When the background pressure was calculated the injected air entered on one side of the zone and immediately vented out to the atmosphere on the other side. In the above example, only one (default) pressure zone was defined, so it included both compartments with both the air injection and open vents. The background pressure is calculated for each pressure zone, while the perturbation pressure varies spatially. The background pressure is typically just a hydrostatic pressure and the perturbation pressure is induced by the flow (see Chapter 9 of the FDS User Guide). The reason for this is that FDS separates the total pressure into a “background” component and a perturbation (see Chapter 3 of the FDS Technical Reference Guide). In the Figure 1 model, although the obstruction separates the room, air flow into the room does not raise the pressure. The surprising result is that even though air is being injected into the model, the pressure in both compartments remains constant at atmospheric pressure. You likely expect that as air flows into the left compartment, the pressure will increase since the obstruction blocks flow out of the room. There are two pressure monitors and the default boundary surfaces are INERT. The compartment on the left has an inlet vent and the one on the right has a vent that is open to the atmosphere. Our model is a 10 m cube room, with an obstruction that completely separates the room into two compartments.
Modeling a Pressure Relief Ventįirst we look at Figure 1, a model that is not correct.
This tutorial will guide you through the steps required to model this type of vent. The key is to include at least two pressure zones in your model. This model requires some extra steps that might not be obvious. Let us solve the problem of a pressure relief vent where air is injected into a room, the pressure in the room is monitored, and a vent is opened when a set pressure is reached. Created with software version: 2020.1 Table of Contents
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