Acoustic power meter APM-1

Purpose

A device APM-1 and a comparative calorimetric method for measurement of acoustical power radiated and absorbed in a liquid at cavitation regime is presented. The device can be used for many scientific and technical requirements and provides high accuracy, simplicity and almost automatic measurements.

Main technical characteristics

Range of acoustic power 3 - 150 W Acoustic power meter APM-1
Temperature of a liquid 10 - 60°C
Relative measurement accuracy 3%
Frequency range 5 - 1000 kHz
Diameter of a horn 0-88 mm
Capacity of ultrasonic bath 0.2 - 2 litre (maximal capacity depends on acoustical power)
Time of measurement cycle 10 min
Electric power supply 220 V, 50 - 60 Hz
Overall dimensions: 
Calorimeter bath 200x220x220 mm
Supply block 150x160x250 mm

Notes

Measurement of acoustical power irradiated by a sound source and acoustical power absorbed in a volume of liquid at cavitation regime is an important problem that hasn't been solved till now though cavitation and is studied for many decades. These measurements are necessary if the efficiency of erosion, emulsification, sonochemical processes etc. is determined under action of ultrasound. Although some acoustic methods of acoustical power determination are known, they provide unreliable results at cavitation regime due to ambiguity of acoustic impedance of bubbly liquid (it ranges stochastically in two orders of magnitude!) etc. Measurement of absorbed acoustical power by a simple calorimetric method is characterized by very low and uncertain accuracy because of at least two reasons: principle difficulty in removing heat transfer through the horn and the walls of vessel; absence of methods for determination of difference between heat capacity of liquid and heat capacity of a system "vessel-liquid-horn-thermometer", this difference is important, though.

Only our comparative calorimetric method can be used for absolute (e.g. in Watts) determination of irradiated and absorbed acoustic power with high accuracy [1]. It is based on continuous registration of temperature T course in time t under the action of ultrasound source and a heater [2]. If the curves T(t) are very close, the heater power is considered as an equivalent to the acoustical power absorbed in liquid. In applying this method, one doesn't need knowing exactly the bubbly liquid impedance, the conversion coefficient of transducer, etc. Measurements can be carried out independently on type of source and sound frequency. In accord to this method, we developed the patented device acoustic power meter APM-1 that can measure absolutely (e.g. in Watts) the irradiated acoustical power and that one absorbed in a total volume of liquid at cavitation regime.

We analyzed the dependence of acoustic power on geometry of a vessel, volume of liquid and depth of horn submergence. At developed cavitation, absorbed and irradiated acoustical power do not depend on volume of liquid and geometry of a vessel if cavitation cloud and irradiating surface are unchangeable. The power depends very weekly on increasing of the irradiating surface at horn submergence or at increasing of level of liquid in ultrasound bath (if irradiators are on the bottom only). We also revealed experimental conditions when practically whole irradiated acoustical power is absorbed by bubbly liquid, and we can measure both absorbed and also the whole irradiated acoustical power.

These results can be used, for example, at calibration of ultrasound equipment, for scientific investigations of cavitation processes etc.

  1. M. A. Margulis, A. N. Maltsev. Russ. J. Phys. Chem., v.43, p.1055, 1969.
  2. M. A. Margulis. Sonochemistry and Cavitation. London, Gordon & Breach, 543 pp., 1996.