uniform cross-section pore, the effect of high displacement amplitudes relative to the stack length is isolated from other high amplitude effects and also from effects due to geometrical discontinuities. The experiment probes displacement amplitudes which lie beyond the range of validity of the linear theory. The complex compressibility of nitrogen gas in the pore is measured for displacement amplitudes ranging from 2.5% to 60% of the stack length. No changes in the thermoacoustic response are observed over this range. Extending the upper limit to 175%, the power flow, as a function of the squared ratio of the displacement amplitude and the stack length, behaves linearly over the entire range.