Tunnel systems can be simple or complex. The simplest case is a single-bore tube of uniform cross-section, typically with two tracks side by side. There are huge numbers of such tunnels in the world so this case is important despite its simplicity.
In addition to simple tunnels, ThermoTun can handle complex systems with hundreds of tunnel elements, each exhibiting variations in cross-sectional area, elevation and wall temperature. It is increasingly common to simulate tunnels with two or more train tubes, inter-connected by cross-passages, with or without safety doors.
The tunnel system may also include jet fans and/or shaft fans. These can be switched on and off as required, either in a prescribed manner or in response to changing conditions in the tunnel (e.g. increasing temperature, decreasing velocity) - see Control.
Account can be taken of differences between atmospheric conditions at the various tunnel and shaft portals.
ThermoTun is a one-dimensional program - see Theoretical Basis - so it should be used only for tunnels that fit this description. Most do, of course, but sufficiently short tunnels do not. In its standard form, ThermoTun is not suitable for simulating flows in tunnels whose length is only a few tunnel diameters. Happily, pressure disturbances are smaller in such tunnels than in longer ones so one-dimensional predictions are conservative. If your tunnel is very short, however, use an engineer as well as ThermoTun.
