Lindeburg Exam TF Problem 134

[LifeSucks]

I am currently working though the Lindeburg Mechanical Sample PE Exam - Afternoon Session for Thermal Fluids. I am having trouble understanding how to do problem 134 (attached). I'm not sure how they come up with the equation used in solution. Can someone help explain how to solve this?

View attachment Lindeburg Mech TF Depth 134.pdf

 

[Audi Driver P.E.]

The equation is derived from Fourier's law (which also isn't given adequate treatment in the MERM).  You will have to refer to a Heat Transfer text book for the explanation.  Mine has a reasonably good one.  Heat flux (q) is equal to -k (dT/dx) (in a vector analysis, that is a partial derivative).  Thus, for a heat generating source (i.e. G=dq/dt), you have a second order derivative.  Don't expect to have to be doing this type of equation deriving on the exam, but it is good to know.

 

[Audi Driver P.E.]

I will also add, that it quickly becomes clear that a) Lindeburg provides what is needed for the exam in his text, and b) asks practice questions that probe into the "why" and "how" behind the subject matter, in an attempt to properly prepare you for the exam.

 

[LifeSucks]

I will also add, that it quickly becomes clear that a) Lindeburg provides what is needed for the exam in his text, and b) asks practice questions that probe into the "why" and "how" behind the subject matter, in an attempt to properly prepare you for the exam.

Thank you Audi! This explaination helps. Too bad I didn't keep my textbooks from college. I am also glad to hear I wasn't going crazy trying to find it in the MERM.  Only 44 days...Not sure my brain can handle it lol 

 

[Audi Driver P.E.]

Thank you Audi! This explaination helps. Too bad I didn't keep my textbooks from college. I am also glad to hear I wasn't going crazy trying to find it in the MERM.  Only 44 days...Not sure my brain can handle it lol 

I don't think you're going to do as well as you could if you don't have some of your college text books.  Most times, if you can recall which ones they were, you can get them pretty cheaply on Amazon or Ebay.  I would definitely try to do that for courses like Thermo, fluids, Heat transfer, and strength of materials.  Shigley is almost a must.  I have my physics book but didn't bring it and wished I'd had.

 

[Ramnares P.E.]

Good explanation Audi.  You will definitely need to refer back to your heat transfer text book in preparation for the TF exam.  If you're not comfortable with heat flux, Nusselt numbers etc.  you may want to brush up on the basics.