Steam Flow Meter Sizings

This is not overwhelmingly true, and is somewhat confused. Although changes in pipe area result in inversely proportional changes in fluid velocity, the ΔP's are quite small in comparison. Ideally they should be accounted for, but the corrections are relatively minor except in the case of very abrupt transitions. Furthermore, a mass flow meter would measure the pressure at its location, correcting for it automatically. This is mostly a non-problem.

As an Example, If we consider that a 6" line is coming from boiler to header of 8" there would be minor pressure changes but if a 2" line is taken from the same header of 8" then there will be significant change in the pressure. Due to the larger Delta P, there will be a change in density of the steam which would affect the flow rate which has to be considerd while sizing.

It would be interesting to see a Colebrook Equation analysis of this alleged large pressure change.

I suggest you read Steady state steady flow process and uniform state uniform flow. What you mean really implies that mass was being accumulated somewhere at the header, with the considerable rate of flow, where is this mass of steam then?

Along one circuit, the mass flow should be constant, otherwise, your headers may be leaking some steam.

This is what you mean

1 kg of steam pass through -> 6" pipe ->8"header ->2" -> 0.8 kg of steam, where is then the 0.2kg?

Regardless of pressure losses, steam will attain equilibrium state at that given point (new pressure, new temperature, new specific volume) not unless your steam is below saturated steam state, so any installed flow meter there will be having the same readings even if it was installed either in 6" or 2" pipe lines.

When you say "..Regardless of pressure losses, steam will attain equilibrium state at that given point (new pressure..".. so new pressure=>>new density (at least for 6" to 2")..

But I agree your statement "..so any installed flow meter there will be having the same readings even if it was installed either in 6" or 2" pipe lines.." because i made some calculations (considering constant pressure) & i got the results proving your statement correct. my point is when the steam flow transfers from a 8" line or a 6" line to a 2" line the pressure drop is significant. This pressure drop has to be taken into account while calculating a mass flow because density changes drastically even for a 1kg of pressure drop, as per the standard steam table.(Which is not taken into account generally)

Regards,

Amey D

Amey,

I think you missed the idea of the Bernoulli's Equation, try to analyze

"because i made some calculations (considering constant pressure)" from 6" to 8" to 2", you calculated this at constant pressure? (see above, this is wrong to correct you)

The two states will have different set variables (pressure, temperature, specific volume & flow velocity)

Any changes with some variable say pressure, the others will compensate for it to maintain the same mass flow basically.

Pressure drop is already accounted on the new pressure at 2", (say from 6" to 8" or to 2") so this will all be compensated on the values of the other steam property( specific volume, temperature, flow velocity) at 2" pipe.

Unless otherwise your steam, either at 6" to 8" or 2" pipe is under the saturation state, the mass flow will not be the same. For you'll probably have condensation somewhere(accumulation of mass) and will not balance the mass flow along the conduit. But as long as the steam is above the saturation state, mass flow along the that branch will be the same all through, certainly.

This is of course considering, all pipes are well insulated (normally and should be) - heat loss is minimal along the conduit from 6" to 8" to 2".

Not only that it is (1kg) this is mass rate, say kg/hr, say at 0.2 kg/hr loss, how much is that at 6 or 12 hours? Where will then the header hide that amount of steam?

It does not matter,

mass rate along pipe conduit should be the same all through out only that steam properties, might not be the same at 2 different points or states but mass flow will be the same.

@cut out piece of pipe mass in = mass out

Your flow meter is installed at a single point or state, it must read the flow parameters with respect to that point/state only.

There is however a standard length downstream and upstream of a flow meter in order to read accurate and it will always be provided in the installation manual of the maker.

Your flow meter should be installed at the preferred down & upstream length and steam at that point/state should be consistently above saturated steam state to avoid errors due to two phase medium.