Image-based modelling for fluid flow and permeability prediction within continuously-evolving mushy zone during melting and solidification

Abstract

Mushy zone permeability is a key parameter that characterizes the fluid flow resistance within the two-phase mixed region during solid-liquid phase transitions. It plays an important role in accurately modelling the melting and solidification processes as well as the related latent heat storage performance. In our previous research, series images of the transient microstructures within the continuously-evolving mushy zone during both paraffin’s melting and solidification have been experimentally obtained by using a confocal optical microscope system. Thus, in this study, based on those experimentally-obtained images, the liquid flow and related permeability within the transient mushy zone were calculated using a pore-scale lattice Boltzmann method. The calculated flow velocity and predicted permeability have been verified against the corresponding reported analytical solutions. In addition, the mechanism behind the microscopic flow was presented and analysed. Moreover, the effects of image resolution on the fluid flow calculation were also studied. It was found that difference in the microstructures between melting and solidification results in distinctly various distributions of local velocity fields within the mushy zone, but makes little difference to the maximum velocity and the average permeability. The results also indicate that the image resolution imposes great effects on the predicted liquid flow by blurring and omitting tiny structures within the mushy zone in lower-resolution images. In addition, the predicted permeability increases more gently with the local liquid fraction as compared with our previously proposed correlations. Therefore, this work presents detailed information on fluid flow within mushy zone with continuously-evolving microstructures, and provides more insights into the fluid dynamics of the solid-liquid phase change.