Thermodynamics: Engineer vs. Physics (1 Viewer)

[Mike Wladyka]

Hey Guys anyone else want to join in? This is going to be a thermo debate started by me and edwin_c

Hey Edwin_C,

i hope that you are going to be in this just for the fun of technical debates...

ok, so my background is this: B.S. Chemical Engineering 2002, Cleveland State University, Magna Cum Laude

i have taken thermo in three standpoints: 1. Engineering (pretty every class used thermo, so 5 years) 2. Physics (1/2 semester) 3. Physical Chemistry (mainly statisical, 1 semester)

Please let me know background so that this can be a good friendly debate

Mike

 

[Bill Catherall]

BS Mechanical Engineer, 1998. I took the required 2 semesters of thermo. I loved the first semester that dealt mainly with the theories and cycles. I caught on to it quickly and aced the course. Second semester was tough as I tried to wade my way through all the number crunching and formulas. I had a hard time catching which formula to use where. Plus the course was accelerated since it was a spring semester. I squeeked by with a C.

So if it's theory you want to debate then I'll enjoy this. If you want to crunch numbers then I'll just watch from the sidelines.

So what's the first topic up for debate?

 

[Mike Wladyka]

For those joining in, such as bill...the initial discussion started in the speaker and subs section under most over priced speakers...starts on page 5 between me and edwin c...about the laws of thermodynamics (1st, 2nd, 3rd) and how they are defined and different between physics (which i believe his major is) and engineering (which i am)...

i would post a link to the forementioned thread but i can't since i am relatively new here

please read up on this thread so that you know what we are talking about it...if you can't find it, i will give a summary:

i said that the 1st law dealt with mechanical energies, such as kinetic, work, heat, for mainly closed systems (i actually said only, but i meant almost only...edwin caught that one)

the 2nd law brings in enthalpy for reactions processes...while he contends that entropy is the dominating factor, and 3rd law we were in almost argeement upon being related to gibbs free energy, although he contends that it defines gibbs free energy

that is a summary, sorry if i mis-paraphrased you edwin

 

[David-S]

BS in materials engineering '02(Vtech), currently at Udel doing grad work...

Agreed on the theory vs number crunching

 

[Mike Wladyka]

Yeah, engineers hate to do the number crunching!!!

it should be mostly theoretical

so what are your guys thoughts on the laws of thermo?

 

[Edwin_C]

b.s. in biomedical engineering at mit, 2003.

the only real standpoint i have is my dad, who's a chemical engineer.

i'll respond later on when i get off work.

 

[Mike Wladyka]

sorry edwin i thought you were saying that i was a biomedical engineer in the previous post...

wow, MIT, this should be fun

 

[Andrew Testa]

B.S. Physics, '88; Something-or-other cum laude, I don't remember; Space Robotics Engineer since then, and I know how to use a browser and a text book.

engineering history of the laws of thermodynamics

Direct definition of the three laws

laws in basic terms

So, what is there to debate? These laws are well known and quite old. The only thing I can see that can be debated is whether or not it's worth the effort to try and correct people's misunderstandings of the second law.

Andy

 

[Bill Catherall]

Okay, I went and read the other thread about high priced speakers and I think I know what Mike is getting at here. Unfortunately, it's been a while since I sat in an engineering thermo class or looked at my text books so I don't remember the exact wording used to define each law. When I get home I'll look at my text books and see if the engineering books differ from the physics books.

Fortunately, it isn't important to know whether or not enthalpy is the 1st or 2nd law as long as one understands what it is.

 

[Mike Wladyka]

the debate comes in between different statements of the second law...in the thermodynamics and engineering books i have, the second law is not listed as deltaS >= 0, but in physics books it is...obviously you can derive the engineering second law from deltaS >= 0, what i am saying that entropy no longer plays a big part in any of the subsequent equations, or in usefullness of solving "real world 2nd law" problems, making entropy meerly a theoretical principle. Therefore, the second law is not about entropy...but about enthalpy and mechanical energies. However, Entropic Energy is usefull in the third law. I believe that this is why my thermo books don't list the same law as it appears in physics books...there has to be thermo PHD's who write and teach thermo books, and they do it without using deltaS >=0 as the real second law

 

[mark alan]

BS Chemical Engineering
MS Environmental Engineering
JD Patent Attorney

If you guys invent a new method of moving information electrically that defies the laws of physics, I will be more than happy to help you patent it.

