Crystal Growth and Viscosity Behaviors of Ammonium Alum Hydrate Solution with PVA in Shear Flow

Abstract

Latent heat transportation systems are operated by the circulation of phase change slurries, which consist of fluids containing fine particles that have high latent heat capacities. Such fine particles are called phase change materials. Since the phase change material sustains a temperature at its fusion temperature, the phase change slurries can transfer high amounts of heat. Therefore, the flow rate of the heat media is reduced, which minifies industrial systems and reduces the energy required for operation. Latent heat transportation systems using phase change slurries have great potential for various applications; however, the slurries have some disadvantages. One significant disadvantage is their low fluidities; due to the presence of particles, phase change materials have higher viscosities compared with solutions without particles. In addition, the particles agglomerate and disperse in the slurry, imparting non-Newtonian characteristics to the slurry. To increase slurry fluidity, the addition of surfactants that form drag-reducing rod-like micelles, polymers, and some types of brines have been tested to prevent particle agglomeration. These additives also enhance the non-Newtonian behavior of the slurries. The elucidation of the rheological properties of slurries is important to achieve effective control of fluid flows in industrial latent heat transportation systems. Different types of latent heat slurries are used in industry depending on a particular situation and the temperature of the process (Table I). For example, ice/water slurries have been previously employed in lower temperature applications. Since ice has a large latent heat of 334 kJ kg at 0 oC, the ice slurries are used for food cold chains. Much research has been performed on the heat transfer characteristics of ice slurries, on techniques for preventing the agglomeration of ice particles, and on techniques to increase fluidity. In these studies, surfactants, some types of brines, and poly vinyl alcohol (PVA) have been tested to prevent agglomeration. Surfactants and PVA are effective as stabilizers for preventing crystal agglomeration and growth even with the PVA concentrations of only several thousand ppm. Phase change materials whose fusion Crystal Growth and Viscosity Behaviors of Ammonium Alum Hydrate Solution with PVA in Shear Flow