Heat Transfer Characteristics and Efficient Utilization on Ice-Water Cold Storage

利用冰水系统的潜热冷库的蓄热能力是不冻结水的显热冷库的数倍。为了使冰水冷库有效运行，必须明确冷冻和融化传热的性质。在本报告中，冰在简单几何形状的冷却表面上的冻结和融化是更好地理解潜热冷库的热量输入和输出特性的基础。采用边界拟合方法，对自由对流条件下垂直壁面冰的冻结和融化换热特性进行了数值分析。对几种温度条件下的冻结和融化进行了数值模拟，并澄清了以下问题。在自由对流条件下，水的回流对换热速率有很大的影响。由于冰-水界面的换热速率较低，因此可以用通常的斯蒂芬问题的解来粗略地估计冻结速率。在熔化过程中，受热面上的传热系数完全取决于表面温度。当表面温度保持在8℃时，出现两个强度几乎相同、流动方向相反的循环流，换热系数最低。实验研究了强制对流条件下水平冰筒的传热特性。实验分别在淡水冰和碳酸钠共晶水溶液冰上进行。在自由流速度为0.008 ~ 0.056 m/s、流体温度为1.4 ~ 8℃、碳酸钠水溶液温度为-0.7 ~ 4.6℃的条件下，给出了熔融速率的计算结果。给出了传热速率与自由流速度之间的简单关系。

The latent heat cold storage utilizing ice-water system has heat storage capacity of several times as high as sensible heat cold storage using water without freezing. For effective operating ice-water cold storage, it is necessary to clear the properties of heat transfer with freezing and melting. In this report, the freezing and melting of ice on the simple geometrical shaped cooling surfaces which are the fundamentals to give better understanding the heat input and output characteristics of the latent heat cold storage.Under the free convection, heat transfer characteristics on freezing and melting of ice on vertical wall were investigated by numerical analysis with applying the boundary fitting method. The numerical simulations were made on both freezing and melting under several temperature conditions, and following matters were clarified.Under free convection, reversing flow of water make badly contributions to heat transfer rate. Because of lower heat transfer rate on ice water interface, freezing rate can roughly be estimated by the solution of usual Stefan Problem. In the melting process, heat transfer coefficient on the heating surface thoroughly depends on the surface temperature. When the surface temperature is kept at 8 degree Celsius, two circulation flows which are the nearly same strength and have mutually opposite flow directions occur and the lowest heat transfer coefficient is observed.Under forced convection, heat transfer characteristics on melting of a horizontal ice cylinder were studied experimentally. The experiences were done on both ice of fresh water and ice of sodium carbonate aqueous solution of eutectic concentration. The results of melting rate are presented for free stream velocity range 0.008 to 0.056 m/s and fluid temperatures of 1.4 to 8 degree Celsius and -0.7 to 4.6 degree Celsius for aqueous solution of sodium carbonate. The simple relation between the heat transfer rates and free stream velocities are also given.