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Orifice Calculator Sizing

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Pipe & Fluid

Calculations

Results

Information and Definitions

Pipe & Fluid Information

Pressure In (P1)

Considering the direction of the fluid, we define P1 as the pressure (gauge or absolut) existing in the pipeline before the restriction orifice.

Pressure Out (P2)

Taking into account the direction of the fluid, we define P2 as the pressure existing in the pipeline after the restriction orifice.

Viscosity (mu)

Viscosity is the measure of a fluid's resistance to flow. Dynamic viscosity is a measure of internal resistance.It measures the tangential force per unit area required to move one horizontal plane with respect to an other plane.

It is commonly expressed, particularly in ASTM standards, as centipoise (cP) since the latter is equal to the SI multiple millipascal seconds (mPa·s).The viscosity of a fluid is highly temperature dependent.

Density (rho)

Density is the relation of mass and volume.The density of a material varies with temperature and pressure. This variation is typically small for solids and liquids but much greater for gases.

...where rho is density, m is mass and V is volume.

Pipe Diameter (D)

Inside diameter of the pipe.All process calculations are based on the volume of the pipe which is the function of internal diameter of the pipe. As per standards, any pipe is specified by two non-dimensional numbers Nominal Diameter (in Inches as per American Standards or mm as per European standards) and Schedule (40, 80, 160,...). The outer diameter of the pipe is the diameter of outer surface of the pipe.

Orifice Diameter (d)

Inside diameter of the orifice hole.

Input Valid Values (Minimum and Maximum)

#	Variable Name	URV (Upper Range Value)
Q	Flow	66
rho	Density	10000
D	Pipe Diameter	100
d	Orifice Diameter	100

Calculations Information

Pressure Drop (dp)

Difference in total pressure between two points of a fluid carrying network. Pressure drop occurs when frictional forces, caused by the resistance to flow, act on a fluid as it flows through the tube.

Reynolds (ReD)

The Reynolds number (Re) is an important dimensionless quantity in fluid mechanics used to help predict flow patterns in different fluid flow situations. It is defined as :

...where rho is density, V is velocity of fluid in pipe, D is pipe diameter and mu is dynamic viscosity.

At low Reynolds numbers, flows tend to be dominated by laminar (sheet-like) flow, while at high Reynolds numbers turbulence results from differences in the fluid's speed and direction, which may sometimes intersect or even move counter to the overall direction of the flow.

Image by C. Fukushima and J. Westerweel, Technical University of Delft, The Netherlands

There are in general three types of fluid flow in pipes

Red <= 2300 --> Laminar
2100 <= Red <= 4000 --> Transient
4000 <= Red --> Turbulent

Beta Ratio

Beta Ratio is the ratio between the line inner diameter to bore size of the orifice. The flow coefficient is found to be stable between beta ratio of 0.2 to 0.7 below which the uncertainity in flow measurement increases. An orifice plate beta ratio of 0.6 means that the orifice plate bore diameter is 60% of the pipe internal diameter.

...where Beta is Beta Ratio, d is orifice diameter and D is orifice diameter.

Discharge Coefficient (Cd)

The discharge coefficient is a dimensionless number used to characterise the flow and pressure loss behaviour of nozzles and orifices in fluid systems.It depends on the orifice shape. The discharge coefficient can be obtained for any differential-pressure meter and any installation by calibrating it in a flowing fluid: for a particular orifice meter the discharge coefficient is a function of the Reynolds number.

Over many years of experiment it has been found that the discharge coefficient can be predicted within a defined uncertainty provided that the orifice meter (i.e. the orifice plate and pipework) are constructed within the standards. If the discharge coefficient is to be used for an orifice meter without calibrating it in a flowing fluid, the discharge coefficient is usually taken from a published discharge coefficient equation. Therefore, the discharge coefficient equation is very important for orifice plates: an error of 0.1 % in discharge coefficient gives an error of 0.1 % in many flow measurements of natural gas. ISO 5167-1:1991 provides an equation for the orifice discharge coefficient calculation, Cd, as a function of Beta Ratio, Reynolds number, L1 and L2, where L1 is the distance of the upstream pressure tap from the orifice plate and L2 is the distance of the downstream pressure tap from the orifice plate.

Results Information

Velocity in orifice

Velocity of the fluid when it passes through the restriction orifice.

...where D is pipe diameter, rho is Density, V1 is velocity of fluid in pipe, d is orifice diameter and V2 is velocity of fluid in orifice.

Velocity in pipe

Velocity of the fluid in the pipe.

Mass Flow Rate

Mass of a substance which passes per unit of time.

...where W is Mass Flow Rate, rho is Density and Q is Volumetric Flow Rate.

Volumetric Flow Rate

It is defined as the volume of fluid which passes per unit time, usually represented by the symbol Q .

Our ISO 5167-1:1991 orifice calculator is based on the use of Corner Taps. L1 = L2 = 0

Orifice meters which have Corner pressure tappings must meet following conditions:

d > 12.5 mm
50 mm < D < 1000 mm
0.1 < Beta Ratio < 0.75
(ReD > 5000) and (ReD > 170xBeta Ratio^2xD)

Disclaimer

The Author has made a reasonable effort to ensure the accuracy of the information herein. However, the information contained on this site is provided without any representation or warranty as to accuracy or completeness or otherwise and should be used only as a general guideline and not as an authoritative source of technical information.

The Author is not offering the information as engineering or other professional services or advice. This site does not constitute an offer or solicitation to perform professional engineering services.