flow measurement using bernoulis principle

 

List of Flow Measuring Devices

 

There are various flow measuring devices, as described below, that are based on Bernoulli's equation.

• 1.      Venturi meter
• 2.      orifice meter
• 3.      Pitot tube
• 4.      flow nozzles
• 5.      Rotameter

 

The Venturi meter is the most widely used flow measurement tool among the aforementioned instruments. There is also some use of the pitot tube and orifice metre. It is crucial to understand the idea behind, formulas for, and design principles behind these devices, all of which are covered in more detail below.

Venturi meter

A venturi meter is a tool used to gauge the flow of fluid via pipes. Three parts make up a venturi meter: the convergent, throat, and divergent segments. These three components' design facets are examined in more detail.

1.    1.  Convergent section

The diameter of the pipe to which the venturi meter is connected is determined by measuring the convergent and divergent parts. Therefore, Dpipe = Dinlet + Doutlet (21° 1°), primarily 20°, is retained as the angle of convergence.

The length of the convergent segment is calculated as 2.7*(D - d), where D is the pipe's diameter and d is the throat's diameter.

2.     2. The throat region

The safety of the pipe and the Venturi meter both depend on the throat's diameter (d). The velocity head increases and the pressure head significantly lowers if d is too small. Due to the negative pressure, the material is notched and bubbles are produced that burst on the downstream side (where pressure is higher). To prevent this, d is assumed to be half the inlet pipe's diameter, or 1/2*D.The diameter of the throat part is determined by measuring how long it is (Lthroat).

3. Divergent Portion

In order to prevent cavitation in the Venturi meter, pressure is gradually increased across the diverging portion. Angles of the diverging part range from 5° to 15°, with 6° being the most common.Other broad considerations comprise, A Utube manometer is used to measure the pressure difference between the input and outflow.Because head loss in the convergent portion is disregarded, the Venturimeter can only measure theoretical discharge.

The co-efficient of discharge (Cd) is multiplied by the theoretical discharge to obtain the actual discharge. Cd values range from 0.95 to 0.99.The main pipe diameter and the venturi meter’s throat diameter are used to describe a venturi meter’s size. A venturi meter, for instance, with a size of 150 * 75 mm, represents the primary pipe diameter (D) as 150 mm.

 

Orifice meter

A comparable instrument used to gauge fluid outflow is an orifice metre. A flat plate with a circular aperture that is provided concentrically with the pipe across the flow makes up the device. The venturi meter’s operating system is the same one used by this device.

Because of the following drawbacks, which a venturi meter does not have, orifice metres are less frequently utilised.

·        inferior to a venturi meter in accuracy

·        exposed to wear

·        The obstructing design collects dirt and debris.

·        As opposed to a venturi meter, it is less efficient.

Even though the orifice metre has some drawbacks, it is still simple to construct and inexpensive.

Tube Pitot

A basic tool for determining the velocity of a flowing fluid at any point is a pitot tube. It is used to monitor the velocity of flow in areas that are open to the atmosphere and looks like an L-shaped bent pipe in its basic form.

Flow Nozzle

An orifice metre, venturi meter, and flow nozzle are related types of equipment. It lacks a diverging portion but has a smooth converging portion like a venturi meter. Flow nozzle is also not a commonly used device.