Encapsulation of copper-based phase change materials for high temperature thermal energy storage

Worldwide attention has been paid to high temperature phase change materials (PCMS) utilized in latent heat storage systems such as solar thermal power generation or industrial waste heat recovery. Current high temperature PCMs on basis of molten salts are suffering from inherent low thermal conductivity, which is detrimental to heat release rate and systematically thermal efficiency. Metal materials, always possessing ultrahigh thermal conductivity and satisfied heat fusion, are highly suitable as PCMs. However, the development of metal-based PCMs must overcome the package problem, namely, packing active, high temperature liquid metal into durable container. In this paper, copper capsules coated with refractory metallic shells were proposed as a novel metal PCM, which could work at temperature up to 1000 degrees C. Copper spheres with diameter of millimeters were encapsulated with a thick chromium-nickel bilayer by a novel chromium periodic-barrel electroplating method and nickel barrel-plating method. The latent heat density of as-prepared capsules is up to 75% of the theoretical value (about 71 J/g) at the melting temperature of 1077 degrees C and the thermal resistance of chromium-nickel layer is 8.27 x 10(-6) m(2) k/w. Particularly, copper capsules could endure 1000 charge-discharge thermal cycles from 1050 degrees C to 1150 degrees C without any leakage. The structure investigations reveal the excellent oxidation resistance of capsules and good stability between copper and chromium-nickel layer, even after long-term charge-discharge cycles. The results demonstrate that as-prepared copper capsules are applicable as high temperature PCMs which can facilitate high temperature thermal energy storage systems. (C) 2014 Elsevier B.V. All rights reserved.