CROSS REFERENCE

This application is the U.S. National Phase under 35 US.C. § 371 of International Application No. PCT/JP2018/019694, filed on May 22, 2018, which claims the benefit of Japanese Application No. 2017-108021, filed on May 31, 2017 and Japanese Application No. 2018-097043, filed on May 21, 2018, the entire contents of each are hereby incorporated by reference.

TECHNICAL FIELD

This invention relates to an in-liquid plasma generation device for generating plasma in a liquid by applying an electric field to a gas to be supplied into the liquid and a liquid treatment apparatus using the same.

BACKGROUND ART

Numeral techniques for producing a liquid containing chemically active species have been proposed as means for producing a reaction product or means for detoxifying toxic substances/bacteria. For example, a technique described in PTL 1 produces a bubble in water to be treated flowing in a dielectric tube and applies a high voltage to between electrodes arranged in a liquid, whereby a plasma is generated by causing a discharge in the bubble. Further, in a technique described in PTL 2, one electrode is provided outside a dielectric tube for allowing a liquid mixed with a gas to flow therein and the other electrode is provided in the tube.

CITATION LIST

Patent Literature

[PTL 1] JP 2015-116561A

[PTL 2] JP 2013-206767A

SUMMARY OF INVENTION

Technical Problem

In the above conventional techniques, at least one electrode is in the liquid and a discharge occurs around that electrode. Thus, components of the electrode exposed to generated plasma may be dissolved into the liquid. Further, since a state of the liquid containing the bubble enclosing the electrode changes every second, the density and amount of the generated plasma tend to be unstable. Thus, the above conventional techniques have room for improvement in enhancing plasma generation efficiency for gas and energy to be injected and plasma generation stability.

Solution to Problem

This invention was developed in view of the above problem and aims to provide a technique enabling highly efficient and stable generation of a plasma in an in-liquid plasma generation device for generating plasma in a gas supplied into a liquid.

An in-liquid plasma generation device according to one aspect of this invention includes a housing which holds a liquid in an internal space, a gas supply tube which includes an opening in the internal space and discharges a gas into the liquid through the opening, a first electrode which has projecting part projecting into the internal space via the opening from inside of the gas supply tube, the projecting part including a conductor covered by a dielectric, a second electrode which surrounds the projecting part of the first electrode and includes a conductor isolated from the liquid by a dielectric, and a voltage applier which applies a voltage to between the first electrode and the second electrode, wherein the projecting part and the second electrode form a flow passage in which the gas discharged from the opening flows at a space therebetween.

In the invention thus configured, since the projecting part of the first electrode projects from the opening of the gas supply tube for supplying the gas into the liquid, the gas discharged from the opening flows in such a manner as to enclose the projecting part and is introduced into the liquid. The space between the projecting part of the first electrode and the second electrode provided to surround the projecting part serves as the flow passage of the gas discharged from the opening and a plasma generation field in which a plasma generation electric field is formed by applying a voltage to between the electrodes. Thus, the gas introduced into the liquid passes through the plasma generation field with a fairly high probability.

The conductors of the first electrode and the second electrode are both isolated from the liquid by the dielectrics. Particularly around the projecting part of the first electrode, the gas ejected from the opening forms a bubble for enclosing the projecting part, whereby a layer of the dielectric for covering the conductor is interposed between the conductor of the first electrode and the gas. Accordingly, a discharge caused by applying a voltage is a dielectric barrier discharge. Thus, a stable discharge can be caused in a wider area than in the case of providing the electrodes in contact with the liquid. Further, since the conductors are covered, the dissolution of materials (e.g. metal) of the conductors into the liquid due to exposure to plasma is also prevented.

Advantageous Effects of Invention

As described above, in the invention, the gas discharged from the opening of the gas supply tube opening in the liquid flows in such a manner as to enclose the projecting part of the first electrode and is introduced into the liquid, and the plasma generation field is formed around the projecting part. Thus, highly efficient and stable plasma can be generated in the gas. Further, by supplying the gas plasmatized in this way into the liquid, the liquid richly containing active species produced by plasmatization can be efficiently produced.

The above and further objects and novel features of the invention will more fully appear from the following detailed description when the same is read in connection with the accompanying drawing. It is to be expressly understood, however, that the drawing is for purpose of illustration only and is not intended as a definition of the limits of the invention.

