Battery cooling in a series circuit.

The challenge and why simulate it

Battery cooling must move heat from the module interior through interfaces and into the coolant. Low through-plane conductivity, local heat generation, cold-plate coverage and coolant warming can produce temperature differences that a single bulk-temperature estimate misses.

I built this independent thermal screening example to examine a series cooling architecture: two cold plates cool opposite faces, while the second plate receives water already warmed by the first. It illustrates why coolant temperature alone does not establish the hottest module temperature, and why transient heat storage must be included when interpreting cooling performance.

This is a Khani Solutions portfolio demonstration using assumed materials and operating conditions. It is not proprietary Wisk or Boeing hardware, an employer analysis, or a validated aircraft battery design. It is an operating-load cooling model, not a thermal-runaway initiation, propagation or exhaust calculation.

Workflow, model and results

I built this conjugate heat transfer study using FreeCAD for the geometry and Elmer for the flow and thermal calculations.

The model represents 30 pouch cells as a single anisotropic thermal block, measuring 352 × 188 × 169 mm, inside a 2 mm titanium casing. Two aluminum cold plates sit on opposite faces, separated from the casing by 0.5 mm thermal interface layers. Each plate contains a five-pass serpentine channel. Coolant passes through the first plate, crosses to the second, and then exits.

The battery conductivity was assumed to be 20 W/m·K in-plane and 1 W/m·K through-plane. That difference matters: a cold plate can remain relatively cool while the module interior heats up because heat cannot reach the cooled faces quickly enough.

The simulation used:

• 300 W of uniform module heat generation.
• 1 L/min water at 25°C, with all regions initially at 25°C.
• Approximately 2.08 million tetrahedral elements.
• A steady incompressible flow calculation followed by transient conduction and coolant advection, using 30-second steps over one hour.

At one hour, the calculated module peak reached 63.5°C, while the coolant reached 26.4°C after the first plate and 27.8°C at the outlet. The coolant was removing approximately 195 W at that instant; the remaining heat was still accumulating in the assembly. This was a transient result, not thermal equilibrium.

Practical design concerns include warmer coolant entering the second plate, pressure losses through both serpentine circuits, insufficient pump flow, channel blockage, and thermal interface gaps or uneven compression. The interfaces here were perfectly bonded; those defects were not simulated.

This is an illustrative screening study. The flow regime is transitional, although modeled as laminar. A mass-conserving flux reconstruction changed the calculated velocity field by about 22%, so flow refinement, turbulence sensitivity, mesh/time-step studies, and experimental comparison are needed before using these temperatures for design decisions.

The video compresses one simulated hour into 10 seconds.

What to do with these results

Use this example to frame architecture and test questions: whether a parallel coolant arrangement changes temperature uniformity, how flow rate affects heat removal and pumping demand, and how interface resistance or cell-to-cell heat variation affects the hotspot. Those variations and defects were not calculated in this run. The imposed 300 W load remains an input, rather than a prediction of electrochemical heat generation.

Design qualification would require representative material and interface measurements, adequate flow resolution, turbulence sensitivity where appropriate, mesh and time-step convergence, and comparison with module and circuit test data. A relatively cool outlet is not proof of a cool module core. A one-hour transient result is not a demonstrated steady operating limit.

Connection to the external plume study

Cooling and venting belong to different parts of battery thermal engineering. This model follows heat conduction and coolant transport in a module assembly. The aircraft plume study follows a hypothetical external hot-gas source after discharge. The two demonstrations share a focus on thermal-fluid behavior but are not coupled and do not establish thermal-runaway prevention.