Pressure drop through strainer mesh

[arunb]

Hi:

I am looking to establish the flow resistance for a rectangular wire mesh strainer fitted in a lube oil tank to handle higher flow requirements. I would like to estimate the pressure drop for different screens. I would appreciate any help on formulae or correlation for this calculation.

Thank you in advance.

 

[TD2K]

Have you checked with the manufacturer? That would be my first place to see what data they have on flow versus dP for wire mesh.

A properly designed clean strainer should have minimal pressure drop. The real question is what is the dP as it becomes clogged (which hopefully isn't happening in a lube oil system) and that's pretty hard to predict. Its a function of how much the wire mesh is plugged and therefore how much is available for flow along with of course, the oil flow rate and properties.

 

[CHD01]

Good answer TD2K! I've tried to estimate dp's due to pluagge and it is not easy. What do you think about the following? It seems to me it should be possible to calculate the equivalent reduced diameter resulting from pluggage of a screened filter (screen free area x % pluggage and back calculate for equivalent reduced diameter); then determine the velocity (total flow/reduced diameter calculated), this velocity is also equal to the velocity thru a mesh opening; then calculate the resistance factor(k = f x L/D) based on the length (i.e. = thickness) of the mesh plus k = 1.5 for the inlet and exit losses for the opening in the mesh; and then use Crane's equations to calculate pressure drop thru the mesh opening which has to be equal to the drop across the entire filter. If the dp calcuated this way isn't correct - at least its one way to determine intake velocity versus pluagge and coreclate it with required pump submergence for example. Thanks for any input, I've just been playing around with this type of problem recently. I recall seeing some specifc equations expressely for calculating screen mesh dp but cannot recall where or when I saw them. I would be interested in knowing how close or far away my proposal is from the real dp.

Regards, Charlie D. The more you learn, the less you are certain of.

 

[abeltio]

That sounds a bit strange, all the lube oil systems I've ever seen have high efficiency filters (5 microns) on the discharge side of the pumps. and a suction strainer on the pump itself about 2 in from the bottom of the tank.
The suction strainer is usually supplied by the pump manufacturer.
Only during initial commissioning are strainers used on the pressure side of the system for the infamous lube oil system flush, bypassing all the lubricated equipment.
In that case an in-line witch-hat strainer, is used with a 20 mesh and a stainless steel backing cone or a wafer type strainer.
The point of the witch hat is pointing AGAINST THE FLOW. and dp gages are installed to determine when the strainers get clogged.
Perhaps if you give more detail regarding the specific application we could help you more.
Saludos.
HTH
a.

 

[arunb]

Thanks to the responses to my query to the above respondents. The responses have given me something to think about,which I think helps in getting the full perspective and solving the problem.

This also requires me to answer some questions.

1) The screen mesh sizing is not adequate as it is causing the flow to back up. Hence the requirement to evaluate its flow resistance and pressure drop. I see it as a pressure drop across a wire of a particular diameter (bluff body) (corrected for flow effects of surrounding wires) and may be calculate and compare it against the pressure drop as if it was a pipe of length D (diameter).

2)The pump has a fine strainer on the discharge before going to turbine seal. The return oil from the loop seal goes goes to a circular strainer (located in the tank) and then to the rectangular wire mesh strainer /screen (also in the tank). There is no separate suction strainer for the pumps.

 

[TD2K]

What is the pressure drop across the mesh?

Have you estimated what is the open area of it versus the pipe? Typically, these don't take much dP unless they are partially clogged or they have been wrongly selected.