how well do you know turbos?
10-14-2005, 11:36 PM
#32
Originally Posted by jonp
9
I missed most of the VNT questions, because I've never researched them. I also missed the invention date range, because they were so close together. I know that turbos were used in WW1.
I don't like their answer to this question:
2. The turbo derives its energy source from:
A. The temperature of the exhaust gas
B. The pressure of the exhaust gas
C. Both the temperature and pressure of the exhaust gas
D. The engine power
They say it is letter C and I say it is letter B. The temperature is something that can create more pressure. Temperature does not add power, but increased pressure resulting from higher temps will increase power. If you are running the same pressure, but only hotter, do you think it will make more power than someone with less temperature and the same pressure?
If 2 scenarios have the same pressure, but one is hotter, I'd take the cooler one.
Someone help me understand how temperature alone without increasing pressure will make more power.
I missed most of the VNT questions, because I've never researched them. I also missed the invention date range, because they were so close together. I know that turbos were used in WW1.
I don't like their answer to this question:
2. The turbo derives its energy source from:
A. The temperature of the exhaust gas
B. The pressure of the exhaust gas
C. Both the temperature and pressure of the exhaust gas
D. The engine power
They say it is letter C and I say it is letter B. The temperature is something that can create more pressure. Temperature does not add power, but increased pressure resulting from higher temps will increase power. If you are running the same pressure, but only hotter, do you think it will make more power than someone with less temperature and the same pressure?
If 2 scenarios have the same pressure, but one is hotter, I'd take the cooler one.
Someone help me understand how temperature alone without increasing pressure will make more power.
Probably has something to do with the ideal gas law PV=nRT.
9 points as well
10-15-2005, 01:27 AM
#33
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Originally Posted by jonp
(paraphrased) Temperature doesn't increase power, but temperature increases pressure and that increases power. It's better to run cool than hot. QUESTION: If you are running the same pressure, but only hotter, will it make more power than less temperature and the same pressure?
Originally Posted by MVWRX
The thing about that question is that they never took physics/chemistry. Pressure and temperature have a positive correlation (PV=nRT)...therefore if it's hotter, it is neccesarily at a higher pressure. I said B also, because the higher temp just leads to a higher pressure, and it's really the pressure that turns the blades in the turbo.
Originally Posted by GotBoost?
+2
Because this is a big mistake a lot of people make: they conflate the stuff like equations and "laws" they learn in science with what is used for actual engineering. Car engines is a pretty good example, and another good example is the gross overshoot of transistor models taught to undergraduate electrical engineering students which many subsequently erroroneously use and cause some satellite somewhere to crash.
Originally Posted by STIdevildog
Probably has something to do with the ideal gas law PV = NRT
Please think of the kittens.
10-15-2005, 01:30 AM
#34
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I guess an analogy of what I'm trying to say with the ideal gas law is with ohm's law.
Most people know V=IR.
Well, that's correct, v equal IR... but, what the heck does that really mean??? You know? Because for R, well you can have imaginary impedences the way you can have imaginary numbers, you can have frequency dependences, this ohm's law has no kind of compensation for any number of billions of phenomena, etc. etc.
Just as you really can't actually do any useful real world evaluation of electronics with JUST ohm's law, same goes w/ the ideal gas law.
People would be VERY surprised how empirical engineering is; people naturally assume it is "scientific", like there's an uber genius at NASA who plugs numbers into equations and does some uber math, and out pops a friggin' space shuttle.
Interesting piece of useless trivia is the way complicated structural components were designed before the advent of computers running finite element analysis: build it, put sandbags/weights on it until it breaks; now you've got the yield stress for one particular point on your airplane wing you just stressed to failure.
Most people know V=IR.
Well, that's correct, v equal IR... but, what the heck does that really mean??? You know? Because for R, well you can have imaginary impedences the way you can have imaginary numbers, you can have frequency dependences, this ohm's law has no kind of compensation for any number of billions of phenomena, etc. etc.
Just as you really can't actually do any useful real world evaluation of electronics with JUST ohm's law, same goes w/ the ideal gas law.
People would be VERY surprised how empirical engineering is; people naturally assume it is "scientific", like there's an uber genius at NASA who plugs numbers into equations and does some uber math, and out pops a friggin' space shuttle.
Interesting piece of useless trivia is the way complicated structural components were designed before the advent of computers running finite element analysis: build it, put sandbags/weights on it until it breaks; now you've got the yield stress for one particular point on your airplane wing you just stressed to failure.
Last edited by verc; 10-15-2005 at 01:39 AM.
10-18-2005, 11:17 AM
#36
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Verc, I appreciate that I didn't use the ideal gas law perfectly...however, in this case, it does model the situation well enough to enrich one's understanding of a turboed engine. I don't need a lecture on when to use and when not to use the physical chemistry I have learned; if you want to discuss the merits of the ideal gas law in THIS example, I'd be more than happy to discuss with you the deviations from ideal and how they are only deviations at the limits of the equation (ie. when volume approaches 0 or when pressure becomes extreamly high). I think you'll find, however, that these minute deviations only affect a quantitative modeling of the situation, and I'm sure you'll agree that a qualitative understanding of a turbo is advanced enough considering we're on an online forum.
The bottom line is that the question in the quiz is very misleading, because it is impossible to seperate the effects of pressure and temperature on a mass of air being forced through an impeler. What they really wanted to ask/show is that the air before a turbo impeler is both hotter AND higher pressure than the air after the impeler, and the energy released as the air gets cooler and lower in pressure goes into turning the impeler.
The bottom line is that the question in the quiz is very misleading, because it is impossible to seperate the effects of pressure and temperature on a mass of air being forced through an impeler. What they really wanted to ask/show is that the air before a turbo impeler is both hotter AND higher pressure than the air after the impeler, and the energy released as the air gets cooler and lower in pressure goes into turning the impeler.
Last edited by MVWRX; 10-18-2005 at 11:21 AM.
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