Concentric Cylinder Viscometer

AE 507 Project

The concentric cylinder viscometer project is a graduate level semester-long project for ERAU's Design, Build, and Test class (AE 507). Here, the team worked to develop this device in a cost-efficient manner with the assistance of Dr. Mark Ricklick for select component funding, assembly and testing facilities, and overall guidance with the project,

Preliminary Research Phase

Throughout this phase, the team drafted a literature review and proposed plan of action for this project. Here, ideas such as using magnets to spin the spindle, use of copper cylinders, orientation of the device, and other ideas were brainstormed. Similarly, basic calculations were performed to get an outline of what the apparatus and device would look like.

Design Phase

Within this time frame, the team split into two groups: structural/electrical and cylindrical components. As a member of the structural/electrical team, I have had the opportunity of running initial calculations using certain design criteria that eventually paved way for a more fine-tuned design of the project. Using the maximum angular velocity of 30,000rpm, the required torque of the motor was calculated. Similarly, the maximum allowable change in diameter of a stainless steel spindle was calculated to be ~0.003", thus influencing the gap size between the cup and spindle. With a MATLAB script, the maximum expected thermal expansion with a temperature range between 100K and 700K and the expected expansion due to centrifugal force was around 39.2 micron.

Ultimately, the team settled on a dual-motor setup with the second motor acting as a verification parameter. Additionally, the spindle is to be lowered into the cup, where the top motor will initiate rotation at various speeds. With the shear sensor out of the budget, the team was instructed to keep one in mind and to create a hole in the cup to hypothetically incorporate the sensor into the final design. 

Testing Phase

Initial testing included GUI functionality, rotor spin, and overall alignment at low voltages. From here, the team ran tests verifying a freely spinning rotor with everything aligned. The first test used a handheld tachometer aimed at the axis of the rotor. Upon further investigation, the recorded speeds were double what was expected at the tested voltages. Future tests aimed the tachometer at an offset from the rotor axis, allowing for the reflective tape to cross the laser once as opposed to twice when aiming at the axis. With the couplings rated to 30,000rpm, the team tested voltages that translated to rotor speeds of just under 23,000rpm.

Upon further testing, and shipping delays, the team shifted to supplying power directly to the motor and skipping the h-bridge, and newly designed MOSFIT, setup. Had the team been given an unlimited amount of time, the MOSFIT setup would have been implemented. After meticulously aligning the rotor, stator, and mounting plates, the final test resulted in a maximum angular velocity of 21,799rpm without the stator and 22,144 with the stator. Interestingly, the average torque increased without the stator by 0.96mN*m (38.36mN*m without the stator and 37.40mN*m with).

Future Considerations

As this project was designed to last only a semester, many aspects were overlooked and documented that would greatly improve the design and functionality of the viscometer in the future. Starting with the structure, utilizing t-slot aluminum proved to be a time-consuming material to work with due to friction and fastening difficulties. Similarly, the rotor and stator were designed to be made of aluminum which resulted in many aluminum flakes falling into the rotor-stator gap. This caused even more rubbing and shedding of the rotor and stator, ultimately prolonging the testing phase. Similarly, with the scale of this project, it would have been helpful to allow for more tolerances throughout the structure as many t-slot elements were put aside as they would misalign the rotor.