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we have added the pressure and temprature compensataion for calculating the mass flow of the superheated steam. The design pressure and temperature of the orifice plate are 43kg/cm2 and 420 C and the differential pressure created by the orifice plate is 10000mmWC.

kindly sugest the corresct formule for the above

Temperature & pressure compensation is not at all required for mass flow rate only is accountable in volumetric flow rate. As you are using differential pressure type flow element, it ensures that the transmitter is having linear and in DCS/PLC square root. And also check the specifications whether mass flow or volumetric flow is considered during the process of manfacturing.

Anyway, I have the formula, it is:

SQUARE ROOT (P+1.033 * Td+273/ Pd+ 1.033 * T+ 293)

P--- Kg/Cm2
T--- ABSOLUTE TEMPERATURE

Make sure that you are using gauge pressure transmitter.

Effect of temperature & pressure is negligible in
mass flow as it is movement of mass/time, but affects volume as density changes with pressure & temperature.

If you are unable to solve this, can you give me a clear picture or contact me at aswasidutt2 @ hotmail. com

I've been interested in this topic for a while as well.

Why is it you dont take into account the size of the orifice?

Also, is it possible to use this (or maybe some other that people know about) to calculate the mass flow through a pipe as it enters a main header (i.e. you have 3 x 8" pipes connected to a common 14" header and you want to know the mass flow through each of the 8" pipes)?

Glenn

Glenn, you use the orifice plate size when you calculate the flow constant. The flow (without compensation for temperature or pressure variations) is then normally calculated as
Q = C * sqrt(dp)
Where C is the flow constant that you normally find bu using an orifice plate sizing program. We use the program FlowCalc http://www.controlengineering.se/flowcalceng.htm

There are also other more accurate formulas you can use. This is described in the FlowCalc manual.

This formula may be used:

Q=Qin X Sq. root (Tr+273.14)/(Tin+273.14)X Sq root (Pin+Pabs)/(Pr+Pabs)

Q - Compensated flow
Qin - measured flow
Tr & Pr are temp & press considered during flow element design
Pabs - absolute press
Tin & Pin - measured temp & press using TT & PT in the line.

Hope that helps.

Regards,

Vinodh