Electrowave

Ultra-Thin Aluminum Metal Erosion Test for Cavitation in Liquids

The most precise method of determining cavitation intensities is by the use of a cavitation meter. ELECTROWAVE EW-100 series cavitation meters can be used in most any liquid at frequency ranges of 5Khz to 500Khz. In lieu of a cavitation meter the following metal erosion test may be employed:

Procedure:

To an ultrasonically cavitating body (or suspected one) of water, with reduced surface tension*, is added a 1.5 in. sq. (3 .8  cm. sq.) piece of aluminum foil’ with a constant thickness not to exceed 0.006 in. (0.15 mm).

The foil may float freely within the water, or may be suspended at a standing wave (or half-wave) length (h=nc/2f] by a thin nichrome wire. The test should be conducted with the cavitation intensity at full strength for ten (10) minutes (+10 seconds), at an optimum temperature of 35° C [See Comparison of Ultrasonic Cavitation Intensity in Various Liquids Chart]

At the end of the test cycle the metal ‘foil’ is removed and multiple perforations (holes) will be seen as a positive indication for ultrasonic cavitation. Examination may he accomplished with microscope, or simply by eye. If tests are to be conducted at precise wavelengths, the ‘foil’ may be weighed before and alter cavitation.

The above procedure will make an effective test for pronounced cavitation in the frequency range from below 10 KHz to over 100 KHz. Higher frequencies (>~50 Khz will require more power for this test than lower frequencies [see Frequency vs. Cavitation Values Chart]. The  failure of this test is indicative only of the power and intensity of the cavitation. Many ultrasonic generators and transducers of low

power or intensity may fail this operational checkout, in these cases a cavitation meter of sensitive design must be employed to either prove or discount the presence of cavitation. All ELCTROWAVE ultrasonic cleaners are tested and guaranteed to generate a cavitational intensity of >750 µA/sq.cm.

Other methods have been devised for determining ultrasonic cavitation, most of them are at best difficult to repeat and in many cases are subjective. The Ultra-Thin Aluminum Metal Erosion Test should provide the tester with an objective method for determining pronounced cavitation in liquid, any commercially available aluminum foil may be used.

*In the above procedure a nonionic surfactant is added to reduce surface tension and facilitate ultrasonic ‘activity’, however, better results may be obtained by allowing the water to ‘degas’. Tap water has a considerable amount of dissolved air and other gasses which may be largely removed by sonicating for 5 to 10 minutes prior to the aluminum foil test.