The History of Ultrasonic Flow Meters

The general consensus regarding the history of ultrasonic flow meters is that scientists began exploring ultrasonic flow meter technology in the 1950s. Initially, ultrasonic technology was used for non-invasive detection in the medical and industrial fields. Subsequently, researchers began to explore the possibility of applying ultrasound to fluid flow measurement. In the 1970s and 1980s, ultrasonic flow meter technology gradually became commercialized. Technological improvements included the use of time-of-flight (TOF) methods and the Doppler effect, both of which enhanced measurement accuracy and reliability.

In the last 20 years, ultrasonic technology has made rapid advancements. Modern ultrasonic flow meters can be connected to central monitoring systems through networks, enabling remote data transmission and device management. This connectivity supports large-scale data analysis and real-time monitoring, especially in water and energy industries. The Doppler and time-of-flight methods are the two most widely used principles in ultrasonic flow meter applications.

While the time-of-flight method is frequently mentioned, this discussion will focus on the application of the Doppler method in flow measurement. The Doppler method is based on the Doppler effect, which is named after the Austrian physicist and mathematician Doppler, who first proposed this theory in 1842.

The Doppler Effect
The Doppler effect uses ultrasonic waves or laser beams to transmit to the fluid and receive the reflected signals. Particles in the fluid, such as bubbles, suspended particles, or droplets, scatter some of the energy, forming scattering bodies, and their motion causes a change in the frequency of the received signal. By analyzing this frequency change, the flow rate of the fluid can be calculated.

Doppler flow measurement technology has wide applications in various fields, including industry, medicine, and environmental monitoring. In the medical field, it is used in cardiovascular ultrasound examinations to non-invasively measure blood flow velocity, assisting doctors in diagnosing cardiovascular diseases. In the industrial sector, Doppler flow meters are widely used in pipeline flow monitoring and control, such as in chemical plants, water treatment plants, and more.

It is important to note that Doppler ultrasonic flow meters require the fluid to contain some reflective particles or bubbles.

Therefore, it can be used in places where other flow meters do not work, such as liquid slurries, aerated liquids (containing a large number of bubbles), or liquids with suspended solids.

However, this method is not suitable for clean fluids. The performance of the Doppler flow meter highly depends on the physical properties of the fluid, such as sound conductivity, particle density, and flow characteristics. The uneven distribution of particles across the pipeline's cross-section can lead to incorrect average speed calculations. The accuracy of the flow meter is sensitive to changes in the velocity profile and the distribution of acoustic reflectors in the measurement section.

Compared to Doppler ultrasonic flow meters, time-of-flight flow meters are suitable for clean fluids (with few particles, bubbles, etc.), whether gases or liquids. Even for slurries or fluids with evenly distributed particles, time-of-flight is also effective. Therefore, combining the two measurement methods allows for a wider range of applications and more accurate measurements.

The Doppler method is suitable for measuring two-phase flows and avoids the issues of clogging, wear, or attachment caused by suspended particles or bubbles that can prevent conventional instruments from functioning. This has led to its rapid development. With industrial progress and energy-saving efforts, the development of the transportation and application of kerosene mix (COM), coal-water mix (CWM) fuels, and energy-saving methods such as water-assisted combustion of fuel oil has opened up broad prospects for the application of Doppler ultrasonic flow meters.