Experimental and in silico characterization of xylitol as seasonal heat storage material

Solid-liquid phase change is one of the most favorable means of compact heat storage in the built environment. Recent studies propose C4-C6 polyalcohols for seasonal storage applications, for their high latent melting enthalpy, evident supercooling effect, and low environmental impact. In this study, we carry out a comprehensive study of xylitol as a seasonal heat storage material, using both experimental techniques and theoretical predictions based on molecular dynamics simulations. In the experimental measurements, the melting enthalpy of xylitol is determined to be 263(13) kJ/kg (0.95 level of confidence) at a melting point of 366.15(50) K. A more than 70 K supercooling is observed during a cooling test, with xylitol being in liquid state at around 300 K. However, at such a low temperature, the molecular mobility is greatly reduced, causing a reduced crystal growth speed. The thermal conductivity of xylitol liquid at 303 K is 0.42(4) W/m/K, roughly independent of the temperature. In the molecular dynamics simulations, multiple molecular models (force fields) are tested and validated. The generalized AMBER force field (gAff) has the best performance. Using this model, the large melting enthalpy of xylitol is found to be related to the rich and strong hydrogen bonds in the solid state.