Particles under the Influence of an ac Field

Conditions for Particle Detachment. A high-frequency alternating field is sometimes used to remove contaminants from surfaces in particular, this technique has been used to clean the rails ahead of a moving locomotive [201,202]. 

In order to determine how the efficiency of an alternating field depends on the particular conditions of particle detachment, the properties of the electrode and the surface being cleaned, and other factors, tests were performed in a unit [198] in which the frequency could be varied from 5 to 2000 Hz and the voltage from 3 to 5 kV also, either one or several needle-shaped electrodes could be used simultaneously, and the distance between the electrode and the treated surface could be varied from 1 to 5 mm. 

Most of the subsequent studies were performed at the optimal frequencies. It was found that with Fq = 2.2 kV, frequencies of 400-800 Hz, and a treating time of 10 sec, the distancebetween the electrode and the surface under treatment should not be greater than 5 mm (with a needle diameter of 0.35 mm)  

Under the same conditions (frequency 400 Hz, H-3 mm), tests were run to determine the dependence of the spot diameter on the electrode potential and the electrode needle diameter  

We can see from these results that with potentials of 3-5 kV the optimal diameter can be considered to be either 0.35 or 0.5 mm. Since the most nearly constant spot diameter (with changes in potential) was obtained with a needle diameter of 0.35 mm, however, all subsequent tests were performed with a needle electrode of this size. 

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