Heat Transfer Experiments on Latent Thermal Storage Units Using Composite Materials for Space Solar Dynamic power Systems O. Nomura, K. Tanaka, Y. Abe, Y. Takahashi, K. Kanari &M. Kamimoto* M. Nakagawa, Y. Mochida, F. Ohtomo and S. Sekita** Summary: Latent thermal storage units with two kinds of composite materials for solar receivers of space dynamic power systems are investigated. The thermal storage units are bayonet type. One kind of the materials is composed of honeycombed matrix of silicon carbide impregnated with lithium fluoride (SiC/LiF). The other is composed of spongy matrix of porous carbon impregnated with lithium fluoride (C/LiF). Heat transfer experiments on the model storage units were performed in a closed Brayton cycle test loop during charge and discharge under various heating conditions. The working fluid of the test loop is a mixture of xenon and helium. Numerical analyses were carried out to find out problems in the model storage units. The numerical analyses utilize a three dimensional heat transfer model including thermal radiation effects. Effective thermal resistance in the model storage units at a steady state of heating during the experiments, are higher than their estimated values from the numerical analysis. Thus latent heat of the storage materials can not be fully utilized because the storage materials achieve a temperature lower than the expected value. Solid phase LiF fills 76.5% of the available volume in the SiC/LiF unit, and 45% of the available volume in the C/LiF unit. Similarly, the outlet temperature of the working fluid varied more from the numerically predicted values in the C/LiF unit than in the SiC/LiF unit. The model storage units are expected to achieve better operating performance characteristics by decreasing the thermal resistance and increasing the amount of storage material. Advantages of the composites and bayonet type receivers are discussed from the point of view of heat transfer and thermal stress in comparison with LiF only for latent thermal storage. Introduction Solar dynamic power generation systems are promising for space stations. In order to apply to low-orbiting stations, this system must store solar energy and supply almost steady thermal energy to the generator even during eclipse. A heat storage device and a heat collecting device are combined into one unit called a "receiver" to reduce their weight. * Electrotechnical Laboratory, 1-1-4 Umezono, Tsukuba, Ibaraki 305, JAPAN ** Toshiba Corporation, 2-4 Suehiro-cho, Tsurumi-ku, Yokohama, 230, JAPAN
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