# Help identify equations from 6MS for Thermal/Fluids



## Ramnares P.E. (Mar 10, 2014)

Hi all,

Can you please help me identify the following equations? If you recognize the equation, can you help me locate the reference also? Is it in the MERM or some other reference?

6MS Thermal / Fluids 2nd Ed. - Problem # 67 - Theoretical adiabatic power - Pth = (k/k-1)*Q1*p1*[(p2/p1)^k-1/k - 1]

6MS Thermal / Fluids 2nd Ed. - Problem 71 - Equation to approx. time needed to increase boiler temperature - ln (Tg,in-T1/Tg,in-T2) = [m.dot*cp*(e^(UA/m.dot*cp-1)) / C * e^(UA/m.dot*cp-1))] * delta t

Thanks for your time and help!


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## ATL Derek (Mar 26, 2014)

The equation from problem #67 is magically derived from the adiabatic compression of an ideal gas (page 15-13 in Merm 13). Problem #71 is just magic. I think they made it up.


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## kfrazie1 (Jan 24, 2015)

I just did problem 71 and that equation is rediculous. No where to be found in MERM. Thought I figured it out without that equation by finding btu needed to heat up boiler and water and setting equal to Mass flow rate of flue gas times cp times temp differential of flue gas. Found exit temp, calculated log mean temp difference and used heat xtr in heat exchanger eq to find time. Only problem I realized is they gave mass flow rate of flue gas rather than total mass flow so I didn't end up with the right answer. Calculated 2.5 min. Anyone else have any practical solutions to this problem?


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## P-E (Jan 24, 2015)

^see. This is why I'm burning this terrible book in tonight's campfire.




The book is that bunch of ashes on the right.


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## Phenomenon083 (Feb 6, 2016)

For problem 67 the closest equation that I have encountered is equation 32:18 on MERM, but this is an energy equation not power.


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## P-E (Feb 7, 2016)

I'm going camping again in two weeks.  I'll gladly burn anyone's TFS 6 min solutions book. Just send me your copy.  I'll provide the white gas free of charge.


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## JHW 3d (Feb 7, 2016)

So glad I didn't bother with the 6MS.


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## P-E (Feb 7, 2016)

You are for sure.  I almost gave up and quit after using the 6 min as a benchmark the week before the exam. . Luckily Mrs P-E didn't let me quit.   i dream of ways to burn that book.


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## Audi Driver P.E. (Feb 8, 2016)

If you could post the problem, that would help with finding the solution.


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## Ramnares P.E. (Feb 8, 2016)

Why is everyone suddenly replying to this? I asked this question 2 years ago. Mods please lock this topic.


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## Audi Driver P.E. (Feb 9, 2016)

Ramnares P.E. said:


> Why is everyone suddenly replying to this? I asked this question 2 years ago. Mods please lock this topic.


Because kfrazie1 had a question relating to 6ms also (albeit a different one)


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## Ramnares P.E. (Feb 9, 2016)

To be fair, this question was one of the few that was really left field on the SMS.  I found the book very helpful overall but I certainly wouldn't use it as my sole source of practice problems.


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## Phenomenon083 (Feb 9, 2016)

Yeah SMS offers dubious explanation on couple of problems, but overall I have found its problems are very realistic compare to MERM and its companion problems.


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## seeseansky (Mar 31, 2016)

The equation in 6MS Thermal / Fluids 2nd Ed. - Problem # 67 can be derived from mdot*cp*(T2-T1) using P=rho*R*T and T2=T1*(P2/P1)^(k/k-1).


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## P-E (Mar 31, 2016)

Ramnares P.E. said:


> To be fair, this question was one of the few that was really left field on the SMS.  I found the book very helpful overall but I certainly wouldn't use it as my sole source of practice problems.


It was very helpful in keeping the camp fire going, but I wouldn't use it as my sole source of kindling.


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