Liquid Cooling for Li-Ion Battery
|A picture of LICH System|
|Team Name||LICH System|
|Duration||Fall 2019 - Spring 2020|
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.
- 1 Problem Definition
- 2 Project Learning
- 3 Concept Design
- 4 Prototype Manufacturing Plan
- 5 Design Validation Plan (Pre-COVID-19)
- 6 Design Validation (Post-COVID-19)
- 7 Final Deliverables
- 8 Team Members
- 9 Additional Documentation
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.
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.
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.
- 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
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
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
|This vapor absorption cycle fortunately has a very high coefficient of performance. Similarly to our vapor compression cycle, it relies on a condenser and evaporator, but it also uses a separate vapor generator and absorber to create vapor of the working fluid, usually ammonia. Unfortunately, these systems often require larger scale operations, since you need to insulate the heat added to the ammonia (often with a flame) from the part of the cycle you wish to keep cold. Because we have such a small space for our design, this option was removed.|
|Another consideration was to use a thermoelectric diode, in this case an IceProbe, to try and cool our fluid. This cooling method has a very low coefficient of performance, and the number of diodes we would need to cool our fluid would have broken our project budget and drawn too much power. Although this option is the most space-efficient, it is not the right choice for this system.|
|Our chosen option for the refrigeration cycle, a vapor compression cycle offers a reasonably high coefficient of performance for the amount of space it requires. Luckily, last year's project already used a vapor compression cycle, so our group was able to salvage the condenser, metering device, and compressor, saving money. Originally we also considered using only the refrigeration cycle -- that is, running the refrigerant directly between the batteries. Because vapor compression cycles don't respond well to constantly being cycled on and off, we decided against it.|
|The final design for our cycle, featuring two separate loops integrated via a heat exchanger. The left side runs a water and ethylene glycol solution to cool the batteries, and the right side runs a vapor compression cycle, for when the glycol needs additional cooling. One advantage of this setup is the glycol side can constantly run without draining too much power, and refrigeration system can turn on during max charge/discharge, when the temperatures will be highest. The addition of a radiator to the glycol side is necessary since the addition of our liquid cooling system removes the possibility for natural convection to cool the batteries during normal operation.|
Battery Interface Alternatives
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.
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
|The final, executed schedule for this project is attached on the left|
Meeting Minutes can be found in the following Google Drive folder
Meeting Presentations can be found in the following Google Drive folder