Flame height: Effect of one- and two-sided boundary surfaces
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Theory suggests that fires placed flush to one- and two-sided boundary surfaces will have an increase in flame height independent of fuel used and size of the fire. Meaning the flame height will increase when flush to a wall and corner for gaseous and liquid fires in small- and large-scale fires. It is published equations to calculate the mean flame height which are based on previous fire experiments . This thesis investigates the behavior of fire conducted in small- and medium scale experiments with three different configurations: open fire, one- and two-sided boundaries. Fires with energy release rate ranging from 6.33 kW to 114 kW using different width square pans. The experiments were carried out to investigate the effect of the three configurations with different sized fires, with regard on the flame height and to see if these configurations had a different outcome when using two different fuels, propane gas and liquid heptane. There were conducted 45 medium scale experiments and 18 small-scale experiments to provide a range of data to compare. It is used dimensionless analysis to determine the relationship for flame height and intermittency for buoyant diffusion flames for the three configurations. For a sequence of photos, the flame height was determined by visualization. The experimental results show that the flame height does change when exposed to different boundaries, but not to the extent that was expected. It is shown that the increase in flame height is different for gaseous and liquid fires, as well the size of the fire. Based on the presented data in this thesis a simple model for predicting the effect of one- and two-sided boundaries on the mean flame height are presented by using Heskestad’s approach to estimate the dimensionless mean flame height . The increase in flame height is between 10 to 40 % for propane fires when placed next to a one-sided boundary, and 80 to 100 % when placed next to a two-sided boundary. For the heptane fires the increase was higher than the propane fires, giving between 70 to 100 % increase in flame height when placed next to a one-sided boundary, and between 200 and 400 % when placed next to a two-sided boundary.
WESTERN NORWAY UNIVERSITY OF APPLIED SCIENCES, Master Thesis in Fire Safety Engineering, Haugesund