Battery knowledge · Thermal management and heat transfer
Heat transfer coefficient
The heat carried away per unit area per kelvin of difference between a surface and the fluid passing it. Typical values are 5–25 W/(m²·K) for still air, 25–250 for forced air and hundreds to thousands for pumped liquid, which is why fast-charging packs are liquid-cooled. Thermal models use it as their cooling boundary. [1]
- Abbreviation
- h
- Also called
- convection coefficient, film coefficient
- Unit
- W/(m²·K)
- Relationship
- Q = h·A·ΔT
Example
Estimate convective cooling
For an illustrative h = 20 W/(m²·K), area 0.1 m² and surface-to-fluid temperature difference 10 K, hAΔT gives 20 W of cooling. The coefficient depends on the actual flow and geometry.
Explore the graph
Thermal resistance sets the steady temperature rise; thermal mass sets the response time.
Steady rise: 10 K. Time constant: 8.333 min.
ΔT = P R_th [1 − exp(−t / (C_th R_th))]
Illustrative model. C_th = 500 J/K, fixed ambient and heat input, uniform temperature.
Use in Lemonergy
Design protocol or analysis tool
Inspect pack temperature
The separate Charge session can include a lumped thermal node.
Equation or tool to use
- Charge session thermal node
Balances heat and exchange
Inputs & settings
- Ambient temperature
- Thermal mass (J/K)
- Conductance (W/K)
- Heater availability
This overview identifies the components to use. Follow the example in Lemonergy for their connections and settings.
- Provide thermal mass and conductance.
- Compare two ambient temperatures.
Example. 100 kJ/K thermal mass and 100 W/K conductance give a 1000 s no-source temperature-difference time constant.
Observe. Temperature limits can pause charge; heater and mass are separate.
One node does not resolve gradients, coolant geometry or runaway. Studio’s native charger instead uses external temperature.
Open Design → Charge session →References & further reading
Technical references
- University Physics Volume 2, §1.6: Mechanisms of Heat Transfer
OpenStax, Rice University
Technical reference · Conduction, convection, radiation and thermal resistance.
Further reading on this topic
These sources provide broader context; they are not presented as citations for every statement in this entry.
- A General Energy Balance for Battery Systems
Dawn Bernardi, Ellen Pawlikowski, John Newman · Journal of The Electrochemical Society · 1985
Topic background · Battery energy balance and irreversible and reversible heat contributions. Reduced thermal models require explicit assumptions and current-sign conventions.