Although ThermoTun is primarily designed to simulate rapid events such as pressure waves generated during train-entry to a tunnel, it is also able to simulate the transport of pollution through the tunnel network. Indeed, it does this without significant numerical dispersion that bedevils most prediction methods.
Pollution sources can be prescribed at any location in the tunnel system and can be switched on and off as required. Allowance is made for variable rates of pollution.
Likewise, heat sources can be specified at any location and can be switched on and off. Their effects are in addition to heat transfers with the surrounding ground and with trains. Account is taken of the thermal capacitance of the trains, of the inefficiencies of their power units and of heat from braking systems and on-board services.
Fires are regarded as combined heat and pollution sources - so they, too, may be prescribed at any location and switched on at the desired time.
ThermoTun/6 can model the effects of large heat sources such as fire allowing for heat transfers with the tunnel wall and train wall due to both radiation and convection. The air density responds to changes in temperature as well as pressure so it is not necessary for users to make empirical allowances for so-called thermal blockage effects at fires (such techniques are sometimes employed when fires are simulated with software based on constant density analyses). As with all one-dimensional software, however, no account is taken of two- or three-dimensional phenomena such as stratification and back-layering.
Releases of ThermoTun up to v5.2 did not have the capability to modify large heat sources. They did, however, enable the simulation of moderate heat transfers between the air and the tunnel and train walls, based on convection alone. This was sufficient for many design purposes related to routine operation.
