This paper investigates phase change phenomena around a horizontal tube during a cooling process of thermal storage. Experiments are performed to investigate the effects of different heat transfer fluid inlet temperatures on ice formation around the tube. Supercooling temperature and the time for the start of nucleation of water are observed by measuring the time variations of temperature profiles at various locations inside the test vessel. The thickness of the ice formed around the tube was measured at different axial positions along the tube during the experiments. A mathematical model to predict ice formation around the tube is proposed. Comparison of the results of the model with that of the experiments showed that the agreement between the two is acceptable, although the model is simple.