Design Process

This section will discuss the team’s approach to designing the Cerebro system, and discuss the layout prototypes created for this project.

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Design Cycles

The team decided to have three design cycles, each with one-week iterations. Each design cycle had the team split into two, so each design challenge had a week to be focused on. Another bonus of this system was that each team member got time to work one on one with every team member. Each design challenge had a group focus on solutions for a week, starting with researching existing solutions, compiling all possible solutions, then structuring a chosen solution to work within the design parameters. At each design iteration’s conclusion groups would present their findings and proposal to the remaining team members and the project sponsor and advisor Dr. Joshua Gess for a full team discussion and the finalization of what proposal would be moved forward with.

In the first design iteration, Brodish and Bailey teamed up and focused on cooling applications of the hat. In week 3 of the project, the sub-team researched multiple cooling methods that could be implemented onto the hard hat. For a compressor, the team initially ideated various cooling methods that used air as the working fluid. The first concept had the compressor oriented towards the back end of the hat for convenience and weight distribution. This concept would allow the compressor to draw air in, then have the air compressed, filtered, and then finally be applied to the user. More research was conducted, and the sub-team came across an air cooler that uses vortex separation of air, to separate hot and cold air from a compressor that could then be filtered and applied to the user [1]. The vortex cooler called Vortec can be seen in Figure 1. However, when the team presented this idea to the client, he desired the main cooling methodology of the system to be the vapor compression cycle with refrigerant 134a as the coolant fluid. Refrigerant 134a is easily accessible, relatively cheap, and it has a low boiling point, which is needed for ensuring the fluid is a vapor when entering the compressor. The other sub-team group, Bergquist and Wise, focused on power supply possibilities and concluded that the best solution was a backpack containing a rechargeable 24-volt battery. This is because the compressor has a 24-volt requirement and could be used to attain one to two hours of usage at a time. The backpack is needed because the battery would not fit on the hat.

With the cooling method of the hat being defined by the client and the power supply figured out, the teams focused on more specific research approaches in the second design iteration. The second iteration team included Bailey and Wise, who focused on the ideation of a heat exchanger for the compressor to ensure that the refrigeration cycle was as efficient as possible. Bailey approached the problem with a conventional finned heat exchanger, that would be brazed to the compressor for good thermal conductivity. Wise approached the problem with a novel idea of having the finned heat exchanger of the compressor being integrated with the condenser of the vapor compression cycle, shown in Figure 2. The team concluded that the heat exchanger will most likely be brazed to the compressor to remain in the scope of the project. Brazing would ensure a high thermal conductivity between the compressor and the fins allowing for the unnecessary heat to be dissipated quickly and efficiently. However, in the interest of time and our project scope, these solutions were unable to be implemented in this iteration. Future teams will be able to implement this into the design in order to improve the product and thermal efficiency.

In the third and final design iteration, team members Bailey and Bergquist collaborated on the condenser and evaporator design of the vapor compression cycle. They started by rough sketching some concept designs for the two components, then modeled them with a computer aid design (CAD) software, and 3D printed one to test the additive manufacturing feasibility of the concept. The below images show the CAD model of the initial condenser and evaporator prototypes. The team concluded that the condenser would be additively manufactured because it was an obscure shape and needed to fit the top of the hat well. The evaporator was not additively manufactured to stay within the budget and to keep a simpler geometry. Wise and Brodish focused on the thermal expansion valve application of the cycle and researched alternative methods. That section of the cycle came down to either applying a common thermal expansion valve (TEV), capillary tubes, or an Electronic Expansion Valve (EEV) to get the refrigerant to sub-zero temperatures. The team chose the EEV based on their simplicity, staying within the scope of the project, and to have greater control of the system in testing.

Through the one-week design iterations, the team was able to converge on a cooling method for the air-conditioned hard hat, a power supply method, a heat exchanger for the compressor, an EEV, the evaporator design, the condenser design, and its manufacturing process.

Initial Layout Prototypes

This team focused on two iterative prototypes. The goals of these prototypes were to frame and shape components across the form of the hat, and to aid in visualizing what final tubing would look like to and from each component. First iterations for the design focused on three main objectives. The first objective of this prototype was to create pathways for tubing from each of the four components. The team had an idea of what the overall shape of each component would look like and implemented their basic geometry during the prototype construction. Figures 2 and 3 demonstrate initial attempts to configure designs around the shape of a traditional hard hat. Through this initial prototype, tubing and weight distribution became important factors to consider moving forward with a second iteration. Tight fitting between components pictured in the figures below would be difficult to implement with less flexible metal tubing. This prototype was also very rear-loaded, requiring further improvements to component positioning.

The largest change from the first iteration was the change in hard hat design. With this iteration, the team decided that more surface area was required for the mounting of the compressor and larger space for radiator area, opting for a large-brim design over more traditional hard hats. The second iteration of this prototype also focused on further clarity of component design. This included radiator fin design, radiator mounting and geometry, compressor placement, and further work on tubing placement. From the first iteration, radiator fin design has been conceptualized to allow for heat to flow from the tubing to the fins and out to the environment. The condenser seated on the top of the hat in particular is designed to reject heat using a fan mounted below the arch out away from the user to the ambient environment. The choice of expansion valves was yet to be determined by the second iteration, instead the team used a pipe fitting to simulate the weight and size of a potential expansion valve.

The primary takeaway from the second prototype was the need to adjust the shape of the condenser. The condenser was arced originally to fit on a standard shaped hardhat, but the team decided to move forward with a cowboy hard hat due to the added mounting area around the brim of the hat. The condenser in all further iterations follows the shape of the top of the cowboy hat, which is discussed in the system section.