China Nonferrous Metallurgy

A combined approach of CFD simulation and heat transfer experiments was employed to investigate the heat transfer performance of a double-layer rotary variable-pitch three-bladed impeller within a stirred tank equipped with a spiral coil heater, using a 0.75% mass fraction CMC solution (a pseudoplastic non-newtonian fluid) as the medium. The findings indicate that the temperature distribution within the reactor follows a descending order: lower section>middle section>upper section, with the overall temperature difference maintained within 3.5 K. The strong axial flow generated by the rotary variable-speed three-bladed impeller effectively mitigates temperature variations at the reactor's top and bottom, keeping the maximum temperature difference below 2.5 K. Increasing the rotational speed enhances the kinetic energy of the flow field and heat transfer efficiency. When the rotational speed N=180 r/min, the small vortices at the bottom of the reactor disappear, and symmetrical circulating vortices form in the flow field, enhancing axial flow and overall mixing; Properly setting the paddle spacing is crucial for maintaining efficient axial circulation within the reactor. When the paddle spacing C₂=175 mm, the Nu reaches its peak, resulting in optimal heat transfer performance; The average temperature boundary layer thickness on the XY plane outside the spiral coil was 2.44 mm. The minimum discrepancy between experimental and simulated Nu values for the Nusselt number Nu on the coil's exterior was 2.62%, with a maximum error of 5.78%, validating the numerical simulation's accuracy. These findings provide reference for practical engineering applications of the rotary variable three-bladed impeller.