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Orifice plate is used for flow rate measuring
in pipe systems. With orifice plate, pressure drop is
created. Based on the magnitude of pressure drop, flow
rate can be calculated. This instrument is very practical
for large tube diameters and for dirty fluid when turbines
are not applicable.
Measure pressure drop from position 1 to position 2 and
calculate flow rate and more with this easy to use calculator
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(requires
Java Runtime Environment http://java.com/en/download/index.jsp
)
| Explanation
of used values |
D1
D2
p1
p2
p1 - p2
ni
mi
T
rho
R
kappa
|
diameter of tube
throat diameter
upstream pressure
downstream pressure
pressure drop through orifice
kinematic viscosity
dynamic viscosity
upstream temperature
upstream density
gas constant
isentropic coefficient |
| Resulting
values |
Q
G
V1
V2
ReD
e
C |
volumetric flow rate
mass flow rate
upstream velocity
throat velocity
upstream Reynolds number
expansion coefficient
coefficient of discharge |
Theory
Calculation of flow rate using orifice plate calculator is
for incompressible flow, based on the Bernoulli principle:
where is:
p - pressure
rho - density
V - velocity
g - gravitational constant (9.81 m/s2)
z - geodetic height
Assumption that pressure lost is negligible (pressure drop
is obvious and included with coefficient of discharge which
is introduced bellow):
and:
and if velocities substituted with flow rate:
 
where is: Q - volumetric flow rate
D - diametar
Pressure drop through the orifice because of velocity increase
can be calculated as follows:
or:
Expressing flow rate from the previous equation leads to:
Substituting:
flow rate can be determined as:
where is:
C - coefficient of discharge
e - expansion coefficient
Coefficient of discharge can be calculated using following
equation (ISO):
where is:
beta - diameter relation D2/D1
ReD - Reynolds number which can be calculated as follows:
where is:
ni - kinematic viscosity
mi - dynamic viscosity
L1 and L2 are functions on tap type and it is:
L1=L2=0 for corner taps
L1=1 L2=0.47 for D & D/2 taps
L1=L2=0.0254/D D[m] for 1" taps
Expansion coefficient e can be calculated (for gases only):
where is:
kappa - isentropic coefficient; kappa = 1.4 for air and other
two atom gas molecules
Other values are calculated using following equations:
mass flow:
velocities:
If flowing fluid is gas, then it is considered as incompressible
and ideal. Equation for ideal gas:
can be used for calculation of temperature T:
as well as density rho:
where R is gas constant (R=287 J/kgK for air).
Appliance
Orifice plate calculator can be used for both liquids and
gases. Fluid is considered as incompressible, so density (rho)
and temperature (T) are constant through tube. Also, gas is
considered as ideal.
Units of measure are both in SI and English system.
Orifice plate calculator can be used for calculation of:
volumetric flow - Q
mass flow - G
velocity on inlet, bigger diameter - V1
velocity on smaller diameter - V2
Reynolds number on bigger diameter - ReD
For calculation of those values, necessary values for input
are:
inlet, bigger diameter - D1
smaller diameter - D2
inlet pressure - p1
either pressure on smaller diameter - p2, or pressure drop
p1-p2
either kinematic viscosity - ni, or dynamic viscosity - mi
for gases only:
either temperature - T, or density - rho
gas constant - R
for liquids:
density - rho
Beside four values (Q, G, V1, V2), which calculation is main
purpose of calculator, values that are not defined by user are
determined in process of calculation (for example: if pressure
p1 and temperature T are specified for gas flow - value for
rho is calculated together with four main values (Q, G, V1,
V2)). Also necessery coeffients: expansion - e and discharge
- C are calculated and results are shown.
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