Closed System Energy Balance

[@joaomarcelino4967]

Hey , how do I know if there is any work done to or by the system?

[@apm]

A pump is an example of work done on the system. A generator is an example of work done by the system.

[@jaiminpatel3505]

When you were calculating the potential energy on the yowling cat problem, I think you were meaning to multiply 8.346 to the gravity and height, right?

[@apm]

Yes! At 21:49, I used 8.314 instead of 8.346 like I had on the line above. I must have been thinking about the universal gas constant (8.314 J/mol-K).

[@salmaalmansoori5565]

thanke you so much , really helped me

[@youtubemaster3374]

And the term q u were saying is actually head provided or released?

[@apm]

Q is heat added to the system.

[@yasminezgb]

Is delta U in our equation equal to Q-W ?? helP !

[@apm]

+yasmine bouguezine Delta U is the internal energy change. If there is no kinetic or potential energy change (for the closed system) then, yes, Delta U = Q (heat) - W (work).

[@yasminezgb]

+APMonitor.com So i deduce here that... the gains or losses of heat or/and work are not due only to its internal energy like it has always been the case for our teacher ? ,(THANK YOU SIR )

[@apm]

Yes, the closed system energy balance should include kinetic and potential energy terms as well. However, in many cases these are negligible.

[@yasminezgb]

+APMonitor.com NOW i GOT it , Thank thee SO much ! thou are awesome :)

[@ferdinandtavarra82]

Thanks a lot..really useful.

[@GreenFootprint]

If your system is composed of the two rivers and the pump, then there will be no potential energy change for that system. I guess your system as per your calculation is from pipe inlet to pipe outlet including the pump ? The potential energy will be based on system inlet to system outlet, which is 40 ft.

[@youtubemaster3374]

That delta u is internal energy isnt it?

[@apm]

Delta U is the internal energy.

[@goldielocks2720]

Yep

[@sedderivativemadera5325]

how did you solve the mass work per mass in ex 2 i cant figure out? My answers are the not same as yours? plss help me. thank you !

[@apm]

My solution is shown at 7:15. Did I make a mistake on the unit conversion?

[@sedderivativemadera5325]

APMonitor.com when I calculated it my answer is 0.05 . how did you get the 0.33? ☺

[@apm]

Thanks for catching that - it may have been a calculator error. The correct answer is 0.05 BTU/lbm or 1.5e-5 kW-hr/lbm.

[@sedderivativemadera5325]

APMonitor.com thank you very much! These really help us!

[@cloretteangel]

very helpful, thank you!!

[@alejandrobenavides5035]

damn those imperial units are very confusing what on earth is Btu??

[@apm]

BTU = British Thermal Unit. Life is much easier in SI units.

[@goldielocks2720]

Thank you. Have you ever heard of this being done on a human?

[@apm]

An energy balance on a human? Yes, I think scientists may do this when studying weight loss, diet, and exercise. I couldn't point you to a particular reference, however, but a quick search in the scientific literature may turn up some results.

[@youtubemaster3374]

Sir i have no clue what my sir teach me. Or what u are teaching.

[@apm]

These videos are part of a Chemical Engineering course on material and energy balances. Here is the complete playlist: kzbin.info/www/bejne/h4bOdJipqa6rfKs I also recommend the LearnChemE channel. You may need some additional background information to understand this material.