Table of Contents
All documents listed on this page can be found in the Sub-Systems Design Documents directory.
Sub-System Overview and Spec DistributionOur system consists of 4 sub-systems: The thermal, electrical, airflow, and user sub-systems. The user sub-system is simply defined with the interface being the on-off switch. The other systems are detailed in the later sections. Overall, the sub-systems map should map as shown in the table below.
Thermal Sub-SystemThe thermal sub-system consists of the thermoelectric and heatsinks on either side to increase the surface area and heat transfer. An overview of the sub-system is shown below.
Currently, the heat sinks in our mock-ups are the best fit for our design. More analysis is going to be performed to see if a machined heatsink that we design will be better. With the number of fins and thin air slots, a significant pressure drop is being seen in the mock-up. With a machined heatsink, we want to see if this can be avoided and the effect that it has. An image of the heatsinks we bought on the thermoelectric for our initial mock-up is shown below.
Airflow Sub-SystemFor the airflow sub-system consists mostly of the fan but also the nozzle to distribute the cool air to the user. For the fan, we have been looking into DC brushless fans. The fan used in our mock-up is a 40x40x10mm 7CFM fan. The nozzle we plan on making small and wide to gain a wide distribution on the user's neck but also getting a greater velocity at the user. The following pictures show the fan in our initial mock-up and the nozzle in our second mock-up.
Electrical Sub-SystemThe electrical sub-system consists of a number of different components, mainly being the battery and power regulation or boosting for the fan and thermoelectric. Another part of the electrical sub-system is the switch that needs to be interfaced for the user. An overview of the electrical sub-system is shown below along with switch options.
Another big component of the electrical sub-system is the battery selection. Below is a table of power densities for different types of batteries. It shows that the best case currently is a Li-ion battery with 3.7V. This would require a booster to reach the fan and thermoelectric voltages however. Depending on how much power is needed in total, one cell or two cells may be chosen for the battery. This also comes with multiple trade-offs in size, weight, and cost.
Mock-UpsOur initial mock-up consisted of foam that we cut to house all the components. It didn't perform well and with the porous foam, we wanted to recreate it with modifications. Our initial mock-up didn't dissipate heat well enough, causing the thermoelectric to overheat entirely. With the second mock-up, we were able to get a cooling effect and better flow at the exit. The following link goes to the pictures for our mock-ups. Some can be seen above in the previous sections. To obtain readings for the mock-ups, we used an anemometer, thermocouples, and a thermocouple reader. These allowed us to obtain ambient temperature, fan velocity, exit velocity, and hot and cold side temperature readings at the heat sinks. The readings are as show below.
|Mock-Up||Fan Velocity||Exit Velocity||Ambient Temperature||Cold Side Temperature||Hot Side Temperature|
|Initial||2.5 m/s||0.24 m/s||71oF||74oF||121oF|
|Second||2.5 m/s||0.45 m/s||75oF||64oF||108oF|
Risk AssessmentOur updated risk assessment is as shown below. The file can be found here.
Sub-Systems Design Review
- The presentation can be found as a  or  file.
- Notes from review