THE INFLUENCE OF FLOW BLOCKAGE ON THE RATE OF PRESSURE RISE IN LARGE L/D CYLINDRICAL CLOSED VESSEL EXPLOSIONS

A quantitative determination was made of the influence of the blockage of a single baffle on the increase in the rate of pressure rise in a large length/diameter (L/D) ratio closed vessel explosion. A 76 mm diameter vessel with an L/D of 2 was used, and a four hole flat grid plate was used to simulate the shear layer size and turbulence levels of practical obstructions of complex shape. The maximum rate of pressure rise was investigated as a function of the baffle blockage and position, relative to the spark at the base of the vessel. The unburned gas set in motion ahead of the flame was measured by determining the differential pressure across the obstacle. This showed that mean velocities ahead of the flame were in the range 15-20 m s-1 upstream of the baffle, and were caused by the high flame speed, with maximum values up to 30 m s-1. These high velocities caused large turbulence levels to be created on interaction with the grid plate, depending on the grid plate blockage. Flame acceleration occurred once the flame reached the turbulence, and this acceleration was shown to be a function of the blockage. An approximate method for relating the increase in the rate of pressure rise to turbulent burning velocity measurements was developed, using a simple method of estimating the turbulence levels generated downstream of the obstacle. © 1990.