Thermal energy storage (TES) system is essential to recover and use intermittent heat, such as industrial waste/excess heat or solar energy. In this paper, a direct-contact erythritol/heat transfer oil (HTO) energy storage system has been studied experimentally, consisting of a thermal energy storage unit, electrical heaters, heat exchanger and water cycle. In the system, erythritol has been used as an energy storage media (melting point = 118 degrees C, heat enthalpy = 330 kJ/kg), and HTO is used as a heat transfer material. Moreover, simulation has been conducted to understand heat transfer enhancement mechanisms of direct-contact heat storage. It is noticed that, at the beginning of heat storage, heat transfer oil has a small flow rate due to the block of solid part. PCM in the middle area of the storage unit melts faster than other parts due to the greater heat transfer on the liquid-solid interface of the both sides, and erythritol attached on the storage unit wall melts slowly since small heat conductivity plays a key role for heat transfer. It is also found that increasing the flow rate of HTO can significantly decrease the melting time by increasing fluid turbulent degree. (C) 2014 Elsevier Ltd. All rights reserved.