To measure in air or other gasses is principally impossible with UVP instrument working with high frequency sound fields, as in those media the acoustic impedance is much more smaller than in liquid or solids. Moreover, echo would be generally very weak.
As far as bubbles are small in comparison with ultrasound beam diameter, bubbles form very good ultrasound scattering centres. If the concentration of bubbles is too high, there occurs a multiple reflection of ultrasound pulse among these bubbles and obtained profile might not be correct.
In such case measured profile extends up to the liquid surface, and measurement points above surface are missing. This effect can also be used for surface level measurement. It should be noted however that a reflection from the surface returning to the transducer may under certain circumstances destroy the measured profile. Such returning occurs randomly depending on the condition of the free surface.
In case of circular pipe or square channel it can, through a geometric integration of the velocity profile. If beam incident angle and pipe diameter/ channel width are known, then UVP Monitor can recalculate measured profile directly to through-flow. This is true assuming that the flow is well developed at the measuring position.
Comparative tests has been made with a weight tank calibration system in water, providing error rate from 0.18 % to 0.59 %. Measurement repeatability was also very good.
Yes, this has already been tested, but measuring distance is decreased and depends on the concentration of seeding particles.
UVP Monitor can also measure in mayonnaise, ketchup, paper pulp, tooth paste, ferromagnetic fluid, glycerol, oil and petrol, and in other liquids and pastes.
Usually it is 10-15% of solid particles. Sometimes even thicker suspensions can be successfully measured, but experimental testing should be mandatory as the correct answer really depends on material, size, depth to be measured, etc.
If we do not know sound velocity in measured media, it is easy to calibrate. Use a vessel of known size, and place transducer perpendicular to the wall. In program, iteratively change speed of sound as long as measured reflection from the wall corresponds to the real distance from transducer to wall. Then the speed of sound is set up correctly. Using oscilloscope and observing the echo gives better and more accurate results.
Yes, this is being performed automatically. Profile measurements are being done repeatedly, results are calculated by local averaging, and at the same time RMS value is also calculated.
The temperature has an effect on the sound velocity. If the speed of sound in the fluid has a strong dependence on the temperature, it has to be corrected. From the practical point of view, the temperature of the fluid affects the condition of mounting a transducer. The present 'standard' transducers have the maximum operating temperature of 60°C. If the temperature is higher than this at the place where the transducer is mounted, special care has to be taken, or special high-temperature transducers up to 150°C used.
More importantly, in application of UVP to high-temperature flow fields, it is not the temperature level which might form a problem, but temperature gradient in the fluid. The temperature gradient has an influence on propagation of ultrasound. Ultrasound beam can be bent or reflected a little, unless the beam direction is normal to the temperature gradient. Clearly, UVP can measure velocity profile as long as the liquid includes reflectors, but the position of the velocity profile could be distorted a little.
Up till now, UVP has been used in water with temperature difference of ca. 30°C per 10 cm, and no significant influence on measurement has been found.
Ultrasound is almost 100% reflected at the interface between liquid and gas, namely gas bubbles. However, the beam size of the ultrasound is relatively large so that if the void fraction of the flow is low and flow regime is nearly dispersed flow where the size of the bubble is smaller than the beam size, the gas bubbles play the role of a reflector and a velocity profile can be well obtained. However, if the void fraction is larger than that for dispersed flow, like chunk flow or annular flow, UVP can only measure the velocity profile for the liquid part (such as liquid film for the annular flow) between the transducer and any large bubbles.
No, our UVP Monitors various models has always been designed to work with 0.5 - 1 - 2 - 4 - 8 MHz fixed set of emitting frequencies. The latter allows velocity measurements for most laboratory-scale applications.
Lower frequencies allow for longer distance range due to their better propagation ability showing less acoustic attenuation, and for larger velocity measurement.
For low velocity measurement or small flow dimensions where high spatial resolution is required higher frequencies are used, featuring shorter wavelength.
Please check our typical measurement limits paragraph for further details.