Crystal growth and viscosity behaviors of ammonium alum hydrate solution with PVA in shear flow

Abstract

Aluminum ammonium sulfate dodecahydrate (ammonium alum hydrate) slurry is a promising latent heat medium for high-temperature systems. However, there exist the significant issues with this medium at high temperature with respect to crystal agglomeration, growth, and sedimentation. Therefore, the effects of adding drag-reducing surfactants and poly vinyl alcohol (PVA) on the formation process of ammonium alum hydrates crystals under a controlled shear flow have been investigated in this study. In addition, in order to investigate the impact of the surface hydrophilicity and hydrophobicity of cooling walls on the crystal growth, a copper plate and a silica coated copper plate were used as the substrates of the wall. From the results, it was found that the mean crystal size of the ammonium alum hydrate decreased with increasing shear rates and with the addition of surfactants and PVA. In addition, the crystals on the silica coated copper plate were smaller than those on the copper plate without a coating. Thus, the addition of dragreducing surfactants and PVA and use of a hydrophilic surface prevented the crystal agglomeration and crysal growth of the ammonium alum hydrate under a shear flow. Furthermore, the viscosity of each solution was also measured, as affected by the various additives and by crystal agglomeration and growth.