Large-Scale Particle Image Velocimetry Measurements of a Fire-Induced Doorway Flow

摘要

Quantifying the ventilation available to a room fire is an important step to understanding fire behavior. The fresh air that moves into an enclosure provides the oxygen necessary to support the combustion while also serving to moderate the temperature of the compartment. The hot fire gases that move out of an enclosure transfer heat and combustion products from the localized point of the fire to remote locations within a built structure. Mass flow rate is the parameter typically used to quantify the ventilation for a fire within a room. Due to the three dimensional nature of flow through vents, a full mapping of the velocity and density fields is necessary to determine the mass flow rate. Early treatments quantifying fire induced flow through vents relied on Bernoulli's equation and a hydraulics-orifice approach, therefore only a few well placed pressure and temperature measurements were required. Later treatments were improved by adding vertical arrays of pressure and temperature measurements and scanning them across the vents in order to address the three dimensional nature of the flows. In order to perform a more complete characterization of the fire-induced velocity field in a vent, non-intrusive and planar measurement techniques such as Particle Image Velocimetry (PIV) may be applied to measure the velocity vector field across the plane of a doorway. The dimensional scale of the flow field in a full-scale doorway of a room presents many challenges for PIV measurements. Challenges such as optical signal and particle selection were addressed for a reduced-scale experiment. Following the lessons learned from the reduced-scale experiment, large-scale PIV measurements of a fire-induced doorway flow were successfully demonstrated in a full-scale fire experiment. Stereoscopic PIV measurements were conducted in the doorway of an ISO 9705 room to measure the flow into the room. Simultaneous temperature and differential pressure measurements were conducted on the vertical centerline using the types of thermocouples and pressure probes typical of fire tests. The independent measurements of the velocity field will be compared.