The concept of plasma flow system by mixing particle, droplet and bubble in a plasma flow and utilizing chemical reaction at the gas-liquid interface and solid surface are proposed based on functional fluids engineering and multiphase flow principle. As the typical examples of advanced applications, nano powder transportation and cleaning in a plasma actuator tube, photo catalytic nano particle synthesis using DC-RF hybrid plasma flow system with precursor droplet injection and nano/micro pulse discharged bubble jet system for water purification are explained by author’s results.
A cavitation bubble plasma, which is a kind of plasma in solution, is a low-temperature plasma generated in a large number of microbubbles of a solvent component generated by a cavitation phenomenon. In this paper, the cavitation bubble plasma technology is explained by introducing the originally developed apparatus, the discharge phenomenon, and the effect of cavitation bubbles. As application examples of cavitation bubble plasma, the results of water dispersion of carbon nanotubes, synthesis of silver nanoparticles, sterilization of Escherichia coli, and decomposition of methylene blue are introduced.
Fine bubbles generated by plasma in water that we named as “Plasma Fine Bubbles,” have high potential to generate long-life ultrafine bubbles due to electrical charges. It is shown that the residual bubbles formed by collapse of streamer gas channels which show a similar process of cavitation bubbles in various points such as growth, shrink, collapse, rebound, and fragmentation. There are also introductions about ultrafine bubbles measured by a dynamic laser scattering method, amount of electrical charge of plasma fine bubbles estimated by analyzing their movements under application of an intense electric field strength, evidence of hydrogen gas generation in laser/spark induced bubbles and a distinguishing method for between gas bubbles and solid particles.
High-voltage and plasma applications for agriculture, fishery and food processing are described in this paper. Repetitive operated compact pulsed power generators with a moderate peak power were developed for the applications in several stages of agriculture and food processing. Pulsed high-voltage produces intense high-electric field which can cause some biological effects such as stress response (stimulation) and electroporation. Types of pulsed power that also have biological effects are caused with gas and water discharges which include reactive species such as ROS and RNS. The repetitive pulse discharge was used for promoting growth of the vegetables and fruits. The growth rate of the vegetables and sugar content in the strawberry harvested after the cultivation increased by the plasma irradiation to the hydroponic solution. The leaf size of the plants increased with plasma treatment time. Number of colony forming units (CFU) of R. solanacearum in the liquid fertilizer decreased from 107 to 102 CFU/mL by the plasma treatment. Seedlings with the plasma treatment were relatively healthy; in contrast, all seedlings in the positive control wilted and died from infection of R. solanacearum. The yielding rate of Shiitake mushroom (L. edodes) was improved with the high-voltage stimulation in fruit-body formation phase. The AC high-voltage keeping freshness for a relatively longer period of agricultural. The electrostatic effects can contribute to remove airborne bacteria and fungi spore from the storage house and container. This removal contributed to reduce the infection risk with fungi and bacteria. These applications can contribute a food supply chain in the world.
The development of the molten core cooling system without the electric power based on a lesson of Fukushima daiichi nuclear power plant accident is carried out over the world. Many researchers reported that the nano-fluid had the capability of critical heat flux enhancement and the nano-fluid could be applied to cool the molten core in combination with natural circulation flow. The purpose of this study is to obtain the better understanding of the flow characteristics of multiphase flow, which mix air and nano-fluid (water and TiO2 nano particle) under natural circulation condition. Experiments were carried out at atmospheric pressure and room temperature. Seven kinds of vertical test section are used; three circular tubes, two rectangular channels and two tapered tubes. The following conclusions can be obtained. (1) As the two-phase flow, the multiphase fluid was found to have stable natural circulation without problems. (2) There was approximately no great difference between the flow characteristics (void fraction, flow rate and pressure drop) of the natural circulation of multiphase flow and the air-water two phase flow.
Three quantities were measured to provide a database for validation of computations with a CFD (computational fluid dynamics) code. The quantities were the radial temperature distributions of steam-air mixture in a vertical circular pipe (diameter, 49.5 mm), the temperature gradients in the pipe wall (thickness, 5.5 mm) and the radial temperature distributions of the cooling water in the annulus gap (8.25 mm) outside the pipe. From these temperature distributions, three kinds of condensation heat fluxes were obtained from the enthalpy decreasing rate of the steam-air mixture based on the assumption of saturated conditions, the temperature gradient in the pipe wall, and the enthalpy increasing rate of the cooling water. These three heat fluxes were different especially in the downstream region, where the heat flux was low, so that the average of the three heat fluxes was used to evaluate factors affecting the condensation heat transfer. This average was expressed by a function of the steam density difference between the main flow of the mixture and the mixture on the wall surface, the average steam velocity and the thermal boundary layer thickness. The suction effect due to condensation was also discussed.
Numerical simulations of two-dimensional curtain coating were performed using VOF method in order to find operational conditions of coating processes. The curtain shape was dependent on the flow rate of liquid, the viscosity of liquid, and the moving speed of a substrate. The results reproduced the previously obtained coating window which represented five regimes of coatable, uncoatable, heel formation, air entrainment, and heal formation with air entrainment. Formation of the curtain and its shape were discussed using the numerically visualized flow fields.