Total temperature

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The total temperature (also known as resting temperature or stagnation temperature ) is used to describe flowing compressible media, i.e. H. flowing gases . It is the established temperature of a gas flow when the flow velocity is reduced adiabatically (i.e. thermally insulated) to a negligibly small value, and is therefore one of the rest quantities .

Mathematically, the total temperature can be described as the sum of the static temperature that an observer moving with the flowing gas would feel and a kinetic component of the medium flowing with the velocity :

It is

  • the specific heat capacity at constant pressure, here assumed to be constant between and
  • the specific total enthalpy
  • the specific enthalpy .

If the flow comes to a standstill without loss of energy ( ), e.g. B. at a stagnation point , the static temperature rises to the stagnation temperature: . The stagnation temperature is therefore important in rocket and aircraft construction for the thermal load on surfaces in supersonic flows .

Analogous to the definition of the resting temperature, there is also a corresponding resting pressure for a one-dimensional gas flow , which, however , presupposes an isentropic ( i.e. not only heat-insulated but also friction-free ) return of the flow velocity .

In contrast to the idle pressure, the idle temperature remains constant even when the flow is subject to friction, provided the gas is ideal . A throttling (pressure reduction through internal friction ) takes place isothermally , provided that the speed increase can also be neglected.

literature

  • Willy JG Bräunling: Aircraft engines: Basics, aero-thermodynamics, cycle processes, thermal turbo machines, component and emissions . Volumes I + II. Springer, 2015, ISBN 978-3-642-34538-8 , pp. 124–129 ( limited preview in Google Book search).
  • VDMA standard sheet 24 575: Flow measurement of pneumatic components - application of ISO 6358: 1989 taking into account the influence of the flow rate
  • Werner Wunderlich, Erwin Bürk, Wolfgang Gauchel: Measurement in fluid technology / flow measurement - special features in pneumatics. In: Zeitschrift für Fluidtechnik O + P. April 2010.