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John, What was the pulse width used from the pulser and what were the rise and fall times? For very short pulse widths, the water will appear "mostly" as a dielectric with a k of about 80, the air bubbles will have a k of 1, and the quartz glass (k between 4 - 8 depending on blend) will only allow capacitive (displacement) curents to flow in the system. The result will be that most of the applied voltage stress during the pulse will appear across the air bubbles within the gap. The air will then break down under the concentrated electrical stress, becoming ionized (conductive). Once this occurs, the E-field is redistributed in the gap, most likely leading to breakdown of the water within the gap. BTW, I'm assuming that the quartz glass is thick enough so that it does not break down even if the water and air have done so. A similar air-water breakdown sequence would occur if you also had suspended particles in the water, only now the water would breakdown at a lower voltage than if it were pure. The suspended particles provide localized areas of concentrated E-field stress inside the water. These areas of higher stress will cause the water to break down at a lower voltage than pure water. BTW, putting an air gap inside any otherwise good liquid or solid dielectric can often result in breakdown of the combined system under pulsed or RF stress since the air usually breaks down first, which can then cause subsequent breakdown of the remaining dielectric material. Best regards, -- Bert --
: : thank you Bert!
: I used a bipolar pulsed power(with a peak to peak voltage of 100kV,pulse
: repetition rate of 0~200Hz).Dicharge was carried out in a DBD configuration
: reactor with a wire to cylinder geometry electrode.Discharge electrode is
: metel rod while the grounded electrode is a reticulate stainless
: steel.Dicharge electrode was fully covered by a quartz glass tube.Air
: bubbles was artificially bubbled into the water.Gap distance varied between
: 5~50 mm.
:
: I found that the increase of the conductivity of water decreased the
: breakdown of the air bubbles. can this be attributed to the decrease of k
: of water,thus induced the change of the electric distribution inside the
: gas bubble? Actually, i have no more idea about that!
: And what's more, when solid dielectric particles and the artificially
: created air bubble simutaneously present in water, the medium system become
: much more complex. How does the polarization electric field of the
: dielectric particles affect the discharge of the bubbles?
: I am not so familar with this field.I occasionally find these phenomena,and
: feel that they are so interesting.I am not sure whether i have made me
: known. thank you for your reply!
: Best regards!
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