Feasibility of an Advanced Waste Heat Transportation System Using High-temperature Phase Change Material (PCM)

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A waste-heat transportation (HT) system whose operation depends on the latent heat (LH) of high-temperature phase change material (PCM) is effective in reducing carbon dioxide (CO2) emission from industries. This paper describes 1) the use of the binary eutectic mixture NaOH/Na2CO3 as a PCM to realize the HT system, 2) the feasibility of HT system using this PCM from viewpoints of energy requirements, exergy loss, and CO2 emissions. In this study, we examined the thermophysical properties of the PCM and its chemical stability with reference to the heat transfer medium of the HT system by differential scanning calorimetry and thermogravimetry-differential thermal analysis. We observed that NaOH/Na2CO3 had a LH of fusion of 252 kJ/kg and a melting point (MP) and a freezing point (FP) of 285±1°C that was suitable for the HT system. There were no significant changes in the chemical and physical properties after aging for 500 h during phase change when dibenzyltoluene was used as the heat transfer medium. On the contrary, in the system analysis, the operating data in the proposed system—as well as in a conventional heat supply system—were calculated based on heat and material balances. The results show it has only 9.5% of the energy requirements, 39.7% of the exergy loss, and 19.6% of the CO2 emissions of conventional systems that lack heat-recovery capabilities.