Two Dimensional Rack Storage Fires

Abstract

Flame heights and air flows in a two dimensional rack storage were investigated. The width of the vertical flue is found to be the predominant geometrical parameter controlling the flue flow. The mass flow rate increases nearly linearly with the width. Variation of the horizontal flue heights was found to have negligible effects on the vertical flue flow. For a certain vertical flue width, the mass flow rate is found to be nearly constant independent of the heat output. Experimental results indicate a linear relationship between the flame height and the ratio of heat output to the vertical flue width. A ratio of entrained air to the stoichiometric air requirements at the flame tip is found to be 7.5. Experiments were carried out using inert boxes and a diffusion propane line burner located at the bottom of the rack. The rack was 0.59 m long and between 1.14 m and 1.34 m in height (4 boxes). The size of the rack is about 113 of what can be expected in a real rack storage. NOMENCLATURE Cp specific heat (kJ/kg K) g gravitational acceleration (m/s2) H height of horizontal flue (m) AH, heat of combustion (Wg) h height of rack storage (m) KL entrance loss coefficient L two dimensional length (m) Lf mean height of the flame tip (m) Lffie, mean height of the flame tip for a free-burning line burner (m) m air mass flow rate (kgls) fuel flow rate (kgls) &I f total heat output from burner (kW) Q, convective heat output from burner (kW) Q ' heat output per metre of burner (kW1m) ambient temperature ("C) mean gas temperature within a flue ("C) mean temperature rise above ambient ("C) mean "cold" velocity in a stack (mls) mean velocity within a flue (m/s) width of the vertical flue (m) height from floor (m) height of virtual origin (m) ambient density (kglm3) density within a flue (kg/m3) ratio of entrained air to stoichiometric air requirements