Overall balance vs. differential balance

[gfd43tg]

Hello,

when doing mass and/or energy balances, how does one know when one should use a differential balance over a total balance? It would help when knowing how to approach a given problem.

 

[Bystander]

Experience. Do it both ways until you see the differences.

 

[Chestermiller]

I think what Bystander is saying is that, if you have enough information to do the overall balance(s) and don't need to know details within the equipment, then you can use the overall balance. But, if you are missing information to do the overall balance, and the differential balance can provide that information, then you need to do the differential balance.

Chet

 

[Bystander]

Is there a universal set of rules? No. Any rough, general principles that can be commonly applied? "Small differences between large numbers argue for differential methods."
What balances are interesting/useful/relevant for the system being analyzed? Pipeline: mass out/mass in (a tough problem in custody transfer). Gold mining: recovered metal mass/ore mass or tailings mass/ore mass. Coal desulfurization: sulfur mass/coal mass or treated coal mass/untreated coal mass.
The approach to the problem is dictated by the problem statement.