Final Design
Our final design pumps milk continuously through a channel cooled by two Peltier thermoelectric plates which operate off a temperature differential. The channel is custom 3D-printed with an aluminum top layer. The Peltier plates press flush against the aluminum top layer, covered by an aluminum heat sink cooled by two fans. The channel, plates, heat sink, and fan are housed in a 3D-printed casing. The system is powered by rechargeable lead batteries running at 432 Whrs charged by a 100W solar panel. Our design cools large volumes of liquid by leveraging the plates’ ability to quickly cool small volumes of liquid and re-circulating milk throughout the system. We have successfully cooled 1.5L of milk from 101F to 45F within 4 hrs, meeting Rwandan Grade II standards.
Issues Encountered
To successfully cool milk from 101F to 45F in four hours with our design and current available technology, we ask users to place their jerry can of 101F milk starting on the ground outside of the cooler until the milk reaches the ambient air temperature, about ~67F in Rwanda.
To use this system, a rural dairy farmer can feed the two pump tubes into the opening of the jerry can and connect the pump and fans to their power source, which in our system testing was 35A scooter batteries and a 100W solar panel. After 1 hour, determined by the average time the system takes to reach ambient temperature, the farmer places the jerry can into the cooler with tubes still attached and the system still running and closes the lid. The system then continues to run until the farmer disconnects the system and removes the jerry can of cooled milk in the morning.
To use this system, a rural dairy farmer can feed the two pump tubes into the opening of the jerry can and connect the pump and fans to their power source, which in our system testing was 35A scooter batteries and a 100W solar panel. After 1 hour, determined by the average time the system takes to reach ambient temperature, the farmer places the jerry can into the cooler with tubes still attached and the system still running and closes the lid. The system then continues to run until the farmer disconnects the system and removes the jerry can of cooled milk in the morning.
Future Improvements
As cooling technologies continue to evolve, we hope to modify our design to operate self-sufficiently without user assistance. With our current powering system, to use the lead batteries for a longer amount of time, it is necessary to charge them with the solar panel for longer. We hope to experiment with our battery/solar powering system carefully in order to maximize the energy gained from the least amount of charging time.
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Full Final Design Schematic
Final Design CAD Drawings
Spring Final Design Prototype 4: Cooling Unit Schematic
Spring Final Design Prototype 4: Tubing CAD
Spring Final Design Prototype 4: Thermoelectric Plates CAD
Spring Final Design Prototype 4: Cooling Unit CAD
Spring Final Design Prototype 4: Heatsink CAD
Spring Final Design Prototype 4: Cooling Channel Tubing Schematic
Spring Final Design Prototype 4: Cooling Channel Plates Schematic
Spring Final Design Prototype 4: Cooling Channel CAD
Spring Final Design Prototype 4: Aluminum Plate Base CAD
Spring Final Design Prototype 4: Fan 1 CAD
Spring Final Design Prototype 4: Fan 2 CAD
Spring Final Design Prototype 4: Fan Housing CAD
Spring Final Design Prototype 4: Full Final Design Schematic
Spring Final Design Prototype 4: Tubing CAD
Spring Final Design Prototype 4: Thermoelectric Plates CAD
Spring Final Design Prototype 4: Cooling Unit CAD
Spring Final Design Prototype 4: Heatsink CAD
Spring Final Design Prototype 4: Cooling Channel Tubing Schematic
Spring Final Design Prototype 4: Cooling Channel Plates Schematic
Spring Final Design Prototype 4: Cooling Channel CAD
Spring Final Design Prototype 4: Aluminum Plate Base CAD
Spring Final Design Prototype 4: Fan 1 CAD
Spring Final Design Prototype 4: Fan 2 CAD
Spring Final Design Prototype 4: Fan Housing CAD
Spring Final Design Prototype 4: Full Final Design Schematic
Final Design Electrical Block Diagram
Electrical & Power Documentation
Test Modeling |
To test our designs, we used a temperature-time model to determine a temperature profile for each prototype test. The graph to the left shows the sub-ambient temperature profile of our final channel prototype. Our final design outperformed any previous test, reaching 45F within 105 minutes. |
Final Design Single Unit Cost
Assuming bulk pricing and that power-source is supplied situationally-based
Final Design- Full Product
Conclusion
Our project explored non-traditional and sustainable cooling techniques throughout our year-long focus on Rwandan dairy farming. Through our work with thermoelectric plates and heat-mass transfer, we were able to successfully cool 1.5L of milk from 101F to 45F in our final prototype, pumping a small amount of milk quickly through a narrow cooling channel. Our final design was insurmountably more successful than our first, second, and even third prototype designs. We successfully reached the measure we set for ourselves of Rwandan Grade II milk. As we pass this project off the the Hunt Institute, we hope they may continue to explore charging a reusable battery using solar power and continue to evolve our functioning design to be a self-sufficient system without the need for a farmer to place their milk product inside the cooler a quarter-way through the system's process. However, dairy farmers using our device would be able to sell more of their product at market the next day at a safe drinking level and without requiring access to an electric grid.