Experimental circuit comprising of four sub-circuits: a charging circuit, with a 60 V dc PSU; a discharging circuit, with a 4.7 kΩ resistor; a storage circuit, with 6900 μF in two capacitors; and a sparking circuit, with a 10 V dc PSU to trigger a n-channel MOSFET connected to touching electrodes submerged in a Plexiglas tank filled with DI water.
Schematic showing electrode configuration. A 0.6 mm diameter wire is soldered at one end to a banana plug and at the other end soldered to a 0.1 mm diameter wire of length L. A 20 mm scale bar is shown at the top right hand corner of the image.
A typical spark bubble growth and collapse. Frame 1 (from left to right) shows a pair of L = 20 mm electrodes in contact initially at t = 0 μs. During capacitive discharge, a spark at the contact point grows into an oscillating bubble (t = 40 μs) which quickly expands to its maximum radius a = 4.53 mm at t = 760 μs. From then on, it contracts until its first collapse at t = 1.30 ms. The frame at t = 1.40 ms shows the second expansion of the disintegrated bubble cloud. A 5 mm scale bar is shown at the top of the first frame and corresponding time (in μs) is shown at the bottom left hand corner of each frame.
Graph of maximum spark-generated bubble radius a against total length of 0.1 mm diameter per electrode, L. Around 150 experimental cases are shown here with standard deviation bars shown for each data set.
Graph of maximum spark-generated bubble radius a against additional discharge circuit resistance R A taking the cases of L = 10 mm as reference (R A = 0 Ω). The respective length of fine electrode wire L used in the experiment is shown above each data set with a standard deviation bar. Circular data points present in the graph represent cases with various additional resistance R A in the discharge circuit, while using L = 10 mm to generate the spark-bubble.
Mean maximum bubble radius a obtained for different initial fine electrode wire length L.
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