1、 Overview
Anuba flowmeter (Anuba) is a novel flow meter developed based on the principle of Pitot tube speed measurement. Its outstanding advantages are relatively simple structure, light weight, low cost, small pressure loss, easy installation and maintenance, strong adaptability of instrument matching, suitable for flow measurement of circular, rectangular, and multi-faceted pipelines. With the increasing diameter of process pipes and the requirement for easy installation, the uniform velocity tube flowmeter is the preferred choice for measuring large pipe flow rates. This flowmeter is widely used in industries such as thermal power, nuclear power, petroleum, textile, papermaking, metallurgy, and chemical for flow measurement and control of liquids, gases, and steam.
Due to the fact that the Annubar flowmeter measures the point velocity of the fluid, the requirements for the straight pipe section are longer than those for general velocity type flowmeters. Only by ensuring sufficient length of the straight pipe section can the fluid inside the pipe have a stable velocity distribution. The minimum length of the front straight pipe section is generally required to be at least 10D. Due to the difficulty in determining the state of a fluid in the transition zone between laminar and turbulent flow,
Therefore, the Reynolds number selected for this flowmeter should not be between 2000 and 5000.

2、 Measurement principle
The Annubar flowmeter is developed based on the principle of pitot tube velocity measurement. It determines the flow rate by multiplying the average flow velocity of the pipeline with the effective cross-sectional area of the pipeline.
The velocity distribution in general pipelines is uneven. If it is a fully developed fluid, its velocity distribution follows an exponential law. For accurate measurement, the entire circular cross-section is divided into two semicircles and two semicircles with equal unit areas. The detection rod of the Anuba flowmeter is composed of a hollow metal tube arranged in a process pipeline perpendicular to the flow direction. Two pairs of total pressure holes are drilled on the upstream side, which are located in the center of each unit area and reflect the flow velocity of each unit area. As each total pressure hole is connected, the average total pressure value transmitted to each point in the detection rod is sent to the positive pressure chamber of the transmitter through the total pressure outlet pipe via the high-pressure joint. When the averaging tube flowmeter is correctly installed on a process pipeline with sufficient length of straight pipe, there should be no vortex on the flow section, and the static pressure of the entire section can be considered constant. There is a detection hole located in the middle of the back of the detection rod, representing the static pressure of the entire cross-section. The static pressure outlet pipe is led from the low-pressure joint to the negative pressure chamber of the transmitter, and the square of the differential pressure measured in the positive and negative pressure chambers is divided by the flow rate
The average flow velocity of the cross-section is proportional, thus obtaining a proportional relationship between differential pressure and flow rate.