NCEES ME TF 507

[landolakes]

I'm running through the latest NCEES Mechanical Thermal Fluids Sample Problems and #507 has got me stumped on where they got the solution for Nusselt Equation...

Maybe I'm problem'ed out or something, but I tried to duplicate the answer with my own notes, MERM, NCEES Ref...but the equation they used for solution does not match any of the givens for turbulent flow in a cylindrical pipe... 

Again I may just be overlooking something, but any help would be appreciated!

 

[Audi Driver P.E.]

It is the turbulent liquid metal flow flow in a tube.  You know it's turbulent based on the Reynold's number.  See MERM 36-7, 18.  Note that when I worked that equation, I had slightly different results for the Prandlt number, and it still got me close enough.  You will note that liquid metal isn't exactly a Newtonian fluid, thus the flow characteristics are kind of whacky.

Also, note that knowing which Nu equation to use is a pretty important aspect of heat transfer that you will want to know for the exam.  Definitely learn when each one applies and why.

 

[landolakes]

Thanks, I will re-work with those references in mind... 

 

[mamba24]

Dearest Audi driver-

May I please ask for a favor? I've worked over problem 507 on the practice TF ...

is the solution correct? I don't believe that's the correct Reynolds, does the solution forget to divide by the gravity constant?

im sorry to trouble you. However there's a post about this problem and you address it however I sincerely believe the computed Reynolds number is not correct. When you get the chance may you please see it? Thank you!

pleasee wish me luck. This is my second time taking the exam and I put in well over 400 hrs. Any help is grand. 

 

[Habib]

Attached is my solution, hope it can help.

I wanted to post entire problem with solution but file size was probably too big.

View attachment 8696

 

[Audi Driver P.E.]

Dearest Audi driver-

May I please ask for a favor? I've worked over problem 507 on the practice TF ...

is the solution correct? I don't believe that's the correct Reynolds, does the solution forget to divide by the gravity constant?

im sorry to trouble you. However there's a post about this problem and you address it however I sincerely believe the computed Reynolds number is not correct. When you get the chance may you please see it? Thank you!

pleasee wish me luck. This is my second time taking the exam and I put in well over 400 hrs. Any help is grand. 

The NCEES solution is correct.  The exact value of the Reynolds number is fairly irrelevant, so long as you can make a determination of turbulent or laminar flow, which are (generally speaking) orders of magnitude determinations.  The NCEES solution uses density in lbm/ft^3, and so gravity is really irrelevant.  If you had a specific wt. in lbf/ft^3 (say from a table value) instead of density, then you would have to use a gravitational constant to make a conversion, because the dynamic viscosity uses lbm/ft^3 -sec units.