carried out a numerical analysis on the performance of a TES by using naphthalene, which has a melting temperature of 353 K. Pre- dictions of time, temperature, and liquid fraction during the melting and solidification of naphthalene in an aluminum plate-fin unit were investigated. Although low-temperature TES devices have been utilized using PCMs as mentioned above, few studies have been carried out at medium temperatures for waste heat re- covery systems to the best of our knowledge. Since there is a de- mand for a recovery system for medium waste heat in various industrial plants, we have investigated high efficiency PCMs that can recover medium waste heat source from industrial plants [8]. Since PCMs have a high latent heat, waste heat from a hot-water supply through a heat exchanger such as PCM can be utilized. When PCMs are applied in waste heat recovery systems, a suitable PCM with properties such as a high latent heat and good corrosion resistance must be chosen. Recently, sugar alcohols have been investigated as a new heat transfer fluid to recover medium tem- perature waste heat from industrial plants since they have a higher