冰生消过程体系导热系数动态变化特性
Dynamic Characteristic of System Thermal Conductivity during the Process of Water-ice Phase Change

本文利用基于瞬变平面热源技术的Hot Disk热常数分析仪研究了冰生消过程中导热系数变化规律。根据体系状态的变化，冰的生消过程可以分为5个阶段：未结冰过程（纯水）、结冰过程（冰水混合）、纯冰过程、融冰过程（冰水混合）、完全融解（纯水）。实验温度从10.3 ℃降至﹣11.0 ℃，然后再升温到10.3 ℃，5个阶段中测得的导热系数分别为0.592~0.669 W/(m?K)、0.603~2.284 W/(m?K)、2.019~3.106 W/(m?K)、0.611~1.945 W/(m?K)和0.596~0.598 W/(m?K)。结果表明：水结冰融冰过程中，体系导热系数发生动态变化，并且体系导热系数值可能不是纯冰或者冰水混合物的导热系数；当温度接近冰点时，水或者冰的结构可能改变，导致体系导热系数突变。由于冰和水的密度不同，在结冰融冰过程中体系局部微环境的冰水两相可能存在微弱的自然对流，进而影响体系的导热系数。在实际生产活动中冰的生消过程一般接连发生，考虑体系导热系数的动态变化的因素，可以避免热平衡失调影响生物环境或涉冰构筑物结构性能。
The Hot Disk thermal constant analyzer based on transient plane source technology is used to study the variation in ice thermal conductivity during the formation and melting. According to the system state, the ice formation and melting process can be divided into five stages, that is, the non-freezing process (pure water), freezing process (ice-water mixture), pure ice process, ice melting process (ice-water mixture), and ice completely melted (pure water). On the basis of the experimental scheme, the temperature was first reduced from 10.3 ℃ to ?11.0 ℃ and then increased to 10.3 ℃. The measured thermal conductivities at these five stages were 0.592?0.669 W/(m?K), 0.603?2.284 W/(m?K), 2.019?3.106 W/(m?K), 0.611?1.945 W/(m?K), and 0.596?0.598 W/(m?K). The results show that the system thermal conductivity varies dynamically during the process of water-ice phase change and the measured thermal conductivity may not be that of pure ice or ice-water mixture. During the ice formation process or ice melting process, the system thermal conductivity will suddenly vary, since the structure of water or ice may be changed when the temperature is near the freezing point. Due to the different densities of ice and water, the thermal conductivity of the system may be affected by the weak natural convection occurring in the local ice-water two-phase microenvironment. In the actual production activities, the formation and melting of ice generally occur successively, so the influence of the thermal imbalance on the biological environment or structural performance of the ice-related structures can be avoided if the dynamic change in thermal conductivity is taken into consideration