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.