explosive hazards in residential buildings.
Almost every house in the Netherlands is linked to the natural gas network. This rises the explosion hazard, which is why a risk assessment is done on the explosion risks of gas leakages. For this, a computational fluid simulation was done, where the air and gas flow through the house were simulated. A mechanical venting system was tested, along with the porosity of the walls. It was shown that after a minute, an explosive mixture spreads over the ground floor. However, sensors would already be triggered after a couple of seconds. The simulation is a useful tool in designing houses on gas safety and can be used to determine gas sensor placement.
Simulating a gas leak
The geometry and setup of the house is shown in the figure on the right. For this simulation, we used a ventilation flowrate of 50m³/hr and a leakage flowrate of 500 l/h. The air is sucked from both rooms through natural ventilation, therefore the walls are simulated as being slightly permeable, and through a ventilation duct. The typical average permeability is a material property of the wall derived from material data sheets.
To ensure a numerical convergence, the simulation is executed in three steps:
1. Steady state air only: In this simulation there are no volume fractions of natural gas in the air present. With this, a first estimation can be made for the velocity and pressure fields. These are needed as initial condition in step 2. Time dependent effects are not taken into account, which means that the fluid field is for a steady state situation.
2. Steady state gas leak: The leak is a natural gas leak, but time dependent effects are not taken into account yet. With use of the velocity and pressure fields we can solve the concentration through the entire numerical domain.
3. Time-dependent gas leak: In this step the time dependent steps are calculated. The velocity is used as an initial condition and will not be recalculated. The initial natural gas concentration is zero everywhere.
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