Heat transfer and phase change in a polystyrene packed bed during melting

Abstract

Abstract Phase change and heat transfer in a polystyrene packed bed during melting were experimentally and numerically investigated. When the polystyrene particles were melted, the calculated porosity decreased at the bottom and side walls and increased at the top wall. The tendency of the calculation agreed qualitatively with the observation of the visualized packed bed. However, the interfacial position between the gas layer and the packed bed near the central axis could not be reproduced by the calculation. This may be accounted for by the following two reasons. Firstly, it is not considered in the calculation that the particles above the interfacial position between the gas layer and the packed bed tend to move over the interfacial level due to the buoyancy of the gas in the not-melted packed bed. Secondly, in the experiments, some of the exhausted gas at the melting positions may move not only upward but also to the central region in the packed bed. For the heating rate of a drying oven at T d = 50 K/h, the measured temperatures at all six positions increased linearly over time and agreed well with the calculated temperatures for all positions. On the other hand, the measured temperatures could not be reproduced by the calculated temperatures except for at the points near the bottom wall at T d = 500 K/h. Numerical simulation of heat transfer with natural convection in the packed bed before melting was conducted. As the natural convection strongly influenced the heat transfer in the packed bed, the calculated temperature in the packed bed did not agree with the experimental temperature before melting at T d = 500 K/h.