通过实验和数值方法研究了水平圆柱蓄热单元蓄、放热过程中换热特性的共性和差异,分析了壁面温度在高于/低于相变温度10 K的间隙性周期热边界条件下,蓄放热单元的热动态特性.结果表明,在相变起始阶段,蓄、放热过程主要以导热换热方式为主;随着蓄放热过程的进行,蓄热过程的换热方式转变为以自然对流主导,放热过程则仍以导热主导.在本文所研究的等温差等时长的间歇交替蓄-放热循环中,由于蓄热融化速率大于放热凝固速率,会出现由不稳定状态发展到周期稳定状态的演变过程;在周期稳定工况下,蓄放热单元会在完全液相到液固两相共存间交替变化.
In this paper,an experimental and numerical study is performed on the charging and discharging characteristics of a horizontal cylinder phase change unit.A further analysis is made for charging-discharging cycle with the wall temperature being uniform and 10 K above/below the melting temperature.The results show that,heat transfer in the PCM unit during the initial phase change stage is dominated by conduction both for charging and discharging processes,however,as the phase change goes on,heat transfer during charging process is dominant by nature convection,and dominant by conduction during discharging process.In periodic charging and discharging cycle where both charging and discharging temperature difference and time keep equal,the charging rate is higher than the discharging rate,and thus the phase change unit evolves from an unsteady periodic mode to a stable periodic mode.In the stable periodic mode,the PCM unit alternates from a complete liquid phase state to a solid-liquid two phase state.
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