For transit time ultrasonic flowmeters, be sure that the fluid can adequately conduct ultrasonic waves, because the flowmeter will not measure when the ultrasonic waves cannot penetrate the flow stream between the transducers. Similarly, ultrasonic waves must be able to penetrate the fluid for Doppler flowmeters to operate accurately. When the fluid is relatively opaque and does not penetrate the fluid, Doppler flowmeters tend to measure the velocity of the fluid at or near the pipe wall, which can cause significant measurement error and/or cause the flowmeter to fail.
For Doppler ultrasonic flowmeters, be sure that the fluid adequately reflects ultrasonic waves, because the flowmeter will not operate without a reflected ultrasonic signal. Depending upon design, reflections can occur due to small bubbles of gas in the flow stream or the presence of eddies in the flow stream. If not already present in the flowing stream, generating these sources of reflection can be difficult in practice. Fortunately, some combination of bubbles of gas and/or eddies are present in most applications.
The velocity of the solid particles in slurry can be different than its liquid carrier fluid. Be careful applying ultrasonic technology when the solid particles can become concentrated in one part of the flowing stream, such as in a horizontal pipe flowing at a relatively low velocity. Be careful when applying Doppler ultrasonic flowmeters in slurry applications because the solid particles can produce strong signals that can cause the Doppler flowmeter to measure the velocity of the solids and not the velocity of the liquid.
Avoid fluids that can coat wetted transducers or coat the pipe wall in front of non-wetted transducers because the flowmeter will not measure when the ultrasonic waves cannot enter the flow stream. Be sure to maintain reliable clamp-on transducer connections to the pipe wall because the flowmeter will not measure when the ultrasonic waves are not able to reach the fluid.
Be sure to understand the process and apply these flowmeters properly. For example, a periodic cleaning process upstream may cause the flowmeter to stop working because the dirt may not allow ultrasonic energy to pass through the fluid. Further, if the dirt coats wetted transducers, the flowmeter may fail to operate until it is cleaned.