The additional thermal resistance seems to be mainly caused by insufficient contact between the composites and the canisters. Thermal resistance may also exist between the LiF and the matrices in the composites. Moreover, the additional thermal resistance on the model storage unit with C/LiF seems to be caused by a lower volume of the composite as shown in Table 1. Several examples of time variation of temperature obtained from the experiments are shown in Figures 8-11. These figures are shown from the first period of the discharge mode. Thermocouples at the return points of the working fluid were broken at beginning of the experiment but were repaired by the beginning of the first discharge cycle. The inlet temperature of the working fluid was kept 690 K and its fluctuation was 3K. The working fluid outlet temperature of the model storage unit with the SiC/LiF showed smaller variation than for the one with the C/LiF. The model storage units with the SiC/LiF seems to have better thermal characteristics than those with the present C/LiF. For the model storage unit with the SiC/LiF, the temperature was almost unchanged when the LiF was melting and freezing, especially at the bottom points. The main reason for this phenomenon seems to be the better thermal contact between the canister and the composite at the bottom of the model storage unit due to the influence of gravity. However, this phenomenon was not so clear for the model storage unit with the C/LiF. This seems to be related to low filled ratio of the C/LiF as shown in Table 1 and also to insufficient thermal contact between the canister and the composite. Figures 8 to 15 also show that surface temperature of the canister was the highest at top points in the steady state of the uniform heating, thus thermal contact between the canister and the composite is considered to be the worst at the top points of the model storage units. Figure 16 shows the surfaces of the model storage units after the experiments. There appear no change on the surfaces of the model storage units. Thermal stress to the canister of the model storage units seems to be sufficiently low.
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