Study On Merging Mechanism And Flame Height Evolution Of Two Interacting Slot-burner Buoyant Turbulent Jets

In recent years,with the development of our country's economy and technology,an enhancing in People Oriented idea and environmental consciousness has changed the configuration of energy resource.Gaseous energy is stepping into our daily life as an irresistible gesture because of its convenience to transport as well as clean and efficiency.Nevertheless,for many reasons,many fires and explosions often occur along the long gas pipelines.Those disasters damage people's life and property security greatly.Generally,fires caused by the breakage in the high pressure pipeline with a high blown-out velocity can be approximately taken as slot-burner diffusion jet fires.When pipelines are broken in many place,the flames can be stretched and deflected from the vertical due to the interaction between those flames.This may result in the formation of a fire whirlwind.The merging of group fires makes the fire more destructive and uncontrolled.Therefore,it is of great significance to study the interactions of jet fires to prevent flame merging from becoming a major cause of an uncontrolled fire.Numerous works have been conducted on the characteristics of multi-flame interactions.However,most of them mainly focused on the axisymmetric flames to investigate the effects of fuel type,diffusion-flame type,the number and distribution of burners,and the various burner pitch.While,the study on the interaction of slot-burner diffusion flames is relatively rarer.Although there have been reports on the interaction of slot-burner laminar diffusion flames,the interaction of slot-burner buoyant turbulent diffusion flames has not been studied yet.The air entrainment mechanism of a turbulent diffusion flame is essentially different from that of the laminar diffusion flames.So,it is necessary to study the interactions of multiple slot-burner buoyant turbulent diffusion flames.This dissertation carried out a series of experiments to explore flame merging mechanism and flame height evolution characteristics of two slot-burner buoyant turbulent diffusion flames.The experiment was conducted with two identical slot burners employed.The internal size of burners was 2mm × 142.5mm.The burners were located with its bottom being 0.4 m above the ground.Propane was used as the fuel and the fuel exit velocities varied from 0.23m/s to 0.70m/s.The flames here are buoyancy-controlled and turbulent based on the calculated Fr and Gr.Burner pitch ranges from 0 to 1 m.The experimental results show that with the increase of the burner pitch,the two flames show four merging behaviors:continuous merging zone,intermittent merging zone,non-merging with interaction and non-merging with no interaction.It is noted that when the two flames are merged,the flame height is much higher than that of a single free flame at the same fuel exit velocity.At the same time,the flame height decreases first,then increases and eventually approaches a single free flame height with increasing burner pitch.It is a complex,non-monotonic process,which is different from the observation in the laminar flame case.What's more,it was found that the lowest flame height happens at nearly the critical burner pitch,and the flame height is lower than the single free flame height.This dissertation extended the model of critical burner pitch derived from laminar flame by Kuwana et al.to the turbulent diffusion flame.And also we developed correlations of the flame merging probability and the critical burner pitch.The flame merging probability can be expressed as a piecewise function into three regimes.The critical burner pitch is found to be scaled(proportional to)the flame height of a single free flame,or have a 2/3 power dependence on the fuel exit velocity.The flame merging height normalized by flame height is shown to be well fitted by an exponential function with normalized burner pitch."Effective" entrainment perimeter is proposed as a characteristic length to quantify air entrainment mechanism of the two interacting two slot-burner buoyant turbulent flames,including the burner width and length as well as the flame base "extension".The obtained flame heights at various burner pitches are shown to be well correlated based on the proposed effective" entrainment perimeter.