MODELS FOR THE HEAT TRANSFERS DURING THE TRANSFORMATIONS INSIDE AN EMULSION .1. CRYSTALLIZATIONS OF THE UNDERCOOLED DROPLETS

Experiments on heat transfers inside an emulsion when the dispersed phase crystallizes or melts have previously been presented [Dumas et al., Eurotherm Seminar 5 (1988)]. The crystallization and melting processes are not symmetrical because of the large undercooling induced by the smallness of the emulsion droplet sizes. The space-time evolution of the temperature inside a metallic cylinder filled with the emulsion is investigated. The dispersed substances are either hexadecane, octadecane or water. In Part 1 of this paper we describe the results obtained during a steady cooling. We observe that, largely below the melting temperature, a stabilization of the temperature occurs in the axis region during a lapse of time depending on the cooling rate, the mass fraction or the final temperature. A simplified model based on a combination of the energy equation and the nucleation theories is proposed and explains the main experimental features.