Temperature Modes

Temperature is an input to this model, never an output. The tool does not solve an energy balance, so it does not know how hot the vented gas is. You tell it, in one of two ways.

The Two Modes

Mode	What it does	Needs
Assumed Constant	Gas temperature stays at Initial Temperature for the whole simulation	Nothing extra
Given Test Data	Gas temperature follows a curve you supply	A temperature against time CSV

Selecting Given Test Data reveals the upload control and greys out Initial Temperature, since the curve supplies that value instead. Switching back re-enables it.

Why It Matters

Temperature enters the governing equation twice.

\frac{dP}{dt} = \frac{P}{T} \frac{dT}{dt} + \frac{RT}{V} \frac{dn_{gen}}{dt} - \frac{PQ}{V}

In the first term, a changing temperature drives pressure directly. In Assumed Constant mode this term is exactly zero.

In the second term, the level of temperature scales how much pressure each mole of released gas produces. This term is active in both modes, which is why the constant you choose still matters even when nothing is changing.

The practical reading: gas released at 400 K produces roughly a third more pressure than the same gas at 300 K. The temperature you assume is not a detail.

Which Mode to Use

Use Assumed Constant when you are screening candidate valves, comparing options against each other, or working before pack level test data exists. It is the right default, and it is what all the tutorials use.

Use Given Test Data when you have thermocouple data from a pack level venting test and you are producing a number that has to match, or be defended against, that test.

The Constant Is Not Obviously Ambient

Leaving Initial Temperature at ambient is convenient, and it understates the peak whenever the vented gas is hot, which it always is. The model treats the pack gas as one well mixed volume, so the temperature you enter should represent the mixed gas, not the ejecta at the vent and not the cool air the pack started with.

Rather than agonise over one value, bracket it:

Run the case at ambient temperature.
Run it again at a plausible elevated mixed gas temperature.
Compare the peaks.

If the peak barely moves, the assumption is not carrying your result and you can proceed. If it moves a lot, you need real data before trusting the number, and you have just demonstrated to a reviewer why the test is necessary.

Supplying a Temperature Curve

File Format

A CSV with a header row and at least two data rows, holding time and temperature.

Time (s),Temperature (C)
0,25
10,48
20,85
30,130

Time can be seconds or minutes. Temperature can be °C, K, or °F, selected during the column mapping step after upload.

Validation Rules

Rule	Applies to
Strictly increasing, starting at 0 or more	Time column
Every value converts to a positive absolute temperature	Temperature column
Header row plus at least two data rows, all values finite	File
2 MB or smaller	File

Note what is not required: the temperature column does not have to be monotonic. Real gas temperature rises and falls during an event, and the tool accepts that. Only time has to march forward.

What the Curve Represents

The average temperature of the gas inside the pack, not the cell surface temperature and not the ejecta temperature at the vent orifice. These differ substantially, and using a cell surface trace in place of a gas trace will overstate the pressure.

Outside the Curve’s Range

If your simulation runs longer than the curve, the last temperature value is held flat for the remainder. Make sure the curve covers your whole simulation window, or shorten the window to match.