Super insulation

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As Super Insulation a is thermal insulation refers to the heat losses under which dry, still air (0.026 m / K W /) is located.

construction

In the case of super insulation, one tries to prevent all three mechanisms of heat transfer . The construction can be done, for example, with evacuated foils or by pouring (also pressure-resistant). The following rules apply to the mechanisms of heat transfer:

  • In order to reduce heat conduction , the contact surfaces (solid contacts) in the insulation and spacers must be kept small, as these represent thermal bridges
  • The convection is prevented by evacuated gaps, whereby gases should have a residual pressure of less than one Pascal
  • The thermal radiation is achieved through surfaces with a low emissivity , in particular through materials that are highly reflective in as many wavelength ranges as possible

In order to be able to compare different superinsulations, the suppression of heat losses is given in the unit of thermal conductivity (usually only as a measure of the heat conduction), but this is strongly dependent on the ambient conditions of the superinsulation. The thickness of the insulation or the size of the insulated vessel can have an influence, since the thermal radiation increases with the surface of the outside without changing other parameters.

Applications

A relatively old example of a container with super insulation is the dewar (used as a thermos , cryogenic container ). In addition, super-insulation is used to store liquefied gases or to insulate superconducting magnets, in space travel or in stratospheric balloon experiments.

literature

Peter Stephan, Stephan Kabelac, Matthias Kind, Dieter Mewes, Karlheinz Schaber, Thomas Wetzel (eds.): VDI-Wärmeatlas . 12th edition. Springer-Verlag GmbH Germany, Berlin 2019, ISBN 978-3-662-52988-1 .

Individual evidence

  1. ↑ Peter Stephan, Stephan Kabelac, Matthias Kind, Dieter Mewes, Karlheinz Schaber, Thomas Wetzel (eds.): VDI-Wärmeatlas . 12th edition. Springer-Verlag GmbH Germany, Berlin 2019, ISBN 978-3-662-52988-1 , Part K6 Thermal radiation - super insulation by Harald Reiss.