7

Sounds like I'm just a bit below average... right where I like to be.

 

Probably has something to do with the ideal gas law PV=nRT.

9 points as well

 

This is not wholly correct, but it is to safe to say you are correct in some cases. The answer to the question asked is: "maybe"

PV = nrt? Well... like, I know a lot of people try to do pv=nrt this and pv=nrt that, but, it doesn't work that way. It actually doesn't even have anything to do with the fact that it's IDEAL gas law, but that equation assumes paramters which they don't teach in a cursory overview of the chemistry/physics, so it would be erroneous to try to apply those equations to the real world. In fact, most people don't realize that even with an undergraduate bachelor's degree in science/engineering they are still equipped with inacurrate models to do accurate design in many cases.

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.

Once again, whenever someone quotes ideal gas law God kills a kitten.
Please think of the kittens.

 

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.

 

9 points

 

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.

 

11 points ftw

 

I got 5.

 

9 mostly guessed haha