Takahiro Yonesaki

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.

Development of hydrogen-absorbing rare earth-Ni alloys for a −20 °C refrigeration system

Abstract The equilibrium and reaction rate performance of pseudo-binary La 1-xYxNi5-yMny (x=0–0.4; y=0–0.2) alloys were investigated with regard to their use in a −20 °C refrigeration system with a 130–150 °C thermally driven heat source, such as solar heat. The substitution of Mn for Ni in LaNi5 improved the reaction rate, while substitution of Y for La raised the equilibrium hydrogen pressure to approximately 1 MPa at room temperature, which is ideal for a refrigeration system. As a consequence, a −20 °C refrigeration heat cycle with La0.6Y0.4Ni4.8Mn0.2 was designed successfully.

Characteristics of hydrogen-absorbing Zr-Mn alloys for heat utilization

Abstract The substitution of various metals into ZrMn2 to produce possible materials for heat utilization systems was studied in the temperature range 200–250 °C. As a result, vanadium was found to be the most effective element for decreasing the equilibrium hydrogen pressure of the ZrMn2 alloy, cobalt was found to be an effective element for reducing the plateau slope of the ZrMn2 alloy and the ternary Zr-Mn-V alloy, and vanadium was found to be an effective element for reducing the hysteresis of the ZrMn2 alloy. Results show that quaternary Zr-Mn-Co-V alloy has excellent equilibrium characteristics in the temperature range 200–250 °C for heat utilization systems.

Poisoning by air of AB5 type rare-earth nickel hydrogen-absorbing alloys

Abstract Poisoning by air of Mm 0.9 Y 0.1 Ni 4.9 Mn 0.1 and LaNi 4.55 Al 0.45 alloys with CaCu 5 structure was studied to clarify their applicability to refrigeration systems. The decrease in hydrogen capacity on hydrogen absorption-desorption cycling with air contamination was limited to a certain degree under an extended air concentration up to 1.0 vol.%. The poisoned alloys recovered their hydrogen-absorbing capacity on reactivation treatment. These results and X-ray powder diffraction analysis suggest that the degradation was not caused by complete oxidation. Thus, we propose that the degradation is caused by adsorption of oxygen in air, and that the poisoned state is an intermediate state which is more stable than the adsorption equilibrium state but less stable than the oxidation state. Poisoning by adsorption was analyzed using Langmuirs adsorption theory to explain the relations between the degradation rate and concentration of air.