Evaluation of the melting process of phase change materials in a tilted rectangular container: Experimental study

Abstract

Natural convection plays a crucial role in improving the heat transfer efficiency during the phase change material (PCM) melting process. A major challenge is understanding the intensity and transformation of natural convection, which was strongly affected by the container's tilt angle. In this study, the effect of tilt angles of a rectangular container on the heat storage process was investigated with paraffin as the PCM. An experimental platform was established to observe the PCM melting process in a hot ambient. A dimensionless parameter Gr·Pr2 as the ratio of buoyancy force and thermal diffusivity was proposed to evaluate the relative magnitude of natural convection and thermal conduction during the phase change process. The larger Gr·Pr² indicates stronger natural convection than thermal conduction. When the tilt angle increased from 30° to 90°, the natural convection intensified and the peak of Gr·Pr² increased from 1.58×104 to 2.30×104 by 46 %. In melting process, the Gr·Pr² increased first and then declined until the melting was completed. When Gr·Pr²≤0.3 × 104, the improvement of melting process was mainly arisen from thermal conduction. When 0.3 × 104<Gr·Pr² ≤ 1.0 × 104, both thermal conduction and natural convection simultaneously enhance the melting process. When Gr·Pr²>1.0 × 104, the acceleration of melting process was dominated by the natural convection. From the experimental results, the optimum tilt angle was 60° for the heat storage of a rectangular container filled with paraffin in a hot ambient.