 

[Mike Wladyka]

Hi Mark,

How about a liquid solution with a high ion concentration?

 

[mark alan]

liquid interconnects?

I can imagine the marketing materials now.

 

[BrianW]

B.S. in Physics, 1982.

Yeah, you heard me. 1982.

I pretty much remember that thermodynamics has something to do with heat.

Am I right?

 

[Edwin_C]

i'm currently working on a technology that defies quantum physics. quantum physics says that 2 electrons can't occupy the same space at the same moment in time. my "device" allows me to put an infinite amount of electrons in the place of one. the new particles i call mulectrons. the most important thing about mulectrons is that they have the capability to remember, much like RAM does. so the multiple particles, seeming like 1 particle, can actually store infinite amount of data.

dunno when it'll be done, however. i figure, if i sleep constantly for the next 2 years... i'll have it finished.

well mark.. you said defies the laws of physics and that's what i gave you .

ok i'm really bored at work... my mind is wandering hahah. i'll throw my arguments once i get home.

 

[Bob Graz]

BS Electrical Engineering 1979,(I guess that beats 82) I never took thermo, but I took electromagnetic wave theory

 

[Andrew Testa]

Mike,

Well, there certainly aren't 2 different laws for engineers and physicists!

Enthalpy, frequently used in steam and refrigeration processes, is an adiabatic element; changes in enthalpy are related only to proportional changes in pressure and volume. No external energy is added or removed from the process (the definition of adiabatic). So enthalpy is properly a result of the first law, since only conservation of energy is required.

The second law does not need to be defined in terms of entropy, although it is necessarily implied. A rigorous definition of the second law without mentioning entropy is:

It is impossible to construct an engine that, operating in a cycle, will produce no other effect than the extraction of heat from a source and the conversion of this heat completely into work.

Quoted from a physics text, BTW.

So entropy isn't mentioned. It just states you can't completely convert heat to work. Entropy is implied by what is omitted: there is no mention about converting work to heat. In fact, it is quite possible to completely convert work into heat with no loss. This introduces a one-sidedness to the universe: Heat can't be completely converted into work, but that work can then be completely converted back to a lesser amount of heat, which can't be completely converted back into work, but that work can be completely converted back into a lesser amount of heat. See the declining heat energy in the repeated conversions?

This one-sidedness is Entropy. This is what separates the 1st law from the 2nd. the first only requires that energy be conserved, whether in adiabatic, isochoric, or isobaric processes. The second adds that you always lose heat when you convert it into work, and that you can never regain that heat. The system always tends toward a lower energy state. Therefore, even if your derivation of the second law doesn't state that deltaS>=0, it is implied. But the nature of the law is that entropy is a factor in ALL "real world" 2nd law problems, even if you don't specifically have to calculate its values: It's built in, so to speak.

Most physics texts in thermodynamics derive the 2nd differently from what you see in engineering mostly because they are concerned with the statistical thermodynamics of particle systems, where entropy is a major concern, rather than the production of work. So their derivations stem from what is omitted in the text statement of the law above. Engineering is more concerned with the mechanics of producing work, so any mention of entropy is secondary. Both derivations stem from the same statement of the 2nd law, however. They both mean the same thing, just aimed at different audiences.

Andy

 

[Nick Sievers]

In this thread we obey the laws of Thermodynmaics!!. Sorry, had to be done.

Simpsons joke

I'm way out of my league here.

 

[Grant B]

I think we all know where this is going....
Battle of thermodynamics and engineering
A new Fox reality show!!!!
Sorry none of you can be contestants; just young females in halter tops.....and you know to much

 

[Andrew Testa]

Grant,

And the 2nd law dictates that those halter tops will eventually move to a lower energy state. See! Physics CAN be fun!

Andy