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# TFS 6ms problems

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All,

I can't find the equition in MERM for the problem 7 in 6 ms  of TFS. I have no clue why they use that equition. I am very disappointed after I tried to work on 6ms based on Ramnares's strategy, because I have to read all solutions for each problems. I have no clue for some problem even though I read solution. I think I may need to change my exam date to next year. I have been out of school for 20 years without TFS background. It will be really appreciate to have some suggestions from you. By the why, here is problem 7:

The air in one large room is at 70f, 1.0 atm of pressure, and 80% relative humidity. A 50 ft long duct with a cross-sectional area of 2 ft2 connects this room to another at 60f, 1.0 atm, and 10% relative humidity. The diffusivity of water vapor in air is 1.0 ft2/hr. What is the rate of vapor transfer by diffusion between the two rooms?

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Do I need take some review course (I.e. M test master) if I want to pass the exam in October? I already register the exam in October, I am not sure if I can cancel it now.

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Ramnares P.E.    1,391

I don't have the 6MS in front of me but if I recall correctly, the equation for this particular question was in the MERM.

It will be very difficult for you if you've been out of school for 20 years and have no thermal/fluid background.  I'm not sure why you chose TFS with no background?

You may want to sign up for Dr. Tom's which has very good reviews and focuses on TFS.

If you read my post on how to prepare, you'll see that I had quite a few difficulties on my first pass through the 6MS and read quite a few of the solutions.  The key is to understand the methodology and equations used.

I would not try to cancel your registration.  You have at least 2 months prior to the exam which is ample time to prepare sufficiently.  Best of luck.

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P-E    1,487

I don't have the 6MS in front of me either.  It's a pile of ash somewhere up in the white mountains.   Don't let that book discourage you.  I was out 20 years and passed.  That book is kindle material.

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Thank you for you suggestion. Dr Tom suggested to choose TFS if you don't know which discipline you want to select. This is the reason why I chose TFS.

P-E: would you please share your experience with me since you was out of school 20 years and passed. What discipline you took? How long have you prepared exam?

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P-E    1,487

I took TFS because I design the mechanical systems for small power and heating plants.  I studied for 5 months.  I read the MERM and did as many problems as I could from the Merm problems book.   I used the 6MS as a practice test the weekend before and nearly quit.  I looked at the sample NCEES test and realized 6MS was much harder and not a good benchmark.

Took a week off at the end and reviewed the power cycles, fluids and thermo sections.

If I had two months only, I'd focus on those sections above and review the basics of the others, skipping the complex topics at the end of each of the non TFS chapters.  I'd skip all the math sections and all of plant engineering.

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P-E, thank you for the suggestion

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I didn't buy the 6MS as a lot of people seem to find more baffling than beneficial. But here is how I'd solve the problem.

First of all, whenever you see diffusion, remember Fick's law which states that the rate of diffusion of a substance in a fluid from a higher concentration to a lower concentration is equal to the diffusivity multiplied by the cross-section area multiplied by the difference in concentration divided by the distance (The negative sign is to indicate the direction of diffusion from higher to lower concentration). The only thing that's not given is the concentration (you might call it density) and in order to get it for each state you can use the psychrometric chart.

I believe that this is a simple way to think about the problem. Let me know if my final answer is correct.

Other than that, don't get discouraged. You have plenty of time to focus on the important topics.

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Sheshtawy, you are answer is exactly correct. Thank you for the details explanation.

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Sheshtawy, is this Fick's law from MERM book?

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I don't think so, but it should be in any half decent Heat and Mass Transfer textbook. Unfortunately the MERM doesn't cover mass transfer as a stand alone topic, but again mass transfer isn't in the specs of the new TFS exam either.

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Sheshtawy, thank you again for the help!