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Final Design of the Dermal Cooling Vest
The final solution creates a long water channel that encompasses the torso with 75 feet of silicone tubing. Using a low volume pump, water flows across 3 Peltier plates and into the vest. 3 high efficient Peltier plates were chosen instead of only 1 high powered Peltier plate in order to increase battery life. Energy is conserved because the coefficient of performance improves at a lower temperature gradient across the plate. In addition, by suing the more efficient Peltier plates, the current through our system was lowered, and the heat load was decreased. This allowed the use of smaller heat sinks since less heat dissipation was required. This greatly increased the wearability and form factor of the vest. For example, by using an integrated heat sink, the height was reduced from 3.5 inches to only 0.42 inches. The low profile design allowed for storing the heat sinks in small pockets on the outside of the vest. These pockets were open to the environment through a mesh screen, allowing the heat sinks to expel heat. Below are some figures and tables that show more details on the final design of the vest.
PID Controller:
From the information of the thermocouple, the PID controller is able to maintain a given set temperature set by the user. The controller also optimizes the power used from the pump and battery to ensure longer lasting cooling ability. A schematic of the controller block diagram is indicated below.
Thermocouple Junction:
This is where the temperature of the water can be sensed and allows the controller to obtain a reference temperature. The thermocouple is placed right before the water is cycled back into the cooling system to get a temperature heat exchanged from the user.
Silicone Water Tubing:
This is a clear plastic tubing of about 75 feet inside the vest. This allows water to flow throughout the vest and allows for heat exchange from the user.
Vest Exterior Components
Fabric Insulation:
The vest has a built in insulated fabric from CompCooler which enables heat to not easily come in and out of the fabric and therefore increases the cooling temperature of the vest through conduction of the tubing.
Mesh Lining:
This was a modified design from the original CompCooler vest. The mesh enables the fans to expel heat away from the vest which would increase the cooling ability of the vest and maintain the cooling temperature longer.
Thermoelectric Cooling System:
The cooling system contains 3 units of these in which 1 unit of a thermoelectric cooler consists of 2 aluminum pin fin heat sinks each with its own fan and motor that are welded together. This allows the Peltier plate to expel heat out of the vest. Underneath the heat sinks is a Peltier plate with the hot side on top and the cold side on the bottom. This is how thermoelectric cooling takes place Below the Peltier plate is an aluminum water block.
Vest Interior Components
Water Pump and Battery:
The pump came with its own battery that lasts about 10 hours. This enables water to flow through the plastic tubing so that the warmer water created from heat exchange from the user can flow back into the thermoelectric cooling system and become cooled to its set temperature again.
Lithium Ion Battery:
There are 2 of these batteries placed in parallel and each battery is capable of 72 Watt-Hours. Together in parallel, the vest is supplied with up to 3 hours of cooling at minimum power consumption and about 1.5 hours of cooling at maximum power consumption.
App Development
Below is an iOS app that was developed for to its simplistic design and user friendly interface. Rather than having a manual control of the vest, the app can be used to control or set the desired temperature of the vest and also allows the vest thermocouple data to be sent back to the phone via Arduino bluetooth connection. The user is also able to manual turn off the vest manually or set a timer to let the app automatically turn off the vest after a certain period of time.
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