Ultrasound measures flow profiles in real time
A new ultrasonic system measures flow velocities cost-effectively and precisely. The system is suitable for flow profile-independent flow measurement in pipes and open channels as well as for flow analysis in mixing vessels and reactors. If several municipalities direct their waste water into the same sewage treatment plant, it must be calculated exactly who lets how much flow through the sewer pipes. After all, no municipality wants to pay for its neighbor's dirt. Many conventional devices for flow measurement have one major disadvantage: they require a specific flow profile – a specific velocity distribution in the pipe. The inlet and outlet sections required to form such a profile are often not available in practice. Measurement errors are the result. In order to eliminate this, the Fraunhofer Institute for Biomedical Engineering IBMT has developed an ultrasonic flow meter that records the current flow conditions. The device, which is equipped with a digital signal processor DSP, enables an exact flow measurement with any profile. It can carry out spatially resolved velocity measurements at specified depths.
The ultrasound system is based on a tracking method. For this purpose, short ultrasonic signals are sent into the liquid at periodic intervals. Scatters that are carried along – such as dirt particles or small air bubbles – reflect these signals.
"With the help of the received echo signals, the change in position of the scatterer can be tracked and the flow velocity at different depths of the liquid can be determined," says Margit Barth from the IBMT. It also measures the flow distribution in mixing, reaction, separation and settling processes in real time. Previous sensors usually protrude into the flow and thus falsify the results, are not real-time capable or failed at high speeds. In mixing processes, for example, the speed distribution has a decisive influence on how quickly different components mix to form a homogeneous mass or the quality of the product. The measurement of the velocity distribution allows an optimal process control as well as the design optimization of the corresponding containers and devices. With the further development of the so-called speckle tracker, the institute wants to respond to requests from the industry. For this reason, around 800 decision-makers from various sectors, such as the pharmaceutical, food and chemical industries as well as water management, are currently being surveyed.
