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How to distinguish between concepts of Temperature

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Old   April 17, 2005, 22:06
Default How to distinguish between concepts of Temperature
  #1
Twiti
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Can anyone help me to distinguish between concepts of Temperature, naming "static, recovery and total temperature". What I cconcentrate on is which temperature I get with thermal couples welded on supersonic flow duct wall. Should this be a recovery temperature provided that the thermal couple without any stagnation effect(e.g. burid into the wall or rubdown)?
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Old   April 18, 2005, 12:58
Default Re: How to distinguish between concepts of Tempera
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Mani
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static T: the actual, thermodynamic temperature, related to internal energy.

total T: imagined temperature that you would get by isentropically decelerating the flow to zero velocity, measure of total energy. Any temperature probe that is inserted in a flow will approximately measure the total temperature, because there will be a stagnation point on the probe.

recovery T: However, because of finite size and convex shape of the probe, there are other effects. Around the stagnation point the flow accelerates, usually causing a reduction (recovery) of temperature. The temperature that you actually measure depends on the temperature distribution over the surface of your probe. Therefore it depends very much on the shape and usage of the probe. If the thermo couple is perfectly buried in the wall, you will essentially measure a combination of wall temperature and flow temperature. Depending on the size of your thermo couple and the material around it, the temperature of the wall may not be very influential. If you allow enough time for the wall to adjust to the flow temperature, i.e. zero temperature gradient near the wall, then you should really get the correct flow temperature. Be aware, however, that this is the temperature at the wall, which will in general not be the same as the static temperature outside the boundary layer. Instead it should be close to the (local) total temperature, since you have zero velocity at the wall.

btw: you are aware that this is not a forum for flow experiments?

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Old   April 18, 2005, 23:34
Default Re: How to distinguish between concepts of Tempera
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Twiti
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Thank you very much for your reply. I have been concentrating on CFD before, and get confused on those flow-experiment concepts (actually recovery temperature). Of couse this is a general-CFD forum, maybe a more suitable place to post such question than anywhere within this website.
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Old   April 19, 2005, 04:40
Default Re: How to distinguish between concepts of Tempera
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This discussion reminds me of the different types of energy equations. Can anyone explain when and why you would use the different forms. How would I specify boundary conditions for an enthalpy form energy transport equation? Furthermore, which enthalpy form would I use?!
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