Battery Cooling (Thermal Management) by PCM, CFD Simulation
The present problem simulates the cooling process of a battery applying phase change material (PCM) using ANSYS Fluent software.
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The present problem simulates the cooling process of a battery (battery cooling) applying phase change material (PCM) using ANSYS Fluent software. Modeling is related to a lithium battery used in vehicles. The battery is the main source of electricity and the essential part of the car’s electrical system. The battery can store electrical energy in the form of chemical energy. If the current is requested from the battery, the chemical energy is converted into electrical energy, and when the battery is charged, the electrical energy is converted into chemical energy. The car battery consists of six cells or elements, and each cell in the car battery consists of alternating plates, which alternate between the cathode plates or the anode plates.
The present simulation is performed in two stages; In the first stage, only one lithium battery is modeled, and in the second stage, two layers of phase change material are used on both sides of the battery. This work aims to investigate the effectiveness of phase change materials in the cooling process of the battery.
Step 1 (without PCM)
In the first step of the simulation, a row of one of the battery elements is modeled. This row consists of five layers: positive and negative collectors, cathode and anode plates, and a separating layer between the cathode and anode plates. Each of these layers has a certain thickness and specific thermophysical properties; But in this simulation, a single layer is assumed whose thickness is equal to the sum of the thickness of its constituent layers, and its thermophysical properties are equivalent to a combination of the thermophysical properties of each layer independently.
So the battery defined in the model has a density equal to 2264.74 kg.m-3 and a specific heat capacity equal to 1224.54 j.kg-1.K-1 and a thermal conductivity equal to 0.98 Wm-1.K-1, and a thickness of 11.3 mm.
Step 2 (with PCM)
In the second stage of the simulation, a layer of phase change material is designed as a coating on both sides of the battery body. In general, phase change materials are materials with organic compounds that can absorb and store large amounts of latent thermal energy. Thermal energy storage in these materials is achieved during the phase change process (solid phase to liquid or vice versa); So that when the phase changes from solid to liquid, it absorbs heat from the environment (causes cooling), and when the phase changes from liquid to solid, it returns heat to the surroundings (causes heating).
The phase change material defined in this model is paraffin which has a density equal to 810 kg.m-3 and a specific heat capacity equal to 2000 j.kg.K-1 and a thermal conductivity equal to 0.2 Wm-1.K- 1 Viscosity is equal to 0.0269 kg.m-1.s-1. Also, this paraffin layer has a thickness of 12 mm on both sides of the battery. In this simulation, the model of solidification and melting is used to define the phase change materials. To define phase change materials, it should be noted that the maximum temperature at which the solid phase temperature is (solidus temperature) is 307 K, and the minimum temperature at which the liquid phase is dominant (liquidus temperature) is 309 K. Also, the pure solvent melting heat is defined as 240000 j.kg-1.
Battery Cooling Project Mechanism
When the battery starts working, an electric current is established inside it. The current inside the battery can generate heat and increase the temperature of the battery. In this simulation, to determine the amount of heat generation inside the battery, we define a volumetric heat source in the battery area. The amount of heat generated in the battery is equal to R*I²; So R is equal to the battery’s internal resistance, and I is equal to the current intensity inside the battery. In this modeling, it is assumed that the battery’s internal resistance is equal to 10 mili ohms, and the amount of current intensity is equal to 86 amps. As a result, the amount of heat generated inside the battery is approximately equal to 120,000 W.m-3.
The present simulation is transient. The duration of the battery performance test in both stages of the simulation was equal to one hour, and a time step size is equal to 1 second.
Geometry & Mesh
We design the present model in three dimensions using Design Modeler software. We design the geometry in two steps. The battery designed in the initial modeling has a thickness of 11.3 mm, and its length and width are 335 mm and 167 mm, respectively. In the second modeling, we add two 12 mm thick layers to both sides of the battery body.
We carry out the model’s meshing using ANSYS Meshing software. The mesh type is structured. The element number is 93090 and 276660 for the first and the second cases, respectively. The following figure shows the mesh.
Battery Cooling CFD Simulation
We consider several assumptions to simulate the present model:
- We perform a pressure-based solver.
- The simulation is unsteady. Because the purpose of this work is to investigate how the PCM heats up or battery cools down over time.
- We ignore the gravity effect.
The following table represents a summary of the defining steps of the problem and its solution:
|solidification & melting||On|
|mushy zone parameter||100000|
|wall motion||stationary wall|
|free stream temperature||300 K|
|heat transfer coefficient||10 W.m-2.K-1|
|momentum||second order upwind|
|energy||second order upwind|
|gauge pessure||0 Pascal|
|velocity (x,y,z)||0 m.s-1|
Results & Discussions
At the end of the solution process, we obtain two-dimensional and three-dimensional temperature contours in both simulation steps. We compare the temperature contours in both stages at the end of the simulation. Also, we obtain the diagram of the average temperature changes of the battery in terms of time for the two states of with and without phase change material. We present this chart in one hour. The results show that if we apply a phase change material coating to the battery body, it will cool the battery and reduce the temperature growth rate.
Also, two-dimensional and three-dimensional contours related to the volume fraction of liquid from the phase change material are obtained in the second stage of the simulation to show its effect on heat transfer with the battery body.
There are a Mesh file and a comprehensive Training Movie that presents how to solve the problem and extract all desired results.