Mass Flow Meter

It's just so very tempting to get back to the Client's technical people on this one.

When in doubt regarding such requirements from your client, ask for a clarification. It's better than making a guess or asking for other people's opinion which may be as numerous as different.

Just to point out a fact: Coriolis flowmeters have very low differential pressure so I don't know why they would be concerned with it. Perhaps they mean something else?

Hi there,

I think the coreolis meter that they are using is a single tube type. From what you have said I can deduce that you will have a differential pressure accross the meter.

1. pressure = height x density x gravity

I think their request means that by taking the above formula into account you should make sure that the height you mount the meter at should be less than the delta P

Now why you should do this?

Pipe stress is introduced not only by in-line pressure and temperature but also by different mounting conditions. These conditions may cause compression, tension and/or shear forces to be apllied to the flow meter which can in turn affect the zero offset of the meter.

The other important thing to bear in mind is that the flow profile can change as the reynolds number changes. i.e. laminar or eddy flow. This is influenced again by density, velocity, viscocity and pipe width. As you can see the elevation could have an effect on this.

You also want to keep the tube full of process fluid at all times.

Also bear in mind that you should not install the tube at the highest point of the system because this will prevent any gas build up in the system from escaping.

Idealy you would want to install the meter either in a goose neck type U with the meter being horizontal at the bottom part of the U ensuring that the meter is always filled with liquid and allowing the gas to escape to the upper leg of the U or you would want to install the meter in the vertical position with the flow moving up the meter. This allows for easier draining (although with the U type installation you can always put in a low point drain for maintenance purposes).

I hope this helps in some way.

Regards,

Craig

I agree with Vulcan and gave him a GA. The rules of contracting never change IF IN DOUBT ASK. Asking the client for clarification will never make you look bad or stupid. Doing something wrong always will. The more you ask and disscuss issues will imptove the relationship and help with future work.

Hi all,

I agree that their should be very minimal pressure drop with coreolis meters, but the pressure drop depends on the tube design, length and inner diameter. Typical DP (according to various manufacturers specifications) at maximum flow vary from 7 to 20 PSIG (0.5 - 1.5 bar)

Also note that CMFs are not suitable for gas flows with low in-line pressure, since low-pressure gasses have low densities. To generate enough mass flow to provide sufficient coreolis signal the gas velocity will have to be high which in turn could cause a large pressure drop.

One other thing about the DP specification (I am not a chemical engineer and do not have the process data for the fluid being measured), but it could be that above a certain DP the liquid flashes causing bubbles. This in turn affects the CMF excitation current hence affecting the CMF accuracy.

Regards,

Craig

Thanks For all the Info

Regards

Jose