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A Little Error In The Technical Paper No. 410 Of Crane: Flow Of Fluids

flow fluid coil pressure drop

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#1 Napo

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Posted 11 March 2016 - 12:50 PM

Sirs,

In the Technical Paper No. 410 of Crane: Flow of Fluids,

in the Example 4-11…. Flat Heating Coils-Water, we have:

In point 4. For seven 180º bends,
KB = 7 [(2-1) (0.25 x 0,023 x 4) + (0.5 x 0.32) + 0.32] = 3.87
but in function of equation 2-20 and the include example in the page 2-13, we can:
7 bend 180º= 14 bends 90º, then,
KB = (14-1)[(0.25 x 0,023 x 4)+(0.5 x 0.32)]+0.32 = 3.33
then,
KTOTAL= 4.87+0.64+3.33 = 8.84 and,
delta P = 0.00225 x 8.84 x 971.8 x 60^2 / 26.6^4 = 0.139 bar (=2.017 psi)
and not 0.152 bar (= 2.205 psi)

I know is little error, but 16.2% of difference in KB counts.

Napo.

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#2 latexman

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Posted 11 March 2016 - 03:48 PM

Sorry, no.  The seven 180 degree bends are not continuous.  Therefore, the 14  90 degree bends are not continuous either.  So, that equation does not apply.

 

The two 90 degree bends that make up one 180 degree bend is continuous.  The books application of the equation for two 90 degree bends to make one 180 degree bend is correct.  Then, since there are seven of them, x 7 is correct too.


Edited by latexman, 11 March 2016 - 03:50 PM.


#3 Napo

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Posted 11 March 2016 - 08:37 PM

Sirs,

The attached page is for clarify my first post.

Napo.

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#4 latexman

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Posted 11 March 2016 - 09:40 PM

Your error is 7 non-continuous bend 180o is NOT = 14 continuous bend 90o.  Example 4-11 is correct.


Edited by latexman, 12 March 2016 - 07:10 AM.


#5 Napo

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Posted 16 March 2016 - 02:56 PM

Latexman and Sirs,

 

I think that in Example 4-11 there are a problem, because if we have 7 close return bend (180º curve), we can employ K = 50 fT, this is, K = 50 x 0.023 = 1.15, and for 7 is 8.05

 

KTOTAL= 4.87+0.64+8.05 = 13.56 and,

 

delta P = 0.00225 x 13.56 x 971.8 x 60^2 / 26.6^4 = 0.213 bar (=3.090 psi)

 

and not 0.152 bar (= 2.205 psi)

 

I attached the sheets from Mr. Art Montemayor of his work for analysis.

 

Napo.

Attached Files



#6 breizh

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Posted 16 March 2016 - 05:28 PM

Napo ,

Consider the table 7 of the document attached.

 

As you can read , the resitance of 2 * 90 elbows in serie is not two times the resistance of a single elbow , only 1.4 to 1.6 times .

 

 

Hope this helps.

Breizh

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Edited by breizh, 16 March 2016 - 11:47 PM.


#7 Napo

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Posted 24 March 2016 - 11:46 AM

Many Thanks for your information appreciated Breizh.

 

I am reviewing for to do the calculations.

 

Best Regards,

 

Napo.



#8 latexman

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Posted 24 March 2016 - 12:51 PM

Napo,

 

Return bends with K = 50 fT are screwed fittings and r/d ~ 1.5.  Example 4-11 "looks" welded to me, and r/d = 4.

 

Sometimes you do have to be creative to come up with a K value for a fitting, but I still think Example 4-11's solution is better than your proposals.



#9 Napo

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Posted 24 March 2016 - 03:09 PM

Latexman,

 

Many Thanks for your comments.

 

I will continue reviewing the information.

 

Napo.



#10 Napo

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Posted 06 April 2016 - 05:14 PM

Sirs,

 

The exact analytic determination of pressure drop in individual pipe components (elbows, curves, bends, etc.), is still an engineering problem.

 

I have found many values for the present problema (Example 4-11), between 0.14 to 0.50, but the original value is aceptable (0.553 for one 180º bend).

 

Finally I have found a error in the sheet "comparison example 4-11" of Mr. Art Montemayor, I have done four sheets, the "Original" with the data base; "Versión 1", it permits to do the original calculations; " 1st correction", I have changed the value 18 ft for 5.49 m (in yellow), and we obtain similar result that the problema in the Crane Tech Paper 410; and the last "2nd correction", I have put other values (in yellow also) for clarify the problem.

 

Napo.

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