4:15 PM - 4:30 PM
[MIS14-08] Thermal energy storage using a metastable liquid phase separating alloy
Keywords:Thermal energy storage, Metastable liquid phase separation, Levitation technique
1. Introduction
Thermal storage is one of the attractive techniques because it has the potential to stabilize unstable renewable energy. The latent heat of a material such as metal can be used for thermal energy storage with a large capacity. Preventing the chemical reaction of the energy storage material at elevated temperatures is essential to develop a stabilized energy storage system. The phase separating alloys is expected to enable to the presence of the chemical reaction by covering the low melting temperature phase with a high-temperature stable phase. To applicate the practical use of this material, an understanding of the microstructure formation process and the evaluation of the energy capacity are required. In this research, the liquid phase separation process was observed in situ and the thermal energy capacity using the latent heat was experimentally evaluated.
2. Experimental
The Fe-Cu samples (Fe50Cu50, Fe60Cu40, Fe75Cu25) with 2 mm diameter were aerodynamically levitated in Ar-H2 gas flow. The samples were heated by CO2 laser irradiation to be molten. The sample temperature was measured by a 2-collar pyrometer, calibrated at liquidus temperature based on Wien’s law. After melting the sample, the CO2 laser was tuned off. The liquid phase separation and solidification process were observed using a high-speed camera. The thermal energy density of the sample was measured using differential scanning calorimetry.
3. Results and discussion
Before the recalescence caused by the solidification, an inflection point was found in the cooling curve. The in-situ observation using the high-speed camera revealed that the liquid phase separation occurred at this inflection point. The Fe-rich phase nucleated on the surface and spread. After covering the whole surface with the Fe-rich liquid phase, the Cu-rich liquid phase secondary appeared on the surface.
The energy density of Fe50Cu50 and Fe60Cu40 relieved from their latent heat was 137 kWh m3, and 76 kWh m3, respectively. These energy densities were higher than the energy density (50-85 kWh m3), which is the development target for 2050 indicated by the International Renewable Energy Agency.
Thermal storage is one of the attractive techniques because it has the potential to stabilize unstable renewable energy. The latent heat of a material such as metal can be used for thermal energy storage with a large capacity. Preventing the chemical reaction of the energy storage material at elevated temperatures is essential to develop a stabilized energy storage system. The phase separating alloys is expected to enable to the presence of the chemical reaction by covering the low melting temperature phase with a high-temperature stable phase. To applicate the practical use of this material, an understanding of the microstructure formation process and the evaluation of the energy capacity are required. In this research, the liquid phase separation process was observed in situ and the thermal energy capacity using the latent heat was experimentally evaluated.
2. Experimental
The Fe-Cu samples (Fe50Cu50, Fe60Cu40, Fe75Cu25) with 2 mm diameter were aerodynamically levitated in Ar-H2 gas flow. The samples were heated by CO2 laser irradiation to be molten. The sample temperature was measured by a 2-collar pyrometer, calibrated at liquidus temperature based on Wien’s law. After melting the sample, the CO2 laser was tuned off. The liquid phase separation and solidification process were observed using a high-speed camera. The thermal energy density of the sample was measured using differential scanning calorimetry.
3. Results and discussion
Before the recalescence caused by the solidification, an inflection point was found in the cooling curve. The in-situ observation using the high-speed camera revealed that the liquid phase separation occurred at this inflection point. The Fe-rich phase nucleated on the surface and spread. After covering the whole surface with the Fe-rich liquid phase, the Cu-rich liquid phase secondary appeared on the surface.
The energy density of Fe50Cu50 and Fe60Cu40 relieved from their latent heat was 137 kWh m3, and 76 kWh m3, respectively. These energy densities were higher than the energy density (50-85 kWh m3), which is the development target for 2050 indicated by the International Renewable Energy Agency.