Masayuki Kamimoto

Electrical energy storage systems for energy networks

Dispersed electrical energy storage systems are expected to work for load leveling, fluctuation smoothing, uninterruptible power supply and emergency power source. Their introduction seems to be essential in order to control the future complicated energy utility networks. In this paper, the characteristics of promising energy storage systems by pumped hydro, compressed air, secondary batteries, superconducting magnet, flywheel or capacitors have been surveyed and discussed. From the results, their characteristics and suitable application fields have been clarified.

Vanadium redox reactions and carbon electrodes for vanadium redox flow battery

The redox reactions of vanadium ions in sulfuric ,acid, which are used for anolyte and catholyte in a redox flow battery, have been investigated on a GRC (graphite reinforcement carbon) electrode. Two types of carbon fiber electrodes (GF-20 and BW-309) have been evaluated for the battery electrode. As a result, the BW-309 was found to be the best. Cyclic voltammetry has been used to estimate electrode reaction rate constants of the ions on a GRC electrode and two carbon fiber electrodes and to determine the suitable concentration of sulfuric acid for vanadium redox reactions in the battery. A charge—discharge experiment of V—V system in 2 M (mol dm−3) sulfuric acid solution has also been carried out on the carbon cloth (BW-309) electrode.

Heat capacities and latent heats of LiNO3, NaNO3, and KNO3

Enthalpies of fusion and transition together with heat capacities in both solid and liquid phases have been measured on LiNO3, NaNO3, and KNO3 with a high accuracy by differential scanning calorimetry (DSC). Polynomial expressions of heat capacities are given.

Investigation of nitrate salts for solar latent heat storage

Abstract Solar thermal applications require some means of thermal energy storage. Amongst several storage concepts, latent heat storage is quite suitable because of its high storage density and almost constant temperature during charging and discharging. The temperature range between 200 and 300°C is considered to be important for solar total energy systems. In this temperature range, sodium nitrate and its mixed salts with other nitrates including eutectic and off-eutectic salts are candidates. The present paper deals with heat transfer in a latent heat storage unit utilizing these salts. A method of rough estimation of the thermal conductivity of the storage materials is described, and the temperature history of the storage material experimentally obtained is compared with numerical solutions and found to be in reasonably good agreement. It is seen that the temperature of the heat transfer surface quickly drops soon after the appearance of a solid phase due to low thermal conductivity of these salts. Ways to avoid this temperature drop are discussed.

Investigation of latent heat thermal energy storage materials: V. thermoanalytical evaluation of binary eutectic mixtures and compounds of NAOH with NaNO3 OR NaNO2

Abstract Differential scanning calorimetry was applied to the evaluation of binary eutectic mixtures and compounds of NaOH with NaNO 3 or NaNO 2 as latent heat thermal energy storage materials. There are two compounds and three eutectic mixtures consisting of NaOH and NaNO 3 and one compound and two eutectic mixtures consisting of NaOH and NaNO 2 . The heats of fusion of all compounds and mixtures were more than 200 J g −1 . The thermal behaviour of these materials was observed, and some compounds and mixtures show a great tendency to supercool. The specific heat capacity was also measured. Because the eutectic mixture 18.5 mol.% NaNO 3 -81.5 mol.% NaOH is the most promising material for use in a nuclear power plant, this mixture made from industrial products was examined further. After 1000 cycles of melting and crystallization in bench-scale equipment the material shows little change.

Investigation of latent heat-thermal energy storage materials. I. Thermoanalytical evaluation of modified polyethylene

Abstract Differential scanning calorimetry is used to evaluate polyethylene for latent heat-thermal energy storage. Polyethylene is a suitable material from the points of view of latent heat, behavior of melting and crystallization, and material cost. The thermal stability is satisfactory when it is used in a closed system with heat transfer media, such as silicone oil, alkyldiphenyl, alkyldiphenylethane, Caloria HT and ethylene glycol, which shield polyethylene from air. Surface-crosslinking by ion bombardment prevents polyethylene from mutual adhesion and it retains its form after melting. Surface-crosslinked polyethylene with silicone oil or ethylene glycol is the most promising, while the heat transfer media, such as alkyldiphenyl, alkyldiphenylethane and Caloria HT, which dissolve polyethylene, decrease the melting point, but have little effect on the latent heat and sharp DSC peaks of melting and crystallization. Thus, the composite of polyethylene with these media can also be used at an adjusted and desirable operating temperature.

Water electrolysis under microgravity condition by parabolic flight

Abstract Behavior of water electrolysis accompanying gas evolution has been observed both under a microgravity and under a normal gravity. The water electrolysis has been performed at constant potentials on a gold plane electrode during about 20–25s of the microgravity condition available from parabolic flights of an aircraft. For each parabola the potential has been kept constant in the range of 2.5–15V vs. Pt wire. The bubble size increased instantly with decreasing gravity. On the other hand, current densities in high potential regions (9–15V vs. Pt) have drastically decreased under microgravity after an induced period of a few seconds. The reduced current densities, however, have never reached zero and have shown a certain minimum value. From the current—potential relationship, it has been suggested that the process of the water electrolysis under the microgravity condition is controlled by the mass transfer of water to the electrode surface, though the process under the normal gravity condition is controlled by the electrode reaction.

Latent thermal storage unit using form-stable high density polyethylene; Part I: Performance of the storage unit

A latent thermal storage unit of 30 kWh using form-stable high density polyethylene (HDPE) rods has been developed mainly for solar thermal applications, and heat transfer experiments have been carried out. A direct contact heat transfer technique between HDPE rods and ethylene glycol (EG: a heat transfer fluid) is adopted. Charge and discharge characteristics have been obtained for various thermal input/output and different initial temperature profiles in the storage unit. The direct contact heat transfer and a formation of a clear thermocline provide a good performance for all the cases. Discussions are given of thermal efficiency, storage density, and thermal insulation.

Enthalpy measurements on LiNO3 and NaNO2 by twin high-temperature calorimeter

Abstract A high-temperature calorimeter of the twin type designed for the enthalpy measurement of latent-heat storage materials is described. The measured enthalpy change of the N.B.S. calorimetric standard sapphire was in agreement with N.B.S. data within ±1.5% from room temperature up to 400°C. The enthalpy changes of LiNO 3 and NaNO 2 were determined through the fusion up to 300°C. Their enthalpies of fusion and heat capacities are presented.

Thermoanalytical investigation of (YBa2)2Cu3O7-y superconductor: II. perovskite formation from coprecipitated oxalate

Abstract Formation of the perovskite structure from the precursor was observed by high-temperature X-ray diffractometry. It proceeds in the temperature range above 750° C. Thermogravimetry (TG)/differential thermal analysis (DTA) was also applied to this temperature range: weight loss and an endothermic peak were observed in a higher temperature range. The endothermic peak is due only to a phase change of BaCO 3 in the precursor and is independent of the weight loss, which is due to evolution of CO 2 from BaCO 3 when perovskite formation proceeds. Kinetic analysis of these processes showed that the weight loss is a phase-boundary-controlling process.