Spec for Mass Meter / pressure drop

If the manufacturer spec'ed out the 0.1 bar pressure drop @ the max flow rate, then you are probably good. The reducers (and approach/exit piping) will increase the pressure drop a small amount, but nowhere near what the instrument itself (at 3") will drop.

I would be more concerned with the 80˚C in relation to the pressure drop. Has anyone checked to see what the vapor pressure of the fluid medium is, and will it be crossed with that drop?

Last but not least, the physical mounting of the instrument is extremely important. Especially with Coriolois mass flow meters. Make sure when they spec that meter, that they know about all those 90 Deg elbows. The upstream and downstream pipe diameters required, are dependent on the geometry of the approach piping configuration.

If Transitions from N.B. 150 TO N.B. 80 --are not sharp and not next to Mass flowmeter --

Then the Mass Flowmeter will show the actual flowrate-as if there was no diameter transition and no right angle Elbows---.

Actual flowrate( indicated by mass flowmeter) will be less than in the situation when these were not there.

Upstream and downstream lengths of pipe before and after the meter should be straight and of adequate length. Beyond that, I believe PD is negligable.

I've never seen a up/down stream specification for a Coriolis type mass meter, so that may not be a requirement, the OP did not say what type.

The Corioilis meters must have a larger than "expected" pressure drop in order to get enough A in F=MA.. We had some flashing take place in one once and the meter could read still measure at small amounts, but what hapens is at larger flashing rates the pressure drop increase greatly the gas releases and the system vibrates and the sensor can no longer detect the the base vibration and the unit shuts down.

"........a Mass Meter (straight through) of size DN80 (3")..............."

Thanks for all of your answers. In relation to the last query:

The specified Mass Meter is a Straight through Tube, same diameter (DN80) Single Bore and is not a Coriolis type.

Finally from all of your answers it looks like you are saying the the control of the "Control Valve" at the end of line will not suffer because there will be minimal PD if this DN80 Mass Meter is installed into the DN150 line?

"Finally from all of your answers it looks like you are saying the the control of the "Control Valve" at the end of line will not suffer because there will be minimal PD if this DN80 Mass Meter is installed into the DN150 line?"

I didn't say that. Since we have no idea what type of valve, only you can crunch those numbers. Most valve manufacturers will have a program you can plug the data into and see if you are going to have a problem with flashing, cavitation, or noise. I would strongly sugest getting it, or calling the maufacturer/vendor and having them run the numbers.

Since it "is not a Coriolis type", what type is it? The only types that are a "Straight through Tube" that come to my mind are ultrasonic, and mag flow meters. But those are not true mass flow meters. They are volumetric. IF the density is constant then you can calculate the mass flow from the volumetric flow.

Dear Guest,
I am looking for some positive feedback and solutions to my question. If you have nothing of substance to contribute please do not participate in this forum, as the other users have kindly posted their thoughts and this is much appreciated. However, in reply to your informative reply to this forum please see the link below.

Krohne actually do manufacture a straight tube Mass meter:

http://www.krohne-mar.com/OPTIMASS_7000__Mass_Flowmeters__en.165.0.html

I'm guessing that you meant that as a reply to post#6.

Thank you for the link on the krohne OPTIMASS_7000. However, if you click on the OPTIMASS overview link ( http://www.krohne-mar.com/OPTIMASS_Overview__Mass_Flowmeter__en.9968.0.html ) you will see: "OPTIMASS the family of Coriolis mass flowmeters."

The preliminary problem still remains: What is going to happen at/to the control valve? You already know what the pressure and flow are going to be at the inlet. But whether a valve will have cavitation/flashing/noise problems is dependent on the fluid properties, the process conditions, and the valve geometry. That is what you have to find out.

If it is going to have problems with the new inlet pressure, then you have some decisions to make. It's a trade-off. If you size the flowmeter too small, you could restrict the max flow. It doesn't sound like this is the case for your current conditions, but what about if the production increases? If you go to another size larger, then you will probably lose resolution, and the cost will be greater (probably why that size was spec'ed out to begin with).

If this is already in the works, then there are things you can do to alleviate the problems. Nothing that I would recommend as an SOP, but at least a way to "make it work".

Thanks for your reply Kilowatt, and yes my reply was in relation to post 6.

For piping systems furnished with instruments such as meters or control valves, there is no problem if the size of instrument is lower than the size of run pipe. Only you are requested to check that the pressure drop is taken into consideration, and that pressure drop shall not affect the required flow rate.

All control manifolds recommended by ISA (Instrument Society of America) state that the control valve size is usually lower than the size of run pipe.

Sometimes we use a reduced bore valves with no problem if we take that into consideration during designing of the system.

DEAR SPONGE,

MY OBSERVATIONS ABOUT MASS FLOW METERS ARE:-

I)THE CALCULATED PRESSURE DROP CALCULATED BY VENDOR WILL BE ALMOST THE TOTAL PR. DROP ACROSS THE FLOW METER & CONCENTRIC REDUCER WHICH YOU HAVE TO PUT BETWEEN THE TWO ENDS OF THE FLOW METER.

II)NO NEED OF STRAIGHT PORTION IN THE CASE OF MASS FLOW METER, WHETHER IT IS STRAIGHT TUBE OR U TUBE.

III)DN-80 MASS FLOWMETER IS QUITE ENOUGH FOR A FLOW OF 120 - 130 M3/HR.

IV)DON'T WORRY ABOUT THE SIZE OF REDUCER i.e. 6" TO 3".AS PER STANDARD PRACTICE WE CAN GO EASILY UPTO THE HALF OF LINE SIZE.

V)THE MOST IMPORTANT THING IN CASE OF MASS FLOW METER IS THAT THE FLOW MUST BE SINGLE PHASE FLOW, FOR THAT YOU HAVE TO CONSIDER THE VAPOUR PRESSURE OF THE FLUID AS WELL AS MIXED AIR IN THE FLUID.

VI)MIXED AIR CAN BE REMOVED BY PRESSURISING THE FLUID, FOR THAT THE LINE PRESSURE OF 2BAR IS ENOUGH AS MENTIONED BY YOU.MORE THE PRESSURE MORE WILL THE ACCURACY.

VII)IT WILL BE BETTER TO ERECT THE MASS FLOW METER NEAR TO PUMP DISCHARGE SO THAT THE STATIC HEAD OF 16 MTR WILL BE ADDED TO THE LINE PRESSURE.

REGARDS

SANJEEV BHARDWAJ