Stress distribution in a packed bed above raceway cavities formed by an air jet

The vertical stress profile in a packed bed above the cavities formed by an upward, high‐velocity air jet is estimated from a force balance analysis and static pressure measurements. The objective is to understand and determine the forces responsible for maintaining the cavity roof. Such cavities, formed in an iron blast furnace, adjacent to the hot air blast emanating from the tuyere pipes, are called raceways. A net upward force provided by the gas pressure drag and the support from the bed walls holds the raceway roof in its position. Abrupt changes in the stress and the gas velocity are observed near the roof. The zero vertical stress is also found close above the roof but fluctuates vertically with the raceway size, which varies irreversibly following a cyclic change in the blast rate.