D-mannitol/erythritol Eutectic Mixture Thermal Chemistry Research

Phase change energy storage material is a kind of functional material which changes with the temperature and changes in the phase state and has latent heat release or absorption.As a kind of organic phase change material,sugar alcohol has many advantages,such as high thermal energy storage density,low cost,non-toxic,non-corrosive,and so on.In this paper,the thermochemical properties of D-mannitol,erythritol and its eutectic mixture were studied.Heat capacity is an important physical property that plays an important role in the study of thermal storage of sugar alcohols.At present,the heat capacities of sugar alcohols have never been studied below 80 K.In this study,the heat capacities of D-mannitol,Myo-inositol,xylitol,D-arabinitol,L-arabinitol and erythritol were first measured using a Physical Property Measurement System calorimeter in the temperature range from T=(1.9-300)K for the first time,and the corresponding thermodynamic functions were derived from T=(0-300)based on the heat capacity curve fitting results.Although sugar alcohols have a higher melting enthalpy,higher melting temperatures limit their use in thermal energy storage.It is urgent to study a sugar-alcohol-based phase change material with a lower melting temperature.Through the literature found: D-mannitol and erythritol have better thermal stability and faster crystallization rate,therefore,using D-mannitol and erythritol by simple physical mixing method to obtain D-mannitol/erythritol eutectic mixture,the thermal properties were measured by differential scanning calorimetry(DSC),thermogravimetric analyzer(TG),X-ray powder diffractometer(XRD),scanning electron microscopy(SEM)and Hot Disk thermal constants.Thermal conductivity is a key factor affecting the storage/exotherm rate and overall efficiency of thermal energy storage systems.The D-mannitol/erythritol eutectic mixture has low thermal conductivity and big degree of subcooling as a phase change material.Graphite can be used as nucleating agent and thermal agent,therefore,in this part of the work,using graphite as an additive to prepare graphite-doped D-mannitol/erythritol eutectic mixture to improve the thermal conductivity of D-mannitol/erythritol eutectic mixture and reduce its undercooling,in addition,the thermal performance of graphite-doped D-mannitol/erythritol eutectic mixture was tested by differential scanning calorimetry(DSC),thermogravimetric analyzer(TG),scanning electron microscopy(SEM)and Hot Disk thermal constants.The result shows that the addition of appropriate amount of graphite not only can significantly improve the thermal conductivity of D-mannitol/erythritol eutectic mixture,but also reduce the degree of subcooling,and will not have a greater impact on the enthalpy of transformation.