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Z31 know-it-all
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But the point we've all been trying to make, is that simple volume is not enough. The heat expansion is required to increase the impelling force, essentially a volume increase, but not in so few words. Besides as Mike K. said other things are at work in the turbine chamber. A turbo is spinning at supersonic speeds in a highly confined area, things tend to work a bit differently.
How does the air get heated and expand inside the turbo? What source creates this heat?
 

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AZ-ZBum said:
By expansion, do you mean more or less pressure?
More pressure, in the direction of impeller rotation. The inside of a turbine housing is made to specifically use this flow and concentrate it, it's not simply a housing for the turbo to sit in. It's just as tuned for specific useage as the rest of the engine is.
 

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More pressure, in the direction of impeller rotation. The inside of a turbine housing is made to specifically use this flow and concentrate it, it's not simply a housing for the turbo to sit in. It's just as tuned for specific useage as the rest of the engine is.
Uh..... :topic: :topic: :topic:
 

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AZ-ZBum said:
How does the air get heated and expand inside the turbo? What source creates this heat?
There is no addition of heat. Not sure where it would be added from. The power cycle in the combustion chamber is the only source. The exhaust gases are over 1000 degrees, coming out of a confined space (the turbine inlet nozzle) into a more open space (the turbine chamber) , expansion pretty much has to happen. As the gases hit the turbine blades, they are also expanding, providing more impelling force. Think of it as throwing a rock at something, and then throwing a stick of dynamite at the same object, exploding right as it touches the target. Which one do you think will go farther, the target hit by the rock, or the target hit by the dynamite........ That's the difference between simple pressurized air flow (as in like the air hose at the gas station), and expanding exhaust gases in the turbine chamber.
 

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Marc Z31 said:
You're not wrong, you're just a little :topic:
Housing design is what focuses the exhaust gases, and everything else, on the turbine blades. It's pretty important in and of itself.
 

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Housing design is what focuses the exhaust gases, and everything else, on the turbine blades. It's pretty important in and of itself.
The compressor side focuses the intaken air and pressurizes it. But the exhaust side is primarily responsible for taking the hot pressurized air and making the turbine spin. Compressing the air take energy. Which is what the turbine side is trying to avoid. So no. The turbine side does not pressurize air. It actually unpressurizes the air a bit. Which is why the exhaust after the turbine is cooler than the exhaust on the manifold side of the turbine. The focusing of the exhaust gases onto the turbine blades is what creates the velocity of the exhaust gas. Simple fluids of motion law says that as volume of fluid (exhaust gas in this case) goes from a large cross-sectional area to a smaller cross-sectional area must increase in velocity. The housing does this velocity change. But the turbine itself is just a fan that captures this high speed air.
 

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AZ-ZBum said:
The compressor side focuses the intaken air and pressurizes it. But the exhaust side is primarily responsible for taking the hot pressurized air and making the turbine spin. Compressing the air take energy. Which is what the turbine side is trying to avoid. So no. The turbine side does not pressurize air. It actually unpressurizes the air a bit. Which is why the exhaust after the turbine is cooler than the exhaust on the manifold side of the turbine. The focusing of the exhaust gases onto the turbine blades is what creates the velocity of the exhaust gas. Simple fluids of motion law says that as volume of fluid (exhaust gas in this case) goes from a large cross-sectional area to a smaller cross-sectional area must increase in velocity. The housing does this velocity change. But the turbine itself is just a fan that captures this high speed air.
I think you misunderstood what I said. The shape of the housing simply directs the exhaust gases to, and to remain in contact with, the turbine blades. That's what I meant by "focus". I agree with the rest of what you said. :cheers: We seem to be on the same page on a few things.

Well guys, it's been real, it's been fun, but it's not been real fun........Time for me to make my appearance in the real world, I have to go to work. See ya guys tommorrow. Try not to tear the place up while I'm gone, K? :)
 

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Well guys, it's been real, it's been fun, but it's not been real fun........Time for me to make my appearance in the real world, I have to go to work. See ya guys tommorrow. Try not to tear the place up while I'm gone, K? :)
A learning experience it has been. Maybe you could seperate this discussion from the original topic and make it it's own thread? Maybe sticky it or something?

Yeah. I need a drink. Now where'd I leave my bar....
 

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Icy Hot Stunta
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AZ-ZBum said:
How does heat and expansion drive the turbo? Where is the heat generated from? What is expanding? If this is such a simple concept, it should be very easy to explain. So please enlighten us.
Look up the tubine power equation in one of your thermal textbooks from when you were in school.

Temp drop accros the turbine

heat transfer rate-power+mass flow(specific enthalopy before turbine-specific enthalopy after turbine+Velocity before turbine squared-Velocity after turbine squared/2)

Expansion power or reaction is the isontropic enthalopy change in the wheel vs the change in isentropic enthalopy across the whole stage.

These are non-rigorus calculations that don't take into consideration blade geometery swirl losses, etc. I could be wrong, its just off the top of my head.

Its not far off though, I don't have time to really get into this, I could write an article and get paid.
 

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Icy Hot Stunta
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AZ-ZBum said:
A learning experience it has been. Maybe you could seperate this discussion from the original topic and make it it's own thread? Maybe sticky it or something?

Yeah. I need a drink. Now where'd I leave my bar....
Haha too bad you are in az, discussing this over drinks would be more fun.
 

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Icy Hot Stunta
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AZ-ZBum said:
The compressor side focuses the intaken air and pressurizes it. But the exhaust side is primarily responsible for taking the hot pressurized air and making the turbine spin. Compressing the air take energy. Which is what the turbine side is trying to avoid. So no. The turbine side does not pressurize air. It actually unpressurizes the air a bit. Which is why the exhaust after the turbine is cooler than the exhaust on the manifold side of the turbine. The focusing of the exhaust gases onto the turbine blades is what creates the velocity of the exhaust gas. Simple fluids of motion law says that as volume of fluid (exhaust gas in this case) goes from a large cross-sectional area to a smaller cross-sectional area must increase in velocity. The housing does this velocity change. But the turbine itself is just a fan that captures this high speed air.
But this is only one componet of power recovery that the turbine uses.
 

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Marc Z31 said:
A gas turbine engine works in this way, but not a turbocharger. EGT's are hotter on turbo cars because of the severely increased backpressure. The turbocharger works as a product of thermal expansion, but it does not actually have any sort of expansion inside of the turbocharger itself. All of the expansion happens in the combustion chamber, and as it passes through the exhaust manifold, it begins to cool actually. This is the reason racecars have heat wrap on the exhaust manifold, to keep the heat from passing to ambient air.

The air passing through the compressor housing is more dense and lesser in volume than the gas passing through the turbine side. Yes, the heat makes the turbo work, but there is only contraction of gasses in the turbo itself, from heat lost through exhaust manifolds and the turbine housing itself.
Turbochargers are gas turbines, the negine is the combustor. There is expansion accross the turbine, just like in a gas turbine. The equations for radial flow tubines apply.

Read some engineering level books on tubos. The best one is the aformentioned watson and genoda book, the only trouble is its out of print and you gotta find an old copy in a library.

Its no use arguing, I am speaking from fact, not opinion.
 

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Ok I'm gonna seperate this from the original scoop thread. Everybody remember where we parked........
 

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James said:
shouldn't this belong in forced induction then?
I'll take it under consideration. It started here, everybody knows where it is, it might as well stay here. Anybody else think it should be moved?
 
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