Mass flow through Venturi tube
Mass flow through Venturi tube
(OP)
Hi,
I have a Venturi tube installed on a superheated steam line. In order to calcula the mass flow I have a couple of questions.
1. does the transmitter have to extract the square root or linear and then which formula would need to be applied to read mass flow and not volumetric flow?
thanks
I have a Venturi tube installed on a superheated steam line. In order to calcula the mass flow I have a couple of questions.
1. does the transmitter have to extract the square root or linear and then which formula would need to be applied to read mass flow and not volumetric flow?
thanks





RE: Mass flow through Venturi tube
The equation that allows you to infer a flow rate from the differential pressure across a known restriction provides volume flow rate. To convert that to mass flow rate you only have to multiply times density. Not terribly difficult.
David
RE: Mass flow through Venturi tube
RE: Mass flow through Venturi tube
RE: Mass flow through Venturi tube
The only difference is that the mass steam flow calculation for the Venturi is done with a DCS function attached while the SG has an orifice with a transmitter ehich corrects the steam flow for P and T.
So basically I woul like to make sure that we are using the function correctly.
RE: Mass flow through Venturi tube
you may need to consult the plant record books for the current design basis
according to the writeup you posted, the scale factor should be multiplied by sqrt(rnew/rold) or simply replace r by the new but actual steam density in units required by your computation block.
updating meter factors for changed plant conditions is pretty normal stuff
since the venturi is reading high, it sounds like the operating pressure is lower than originally expected, or the steam temperature higher
RE: Mass flow through Venturi tube
I am still not sure whether the fscale value i use is correct, the venturi datasheet says a max flow of 250 tn/h and i use it a fscale, the rest of variables are ok.
I use the datasheet parameters on the formula. The densiy I calculate it using a macro in excel called water97,
ht
Please find attached the venturi datasheet. Could you please let me know whether I am using the datasheet correctly?
Does it really matter what the max flow is s long as the max dp in venturi is changed accrodingly? Should I be using operating values inthe formula or maximum values?
thank you very much.
RE: Mass flow through Venturi tube
I get virtually identical results steam data, discharge coefficient, etc. for the given condtions. What you have to confirm is the current pressure and temperature (at least the average readings). The get a reading of the actual transmitter differential in mmH2O and the indicated flow in t/hr at the same instant.
RE: Mass flow through Venturi tube
The transmitter gives an output in mmH20, the DCS does the conversion to t/hr.
For example with these values,
T= 376,9 ºC
P= 99 barg
dp= 155 kPa
The DCS function outputs 214 tn/h while te steam generator which has a rosemount Annubar flowmeter outputs 199 tn/h (there are two steam trains each showing 28 kg/s, so approx 199 tn/h)
This difference is what I dont understand.
I also attach the calc for the steam generator annubar.
RE: Mass flow through Venturi tube
FLOW METER SIZING CALCULATION
Tag no
Service
Fluid Steam
Meter Square Edge Orifice Plate
Connections Flange Taps
Pressure 99.000 Barg(100.013 Bar(A))
Temperature 378.0 Deg C
Ambient Pressure 1.013 Bar(A) ( 0 Meters Above msl)
Base Conditions (STP) 1.013 Bar(A) , 0.0 Deg C
Specific Volume (Vf) 0.0248 M3/kg
Isentropic Exponent 1.271
Viscosity 0.025 cP
normal | maximum
Flow 196000 | 250000 kg/hr
Pipe Reynolds No. (Rd) 12115205 | 15453067
Mean Fluid Velocity (Pipe) 32.4 | 41.4 m/s
Line Loss 1.27 | 2.07 (Bar)/100 m
Friction Factor (f) 0.0138| 0.0138
Meter Loss(Installed) 0.61 | 1.00 Bar
Meter Velocity 58.3 | 74.4 m/s
**** METER CONSTANTS ****
Meter Bore (d) 6.7587 @ 20 Deg C
Pipe i.d. (D) 9.0618 Inches
Beta Ratio (d/D) 0.7458 Inches/Inch Caution
Metal Expansion (Fa) 1.0126 (316 Stainless Steel)
Expansion Factor (Y1) 0.9946
Reynolds Factor (Fc) 0.9593
Drain/Vent Corr. (Fh) 1.0000
Discharge Coef. (Cd) 0.59547
Spinks Factor (S) 0.41553
**** TRANSMITTER DATA ****
normal | maximum
Meter Differential (h) 13448.0 | 21878.9 mm w.c.
