A plasma induced flow is a gas flow generated by application of high voltage of high frequency between electrodes separated by a dielectric. As a result that discharge is carried out in a state where one of the two electrodes is not insulated from outside air and the other is insulated from outside air, a gas flow (plasma induced flow) from the former to the latter occurs.
The plasma induced flow has a smaller flow amount per input power and a lower efficiency compared with a gas flow from a general air blower such as a fan and a blower, but the plasma induced flow can be made to flow only in a neighborhood of a surface of the electrode. Thus, by providing a plasma induced flow generation device in a wing of an aircraft or a blade of wind power generation to prevent a rear turbulent flow clue to flow peeling, it is possible to suppress reduction of lift and increase in an air resistance.
Meanwhile, attention is paid to plasma itself in the plasma induced flow as a new means of air purification replacing a catalyst and an adsorbent, and discharge methods by various electrode configurations such as point discharge and mesh discharge are devised. As active species occurring in discharge in the atmosphere, there can be cited negative ion and the like such as ozone, OH radical and O2−. Among the above. OH radical has a large air purification ability but also has a short life because of being active. Thus, a method is devised in which OH radical is made to be contained in a cluster of water and used for air purification.
Here, a density of the active species is preferable to be high in terms of an efficiency of processing. Meanwhile, in view of human health, it is necessary to limit the density of the active species in air. Thus, in order to achieve both efficiency of processing and human health, it is conceived to take in air to be purified by a fan or a blower and to carry out purification in a local space in which the density of the active species is high.
As a discharge structure for active species generation, a point discharge structure or a mesh discharge structure is adopted. However, it is difficult to mention these discharge structures as being able to efficiently use OH radical which only has a diffusion operating life of about several mm from a discharge point. Therefore, there is devised a device in which electrode fins that generate plasma induced flows are stacked (plasma induced flow electrode stack (hereinafter, abbreviated as “PA stack”)) and air is taken in by the plasma induced flows, to improve a processing efficiency.
Though the PA stack can be formed by stacking electrodes, its shape is limited. For the purpose of air purification, an electrode configuration in which parallel slits (spaces between electrodes) are disposed in multiple stages is not necessarily optimum. It is sometimes desirable that an outer shape of the electrode configuration is circular and that the slits are concentric. However, it is not easy to make a proper structure by stacking electrodes.