定热流边界下重力作用PCM熔化过程规律

为提升相变储热单元的相变材料(PCM)熔化速率,本文定义基于热源输入方向与重力方向的通用坐标,建立可视化实验装置与数学模型,探究定热流边界下夹角γ对方腔内PCM熔化的作用规律。结果表明,当夹角γ从0°增加到180°时,PCM熔化时间先增加后减少,最后轻微上升。当夹角γ为0°时,PCM以纯导热完成熔化;夹角为15°时,对应的熔化时间最长,相对纯导热过程增加了40.32%;夹角为120°时,对应的熔化时间最短,相对纯导热过程减少了63.11%。当夹角较小时,自然对流对PCM的整体熔化过程有抑制作用,只有在夹角大于一定数值时,自然对流才能促进PCM的熔化过程。此外,多工况下获取的最优夹角γ均在90°～180°,且相对更趋近90°。所以在实际工程应用中,规整相变储热单元的热源端最低点应该低于PCM端最低点。

Gravity effect on PCM melting process under constant heat flux boundary

To improve the melting rate of PCM in latent heat storage unit, a universal coordinate based on the heat source input direction and gravity direction was defined, and a visual experimental device and corresponding mathematical model were established to investigate the effect of the included angle γ on the melting of PCM in the square cavity under the constant heat flux boundary. The results showed that when the included angle γ increased from 0° to 180°, the melting time first increased, then decreased, and rise slightly again. When the included angle γ was 0°, the heat transfer in PCM was only heat conduction. When the included angle γ was 15°, the melting time was the longest and increased by 40.32% compared with that of the single heat conduction process. When the included angle γ was 120°, the melting time was the shortest and reduced by 63.11% compared with that of the single heat conduction process. Therefore, when the included angle is small, natural convection has an inhibitory effect on the PCM melting. Only when the included angle γ is greater than a certain value, could natural convection promote the PCM melting. Also, the optimal included angle γ obtained under different working conditions was between 90° and 180°, and relatively close to 90°. Therefore, the lowest point on the heat source side should be lower than that on the PCM side for the regular latent heat storage unit in practical engineering applications.