Last Updated on March 16, 2022 by Electricalvolt
The TORBAR is a multi-port self-averaging flow meter. In this article, we will discuss what is torbar, its working, operation, application, advantages & disadvantages.
Torbar is a manufacturing brand name, while an Averaging Pitot tube is a technology. .But it is also popular by another manufacturer brand name “Annubar”. In this article, we use any of these names while describing going through the article.
The Torbar tube or averaging Pitot tube is a flow measurement instrument. It contains multiple pressure taps in order to take an average of the fluid flow. Thus, compensating for a non-linear flow profile.
It is one of the types of volumetric flow meters most popular in industrial applications. Torbar is the device that provides an estimate of the amount of fluid that passes through a pipe.
Definition of Averaging Pitot tube Flowmeter or Annubar Tube
Averaging Pitot tube flow meter or Annubar tube is an advanced flow sensing device. It is an advanced version of the Pitot tube. Averaging Pitot tube consists of an outer tube. The outer tube has its location perpendicular to the cross-sectional area of the pipe and inside there are two tubes.
The outer tube has a series of holes that face the upstream of the flow stream. And, the same number of holes in parallel face the downstream face of the flow stream. Thus, the holes on the outer tube estimate the profile of speed and average those estimates.
The Averaging Pitot tube has holes in the central part of the outer tube. The other holes are on the downstream face of the current. One of the internal tubes of the torbar estimates an average of the pressures measured through the holes (total pressure). The other internal tube measures the static pressure through the central hole.
We can define the Averaging Pitot tube (Annubar tube) or Annubar flow meter as follows.
An Averaging Pitot tube is a flow meter. It has its widespread application for the estimation of the flow of fluid passing through a conduit or pipe.
The averaging pitot tube is more reliable and precise than the conventional Pitot tube. Therefore, we use it as a flow meter to measure the flow of liquids, gases, and vapors.
A much simpler way to describe the Averaging Pitot tube or Annubar tube is:
Operation of Torbar
It is a measuring instrument that is inserted into a conduit or pipe. It consists of a series of pressure outlets oriented towards the side where the fluid flows. These intakes are coupled to an averaging chamber where the total pressure of a fluid (static plus dynamic) is measured.
The difference between the total and static pressures is effectively a head measurement of fluid velocity.
Working principle of the Torbar
The averaging Pitot tube is a primary measuring instrument that measures the flow of fluid. Annubar creates a differential pressure (DP) across the pipeline in order to estimate the flow rate of the fluid. According to Bernoulli’s equation, this pressure difference is proportional to the square of the fluid velocity in the pipeline.
Likewise, this pressure difference is measured and converted into a flow measurement through a DP pressure transmitter. The flow rate is directly related to the DP through the following relationship:
What are the relationship between the differential pressure (DP) in a pipe and the volumetric flow rate?
Q: Volumetric flow
K: Flow coefficient of Annubar.
DP: Differential pressure across the Averaging Pitot tube.
The Averaging Pitot tube creates differential pressure (DP) by creating an obstruction for the fluid in the pipeline.
The velocity of the fluid decreases and finally stagnates upon reaching the front surface of the Annubar sensor. Thus, it creates impact pressure or high pressure. The Annubar detects impact pressure using a DP transmitter.
Advantages of Torbar
- In the flow line, pressure drop across the averaging Pitot tube is low.
- Averaging Pitot tube accuracy is more than normal Pitot tube.
- Installation of the tube is as cheap as a normal Pitot tube.
- The main advantage is that, averaging Pitot tube is used for both liquids and gases.
- We can install the averaging pitot tubes by the hot tap or wet tap method without process shutdown.
- Flexible design
- It is suitable for wide range of processes and their conditions from high vacuum to high pressure.
- Robust construction, and negligible wear.
disadvantages of the Torbar(Averaging Pitot tube)
- Not recommended for viscous fluids.
- Does not estimate the velocity profile along the pipe section.
- Fluid must be clean. Use when it is suitable for the acceptable size of solid particles within a specified range.
- Gives better accuracy with high-velocity fluids.
Application of Averaging Pitot tube
- Torbar is helpful for mapping flow profile in large-sized ducts, channels.
- Oil production (onshore, offshore)
- Oil refining
- Power generation