Battery knowledge · Thermal management and heat transfer
Biot number
The ratio of the resistance to heat conduction inside a body to the resistance to convection at its surface. Below about 0.1 the body heats almost uniformly and a lumped thermal model is adequate; large, strongly cooled cells with poor through-plane conductivity exceed it and need a model that resolves the internal gradient.
- Abbreviation
- Bi
- Relationship
- Bi = h·L / k
Example
Check a lumped-temperature assumption
For h = 10 W/(m²·K), characteristic length L = 0.005 m and k = 1 W/(m·K), Bi = 0.05. Small Bi supports a lumped-temperature approximation; the characteristic length must match the geometry.
Explore the graph
Increasing surface cooling can make internal gradients more important.
At h = 100 W/(m²·K), Bi = 0.5. The 0.1 line is a modeling heuristic, not a pass/fail safety limit.
Bi = h L_characteristic / k
Illustrative model. Declare characteristic length consistently, often volume/cooled area. Uses one scalar conductivity and convection coefficient.
Use in Lemonergy
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This is a reference concept. No executable Lemonergy block has been verified for this term.
References & further reading
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.
- University Physics Volume 2, §1.6: Mechanisms of Heat Transfer
OpenStax, Rice University
Topic background · Conduction, convection, radiation and thermal resistance.