Investigation of the length-to-diameter ratio of ducts effect on the oscillation propagation behavior and vented characteristics for propane-air vented explosions

The effects of length-to-diameter (L/D) ratio on oscillation propagation behavior and vented characteristics of propane explosions have been explored in a rectangular explosion duct. The results show that as the L/D ratio increased, the turbulence of the internal flame was enhanced, and the flame area and gas reaction rate increased sharply, which promoted the appearance of the Mach diamond structure in the vented flame. Due to heat and energy loss, the maximum reduced pressure (Pred) decreased with the increase of L/D ratio, but the maximum pressure rise rate ((dp/dt)max) and the deflagration index (KG) still increased significantly. Besides, the venting diameter (Dv) where the maximum external pressure was obtained increased with the L/D ratio, and the critical venting diameters of the vented propane-air explosions to reach the equilibrium venting state under different L/D ratios were determined. An empirically modified model of Pred was established by introducing the L/D ratio and vent coefficient KV, and the maximum relative error of this model is 137% lower than that of the international standard model. The excellent performance of the results would provide a new idea for the venting safety design of the large L/D ratio duct in process industry applications.