Examination of entrainment, combustibility, and heat transfer due to cell venting inside simplified battery energy storage enclosures
Battery energy storage systems (ESS) assembled of modules containing lithium-ion batteries can pose fire and explosion hazards during thermal runaway because vented gases may accumulate, combust, or escape enclosures. Here, we propose a prototypical configuration composed of the main components of an ESS rack, where modules are represented as rectangles within an enclosure and vent gas is injected steadily through the top of a module. This idealized geometry allows for exploration of how rack-level characteristics can influence smaller single-cell or module-level scales. Through this geometry, we conduct numerical simulations to understand how variations in the vent velocity, temperature, and vertical location affect entrainment rates, fraction of uncombusted fuel, rich-gas coverage, and heat flux to other modules. At lower vent velocities and vertical positions, buoyancy drives enough entrainment and mixing to react with most of the vent gases on the converging plenum. As jet momentum increases and/or buoyancy decreases via higher vent position in the rack, vent gases can propagate into and burn in the divergence plenum. Heat flux to the impinged module scales strongly with vent momentum and temperature, while heat transfer to upper modules peaks when flames in the diverging plenum reach the surface and declines when combustion is suppressed.