i am using an orifice plate with DP transmitter to measure steam flow. i need to know the formula for converting pressure developed to steam flow (i have to put the pressure range in the DP transmitter).

 

either this is too stupid a question or i have not made it clear,
supposing the later case (i can't help if it's the first). i have an orifice plate installed on a steam line. i have attached a differential pressure sensor to the two ports of the orifice plate through POTs. now the problem is that when the steam flows, i get a reading of pressure in the differential pressure sensor, how do i convert this measure of pressure to a measure of steam flow which i need?

somebody please do help, thanks in advance.

 

1) Figure out what means you have available to configure the transmitter (Hart, push buttons, FF, whatever)

2) Use those configuration means to enable the square root function on the transmitter.

3) Locate the orifice plate sizing sheet and
- Note the engineering units for both pressure and flow.
- make note of the value stated for "differential pressure at maximum flow rate".

4) Configure the transmitter's pressure engineering units to those in #3

5) Configure the URV (upper range value) to the differential pressure value in #3.

6) Configure the LRV (lower range value) pressure to zero

7) The 4-20ma output will now span from zero flow rate to your maximum flow rate in whatever engineering units are stated on the sizing sheet.

 

Additional explanations and equations can be found here: http://www.efunda.com/formulae/fluids/calc_orifice_flowmeter.cfm

 

General Equation is <pre>
Mass flow(kg/s) = AeCv*SQRT(2gH)* w

Where

Ae = effective area of the regulated flow passage (m2)-regulated cross section

Cv = Coefficient of velocity (ratio)

g = gravitational acceleration (m/s2)

H = differential pressure (m steam equivalent)

w = steam density (shall be as a function of temp& pressure</pre>
You have to calibrate your equation based on the known mass flow for the first time for various pressure level. Otherwise you might have problem to determine Cv. If by any mean you know the Cv then I think to determine Ae is not a big deal.

For accurate value there shall be no other flow regulation valve beside regulation valve that is used to determine Ae. The main assumption related to the above formula is that there is no significant change in tubes diameters over time.