In
fluid dynamics, the Ledinegg instability occurs in
two-phase flow
In fluid mechanics, two-phase flow is a flow of gas and liquid — a particular example of multiphase flow. Two-phase flow can occur in various forms, such as flows transitioning from pure liquid to vapor as a result of external heating, separ ...
, especially in a
boiler tube, when the boiling boundary is within the tube. For a given
mass flux
In physics and engineering, mass flux is the rate of mass flow. Its SI units are kg m−2 s−1. The common symbols are ''j'', ''J'', ''q'', ''Q'', ''φ'', or Φ (Greek lower or capital Phi), sometimes with subscript ''m'' to indicate mass is th ...
J through the tube, the pressure drop per unit length (which typically varies as the square of the mass flux and inversely as the density, i.e., as
) is much less when the flow is wholly of liquid than when the flow is wholly of steam. Thus, as the boiling boundary moves up the tube, the total pressure drop falls, potentially increasing the flow in an unstable manner. Boiler tubes normally overcome this (which is effectively a 'negative resistance' regime) by incorporating a narrow orifice at the entry, to give a stabilising pressure drop on entry.
References
Ruspini, Two-phase flow instabilities: A review, IJHMT, 71, 2013
System Instabilities https://web.archive.org/web/20060721232210/http://caltechbook.library.caltech.edu/51/01/chap15.pdfhttp://authors.library.caltech.edu/25021/1/chap15.pdf
Fluid dynamics
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