Flow Rate 196000 | 250000 kg/hr
W (kg/hr) = 8.121 * S * D^2 * Fa * Fc * Fh * Y1 * sqrt( h / Vf )
RE: Mass flow through Venturi tube
With a value of 15809 mm w.c. and your formula I obtain 215 tn/h so it seems to coincide with my calculation. I guess maybe the error is in the pitot on the Steam generator?
What is the difference between the value in **** TRANSMITTER DATA **** of 21878.9 mm w.c. and the span of 22000 mm w.c.? I guess none.
I need if possible the formula for the LP flowmeter, this is the next strange thing, is that the flow in HP is 215 tn/h and the LP is 183 tn/h, how can there be so much loss in steam between Hp and lp.
Op T: 325 ºC
Op P: 16,4 barg
Attached is the Venturi data sheet.
What SW are you using for the calculation and to derive the formula? Is it Flowcalc32?
btw: Remind me to include you in my Christmas cards lists!! you are awesome, thank you.
RE: Mass flow through Venturi tube
You haven't lost steam, unless you've an extraction turbine, usually it is the changed process conditions. Often the LP steam will have wildly varying temps depending on the turbine load, with the higher temps at reduced load
the sw is custom developed, but used in lots of meter surveys to sort out the non-sense and keep suppliers in line. Uses the equation of state for steam/condensate.
hopefully with attachments
RE: Mass flow through Venturi tube
Tag no
Service
Fluid Steam
Meter Venturi W / 15 Deg Exit Cone
Pressure 17.000 Barg(18.013 Bar(A))
Temperature 378.0 Deg C
Ambient Pressure 1.013 Bar(A) ( 0 Meters Above msl)
Base Conditions (STP) 1.013 Bar(A) , 0.0 Deg C
Specific Volume (Vf) 0.1623 M3/kg
Isentropic Exponent 1.289
Viscosity 0.024 cP
normal | maximum
Flow 183000 | 200000 kg/hr
Pipe Reynolds No. (Rd) 5230769 | 5716687
Mean Fluid Velocity (Pipe) 39.7 | 43.3 m/s
Line Loss 0.11 | 0.14 (Bar)/100 m
Friction Factor (f) 0.0121| 0.0121
Meter Loss(Installed) 0.02 | 0.03 Bar
Meter Velocity 87.5 | 95.6 m/s
**** METER CONSTANTS ****
Meter Bore (d) 13.6450 @ 20 Deg C
Pipe i.d. (D) 20.2618 Inches
Beta Ratio (d/D) 0.6734 Inches/Inch
Metal Expansion (Fa) 1.0126 (316 Stainless Steel)
Expansion Factor (Y1) 0.9918
Reynolds Factor (Fc) 1.0000
Drain/Vent Corr. (Fh) 0.0000
Discharge Coef. (Cd) 0.99349
Spinks Factor (S) 0.50554
**** TRANSMITTER DATA ****
normal | maximum
Meter Differential (h) 1920.3 | 2293.6 mm w.c.
