Liquid Cooling for Li-Ion Battery

The Hyster-Yale group needs a custom cooling solution for a diesel to electric forklift conversion. The company is using a battery pack consisting of seven lithium ion batteries and that produce more heat than the forklift can remove by itself. The goal is to solve this problem by using a two fluid refrigeration system that fits between the batteries. Our solution will cool the batteries to a stable temperature autonomously and will cycle on and off as needed to reduce the energy usage of the system.

=Problem Definition= The capstone team must find a liquid cooling method to run in between the batteries and keep them under a specific temperature at all times, even when charging.

COVID-19 Update
Due to the COVID-19 Pandemic during the second half of Spring 2020, the scope of this project was changed to be modeled and completed virtually.

Background
In an attempt to help reduce carbon emissions, the Hyster-Yale Group is converting the above internal combustion 9-ton forklift into an electric one. The battery pack they use, however, requires additional cooling to operate in hot environments.

After the work of last year's capstone team to attempt to cool these lithium ion batteries using air, Hyster Yale Group decided in order to get the cooling capacity they need, a liquid cooling method will be required.

Deliverables

 * Proof of Concept Prototype
 * Prototype to cost less than $750 per unit to produce.
 * CAD Models & Drawings
 * The prototype model is to be modeled in SolidWorks.
 * The design is to be validated using SolidWorks Simulation

Functional
The system must:
 * Remove 180W of heat from each battery
 * Cool batteries below 45 °C in 45 °C ambient environments
 * Begin and end operation after batteries pass an internal temperature of no more than 40°C
 * Minimize temperature gradient across the battery system

Spatial
The cooling system needs to fit within the space defined above In addition, it must have these dimensions:
 * Height < 502mm
 * Width < 652mm
 * Depth < 272mm

The interface between batteries must be no more than a total of 10mm wide

=Project Learning= Since they summarize the project learning for the project, please see the Fall Design Review Presentation and Spring Engineering Release Presentation

Battery Interface Alternatives
=Concept Design= The most recent concept as of midterms for the Spring 2020 semester, most of the refrigeration-cycle components are salvaged from last year's project. Some key features include the nested tube design and custom inlet and outlet manifolds, both of which are detailed in the Spring Engineering Release Presentation. Although our system will be controlled manually, the final, temperature-dependent control systems will be handled by our sponsor after project hand-off.

=Prototype Manufacturing Plan= The 1/2" copper tubes used to interface between the batteries need to be pressed to fit within each 10mm gap. This tube pressing jig will let the team flatten each tube evenly prior to cutting, and finally brazing the joints together. Due to the complicated nature of this process, it is not recommended for final product manufacturing.

The three manifolds (one inlet, two outlets) will be manufactured using 0.060in aluminum sheet metal. This will be plasma cut, then bent to shape, and finally welded together as shown. The various pipes and fittings used to connect the manifold to the system will be welded on over each of the cut holes.

=Design Validation Plan (Pre-COVID-19)= Because the system consists of these three major components, we hope to run the following tests once their necessary parts are finished:

Pump and Manifold
By hooking the pump up to a water reservoir and measuring how fast it drains, we can get the total volume flow rate our pump can output. The outlet of the pump will run into our inlet manifold, and each outlet of the manifold will run to its own separate container. This will validate that the manifold splits the flow rate evenly between our interfacing tubes.

Refrigeration System
After all of the parts of the refrigeration system are assembled, we will pressurize the system to ensure there are no leaks or failures. When it is filled with refrigerant, we will run the refrigeration loop and measure the temperature of the fluid entering the heat exchanger, to ensure our refrigeration system cools well below ambient temperature.

Heat Removal Interface
Our prototype will feature one separate heat removal "mockup" in which the interfacing tubes are thermally epoxied to sheet metal and pressed against a 180W heat source. While the heat source is running, we can measure the average temperature of the sheet metal plates for an approximation of how well the interfacing tubes remove heat from the batteries

Proof of Concept Prototype
After testing these components separately, we will assemble everything into a proof of concept prototype to make sure everything fits within our spatial restrictions, and our various pipes and connections are watertight. This prototype should be easy for our sponsor to "drop in" to a functioning battery pack.

=Design Validation (Post-COVID-19)= The main goal of our design validation plan was to validate the heat removal of the batteries and determine how much of a temperature gradient forms during the battery operation. Although the image shows a heat gradient forming of approximately 20°C, this could be minimized by increasing the flow speed, and the hottest temperatures are still below our 45°C goal

=Final Deliverables= Please click here to view the Final Presentation, and see the attached final report.

=Team Members=

=Additional Documentation=

Project Schedule

Meeting Minutes Meeting Minutes can be found in the following Google Drive folder

Presentations Meeting Presentations can be found in the following Google Drive folder