Objectives:
A

The purpose of experiment A was to observe the various flow patterns of different types of impellers with and without baffles. By using different dimensions of baffles at varying speeds, we could observe the how flow occurs in stir tanks with and without baffles. We hoped to observe the effect that velocity had on mixing as well as the diameter of varying flat impellers had on mixing. We also hoped to observe the different flow profiles during the mixing process with varying speeds and impeller dimensions with and without baffles

B
The purpose of experiment B was to observe the varying power numbers recorded given the varying impeller dimensions and speeds as well as type of impellers with and without baffles. We observe the differences in forces observed given the parameters stated above.

Materials and Methods:
A

Include stills of video of apparatus, one during mixing one static(with beads). Include one picture with baffles. Include other recording devices (speed controller).
A cylindrical vessel with a __ diameter is used with a shaft that drives an impeller at a depth of ____. The table shown below lays out the various sizes of each impeller used. The baffle being used is inserted in the most radial part of the apparatus and hinders flow in the radial direction closest to the diameter of the tank.

In order to observe the mixing that occurs from the various impellers, the apparatus was filled with water to a height of ______. By slowly increasing the speed of the various impellers, different flow patterns were observed(with and without baffles), A small number of various bead sizes were submerged in the water to observe different flow profiles.
B

The apparatus used are stated above in experiment A. A dynamometer was used to record the force of the motor??

The methods used are stated in experiment A; however, force was now recorded in intervals of 25 rpm. Due to the maximum force of 1.85 N on the motor, different increments of rpms were used on the following impeller dimensions.....

Theory:

A

By keeping the water and tank volume constant, impeller diameter, width, and impeller velocity are expected to have an effect on the mixing. Higher values for all of these variables will create greater mixing according to the power number, given in the following equation ____. The baffles also increase mixing due to the increase in turbulence caused by ______. Theoretical profiles can be seen in figure ___. These flow profiles were only found in higher flat impeller speeds and only when baffles were included??

B

Similar theory in experiment A. At higher rpms, large forces can be observed. Larger power numbers at lower rpms can be observed with larger impellers. Discuss differences between types of impellers. Discuss the expectations from baffles/no baffles.

Results and Discussion:

A

No numerical results to include. Provide pictures of flow at max velocity? Discuss what was observed, for example, vortex during start up as well as vortex increasing in height as experiment continued. At high velocities turbulence increased (as expected with Re). Discuss types of flow that occurred with propeller and turbine. Discuss that at higher velocities certain data could not be observed due to the water overflowing. Note that the dye was not used in the experiment. Water height was lowered to accommodate for faster speeds? These are significant for observing how flow occurs in industrial processes??

B

List table of results found in prompt (data recorded with different rpms, forces and power). Include graphs of power vs speed for each impeller blades, with and without baffles. Discuss the problem of maximum force (1.85?) and vortex exceeding the height of the tank. Discuss the effect of baffle on power. Include discussion about problem with apparatus (dynamometer string interfering with force readings due to hooking). Discuss the effect of power and efficiency in mixing in possible industrial processes (ie: best to use larger panels with baffles for best mixing with least power input?)


There are two regimes in mixing, laminar regimes and turbulent regimes. Low mixing speeds create laminar flow which is characterized by fluid layers that move past one another in the parallel direction with interaction limited to layers in direct contact with each other. During laminar flow, the bulk fluid motion is in the radial direction, with little movement along the parallel axis of the mixing apparatus. This flow pattern is usually characterized by the presence of a vortex forming in the innermost region of the tank and expanding outward. The flow pattern of a vortex is inherently circular, with the bulk motion of the fluid moving about the circumference of the vessel. Little radial or axial motion exists, limiting the interaction between inner and outer layers of the fluid as well as interaction between the bottom and top sections of the tank. The turbulent regime is most useful to reach a homogenous system in a mixing application; turbulence creates large eddies that move the different sections of the fluid past one another in all different directions and speeds. The eddies cause greater fluid motion and allow the upward movement of the bottom layer to be circulated to the top and vise versa. This allows for the most interaction throughout the bulk of the fluid and therefore creates a more uniform solution. Baffles create an effective disturbance in the circular flow of fluid, causing greater top to bottom fluid motion (axial motion) as well as radial motion. **THEORY BEHIND BAFFLES**Baffles increase power consumption how?