Meaning
The rate of thermal energy transfer per unit area through a boundary surface fluctuates over time as a function of changing electrical and electrochemical states. This dynamic heat flux is a primary consideration in design optimization of high-power battery packs where rapid charging or acceleration generates transient thermal peaks. Sourcing specialists analyze this variable to select materials that can absorb or dissipate heat during these peaks.
Transient Behavior
Fluctuations in current demand produce corresponding spikes in thermal energy transfer that do not align with steady-state thermal models. During rapid acceleration, the internal cell temperature rises faster than the surface cooling can resolve, creating a high heat transfer rate through the interface. The peak heat flow occurs minutes after the electrical event is completed due to the thermal mass of the cell.
Understanding this delay is required for designing effective control algorithms for the cooling system, preventing thermal lag from causing localized overheating.
Measurement Technique
Calibrated heat flux sensors placed between the cell and the cooling plate measure the actual thermal transfer in real time. Engineers use this data to validate computational fluid dynamics models under dynamic driving profiles.
Thermal Protection
Transient thermal spikes require the thermal interface materials to possess high diffusivity to quickly route the heat to the cold plate. Phase change materials can absorb these transient loads by melting at a specific transition temperature. This absorption prevents the cell temperature from exceeding safety limits during brief periods of high power demand.
The selection of these materials directly impacts the safety and longevity of the battery system.
