Project 2 - 3D CFD modelling of Air cooling system and liquid cooling system for battery thermal management

1. Understanding the System

• Battery Module: 5 prismatic cells enclosed in an aluminum casing.
• Cooling Types: Air cooling vs. Liquid cooling.
• Worst-Case Scenario: Cells soaked at 45°C ambient temperature.
• Heat Generation: Corresponding to 0.5C discharge rate.
• Cooling Inlet Temperature: 20°C for both air and liquid.

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2. Governing Equations

We need to analyze the heat transfer through conduction, convection, and possible radiation. The heat dissipation follows:

Heat Generation in the Cell

Heat generated per cell:

$$Q_{\text{gen}} = I^2 R_{\text{int}}$$Qgen​=I2Rint​

where

• $I$I is the discharge current (calculated from $0.5C$0.5C rate),
• $R_{\text{int}}$Rint​ is the internal resistance of the cell.

Cooling Mechanisms

• Air Cooling: Convective heat transfer with forced convection.$$q_{\text{air}} = h_{\text{air}} A \Delta T$$qair​=hair​AΔT
• Liquid Cooling: Higher heat transfer coefficient $h_{\text{liq}}$hliq​ due to better thermal conductivity.$$q_{\text{liq}} = h_{\text{liq}} A \Delta T$$qliq​=hliq​AΔT

where

• $h_{\text{air}} \approx 20-50$hair​≈20−50 W/m²K (depends on airflow speed),
• $h_{\text{liq}} \approx 500-3000$hliq​≈500−3000 W/m²K (depends on coolant type and flow rate),
• $A$A is the heat transfer surface area,
• $\Delta T = (T_{\text{cell}} - T_{\text{coolant}})$ΔT=(Tcell​−Tcoolant​) is the temperature difference.

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3. Simulation Approach

1. Define Assumptions:

   • Cells are identical with uniform heat generation.
   • Steady-state heat transfer.
   • No phase change in coolant.
   • Neglect radiation losses.

2. Modeling in a Thermal Simulation Software:

   • Set up the geometry (5-cell module, aluminum casing).
   • Apply boundary conditions (heat generation, ambient temperature, inlet temperature).
   • Solve for steady-state temperature distribution.

3. Analytical Estimation (Simplified Approximation):

   • Calculate the heat dissipation rate for air and liquid cooling.
   • Estimate maximum cell temperature in both cases.

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4. Expected Results

• Air Cooling: Higher cell temperatures due to lower heat transfer coefficient.
• Liquid Cooling: Better thermal performance, leading to lower cell temperatures.
• Comparison: Plot temperature profiles, heat dissipation rates, and cooling effectiveness.