Thanks to a transmission property of ultrasound, a flow measurement in opaque liquids has become possible. These liquids includes, liquid metals, food materials, chemicals, waste water, industrial materials etc. They have been all experienced by UVP.
It is obviously an advantage that not only liquids but also container wall can be opaque. Usually artificial construction materials are opaque. It should, however, be carefully prepared with metallic wall to normal liquids.
The use of liquid metal is not only important in some engineering problems, but also interesting in scientific study, especially turbulent study, sicne its dynamics visxosity is small compared to water which can lead the Reynodls number of the system much higher.
Many of the ordinary opaque liquids show non-Newtonian property. So, the UVP would be powerful in rheological fluid dynamics.