Thermal Effects Due to the Phases Changes of the Dispersed Droplets Inside Emulsions

In this chapter, we describe the crystallizations of the supercooled droplets of the emulsion but we take into account the corresponding released energy. It is sufficient to warm up the emulsion at a temperature sufficiently high to be in a range where the nucleation rate vanishes stopping the crystallizations. So, we observe a local self-regulation of the temperature. On the contrary, the melting of the crystallized droplets occurs when the local temperature induces the thermodynamic equilibrium. These phases transforms are shown whether on a cylinder about 500 cm3 in volume or by calorimetry experiments on smaller samples. Models are presented to explain in all cases the observed phenomena. They are based on the resolution of the equation of the heat conduction with a heat source proportional to the probability of crystallization, given by the nucleation laws, and to the number of the remaining unfrozen droplets. In the particular case of a high concentrated emulsion of water, it is demonstrated the possibility of seedings increasing the number of crystallizations. Different methods are presented to determine the nucleation rate function and, in particular, a characterization by an inverse method. We describe also the case of emulsions flowing in a pipe. We mainly treat the case of the pure substances, but the case of binary solutions is approached.

Keywords: Binary solutions, calorimetry, crystallization, emulsions, flows, heat transfers, melting, seeding, self-regulation, supercooling.