Study of the Influence of Cooling Rate on Water Supercooling

Supercooling occurs when a liquid does not crystallize although its temperature is below the liquid–solid equilibrium temperature (melting temperature). Supercooling phenomenon is an attribute of some phase change materials which can have a negative impact on the overall performance of energy storage/retrieval process. The factors involved in influencing the nucleation process such as volume of the sample, thermal history, cooling rate and surface roughness of the container need to be studied in detail to better understand this problem. Few researchers have addressed supercooling in depth due to the erratic nature of the phenomenon, and there is no consensus in literature about the effect of some parameters. This is the case for the influence of the cooling rate, which is studied in our research. The effect of cooling rate is investigated using water samples immersed in a bath containing a temperature-controlled fluid. The samples have a volume of 3 ml in cylindrical tubes having diameter of 10 mm. The measurement of supercooling being usually performed using temperature sensors, the impact of their position on the degree of supercooling of the phase change materials (PCM) is considered in this work. The first objective is to infer to which extent the location of thermocouple can affect the degree of supercooling. Two different cases are considered for evaluating the impact of thermocouples on the supercooling phenomenon by placing the thermocouple inside the PCM sample and outside the sample. After establishing the right protocol, the effect of cooling rate is studied. The first results show that varying cooling rate from 1∘^{\circ}C/min to 0.08∘^{\circ}C/min has no significant effect on degree of supercooling. Thermal gradient within the water samples is also studied by using both experimental setup and a CFD model. The goal is to determine the most accurate value of the supercooling.