Orifice plate (diaphragm) flow and pressure drop calculation

1. Introduction
2. Pressure drop through an orifice
3. Orifice flow and pressure drop calculation tool

1. Introduction

Orifices are often used in fluid mechanics to limit mechanically the flow. It is important to be able to size them.

The restriction orifice mentioned here is a thin perforated plate, also called orifice plate or diaphragm.

2. Pressure drop through an orifice

How to calculate the pressure drop through an orifice plate ?

The following correlation is given by Gibson, it is reproduced in many books.It relates the flow through the orifice and the pressure drop.

Equation 1 : singularity pressure drop coefficient for an orifice

With :
K = Pressure drop coefficient
D = Pipe diameter (m)
d = orifice diameter (m)
um = fluid velocity, before diaphragm, (m/s)
ΔHs = Pressure drop in m

The coefficient K can also be calculated thanks to the following graph :

Graph 1 : K coefficient as a function of d/D

3. Orifice flow and pressure drop calculation tool

How to calculate the flow through an orifice plate ?

You can access to an Excel calculation tool in order to assess the flow and pressure drop through an orifice plate : Excel calculation tool

Source

Gibson et al., Hydraulics and its applications, 5th edition, Constable London, 1952