TFS practice problem of the week...

[McEng PE]

No idea. But then again, in my circle of mechanical friends I'm the only TFS taker. Literally everyone around me took MDM once and passed (not looking at you @SacMe24). Any person who I heard about anecdotally who took TFS usually had to retake it. I definitely know zero HVAC'ers.

I have only worked with and have met mechanical PE's that took the TFS exam, and the consensus is that everyone they know that took the exam had to take it multiply times. Same, never met an HVAC exam taker. 

This is my second go at the TFS exam, I was pretty close the first time (60%) but the HVAC and power cycles killed it for me. I feel much more prepared this time though, and covered in depth power cycles and HVAC this time lol.

 

[Slay the P.E.]

I am looking at the external pipe heat transfer.   With an 80F external wall pipe temperature in a space that is somewhat colder that -320F.  

There should be an increased transfer rate above that of the radiant heat transfer:

(a) natural convection - Assuming no velocity is induced from the expansion of the Nitrogen

(b) quasi forced convection from the expansion of Nitrogen.

Hope that makes sense...

No.

the nitrogen is flowing through an external jacket around the chamber. Look at the figure. One surface of the jacket is at -320F the other is adjacent to insulation.

the 80F is the surface temperature of a heat source (because it has a heating element inside) inside the vacuum chamber. There is no nitrogen in the heater. There is no media between the heater and the jacket.

heat is transferred by radiation between the heater surface and the nitrogen-cooled jacket. This heat must equal the latent heat of vaporization for nitrogen.

 

[MikeGlass1969]

No.

the nitrogen is flowing through an external jacket around the chamber. Look at the figure. One surface of the jacket is at -320F the other is adjacent to insulation.

the 80F is the surface temperature of a heat source (because it has a heating element inside) inside the vacuum chamber. There is no nitrogen in the heater. There is no media between the heater and the jacket.

heat is transferred by radiation between the heater surface and the nitrogen-cooled jacket. This heat must equal the latent heat of vaporization for nitrogen.

OHHH!!!!!  ...   Now I see it.  

 

[squaretaper LIT AF PE]

I have only worked with and have met mechanical PE's that took the TFS exam, and the consensus is that everyone they know that took the exam had to take it multiply times. Same, never met an HVAC exam taker. 

This is my second go at the TFS exam, I was pretty close the first time (60%) but the HVAC and power cycles killed it for me. I feel much more prepared this time though, and covered in depth power cycles and HVAC this time lol.

You got this @McEng!! Remember to go to Mollier first. I don't bother with the steam tables unless I have to.

 

[McEng PE]

You got this @McEng!! Remember to go to Mollier first. I don't bother with the steam tables unless I have to.

Thanks @squaretaper PE! Yes!! Mollier is much faster route. 

 

[Slay the P.E.]

Thanks @squaretaper PE! Yes!! Mollier is much faster route. 

We also advocate for this approach. The very first post in this thread is a good example showing how much time can be saved.

Of course, Mollier diagrams are useful for superheated steam and high quality water-steam mixtures, that is, the typical steam turbine problem.

 

[Vel2018]

Tomorrow is your big day. Today, go walk in the park for some fresh air, run 10 miles and give your calculators a break. Go eat your favorite meal, relax, drink a glass of wine, sleep early and pray. 

Good luck everyone! 

 

[Slay the P.E.]

Don’t know if people are aware of this thread. We won’t be adding more problems to it, but all problems here are still very relevant.