Mastering Flow Measurement: Pitot Tube as an Insertion Flow Meter - Principles, Construction, and Working Explained

• by Prasad Harichandra
• 19 Jun 2011
• Equipments

In the realm of flow measurement, the Pitot Tube stands out as a versatile and effective insertion flow meter. This article dives into the intricacies of the Pitot Tube, exploring its principles, construction, and working mechanisms. From understanding its unique design to comprehending its role in measuring fluid flow, this comprehensive guide unravels the science behind Pitot Tubes. Whether you're an engineer, researcher, or enthusiast, grasp the principles that make Pitot Tubes a valuable tool in the world of fluid dynamics.

A Pitot tube, also known as a Pitot probe or Pitot sensor, is a type of insertion flow meter used to measure the velocity of fluid flow, typically in pipes or conduits. It operates on the principle of Bernoulli&39;s equation, which relates fluid velocity to pressure. Pitot tubes are commonly used in various industries, including aerospace, meteorology, and fluid mechanics, as well as for flow measurement in pipes and ducts. Here&39;s an overview of the principle, construction, and working of a Pitot tube:

Principle: The principle behind a Pitot tube is based on Bernoulli&39;s equation, which states that the total energy of a fluid in a steady flow remains constant along a streamline. In a simplified form, the equation relates fluid velocity (V), pressure (P), and fluid density (ρ):

�+0.5∗�∗�2=��������P+0.5∗ρ∗V2=constant

In the case of a Pitot tube, it utilizes the difference in pressure between two points within a fluid flow:

1. Stagnation Point (Pitot Tube Tip): The open end of the Pitot tube, typically shaped like a pointed probe, is aligned with the fluid flow. At this point, the fluid comes to a complete stop, and its velocity is zero. Thus, the pressure at the stagnation point is the total or "stagnation" pressure (Pt).

2. Static Pressure Port: Located on the side of the Pitot tube and perpendicular to the flow, the static pressure port senses the static pressure (Ps) of the fluid in the pipe or conduit.

The difference between the stagnation pressure and the static pressure is directly related to the velocity of the fluid flow:

��−��=0.5∗�∗�2Pt−Ps=0.5∗ρ∗V2

By measuring the pressure difference (Pt - Ps), the velocity of the fluid can be determined.

Construction: A Pitot tube typically consists of the following components:

1. Probe: The probe is the main body of the Pitot tube, with a pointed tip that faces the fluid flow.

2. Pressure Sensing Port: A small opening or port on the side of the probe that connects to a pressure sensor or manometer.

3. Mounting Hardware: The Pitot tube may include mounting hardware to secure it in place within the pipe or conduit.

Working: The working of a Pitot tube involves the following steps:

1. The Pitot tube is inserted into the fluid flow so that the pointed tip faces upstream and directly aligns with the flow.

2. The fluid flows into the Pitot tube, where it comes to a complete stop at the stagnation point, creating a stagnation pressure (Pt).

3. The pressure sensing port on the side of the probe senses the static pressure (Ps) of the fluid at that location within the pipe or conduit.

4. The pressure difference (Pt - Ps) is measured using a pressure sensor or manometer, and it is directly related to the fluid velocity using Bernoulli&39;s equation.

5. The velocity of the fluid flow is calculated based on the pressure difference and fluid density (ρ).

Pitot tubes are commonly used in applications such as aircraft airspeed measurement, flow measurement in pipes, and airflow measurement in HVAC systems. They provide a simple and reliable means of measuring fluid velocity by utilizing the principles of fluid dynamics and pressure differential.