This paper numerically investigated the heat storage behaviors of a shell-and-tube storage unit filled with high-temperature phase change material (PCM) using steam as the heat transfer fluid. A two dimensional heat transfer model using the enthalpy method was established, and the characteristics of the variations in the PCM melting time, charging rates from the steam to the PCM, and the steam condensation with time were studied. The influences of the thermal conductivity of PCM, the steam flow rate and the diameter ratio on the charging performance were evaluated. The results show that the heat charging rate can be not only significantly increased by increasing the PCM thermal conductivity, but also considerably increased by increasing the steam flow rate or decreasing the diameter ratio. As a result, the total charging time decreases with the increase of the PCM thermal conductivity or the decrease of the diameter ratio, and it can also be regulated by adjusting the steam flow rate. The liquefaction ratio can also be increased by increasing the PCM thermal conductivity during the design procedure, and can be effectively regulated by varying the steam flow rate during the operation. (C) 2015 Elsevier Ltd. All rights reserved.