Naoki Hiro

Stress on a reaction vessel by the swelling of a hydrogen absorbing alloy

There is a possibility that hydrogen absorbing alloys will generate unexpected stress in an alloy bed and deform or destroy the vessel because the alloys expand when they absorb hydrogen. The amount of stress generated on the vessel surface by alloy swelling was measured with the object of elongating the life time of the reaction vessel in heat utilization systems that use hydrogen absorbing alloys. As a result, it was found that 1) localized stress is generated at the bottom of the vessel due to hydrogen ab-/desorption cycles with an alloy packing fraction of 50 vol %, and this stress not only increases with each cycle, but also continues to increase even after plastic deformation of the vessel, 2) stress accumulation depends on the amount of hydrogen ab-/desorption and on the initial packing fraction, and 3) the mechanism for stress accumulation can be estimated as a two-step process in which agglomeration between the hydride particles occurs when the packing fraction of hydride is higher than 61 vol % in the initial cycles (Step 1), and then fine powder generated by pulverization during the cycles falls in gaps at the bottom of the vessel and causes the hydride packing fraction at the bottom of the vessel to gradually increase (Step 2).

Development of an F-class refrigeration system using hydrogen-absorbing alloys

Abstract This paper presents a new refrigeration system to generate refrigeration heat below −20 °C and a coefficient of performance (COP) over 0.4 by using driving heat in the vicinity of 150 °C which can be supplied by solar collectors. The performance of the system was achieved mainly by development of a quaternary La-Y-Ni-Mn alloy with appropriate performance in the vicinity of −20 °C with regard to both equilibrium and kinetic characteristics for generating refrigeration heat.

Relaxation of internal stress generated in hydrogen absorbing alloy vessels

Hydrogen absorbing alloys cause internal stress in reaction vessels due to the expansion that occurs when they absorb hydrogen. This stress is affected not only by the amount of reacting hydrogen but also by the ab/desorption cycles. In this paper, we analyze the reaction distribution in a reaction vessel through simulations and show that locally excess internal stress occurs near the heat media inlet. We also show that this excess stress is decreased by unifying the reaction ratio by exchanging heat between the heat media inlet and the outlet in the reaction vessel.

Evaluation of an electrolysis apparatus for inactivating antineoplastics in clinical wastewater

We recently reported a system for inactivating antineoplastics in which sodium hypochlorite is supplied by the electrolysis of sodium chloride solution. In this study, we designed an electrolysis apparatus for inactivating the cytotoxicity of antineoplastics in clinical wastewater using the system. The apparatus consists of an electrolysis cell with platinum-iridium electrodes, a pool tank, a circulating system for wastewater, a safety system for explosive gas and overflow, and an exhaust duct. The free chlorine concentration increased linearly up to 6500 mg l(-1), and pH also increased to 9.0-10.0 within 2h, when 0.9% sodium chloride solution was electrolyzed. We examined its efficacy with model and clinical wastewaters. The reciprocal of dilution factor for disappearance of cytotoxicity using Molt-4 cells was compared before and after electrolysis. In the model wastewater, that was 9.10 x 10(4) before electrolysis, and 3.56 x 10(2) after 2h of electrolysis. In the clinical wastewater (n=26), that was 6.90 x 10(3)-1.02 x 10(6) before electrolysis, and 1.08 x 10(2)-1.45 x 10(4) after 2h of electrolysis. Poisonous and explosive gases released by the electrolysis were measured; however, they were found to be negligible in terms of safety. The environmental load was evaluated by carbon dioxide generation as an index and it was found that the carbon dioxide generated by the electrolysis method was 1/70 lower than that by the dilution method with tap water. Moreover, the cost of the electrolysis method was 1/170 lower than that of the dilution method. This method was found to be both effective and economically valuable.