Shigeki Muto

Development of a Mist Singlet Oxygen Generator.

The singlet oxygen generator (SOG) generates singlet oxygen for a chemical oxygen iodine laser (COIL), using the gas-liquid reaction between basic hydrogen peroxide (BHP) and Cl2 gas. The Jet-SOG has been widely used, wherein jet BHP from small orifices reacts with Cl2 gas, and the BHP utilization is less than 1% in a single pass through the reaction zone. To improve BHP utilization, the reaction surface with Cl2 gas should be increased, and the droplet diameter of BHP should be decreased. In this study, two types of mist generators were tested for the SOG, with which 65-µm- and 15-µm-diameter droplets were generated. In the 65 µm mist generator, BHP utilization was 22.5% at the Cl2 flow rate of 8.3 mmol/s, and in the 15 µm mist generator, BHP utilization was 41.5% at the Cl2 flow rate of 9.0 mmol/s, that is, BHP utilization of the new SOG, Mist-SOG, markedly exceeded that of the conventional Jet-SOG.

Technical progress in industrial COIL

Chemical oxygen-iodine laser (COIL) has a great potential for applications such as decommissioning and dismantlement (D&D) of nuclear reactor, rock destruction and removal and extraction of a natural resource (Methane hydrate) because of the unique characteristics such as power scalability, high optical beam quality and optical fiber beam. Five-kilowatt Chemical oxygen-iodine laser (COIL) test facility has been developed. The chemical efficiency of 27% has been demonstrated with a moderate beam quality for optical fiber coupling. Our research program contains conventional/ejector-COIL scheme, Jet-SOG/Mist-SOG optimization, fiber delivery and long-term operation.

Parametric study of a mist singlet oxygen generator

New type mist singlet oxygen generator (Mist-SOG) for the chemical oxygen-iodine laser (COIL) has been developed. This SOG is devoted to make the liquid recirculation unnecessary with the complete reaction through a single pass of basic hydrogen peroxide (BHP). 75% of Cl2 utilization and 76% of O2(1AE) yield were obtained with Cl2 molar flow rate of 3.0 mmol/s. H2O2 utilization in the BHP was achieved as high as 12.3%. This value is about 24 times larger than that obtained by the liquid-jet SOG.

Development of a laser-based hybrid drill for concrete and rocks

A drill for concrete and rocks is being developed using a laser-based hybrid technique. The design locates the outlet hole of laser beam and drill blades on a common rotational axis. The laser beam weakens the concrete, and the blade breaks the weakened layer. The target performance is a drilling speed of 30 mm/min at a sound level less than 70 dB using 1-2 kW laser power to produce a φ20 mm × 300 mm hole.

Removal of Water Vapor in a Mist Singlet Oxygen Generator for Chemical Oxygen Iodine Laser

The mist singlet oxygen generator (Mist-SOG) for a chemical oxygen iodine laser (COIL) has been developed in order to increase basic hydrogen peroxide (BHP) utilization. It was clarified that the Mist-SOG generated much more water vapor than conventional SOGs because the heat capacity of BHP is small. The water vapor deactivates the excited iodine and depresses the laser power. Therefore, a jet-cold trap was developed in order to remove the water vapor while maintaining a minimum deactivation of singlet oxygen. In this method, a nozzle was used to spray chilled H2O2 at 238 K as a thin layer directly to the gas flow to achieve a large specific surface area for water vapor. As a result, the water vapor mole fraction was reduced to 7% from 18% with the BHP utilization of 21% at the Cl2 consumption rate of 3.5 mmol/s (Cl2 input flow rate of 8.0 mmol/s) for 65-µm-diameter BHP droplets.

Numerical Simulation of a Mist Singlet Oxygen Generator.

A numerical simulation code for a mist singlet oxygen generator (SOG) is developed. Unlike previous SOGs, a mist SOG utilizes fine droplets of basic hydrogen peroxide (BHP) to achieve a stoichiometric reaction with chlorine gas in a single pass through a reaction zone. The numerical model presented in the present paper deals with the depletion of superficial HO2- density and the diffusive redistribution of each droplet, water evaporation, temperature variation of the droplet due to chemical reaction and evaporation, and heat exchange between the gas and liquid phases. Under identical initial conditions, the calculated results are consistent with the results from previous experiments. The heterogeneous quenching probability of O2(1Δ) to the BHP surface (γ) was determined by a comparison between the experimental and calculated results, and was found to be 2×10-3. The process conditions were then varied to establish the theoretical limit of BHP utilization. For a very small (15 µm) droplet diameter, it was shown that 50% BHP could be utilized with an output of 64% O2(1Δ) yield and 88% Cl2 utilization.

Parametric study of a laser-based hybrid drill for concrete

A drill for concrete is being developed using a laser-based hybrid technique. The design locates the outlet hole of laser beam and drill blades on a common rotational axis. The laser beam weakens the concrete, and the blade breaks the weakened layer. Drilling speed was achieved 100 mm/min to produce a 22 mm diameter hole using 2 kW laser power.A drill for concrete is being developed using a laser-based hybrid technique. The design locates the outlet hole of laser beam and drill blades on a common rotational axis. The laser beam weakens the concrete, and the blade breaks the weakened layer. Drilling speed was achieved 100 mm/min to produce a 22 mm diameter hole using 2 kW laser power.

Laser based hybrid technique for civil engineering

A laser-based hybrid technique is shown to be effective for cutting concrete and drilling rock. Experimental conditions used included a laser power of 1-10 kW, 10 mm laser beam diameter and 1.25-50 mm/s scanning speed. The results of surface scanning tests and 100 mm deep cut tests indicated that the shortest operation time was about 3.5 hr/m2 for plain concrete and 4.5 hr/m2 for heavy concrete. The specific energy for the rocks (the amount of energy required to remove a unit volume of rock), which were granite and sandstone, was as same as that for heavy concrete. Thermal decomposition was observed for limestone. The specific energy of limestone was more than 1.5 times higher than that for granite and sandstone.

Ejector Chemical Oxygen–Iodine Laser with Supersonic Nozzle Bank Based on a Trip-Jet Mixing System

Nozzle banks for an ejector chemical oxygen–iodine laser consisting of two-dimensional slit nozzles with a trip-jet mixing system were tested in the cold- and hot-flow operation regimes. Horizontal Pitot scan experiments demonstrated that the mixing ability of the trips is excellent. The Mach number of the mixed flow was approximately 3. Gain measurements were conducted, and the results of these measurements revealed that the maximum gain was approximately 0.54 m-1. The gain cut off length exceeded 200 mm. Lasing experiments were also conducted, and the power was approximately 3 kW at a chemical efficiency of approximately 18%.

Characteristics of prototype mist singlet-oxygen generator for COIL

A mist singlet oxygen generator is possible to improve the HO2 utilization at the one pass reaction between basic hydrogen peroxide (BHP) and chlorine. In this investigation, BHP was atomized to small droplets by the gas flow. Chlorine, which is required for stoichiometric reaction with HO2 in the BHP, was used for atomization of BHP in order to reduce the buffer flow rate for atomization. We obtained the results that the conversion efficiency from chlorine to singlet oxygen (Ux Y) was 9.7% with purely chlorine atomization and 16% with x0.93 dilution ratio of nitrogen buffer at 18.7 mmol/s input chlorine flow and 5.8 ml/s BHP flow rate in a free space reaction chamber.