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.