Flow Rate 183000 | 200000 kg/hr
W (kg/hr) = 8.121 * S * D^2 * Fa * Fc * Fh * Y1 * sqrt( h / Vf )
RE: Mass flow through Venturi tube
FLOW METER SIZING CALCULATION
Tag no
Service
Fluid Steam
Meter Venturi W / 15 Deg Exit Cone
Pressure 16.400 Barg(17.413 Bar(A))
Temperature 325.0 Deg C
Ambient Pressure 1.013 Bar(A) ( 0 Meters Above msl)
Base Conditions (STP) 1.013 Bar(A) , 0.0 Deg C
Specific Volume (Vf) 0.1527 M3/kg
Isentropic Exponent 1.293
Viscosity 0.022 cP
normal | maximum
Flow 183000 | 200000 kg/hr
Pipe Reynolds No. (Rd) 5740138 | 6273375
Mean Fluid Velocity (Pipe) 37.3 | 40.8 m/s
Line Loss 0.11 | 0.13 (Bar)/100 m
Friction Factor (f) 0.0121| 0.0121
Meter Loss(Installed) 0.02 | 0.03 Bar
Meter Velocity 82.3 | 89.9 m/s
**** METER CONSTANTS ****
Meter Bore (d) 13.6450 @ 20 Deg C
Pipe i.d. (D) 20.2618 Inches
Beta Ratio (d/D) 0.6734 Inches/Inch
Metal Expansion (Fa) 1.0106 (316 Stainless Steel)
Expansion Factor (Y1) 0.9920
Reynolds Factor (Fc) 1.0000
Drain/Vent Corr. (Fh) 0.0000
Discharge Coef. (Cd) 0.99354
Spinks Factor (S) 0.50557
**** TRANSMITTER DATA ****
normal | maximum
Meter Differential (h) 1813.1 | 2165.6 mm w.c.
Flow Rate 183000 | 200000 kg/hr
W (kg/hr) = 8.121 * S * D^2 * Fa * Fc * Fh * Y1 * sqrt( h / Vf )
RE: Mass flow through Venturi tube
RE: Mass flow through Venturi tube
by the way, good luck on sorting the meters out, it is always a lot of hard work and fun
RE: Mass flow through Venturi tube
RE: Mass flow through Venturi tube
RE: Mass flow through Venturi tube
RE: Mass flow through Venturi tube
RE: Mass flow through Venturi tube
good luck, btw
RE: Mass flow through Venturi tube
also a bit puzzled by the change in flow units from t/h with your other meters to kg/s
RE: Mass flow through Venturi tube
The pitot from the steam generator uses kg/s and we use t/h.
RE: Mass flow through Venturi tube
RE: Mass flow through Venturi tube
Sorted out the differences in the annubar meter d/p calculations. The calculation at the given flow and pipe size is extremely sensitive to fluid density. I am using an older equation of state with a fluid density that differs from the supplier calc by 0.14%. The accepted equations of state for steam have been improved since the calc was developed.
RE: Mass flow through Venturi tube
RE: Mass flow through Venturi tube
Attached is the FW FM
RE: Mass flow through Venturi tube
no drain hole was assumed
FLOW METER SIZING CALCULATION
Tag no
Service
Fluid Water
Meter ASME Long Radius Flow Nozzle
Pressure 115.000 Barg(116.013 Bar(A))
Temperature 179.0 Deg C
Ambient Pressure 1.013 Bar(A) ( 0 Meters Above msl)
Liquid Gravity (Gf) 0.889
Viscosity 0.160 cP
normal | maximum
Flow 235000 | 250000 kg/hr
Pipe Reynolds No. (Rd) 3936751 | 4188033
Mean Fluid Velocity (Pipe) 5.4 | 5.7 m/s
Line Loss 1.52 | 1.73 (Bar)/100 m
Friction Factor (f) 0.0156| 0.0156
Meter Loss(Installed) 0.46 | 0.52 Bar
Meter Velocity 15.0 | 16.0 m/s
**** METER CONSTANTS ****
Meter Bore (d) 3.1070 @ 20 Deg C
Pipe i.d. (D) 5.1870 Inches
Beta Ratio (d/D) 0.5990 Inches/Inch
Metal Expansion (Fa) 1.0053 (316 Stainless Steel)
Expansion Factor (Y1) 1.0000
Reynolds Factor (Fc) 1.0000
Drain/Vent Corr. (Fh) 1.0000
Discharge Coef. (Cd) 0.99320
Spinks Factor (S) 0.38178
**** TRANSMITTER DATA ****
normal | maximum
Meter Differential (h) 8952.7 | 10132.1 mm w.c.
Flow Rate 235000 | 250000 kg/hr
W (kg/hr) = 255.2 * S * D^2 * Fa * Fc * Fh * Y1 * sqrt( Gf * h )
RE: Mass flow through Venturi tube