Comparative Study on the Power Consumption and Flow Field Characteristics of a Three-Blade Combined Agitator

Abstract

The three-blade combined agitator consists of two propulsion blades of the same type (including planar propeller blades b, δ = 36.87°) and a curved blade (θ = 30°). Using numerical simulation methods, the power characteristics, flow field distribution, turbulence characteristics and dead zone percentage of two kinds of three-blade combined agitators (TBCAs) from laminar flow to turbulent flow in a mixing vessel were studied. Moreover, the torque measurement method was used to perform experimental verification. The results show that the predicted power curve is consistent with the experimental results. The fluid velocity near the propeller blades in the TBC-B type agitator (δ = 36.87°) is significantly high, and the maximum increase of the total velocity can reach 30.3%. The fluid flow velocity near the curved blades is increased, and the radial diffusion ability of the fluid at the bottom of the stirring vessel is enhanced. When mixing low-viscosity fluids, the TBC-B type agitator can increase the fluid velocity near the paddle area, with a maximum increase of 22.1%. The vertical combination of curved blades and planar propeller blades can effectively reduce the tangential velocity and increase the axial and radial velocities. When stirring high-viscosity fluids, the speed of the TBC-B type agitator in the near paddle area and far end of the blade is higher than that of the TBC-A type agitator. Under the same conditions, the TBC-B-type agitator exhibits superior fluid discharge performance and can be used in a wider range of viscosities. When Re = 44,910, the dead zone percentage of the TBC-A type agitator is 0.0216. The percentage of dead zones produced by the TBC-B-type agitator is smaller, and the mixing effect is superior to that of the TBC-A-type agitator.

Study on the Influence of Working-Fluid’s Thermophysical Properties on the Stirring-Heating

“…Although turbulent viscosity is not a physical property of the working-fluid, it also has a viscous dimension and causes dissipative heat generation. In fluid mechanics, the formula for estimating turbulent viscosity is shown in Formula (11). It can be seen that in the low Re region, N p decreases with the increase of Re, and then increases slowly.…”

“…Different from the general agitator in pursuit of high uniformity and rotational speed, low air mixing, and power consumption [11], the stirring-heating device requires high power consumption under low rotational speed. This means that the design method of the classical agitator [12] is not suitable for a stirring-heating device.…”