Orifice plate ( superheated steam)

[KGBaker]

My Orifice plate calculator gives me my permanant pressure loss, but on superheated steam do I get a temperature change.

For example 750 psi 750 F steam, I require a DP across my orifice of about 500" water to get turndown and Beta ratio. ( yes I know its high but pipe dia fixed.)

My permanant pressure loss is 7" water, about the same as a vortex meter, but do I get a temperature effect.

I cant find data for this, I can argue its a pressure to velocity to pressure effect and thus the steam does not expand, therefore no cooling. But I can say the jet out of the orifice expands to the larger pipe diameter and thus must cool.

Anyone with hard data or a table

 

[zdas04]

Superheated steam is just another superheated gas and should act like the rest of the gases that are measured with orifice plates. For methane (for example), careful measurement of temperature on both sides of many orifice plates has shown that it is immaterial to the flow calculation which side of the plate has the temperature sensor (i.e., there is no change to the bulk temperature across an orifice plate). I'd say that superheated steam would act the same way.

David

 

[katmar]

Any temperature change you get with 7" (=0.25psi) pressure drop will be a fraction of a degree, and in any case much less than your expected error in other parameters. Neglect it.

Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com

 

[TD2K]

The expansion across an orifice plate would be an isenthalphic process (constant enthalphy) just as across a control valve.

You can check how much cooling you will see using the steam tables for the inlet pressure and temperature to determine the inlet enthalphy. Determine the outlet temperature for the outlet pressure (based on your permanent dP) keeping dH = 0 but it won't be very much.

Google SteamTab, good program for steam properties.

 

[hacksaw]

7" permanent loss sound small for a 500" meter d/p, are you sure that it is not a 7 psi loss?

Yes, you lower the flowing temperature while the stagnation temperature stays more or less unchanged.

 

[FredRosse]

Hacksaw is correct, 7 inches WC unrecoverable loss on a meter producing 500 inches WC signal is too low, probably at least 7 PSID unrecoverable loss. What are the dimensions of your pipe and orifice?

In general, for flowing steam in insulated piping, the enthalpy plus kinetic energy are constant, H1 + KE1 = H2 + KE2. This will define temperatures at every point along the flow path.

Enthalpy is from ASME steam tables, Kinetic Energy is = 1/2 M*V*V

Be sure to use proper dimensional units, the equations given above are dimensionally consistant, and will prove correct in any rational system of units.

 

[KGBaker]

Sorry, yes it was a typo it is 7 psi permanant pressure drop.

And I have done the enthalphy calc, and i didnt see any real temperature lose till far higher pressure losses.

Thanks all for confirming...