Flow Measurment

Less entrapment of bubbles, smoother flow, liquid won't just stick to the outer walls and run down them... The water flowing down a drainpipe just forms a meandering stream down the inner face of the tube.

Much the same reason as when you fill your cup of coffee, the level rises from the bottom up

Del

For most of the flow meters, the pipe should be full of liquid. This is because, what the meter measures is velocity of the liquid and not the volume. Using the velocity and nominal diameter, it calculates the flow.

Full pipe flow can not be assured if liquid is flowing top to bottom. But you are sure of full pipe flow in case of bottom to top flow.

Mass flowmeters have no such requirement.

No such restriction for gas (as you say).

Yes Del the cat and gsuhas, you are right.

For the same reasons, in piping systems when we need to make a branch to a main header of a liquid line, we recommend to connect the branch into the bottom of run to avoid flowing of gases/vapours/air pockets with the liquid. Also when we connect a branch to a main header of a gas line, we recommend to connect the branch into the top of run to avoid the flowing of condensates or any liquids with the gas.

For liquids you want the pipe to always to be full of water and free of bubbles - the only way to ensure that is to have the water rise from the lowest point upward (think your garden hose pointing up).

For gas - you want to make sure (such as with steam) that you are seeing primarily gas flow and don't ever have water/condensate existing in the space.

In addition to orientation, you need to observe the proper upstream & downstream pipe diameters from elbows, valves, etc as this can affect the accuracy of the meter.

When in doubt, trust that the manufacturers installation & maintenance instructions are correct based on experience and assured meter performance.

Hello all,

Thanks you all for your vauable answers..it was of gr8 help!!

This was very basic question but as always it is basics that are intresting to learn!

just a quick addition -

Gravity is pretty constant about everywhere on the earth (yes I know, some slight difference at altitude etc) and can be counted upon to pull the indicator down at an even rate no matter what the flow rate -

Jim

Hi everyone!

Another interesting observation - if you are measuring the flow of volatile hydrocarbons, you better be sure that the flowmeter is always filled with the liquid. Else the vapors flowing through the meter will give a "flow" which, when accumulated might give a salient misreading of the actual flow quantity. (Though in certain cases you can set a "cut" based on density, not all flow transmitters allow this :-) )