FIRE IN A ROOM - DEMONSTRATION CASE -

FOR: J. Palmer from NIST (National Institute of Standards and Technology).

1. Problem.


Geometrical considerations:

This case models a fire a a three dimensional room with one door and partitions. Supply and return vents are located below the ceiling. The room dimensions are 28'(length) by 21'(width) by 9.5'(height). The partitions are 6' high and 6" wide. The dimensions of the supply and return vents were 3'*1'.

Geometry.
 

Boundary conditions and sources:

The inflow through the supply vents is 0.5 kg/s, coming at a temperature of 15 degrees C, and the return vents extracts 0.4 kg/s.

The open door is set as fixed pressure boundary condition (relative to hydrostatic). The temperature of air entering form outside is also set to 15 degrees C.

The fire was modelled as heat source, uniformly distributed over a volume (30cm*30cm*30cm), releasing 70 kW.

Flow considerations:

The flow was simulated as turbulent using the 2-equation k-epsilon model.

Buoyancy was taken into account using the Boussinesq approximation.

2. Results.

Velocity
 
 
 
• Velocity vectors at height of 0.7 metres from the floor: this  figure shows the important recirculation near the fire location.

• Magnification of the velocity vectors near the fire: A   magnification of the previous picture showing that the recirculation is 3-dimensional: The hot air released by the fire is going upward at a high speed leaving a zone of low pressure sucking air from the room outside.

• Velocity vectors at vents height: This figure shows the velocity vectors in a horizontal plane across the vents showing the inflow through the supply, and outflow though the return and through the door.
Temperature

The temperature contour scale has been set to 15-150 degrees C, to enable variations within the room to be viewed. The red band also includes temperatures above 150 degrees C, up to a maximum of 500 degrees C in the fire.

Temperature contours are given at different height if the room, showing the average temperature in the plane increasing with the height, and also the peak of temperature above the fire.
 
 

 
• Temperature contours at 0.8 meters.
• Temperature contours at 1.2 metres.
• Temperature contour at 2.0 metres.
• Temperature contours at 2.4 metres.
• Temperature contours in a cross section showing the fire.

Pressure
 
 
 
• Pressure contours at 0.7 metres (same plane as the velocity vectors above). It shows the low pressure mentioned in the comments on velocity.

• Pressure under the ceiling. The maximum of pressure is located just below the ceiling and above the fire. The hot air is driven upward until it hits the ceiling, losing its speed and resulting in a peak of (stagnation) pressure.