Lämpövihe

Lämpövihe is a Finnish term used primarily in educational contexts to describe an audible effect produced when heat interacts with a gas in a narrow channel or confined cavity, causing sound. The word combines lämpö meaning heat and vihe from viheltää, to whistle. In practice, lämpövihe refers to demonstrations that illustrate thermoacoustic coupling, where rapid heating creates pressure fluctuations that excite acoustic resonances, producing a whistle-like tone. The phenomenon is related to thermoacoustic oscillations and to devices such as the Rijke tube, which generate sound when a heater is placed in a column of air.

Mechanismally, when a gas is heated in a restricted geometry, its pressure rises and can drive oscillations if the system supports resonant acoustic modes. If heat input and the resulting pressure waves reinforce a particular sound mode, a periodic whistle emerges. The observed frequency and timbre depend on the temperature, the dimensions of the channel or cavity, and the gas properties.

In educational use, lämpövihe demonstrations help illustrate connections between thermodynamics and acoustics, such as the temperature dependence of the speed of sound, the behavior of compressible flows, and the concept of resonance. In professional physics literature, however, the term is not a standardized technical label; similar phenomena are usually described as thermoacoustic oscillations or flow-induced acoustic instabilities.

See also: thermoacoustics, Rijke tube, acoustics, adiabatic process. References to the term are mainly found in Finnish educational materials rather than in international scientific journals.