CFD modeling of a liquid round jet impinging on a sphere in a hydrofluidization system

PERALTA, J. M.; RUBIOLO, A. C.; ZORRILLA, S. E.

Viña del Mar - Chile

Congreso; 10th International Congress on Engineering and Food (ICEF10); 2008

Instituto Chileno de Ingeniería para Alimentos (IChIA)

The hidrofluidization method is a technique for freezing and refrigerating of foods that consists in using a circulating system that pumps the refrigerating liquid upwards, through orifices or nozzles into a refrigerating vessel, thereby creating agitating jets. A fluidized bed of highly turbulent liquid and moving products is formed, and as a result extremely high surface heat transfer coefficients are obtained. Computational Fluid Dynamics (CFD) was used to study the heat transfer and flow field of this system. The physical domain was composed by a cylinder of 100-mm height and 250-mm diameter with a single centered orifice at its bottom. A 20-mm diameter sphere co-linearly placed at 20-mm from the orifice was used as a food sample. A NaCl-water solution was used as a refrigerating medium. The liquid exit was a 3-mm slit placed at the top of the cylinder wall. A 60º cylindrical section of the domain was considered to reduce computing requirements. The Reynolds number studied was in the range of 2x10^4 - 7x10^4. An unstructured mesh composed by tetrahedral elements with layers of prisms near the sphere was used. The shear stress transport (SST) turbulence model was used. The parameters studied were the Nusselt number (Nu), the drag coefficient (CD) and the boundary layer separation angle measured from the stagnation point. Experimental values from literature were used to validate the model. The highest Nu values were obtained at stagnation point and the lowest values were found near the separation of the boundary layer. The mean values of the wall heat transfer coefficient were in the range of 6x10^3 to 15x10^3 W m^-2 K^-1. The boundary layer separation angle was in the range of 132º to 138º. The drag coefficient was mainly affected by pressure. The local values of the pressure coefficient showed a minimum approximately at 35º. The mean values of CD were in the range of 0.0135 to 0.0150. Mathematical modeling using CFD is a powerful tool that may help to gain a better understanding of the flow and the heat transfer processes involved in hydrofluidization and to design appropriately efficient equipments.