5 replies to this topic

[PENGG]

I have Pressure drop data for Normal flow rate for FE and Heat exchanger.I want to prorate it for rated and Turndown flow. How can I do it ?

[S.AHMAD]

YES! you can do it provided you know the concepts behind the system and the theoretical basis related to scenarios at hand. Line pressure drop and most all equipment, the pressure drop is proportional to the square of the flowrate. Therefore, total pressure drop or the system pressure drop can be expressed in general as:
DP=DP_o + kQ²
You can determine the constants DP_o and k from actual plant data at various flowrate Q.

[PENGG]

Mr. S. Ahmad,
Can you elaborate your explaination with theoretical basis and pratical example?

[S.AHMAD]

For example, for line pressure drop the equation is DP = 4f(L/D)V²/2g for orifice plate and heat exchangers have their own correlation and which variables can be assumed to be constant in order to simplify your computation.

Edited by S.AHMAD, 01 January 2013 - 07:50 PM.

[PENGG]

Thanks Mr. S.Ahmad.
Excellent answer.

[sheiko]

I believe the shortcut proposed by S. Ahmad is correct in the ranges 500<Re<2100 (but considering DP = K*Q) or Re>5000 (where indeed DP = K*Q²).
And, as K varies with Reynolds, you should not use data in one range to make predictions in the other range - the K values would not be equal for the 2 different ranges. So check that the rated and turndown flows remain in the same flow regime (Re range).

Edited by sheiko, 04 January 2013 - 03:34 PM.