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Formula For Tema Ligament Efficiency


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#1 vovo

vovo

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Posted 06 June 2007 - 09:49 AM

Hi,

An assignment for Uni, requires that i calculate the minimum thickness of the tubesheet

So i will use the TEMA formula

T=F(G/3)SQRT(P/(ηS)

I can't for the life of me find out how to calculate η (ligament Efficiency)

I have a copy of another students formula

η=1-(0.907/(21/15)^2)=0.54

The Tube diameter = 15mm
The pitch is = 21mm

So i have no clue what the 0.907 is

Help please

~vovo

#2 Art Montemayor

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Posted 06 June 2007 - 12:01 PM


vovo:

The best quality and quantity of advice and recommendations you can receive is from a professional and experienced engineer. Therefore, take the following with a serious and constructive outlook.

1. If you are going to use a referenced, published standard then cite the source and clearly identify its location. My 7th edition (1988) of Standards of the Tubular Exchanger Manufacturers Association (TEMA) cites the design of tubesheet thickness in Section 5, RCB-7 Tubesheets. The equation you cite is the correct one.

2. If you are going to cite an engineering equation, then also specifically cite the nomenclature related to that equation. To fail to do this is shabby engineering and will cause your downfall in future projects and calculations. I presume you have a copy of the TEMA standards. If not, then obtain a copy – either through your engineering library, a friend, or buy one. Otherwise, you don’t know (since you haven’t read them) what the instructions and directions are – just the equation. Nowhere in my copy is the term “ligament Efficiency” used. On page 40 of the TEMA standards is found the definition of η for both square and triangular tube pitch. In case you don’t know it, the other student used the triangular version.

3. Never use someone else’s undocumented or un-explained detailed calculations as a “go-by”. This is simply foolish and very stupid engineering. Engineers cannot afford to repeat other person’s mistakes and when you employ another’s undocumented or explained calculations you are coming close to committing professional suicide. You simply don’t know what you are copying. This is dumb.

The best help I can offer you as a student is that you obtain the cited TEMA Standards and read and study Paragraph RCB-7. As in all respected and recognized professional standards, TEMA carefully details out the explanation, equations, references, and algorithms for their recommendations. You will find the equation well explained and referenced. You will profit by following my advice because it will result in your resolving the assignment in a proper, professional manner together with an excellent learning experience that will come back to help you in the future. As an engineering student you should reference everything you report in an assignment anyway. So the TEMA reading and research is mandatory to begin with.

Good luck and good learning in your effort.



#3 vovo

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Posted 06 June 2007 - 09:09 PM

Thanks, sadly i do not have a copy nor did i know where to find one at such short notice, i have read the AS1210 and the AS3857 which are the standards pertaining to Pressure Vessel Design and Heat Exchanger Design here in Australia. Through speaking to other students i was advised to use TEMA's Formula, however i cannot find a value for η.

Just for informations sakes

Tube OD - 15mm
Tube Pitch - 21mm
60degree triangular pitch.

Thanks for your help anyway, it was 2am and my assignment was due in this morning. In industry for i would have access to all the relevant standards as well as a thorough QA process. Where as i just wanted to finish the question to go to bed. Is this professional, no, i know this myself and this would not be done by myself in industry.

Surely we were all once students

~vovo

#4 ChemEnger

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Posted 10 April 2008 - 05:30 AM

QUOTE (vovo @ Jun 6 2007, 03:49 PM) <{POST_SNAPBACK}>
η=1-(0.907/(21/15)^2)=0.54

The Tube diameter = 15mm
The pitch is = 21mm

So i have no clue what the 0.907 is

Help please

~vovo


The 0.907 is from the area ratio of tubes on a 60 degree (equilateral) triangular pitch:

If you draw out the tubes, connecting the centres of three tubes to form the pitch triangle, you will find that the area of each tube enclosed by the triangle is:

PI . D² / (4 . 6)

As there are three tubes intersected, the total area becomes:

3 . PI . D² / (4 . 6)

The area of the intersecting triangle can be shown to be:

1/2 . Pitch² . Sin (60)

Where the pitch is the separation between tube centres (and the length of the sides of the triangle).

Working out the ratio of intersected tubes and the triangle, we get:

3 . PI . D² / (4 . 6) * 2 / (Pitch² . Sin(60))

or:

0.9069 . D² / Pitch²


Hope this helps future readers!




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