Flow and heat transfer characteristics of non-Newtonian fluids in a stirred tank with a dual-layer wide-folded blade impeller

Based on a combination of experiment and simulation, the heat transfer and flow performance of a dual-layer wide-folded blade impeller in a stirred tank equipped with an inner-heat coil have been investigated for different impeller spacings. Sodium carboxymethyl cellulose solution (a non-Newtonian fluid) was used as the working fluid. The results show that the impeller spacing has a significant influence on the distribution of the flow field and temperature field in the tank. When the impeller spacing increases from 0.32T (where T is the diameter of the stirred tank) to 0.39T, the changes in the flow field and velocity distribution in the tank are relatively small, but the average temperature of the fluid in the tank increases, the temperature difference decreases, and the stirring power decreases by 3.82%. When the impeller spacing increases from 0.39T to 0.46T, the temperature increase inside the tank is relatively small, but the temperature difference increases. The connection flow between the upper and lower layers of the impeller decreases, resulting in an area where the axial velocity is close to zero, which results in an extension of the mixing time. During the stirring process, the viscosity of the fluid in the tank decreases with increasing shear rate and temperature. In the initial stages of stirring, the viscosity of the fluid drops rapidly due to the increase in shear rate. Subsequently, the viscosity is affected by the combined effects of shear and temperature. Finally, after uniform mixing, the viscosity is mainly affected by temperature. These results provide a reference for the practical industrial application of non-Newtonian fluid stirring.