Hilsch

Hilsch refers to the Hilsch effect, also known as the Ranque–Hilsch effect, a phenomenon in which a stream of compressed gas passing through a vortex tube separates into a hot and a cold outlet without external heat exchange or moving parts. The device is commonly called a Hilsch tube or Ranque–Hilsch tube.

A vortex tube consists of a short cylindrical chamber with a tangential or converging inlet and outlets at each end. Compressed gas is forced into the tube, generating a strong swirl. A flow divider or valve adjusts the distribution of gas between the hot and cold outlets, which lie at opposite ends of the tube. The cooling effect is obtained at the cold outlet, typically with the hot outlet serving as the exhaust for the remaining gas.

In 1934 Georges Ranque first reported temperature separation in a vortex tube; Rudolf Hilsch later provided analysis and demonstrations in the late 1940s, leading to the combined names Ranque–Hilsch. The precise mechanism remains the subject of ongoing research; explanations emphasize energy separation due to swirling, viscous dissipation, radial and axial transport of energy, and other complex flow interactions within a compressible, non-equilibrium flow.

Performance depends on inlet pressure, gas type, tube length, diameter, and the split between hot and cold flows. Cold outlet temperatures can be substantially cooler than the ambient, while the hot outlet is correspondingly hotter, with no external heat added. Vortex tubes have no moving parts, require only a compressed gas supply, and are used for spot cooling, electronics cooling, plastic welding, and laboratory demonstrations. Limitations include modest cooling power for a given pressure, energy waste with the hot stream, sensitivity to operating conditions, and noise.