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elogesh January 1, 2007 12:52

Pressure drop of valve with valve opening of 30%

This is regarding the flow analysis of pneumatic valve of plunger type with 30% valve opening.The objective of the analysis is detemination of pressure drop for specified mass flow rate.

In this problem, following flow conditions are known.

a)atmospheric pressure at inlet b)total mass flow rate through the system

We planned to solve the problem with setting up pressure inlet and negative velocity boundary conditions at the outlet.Velocity boundary conditions at the outlet is determined from the mass flow rate and from hydraulic diameter of the outlet. whether these boundary conditions are resonable? We use fluent software for the analysis...

Since the mach number is less than 0.3, we are solving it as incompressible and also as steady state, turbuilent flow (Re>50,000)

Whether it is possible to do hand calculations for this problem? Even a ball park figure with + or -10% variation is reasonable to start with...

I don't have crane hand book to perform the equivalent length method calculations accounting the valves.

Hence, I planned to do pressure drop calculation as follows,

1) Pressure loss due to cross section change (change in shape of the cross-section is not accounted)

= density *gravity *(v^2/(2g)

2) Pressure loss due to obstructions,

Loss due to drag = Cd*0.5*density*v^2/(2g)

Where Cd- drag co-efficient

3) Pressure loss due to direction change (90 deg elbow)

= don't know how to calculate.

4) Pressure loss due to viscous friction

= Possible to calulate using head loss formula

f (L/D) * (v^2/2g)

Where f - friction factor

I would like your valuable comments about this approach.

If there are any corrections required in the computation or understanding, kindly let me know.

My intention is to know, whether the software calculated results are reasonable by comparing with the hand calculated results (Ball park figure).

Thanks for your time.

Regards, Elogesh

Tom January 2, 2007 13:48

Re: Pressure drop of valve with valve opening of 3
Elogesh, I would highly recommend that you get a copy of Handbook of Hydraulic Resistance by I.E. Idelchik. Section 9 is about pressure drop through valves. Since it has diagrams of the valves it is easier to pick out the formula that suits your conditions. The handbook is published by Hemisphere Publishing Co and is quite expensive. However, there are some old copies that were made for the old Atomic Energy Commission in 1966 (AEC-TR-6630). tOM

elogesh January 5, 2007 13:30

Re: Pressure drop of valve with valve opening of 3
Dear Tom,

Thanks for the reference.

I was able to preview the book "Handbook of Hydraulic Resistance by I.E. Idelchik" through web. It looks quite good. I will just see whether our library has a copy of the book?


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