turbos and heat

[absolute]

ok i have read enough posts and heard enough of the babble, someone who knows enough about turbos to speak on the topic, please do so. I know about heat and the excitement of molecules, and all of that but what im asking for is this. Eplain to me, how HEAT, drives a turbo? Is it not just the forced air itself?, or it has to be hot air because I just dont beleive it. Someone actually knowledgable speak on it. Church.

[Checkered-Member]

ok i have read enough posts and heard enough of the babble, someone who knows enough about turbos to speak on the topic, please do so. I know about heat and the excitement of molecules, and all of that but what im asking for is this. Eplain to me, how HEAT, drives a turbo? Is it not just the forced air itself?, or it has to be hot air because I just dont beleive it. Someone actually knowledgable speak on it. Church.

Heat has absolutely nothing to do with spooling (spinning) a turbo, it is only the air velocity coming off the combustion camber.

[C-Kwik]

It's not really the velocity. It's the pressure differential. However, heat is a big part of the pressure as hot gasses within a fixed volume has more pressure. Also, the hot gasses when released through the nozzle of the turbine are then allowed to expand very quickly, which further helps to drive the turbine as the only place the expanding gas has to go is through the turbine wheel. The reason why the exhaust gasses cool when passing through a turbo is because of this expansion process. The hotter the gasses, the more the gasses will expand when it passes through the turbine. The more the gasses expand, the volume of gas will be available to drive the turbine.

[Def]

C-Kwik got it right with the expansion of the hot gas through the turbine. This is what cools the exhaust gas and powers the turbine. Velocity is also not factored into this AT ALL, as weird as it sounds.

If you could measure the enthalpy(heat energy) at the entrance and exit of the turbine then multiply this difference by the efficiency of the turbine then you will get the power production of that turbine in real time. Unfortunately this is more complicated and expensive than it sounds.

Search for turbines and thermodynamics, and maybe enthalpy to get an explanation on the web. Although I doubt most people will be able to read the graphs or understand most the terminology, as thermodynamics practically has its own vocabulary.

[C-Kwik]

I wouldn't say velocity has nothing to do with the spool. TYhe velocity of the air coming out of the turbine nozzle can affect spool greatly. But I would say the driving force behind the velocity is the result of the pressure differential and the expansion of the hot gasses.

[absolute]

thanks

[absolute]

sorry for the short one above my computer was trippin i typed a long one and it didnt work, "lab computer heh" anyway thanks kwik, for the explanation, and def i should probably look up some stuff on the web in general, i do have to take thermo, like next sem. we touch on it a bit in chem and engineering physics, shouldn't be a comprehend prob, but my turbo knowledge is growing and not as extensive as some here, I just wasn't going to accept hearing heat drives a turbo, when i know it has something to do with the pressure, i do understand that excited gases "expansion" helps the process though. I apreciate everyones response. preach.

[C-Kwik]

Good to hear you have this curious mindset. Not only will it help you become better in life, but that's the type of mentality that has gotten humanity this far with technology.

[Def]

I wouldn't say velocity has nothing to do with the spool. TYhe velocity of the air coming out of the turbine nozzle can affect spool greatly. But I would say the driving force behind the velocity is the result of the pressure differential and the expansion of the hot gasses.

Local velocity is a function of the turbine flowrate and cross sectional area. Flowrate is dependent on the restriction of the turbine and pressure differential(Q=Delta(P)/Delta(R) with correct units).

So I'm not saying a high velocity is not a good thing(it is), it will just naturally happen when you have a favorable flowrate. The more flowrate, the more the gas can expand(larger pressure differential or larger difference in restriction to the flow).

I'm not a thermo expert, but I've certainly never seen or heard of a formula involving turbine power/flow that even factored in gas flow velocity explicitly. They do take into account restriction and flowrate though, so I guess indirectly they look at velocity...

absolute, I wasn't trying to say you aren't intelligent(as your question shows that you are thinking about things and striving for a greater understanding, which is good), but there is an amazing amount of confusion vocabulary that goes along with ANY thermodynamics related graph. It really does take at least 1 class to really have any hope in having a working knowledge of all the variables and terminology one would need to even grasp the basics from most graphs and information. Thermo can be fun though, you should enjoy it when you take it. Analyzing powerplants can be annoying after a while though.