Thermal conductivity of sugar alcohols

During the past decade sugar alcohols have been extensively studied for thermal storage purposes. One of the recent focuses of research has been in improving their heat charge and discharge rate by enhancing the thermal conductivity with different types of additives. However, the current literature shows a vast discrepancy in measured values of sugar alcohols. This work presents an experimental study on thermal conductivity of seven sugar alcohols. The aim is to find out the reason for the discrepancy of literature values for erythritol, mannitol and xylitol, and to present new reference data for galacticol, myo-inositol, maltitol and sorbitol. We study the impact of material preparation method, raw material grade and sensor contact on the crystalline structure and the conductivity. The crystalline structure was inspected with optical and scanning electron microscopy and X-ray diffraction, and melting properties with differential scanning calorimetry. We found that different polymorphs, grain structure and crystallite sizes can be obtained by different preparation methods. This caused the conductivity of mannitol, galacticol and myo-inositol to vary by tens of percentages. Crystallization temperatures of xylitol and erythritol were found to affect their grain size but had only a minor effect on the conductivity. Overall, the conductivities of solid phase sugar alcohols were found to be within the upper range of the previous literature; based on the methods of this work, we did not find any evidence for the low and intermediate values for erythritol, xylitol and mannitol. Due to the high amorphous content of maltitol and sorbitol their conductivity was substantially lower than that of the other sugar alcohols. Thermal conductivity of liquid phases was found to accurately follow a linear relationship with the molar mass for sugar alcohols with carbon number between 4 and 6.