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How can I represent losses in pipes?

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To whom it may concern,
I am using the block model of Hydraulic Pipe with resistive and fluid compressibility properties. So far I understand, it takes into consideration losses through the paramenter (*)Aggregate equivalent length of local resistances. A fluid experiences pressure losses due to pipe geometry, changes in its cross sectional area, and change of direction. The Darcy-Weisbach equation for losses is Delta(p) = K (ρ/2) * v^2, where K is the loss coefficient. The loss coefficient can be then represented as K = f L/D, where f is the friction coefficient, L the length, and D the diamenter of the pipe.
So far I understood, the equivalent lenght was the ratio L/D, which is dimensionless. However, the paramenter (*) has a dimension of meters in Simulink. Therefore, I think I am misunderstanding something here. What does (*) truly represent? How can I use it in order to account for losses due to pipe length and bends?
I thank you very much in advance for your help!
Kind regards,
Isaac L.


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Answers (1)

Akshay Khadse
Akshay Khadse on 27 Dec 2018
As per my knowledge, equivalent length is given by . Here, the K and f are dimensionless and unit of D is meters. Hence, the unit of equivalent length is meters.
I was able to find this information on the following page:
(Please verify the contents of this page from a reliable source to be sure about this.)
So, the parameter Aggregate equivalent length of local resistances refers to the sum of the equivalent lengths of all the Valves, fittings and, straight pipes.

  1 Comment

Isaac Asiel Lorenzo Mercado
Hello Akshay! Sorry for replying so late.
Thank you very much for your help and answer. I managed to solve my question some time ago. What confused me at the time was how to obtain this specific value, but after measuring first the pressure changes in the system, then I was able to obtain the aggregate lenght of all my fittings, like elbows, 180 degree bends, reducers, and so on.
Once more, thanks for your help!
Kind regards,
Isaac L.

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