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As the mixer rotates, it transfers mechanical energy to the fluid, which then circulates within the mixer. This path of cyclic flow is called a flow pattern. The flow pattern of the mixer is closely related to the mixing efficiency and mixing power. Improvements to mixers and the development of new types of mixers often start with flow patterns. As the mixer rotates, it transfers mechanical energy to the fluid, creating a highly turbulent and well-mixed zone near the mixer, and generates a high-speed jet that drives the liquid to circulate within the mixer. There are three basic flow patterns: a radial flow, in which the fluid moves perpendicular to the stirring shaft, flowing radially; upon hitting the container walls, it splits into two streams that move upward and downward respectively, before returning to the shaft without passing through the blades, thus forming two circulating flows at the top and bottom. b Axial flow: the direction of fluid flow is parallel to the stirring shaft; the fluid is propelled by the impellers, causing it to flow downward, and then turns upward upon reaching the bottom of the container, thus creating an up-and-down circulating flow. c Tangential flow: In a container without baffles, the fluid moves in a rotational motion around the axis; when the flow velocity is high, vortices form on the liquid surface, and this type of flow is known as tangential flow. The above three types of flow typically occur simultaneously; among them, axial flow and radial flow play a key role in mixing, while tangential flow should be suppressed. The use of baffles can reduce tangential flow and enhance axial and radial flow, thereby improving mixing efficiency. (3) Baffles and guide cylinders: Baffles: The agitator is installed along the center of the container; when the viscosity of the material to be stirred is not high and the rotation speed of the agitator is high, the liquid moves in the same direction as the rotation of the blades. Under the effect of centrifugal force, the liquid in the middle part of the container moves toward the inner wall and rises, while the liquid level in the central area drops, forming vortices – this area is collectively referred to as the swirling zone. As the rotation speed increases, the liquid level in the center of the vortex sinks to the point where it comes into contact with the blades. Additionally, air from the outside enters the blades and is drawn into the liquid; as the liquid becomes mixed with gas, its density decreases, which reduces the efficiency of mixing. To eliminate this phenomenon, baffles can usually be added to the container. Generally, 4 baffles are evenly installed on the inner wall of the container, with a width of 1/12 to 1/10 of the container’s diameter. When increasing the number of baffles and their width further results in no increase in power consumption, it is referred to as the full baffle condition. b Guide cylinder: It is a cylindrical vessel with openings at the top and bottom, installed inside the container to guide the flow during mixing by the stirrer. For turbine or paddle mixers, the guide cylinder is positioned right above the paddle blades. For progressive stirrers, the guide cylinder is fitted outside or slightly above the impeller blades; usually, the upper end of the guide cylinder is below the hydrostatic blade surface. The cylinder body is provided with holes or grooves, allowing fluid to enter the guide cylinder even when the liquid level drops. The guide cylinder divides the mixing container into two equal-sized sections; its diameter is approximately 70% of the container’s diameter. When the mixer is placed below the guide cylinder and the container has a large diameter, the diameter at the lower end of the guide cylinder should be reduced, so that the opening at the bottom is smaller than the diameter of the mixer.