A high velocity jet fire can cause catastrophic failure due to flame impingement or radiation. The scenario becomes more complicated when multiple jet fires exist following ignition of release from pressure relief valves as the thermal effect not only distorts the individual jet flame but also changes the flame height and temperature profile and such kind of high velocity jet flames have not been studied in the past. Therefore, prediction of the flame shape including the merging and interaction of multiple jet fires is essential in risk analysis. In this study, fire interaction of two high velocity (>10 m/s) jet fires was investigated using computational fluid dynamics techniques and experimental approach. Different radiation models were analyzed and validated by experimental data from the literature. Based on the simulation and experimental results, the merging of high velocity jet fires is divided into three main stages. Empirical equations considering the fire interaction for the average flame height, persistent flame height and temperature distribution with different release velocities and separation distances were developed. The flame height increases dramatically when the separation distance decreases due to a shortage of oxygen supply. So, part of the methane reacts in a higher height which explains the change in the merging height and temperature. The temperature distribution at the centreline between two releases is changed according to the locations of persistent and intermittent regions and the locations can be identified by flame heights. The investigation of thermal radiation revealed that the maximum radiative heat flux received by structure is the highest under a critical separation distance, which is at the beginning of stage 3. The effect of flame merging in flame height is still valid for the flame length under wind effect but not for the thermal radiation as wind is the dominate factor for heat transfer.
(Supervisor: Prof. Christopher Chao)