10 replies to this topic

[processengbd]

I need to perform a centrifugal pump calculation. Piping contains some brunching section. It would be very helpful if anyone suggest any reference specifically address these type of problem wold be very much helpful.

 

Horizontal line means horizontal in the field. Vertical line means vertical in the field.

 

All measurement are given in ft.

 

I want only the references which I need to follow. Please advice. I am interested about actual industrial practice how engineers usually do this. I guess chemcad or hysys can perform such work.

 

 DSC_0023.png   213.1KB   95 downloads

Edited by processengbd, 17 February 2013 - 11:51 PM.

[breizh]

Consider to get a copy of flow of fluid  TP 410 M  by Crane . . > 60 US $ + mail fee

 

You can download from Internet : PSIM a free software for hydraulic calculations (with examples).

 

http://www.pumps.org...ail.aspx?id=110

 

Breizh 

Edited by breizh, 18 February 2013 - 01:59 AM.

[thorium90]

If you have hysys, you can read this article.

 

http://users.rowan.e... piping2002.pdf

[S.AHMAD]

1. You need to have the pump's performance curve and then a trial and error method as below. Also you need to know the pressure at V101 and V103 (let say P1 and P3 respectively).
2.  Assume the pump pressure and determine the flow rate from the pump curve, let say Qt. Initially use static pressure for the suction neglecting frictional pressure drop at suction
3.  By knowing pressure differential between pump discharge and vessels, you can determine the flowrate for each branch let say Q1 and Q3
4.  Do material balance Q1 + Q3 = Qt(calculated)
5 Iterate (step 2) until Qt(calculated) = Qt
6. I hope the above is clear enough for you to start you work.
7. The above calculation can be done easily using SOLVER in EXCEL spreadsheet

Edited by S.AHMAD, 19 February 2013 - 04:54 AM.

[breizh]

Following S AHMAD's recommendation you may find this xcel sheet useful !

 

More important is the method .

 

Hope this help

 

Breizh

Edited by breizh, 19 February 2013 - 06:27 AM.

[Art Montemayor]

The term "Brunching" in the USA means a snack taken between breakfast and lunch, around 10am or so.  Is that what you mean to write?  I don't think so.  Perhaps you mean "branching" - something totally different.

 

If you don't have a good knowledge or vocabulary in the English language, I recommend you use the Spell Check feature in Word for Windows.

[kkala]

Following notes could be of interest, in addition to above useful suggestions.

1. A relevant reference is Schaum's outline of Fluid Mechanics and Hydraulics, McGrawHill (SI edition from 1976 on), Chapter 8 - Equivalent, Compound, Looping and Branching Pipes.

2. Specialized software on liquid flow (e.g. TL NET, etc) could do the task. However it is not worth while getting TL NET just for one simple application as this.

3. To get the essence of hydraulic calculation, I would try to follow trial and error method (post no 4), or an alternative to it as follows.

-Using pump curve, specify function P=f(Q), or better Q=f(P) (where P=pressure at the branch point), graphically or algebraically (e.g. through MS excel). ΔP for the 5 ft discharge line to branch point to be deducted from pump discharge pressure (even though it may not make big difference).

-accept flow Q1 to tank B1 (black line on diagram ), estimate ΔP1. Then P=P1+ΔP1.

- for this P find Q from function specified above.

-flow Q2 to tank B2 (blue line on diagram) would be Q-Q1.

- estimate ΔP2. Then pressure at branch point P'=P2+ΔP2

- difference = P-P'. Vary accepted Q and repeat the above, until difference = 0.

ΔP is frictional pressure drop+static pressure difference; but diagram indicates static difference = 0 ft from branch point to tank B1 and similarly +3 ft to B2.

Frictional pressure drop can be practically proportional to Q², simplifying iterations.

3. Spelling checker of the forum is also quite useful. But brunching is an existing word, the error could not be traced. The diagram of post no 1 was useful in eliminating confusion.

Edited by kkala, 19 February 2013 - 12:57 PM.

[thorium90]

Art and kkala got me to search google for "brunching dictionary" and I clicked on the first link. The meaning is not what both of you said...

Then I clicked on the second link, ohhh...

[S.AHMAD]

Mathematically, this branching problem can be solved easily::

1. We have 4 unknowns. Pump discharge pressure (Pd), total flowrate Q_t, branches flowrate Q₁ and Q₂ respectively

2. In solving the 4 unknowns, we need 4 equations:

Equation 1: Material balance Q_t = Q₁ + Q₂

Equation 2: Pressure drop for branch 1 (assume turbulent f = constant)

Equation 3: Pressure drop for branch 2 (assume turbulent f = constant)

Equation 4: Pump performance curve that can be curve-fitted to quadratic equation Pd = A + BQ_t + CQ_t²

We get the answer by solving the 4 equations

Edited by S.AHMAD, 19 February 2013 - 10:17 PM.

[processengbd]

Thanks everyone for your valuable input.

Processengbd

[kkala]

Yes, S.AHMAD, final equations can be P1+k1*Q1²=P2+P'2+k2*Q2²=A+B*(Q1+Q2)+C*(Q1+Q2)², where k1, k2 constants that can be defined, P'2=hydrostatic pressure of 3 ft, other symbols as above. Iterative methods give more insight, but this is a straightforward solution.