金属泡沫内石蜡固液相变蓄热/放热实验

Experimental Study on the Heat Storage and Release of the Solid-Liquid Phase Change in Metal-Foam-Filled Tube

针对解决太阳能热利用过程中所面临的辐射强度不稳定、不连续和不均匀等关键问题,相变蓄热技术常与太阳能热利用系统耦合协同匹配,以实现稳定连续的热量输出。为了强化固液相变蓄热/放热过程、提高系统热储能效率,对金属泡沫内石蜡类相变材料(PCMs)在不同蓄热流体温度下的固液相变蓄热/放热特性开展了实验研究。设计并搭建了相界面可视化的蓄热/放热实验系统,实验过程中使用高清相机对相变过程中的相界面变化进行了记录。同时,通过在蓄热单元内部布置多个热电偶测点,对蓄热/放热过程中的温度变化规律进行了探究。实验结果表明,受自然对流影响,熔化过程中相界面由上至下变化;而凝固过程中由于初始时蓄热单元下部温度较低且存在自然对流,此时相界面自下而上变化。蓄热流体温度越高,熔化所需时间越短,与蓄热流体温度为65℃的工况相比,蓄热流体温度为85℃、80℃、75℃、70℃工况的完全熔化时间分别减少了56.0%、46.7%、15.4%和26.7%。当采用不同温度的流体进行蓄热工况时,相变材料内部温度呈现出具有明显差别的温升规律。尽管如此,当采用相同温度的换热流体进行放热工况时,相变材料的放热温度仍趋于一致。

To solve the key problems of unstable, discontinuous, and uneven radiation intensity in the process of solar heat utilization, phase change heat storage technology and solar heat utilization system are commonly synergized and coupled to achieve a stable and continuous heat output. To enhance the solid-liquid thermal storage/release process and improve the efficiency of thermal storage, the solid-liquid thermal storage/release characteristics of phase change materials(PCMs)(paraffin) in metal foam were experimentally studied at different temperatures of a heat transfer fluid. An experimental system for phase interface visualization was designed and built. During the experiment, a high-definition camera was set to record the phase interface changes during the melting and solidification phase change. By arranging multiple thermocouple measuring points inside the heat storage unit, the law of temperature change during the heat storage/release process was explored. The experimental results demonstrated that, under the influence of natural convection, the phase interface changed from top to bottom during the melting process. In the solidification process, the lower part of the heat storage unit had a lower temperature. Natural convection occurred merely at the beginning, and heat conduction dominated the whole solidification phase change. The phase interface moved from bottom to top with time elapsed. The higher the melting temperature was, the shorter the time required for melting was. Compared with the cases with a heat transfer fluid temperature of 65 ℃, the complete melting time at the heat transfer fluid temperatures of 85 ℃, 80 ℃, 75 ℃, and 70 ℃ was reduced by 56.0%, 46.7%, 15.4%, and26.7%, respectively. The internal temperature of the PCM exhibited a distinct temperature rise when different heat storage temperatures were set. However, at the same cooling temperature for heat release, the law of temperature variation for the PCM tended to be the same.