Quote:
Originally Posted by 123bobby123
The exhaust heat is resonsible for most of the kinetic energy that drives the turbine/rotating assembly in a turbocharger. This is becasue there is a large temperature drop across the turbo and this equates to a large pressure drop across the turbocharger. You can think of it as the opposite of what is happening in the compressor, the air is compressed and it heats up. Now the exhasut veolocity does of course contribute to the kinetic energy, but as I said before the mojority of this energy comes from the exhasut temperature drop. This is one of the reasons why you cermaic coat or wrap your exhasut manifold, to keep the exhasut as hot as possible when it enters the turbocharger.
Now as far as getting the turbo spinning with high pressure shop air, I'm not sure if you could get it upto proper operating speed, but you would not want too, becaue the temperature drop would cause the moisture in the shop air to freeze out and wreck the turbine wheel or freeze the turbine wheel to the housing, which is not good.
At school, in my senior design project, we test turbocharger bearings and we also are designing a test stand to test the turbocharger with compressed shop air. The hardest part of this was to see what tempearture we needed to get the air upto before it entered the turbine.
Bill
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What school do you go to? I'm not going to say you're wrong, you obviously work with the thing. However, I've got my thermodynamics book in front of me, turbines are modeled as isentropic (geez, it's been a while, isn't that the right word?).
"Heat transfer from turbines is usually considered negligible..." and if you think about the amount of insulating air around the thing, it makes sense.
Also, it says that the change in pressure at the same temperature causes a change in enthalpy, and the kinetic energy (opposite of the compressor which accelerates the particles, the turbine decelerates them).
Furthermore, EGT gauge manufacturers advise that thet the sensor can be placed up to 2" from the turbine with a drop of only 200 degrees F
http://www.autometer.com/productPDF/2650-1088.pdf
"If the exhaust manifold can not be removed, install the probe 1-2 inches after the turbo exhaust outlet (Exhaust gas temps could drop over 200˚ when installing after the turbo)."
If I'm reading that right, that's the difference from 1-2" from the port vs. 1-2" from the turbine outlet... So I'm not really sure where this huge temp drop comes from.
It's been a while, go easy on me
