System

Here the finalized system is described and thoroughly explained. The teams goes through the various mechanical and electrical components that allow this system to function as a true vapor compression hard hat.

Assembly Render

Figures 1 and 2 show the full 3D render of the Cerebro hard hat system, and the actual form it took on. This system includes all aspects of the vapor compression cycle; a compressor, condenser, expansion valve, and evaporator. Additionally, there are push fans attached to each radiator to improve their thermal performance. Finally, a 24V battery is hooked up to the system.

Condenser

At the end of the first half of the project, the condenser design selected for project Cerebro was a radial mounted fin and tube radiator mounted on the top exterior of the hat. As seen in Figures 3 & 4, the bowed design over the top of the hat allowed for a fan to cool the refrigerant in the condenser and it sat far enough away from the user as to not burn or radiate heat down towards the user. The team also concluded that the condenser will be additively manufactured because it is an obscure shape and needs to fit the dome of the hat almost perfectly.

The initial proposed design was not used in the final assembly of the hat, however, the condenser was additively manufactured as originally determined. Figure 9 shows the actual finalized condenser, which keeps the vertical fins and snaking coolant tubing, but this condenser loses the solid base for better airflow and the arced shape. Mounting brackets were also added to attach to a push fan. A condenser efficiency analysis was conducted of the actual finalized condenser which appears in the data page.

Evaporator

The most important factor when designing for the evaporator was to direct cold air directly from the radiator to the individual user. Direct access on the hat capable of achieving this goal was located on the brim of the hard hat, where a radial design would have to cover the underside of the brim. Small fans are mounted to the brim over the top of the radiator to ensure cold air is blown over the evaporator and onto the user, Figure 5.

The team manufactured a prototype radiator using aluminum egg carton, with copper tubing running through. Because the fins in the initial cold radiator proposal are aligned along the same plane, egg carton is a feasible alternative for prototyping purposes. The team has acknowledged that this solution would work for prototyping, but if the hat ever goes into mass manufacturing, a more traditional radiator would need to be designed. Figure 6 shows the modeled radiator proposed, and Figure 7 shows the constructed radiator based off of the original proposed design. The team manufactured the evaporator to the best of their ability, but large copper loops remained at each end of the radiator due to the team fearing that the tubing would kink.

Expansion Valve

The initial proposed plan for the refrigeration cycle’s expansion valve was to use a thermal expansion valve for the first Cerebro hat. Thermal expansion valves have more moving parts than capillary tubing, but they allow for adjustments, which would be useful for the team when determining baselines of the system. Additionally, if future work on the Cerebro hat included use of capillary tubing as an expansion valve, the initial use of a thermal expansion valve would be beneficial for determining the necessary parameters the capillary tubing would need to meet to achieve desired performance. Unfortunately, due to shipping delays the team ended up having to install a manual valve into the system to serve as the expansion valve. This final solution is not ideal when it comes to gathering data for the system parameters, and creating an well sealed system, but it still allowed the team to adjust cooling capabilities to determine the ideal setup of the refrigeration cycle. The manual valve provided the needed functionality in the vapor compression cycle, but lacks the finesse that the proposed thermal expansion valve would have provided. The manual valve was mounted on the rear of the hard hat with the majority of the system plumbing.

Compressor

Due to the pre-selection of the Aspen miniature compressor, Figure 9, by the project sponsor before the team began work on the Cerebro project, placement of the compressor was the main decision the team had to make regarding the compressor. The team initially proposed placing the condenser on the left side of the helmet, with the expansion valve opposite of the compressor to balance out the weight of the hat. The final design saw the team amend this proposal and move the compressor to the back of the helmet for an easier plumbing process. As expected, this created too much backweight on the hat, but as the deadline for the project rapidly approached, the team knew from discussions with the sponsor that functionality was more important than weight distribution.

Power supply

The compressor and push fans in the system require power to operate, so the system must include a power supply to work. The voltage and amperage that the compressor requires according to the data sheet is 24V with a maximum of 9.5A, and if the device were to run consistently, the Cerebro hat requires a massive battery. A 24V 20Ah battery can be purchased shown in Figure 10, but this size of battery obviously can not be put onto a hardhat. The proposed solution for carrying this battery is to have the battery in a separate pack that the user carries, to prevent the hardhat from becoming too heavy. Additionally the team utilized a variable power supply, Figure 11, that the lab already owns. This solution works only for prototyping due to the variable power supply needing to be plugged into the wall. However, this allowed the team to test components while easily monitoring the drawn current and the testing of components was able to begin early on in term 2 of the project. The battery specifications that were proposed at the end of term 1 were not adjusted during the remainder of the project, and this battery was purchased for the project.

Electrical Schematic

The electrical schematic of the compressor drive board which is also attached to a potentiometer to control compressor speed and the fan array for both radiators.