Parametric and thermal analysis of horizontal jet flames

Abstract

Jet fire occurrence in an industrial installation can be severe as it can trigger a series of related events. The main hazard associated with jet fire occurrence is the heat released by radiation, which can be very high at a very short distance. The evaluation of jet flame geometry could assist the safety officer to prevent flame impingement on the nearby equipment and therefore, reduce the inventory losses and structural collapse. Previous observation indicates that the horizontal jet fire poses more significant thermal hazards as compared to that of other types of fire. However, to date, scarce and limited data are available as a reference on a jet flame for horizontal orientation, particularly for parametric characteristics and correlation model development. Thus, this study aims to investigate the thermal radiation and geometrical flame features of buoyant horizontal jet fires. Two scenarios were considered for this work i.e. free jet fires and jet fire impingement. This study used propane as the fuel that was released from a circular nozzle with a diameter of 7.15 mm and 9.8 mm. The jet fire tests were performed with different ranges of flow rates between 30 – 600 g/min at a release distance of 0.8 m and 1.2 m. Differences in flame shapes are evaluated with the use of the MATLAB. Meanwhile, linear correlations of the main geometrical parameters of interest are determined as a function of Reynolds number and Froude number (i.e. lift-off distance, projected flame length, flame height, flame trajectory, flame width). For thermal radiation analysis measurement, semi-empirical model prediction of the line-source (LSM) model was adopted to account the flame geometrical features. From the findings, it was found that the lift-off length, Lf estimation from this work was in a good agreement with Bradley’s correlation for both free and impinging jet release with R2 of 0.95. Due to the flame Froude number value is between 0.8 to 3.5, it signifies that the flame is controlled by buoyancy and momentum, thus flame trajectory, Lt was proposed to be used to estimate the radiant heat release. Using the flame trajectory, Lt for radiant heat estimation, it was observed that Lt could give a better prediction of radiant heat release for free jet fire release with R2 of 0.99 as compared to projected flame length, Lp (horizontal kite flame shape) (R2 = 0.94). It also gave consistent results with the measured data for an impinging jet release with R2=0.99 for all release scenario, using a similar approach. It can be deduced that the modified LSM using the flame trajectory parameter is a reliable method for radiant heat prediction, on both scenario in this work; free jet release and impinging jet. Implicitly, it can be suggested that the applicability of LSM becomes wider to include the effects of buoyancy and impingement scenario. Furthermore, it offers additional provision to determine the minimum spacing distance of the equipment sitting for the plant layout.