Blog 3 Capstone - Team 10
Blog 3
Team 10 has been working on designing a casing for a wheelchair motor that waterproofs and cools it. For the duration period from October 28th to November 11th, the team has completed its second milestone which was performing the analysis for simulated models and entered its third milestone which is generating a production plan.
The work completed for the second milestone specifically includes performing the heat transfer analysis for the fins and performing the pressure calculations for the seal. For the third milestone, the team has started with identifying all the potential materials that will be required to build and install the casing.
When the team performed heat transfer calculations for fin dissipation, we realized that the initial constraint of keeping the casing exterior below 44°C was unrealistic due to the casing's low Biot number of roughly 0.003. The casing's extensive surface area compared to its volume, coupled with high thermal conductivity, results in a low Biot number, indicating similar temperatures throughout the casing. Achieving a significant temperature difference between the casing's exterior and the motor temperature would require motor insulation, contrary to the team's goals.
Most heat dissipation in the casing is expected to occur through the fin array. Table [1] displays heat transfer data in watts for one of the two identical arrays, considering various convection heat coefficients (h) and temperature differences between fin bases and ambient air (theta). Different h and theta values account for outdoor use, where ambient conditions vary. These calculations assume uniform base temperature (due to low Biot number), fin shape, and convection tip conditions. The array comprises 15 fins, which represents the maximum number of long rectangular fins the team can accommodate in a single array. Increasing the number of fins enhances the array's heat dissipation capacity which is why the team chose 15. Other fin arrangements were not possible to manufacture or were less efficient. The motor produces approximately 300W, requiring each fin array to dissipate around 150W. If the fins dissipate less heat than the motor produces, the motor heats up. The motor temperature target is below 105°C, assuming a 30°C ambient temperature, resulting in a theta of about 70°C. At this level, the fins effectively dissipate heat from the motor, preventing it from exceeding 105°C. This estimate is conservative as it doesn't account for the surface area of the rest of the case without fins.
The result of the heat transfer calculation shows a complete dissipation of any heat produced by the motor that would result in unsafe operating conditions for the motor. The maximum possible output of heat by the motor is 300 W of heat. Assuming the worst possible ambient conditions for the calculations of heat transfer rate, the fins on the casing can dissipate 44% more heat than the maximum heat generated by the motor.
Table 1: Heat dissipated in Watts
The pressure calculations were performed by the team to figure out how much pressure the seals on the casing needed to withstand. These results satisfy the goal of resisting hydrostatic water pressure in 1 meter of water and are shown below in Table 2. The silicone seals that surround the motor can resist a hydrostatic pressure of 600 kPa while the hydrostatic pressure that is generated at 1 meter of submersion in water is 10 kPa.
For the bill of materials, the team has identified a comprehensive list of all the materials it would need to build the casing and install it on the motor. Table 3 shown below gives the list of materials and the categories for which they would be needed.
Between November 11th and the 25th, Team 10 aims to initiate and accomplish the milestone of creating a production plan while also commencing the milestone of finalizing the design. The production plan will outline the team's strategy for procuring the necessary tools and materials to construct the prototype, including the anticipated costs and lead times for these materials. The plan will encompass specific details of this process, outlining the location and methodology for prototype creation, as well as specifying the tools to be employed in the procedure. Following the finalization of the production plan, the team will generate 2D drawings of the prototype for manufacturing reference and may also produce a scaled 3D printed model. The team is contemplating the possibility of skipping the production of the 3D model, leaning towards the belief that the current CAD and 2D drawings provide satisfactory reference points for production. If this were to happen, the team would find additional time to focus on other project elements.
Team 10 is not expecting any major problems in the next two weeks time. The end of November is the back end of the semester when most of the classes are gearing up for their finals. Other classes around this time will need much more of the student’s attention and during this time it will be difficult to make a lot of significant progress in the project. This was however taken into account when the project plan was made. This was taken into account when creating the milestones as the last two milestones of the semester have either few tasks or the time expected for completing the task was overestimated to give extra time to the team.
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