Glossary

Definitions as this tool uses them. Some of these words carry broader meanings elsewhere in battery engineering.

Grouped by what they describe rather than alphabetically, since most of them only make sense next to their neighbours. Terms are alphabetical within each group, and the site search will find any of them directly.

The Event

Cell safety vent. The rupture element on the cell casing itself, which opens once and stays open, releasing gas into the pack. Not the device you are sizing here. Its behaviour is already contained in the venting curve you supply.

Cumulative gas moles. The running total of gas released, as opposed to the rate of release. Venting curves are supplied cumulatively, so they never decrease.

Thermal propagation. Thermal runaway spreading from one cell to its neighbours. Determines how many cells vent, which you enter as Number of Venting Cells.

Thermal runaway, TR. The self-sustaining chain of exothermic reactions in a cell that cannot be arrested by cooling, and which releases the gas this tool is concerned with.

Venting curve. Cumulative gas moles released by a single cell against time. The primary input driving the whole calculation.

The Pack

Ambient pressure. Pressure outside the pack. The reference the valve’s differential pressure is measured against, and the floor the model does not let pack pressure fall below.

Control volume. The single well mixed region of gas the model tracks, namely everything inside the enclosure that is not solid.

Differential pressure. The pressure difference across the valve, that is, pack pressure minus ambient. Valve flow curves are plotted against it, and opening pressures are quoted in it.

Enclosure, or pack housing. The sealed structure the cells and modules sit in, and the boundary the model draws its control volume at. Both names are in common use for the same part. This documentation says enclosure throughout, and what that structure can withstand is what you enter as Max Pressure Limit.

Max Pressure Limit. The pressure your enclosure can withstand, relative to ambient, entered by you. It is a pass or fail threshold, not a simulation input, and it does not affect the computed pressure.

Void volume. The free gas volume inside the sealed enclosure, with cells, modules, cooling plates, and other solids subtracted. Not the enclosure’s outer volume.

The Valve

Burst disc. A one-time relief element that ruptures at a set pressure and stays open. Behaves as Membrane in this tool.

Hysteresis. The gap between a spring valve’s opening pressure and its closing pressure. It follows from the force balance on the plug, and it is why a spring valve can vent intermittently. See PRV Behaviour.

Membrane. In this tool, a valve type that opens once and cannot reclose. Covers burst discs and pin-pierced diaphragms.

Opening pressure, or setpoint. The differential pressure at which the valve opens. A property of the part, fixed by its manufacturer.

P–Q curve. Pressure to flow curve. The relationship between differential pressure across the valve and volumetric flow through it. Every valve here carries two: one for the closed state, one for the open state.

Pressure relief valve, PRV. The device on the enclosure wall that opens above a setpoint to release gas. The subject of this tool. Also called a safety valve, and listed as an explosion-proof valve in some supplier catalogues. Note that explosion-proof has a separate, formal meaning in electrical equipment certification, where it describes an enclosure rating rather than a relief device.

Spring. In this tool, a valve type that recloses when pressure falls back below its closing threshold.

The Model

Ideal gas law. P·V = n·R·T. The equation of state the model uses to relate pressure, volume, gas quantity, and temperature.

Lumped parameter model. A model that treats a region as a single point with no internal spatial variation. Here it means one pressure and one temperature everywhere inside the pack.

Quasi-static. The assumption that the gas reaches equilibrium within each instant, which is what allows an equilibrium equation of state to describe a transient event.

The Results

Absolute peak pressure. The highest pressure reached inside the pack, measured from vacuum, including atmospheric pressure. Compare relative peak pressure.

First open time. When pack pressure first crossed the valve’s opening threshold, in seconds from the start of the simulation.

Relative peak pressure. The peak measured from ambient rather than from vacuum. The figure to compare against enclosure ratings, since those describe a differential across the wall.

Valve status. A 0 or 1 series in the results indicating whether the valve was closed or open at each instant.