Behavior And Thermal Analysis Of Horizontal Spilling Fire Spread Over Steady N-Butanol Fuel

Since the 21st century,with the great development of China's economy,the national demand for oil is increasing,and the oil strategic reserves level is also increasing.However,the oil leakage incidents frequently occur during the production,transportation,storage and usage of oil products.After the fuel leaks,it finally diffuses over a large area.The spilling fire is subsequently induced once the flowing fuels are ignited.Owing to the flowing characteristics,the damage and contamination area caused by the spilling fire are relatively larger,and the rapid spred of spilling fire puts a great threat to the surrounding facilities and people.Therefore,further study on the behavior and heat transfer mechanism of spilling fire spread will have great practical value for the prevention of spilling fire.A small-scale test platform on horizontal spilling fire was designed to accurately analyze the behavior of spilling fire,hydrodynamic characteristics and heat transfer mechanism.An abundant of horizontal spilling fire experiments were conducted by changing the flow speed,spreading direction of n-butanol and thermal conductivity of the substrate.The characteristics of spilling fire spread and heat transfer were analyzed.Two digital cameras were used to monitor the top and lateral view of spilling fire in real time.The flame images were processed and calculated to obtain dynamic parameters such as flame height,flame pulsation frequency,and velocity of spilling fire.Besides,infrared imager and thermocouples were used to measure the temperature near the oil surface,which provided fundamental data for analyzing the heat transfer process.The details are as follows:The research reveals the kinetic characteristics of horizontal diffusion of unburned n-butanol fuel.The horizontal diffusion process of n-butanol fuel is divided into the unstabilized early diffusion stage and the stabilized steady flow stage.The oil film in the early diffusion process is analyzed mechanically and it is found that the oil film is mainly affected by gravity,inertial force,surface tension and frictional resistance.It mainly experiences the"gravity-inertia"diffusion stage and the"gravity-viscous"diffusion stage.The flow model of steady flow liquid fuel was established,and it is found that the discharge rate and flow speed of n-butanol fuel satisfies the power function relationship,and the flow speed and the square root of layer thickness for n-butanol fuel satisfy the linear relationship.The research reveals dynamic characteristics of horizontal spilling fire spread over steady flow n-butanol fuel.The parameters like flame height,flame pulsation frequency,the velocity of spilling fire,and the relative velocity of spilling fire?V_f-u?were used to revealed the dynamic characteristics of steady-flow spilling fires.According to the effect of the flow speed and flow direction at different stages,it can be divided into four stages.As the flow speed increases,the opposed-flow spilling fire can be divided into:???retardation stage;???non-spreading stage;the concurrent-flow spilling fire can be divided into:? ??acceleration stage;???detachment stage.In opposed flow,the flame height remains constant as the flow speed of n-butanol fuel increases.In concurrent flow,the flame height decreases with the increase of flow speed for the? ??and???stages.Whether it is in opposed or concurrent flow,the spilling flame pulsates forward in an alternating manner of"jumping","receding"and"crawling".The research reveals the influence of heat dissipation from substrate on the velocity of spilling fire over horizontal steady flow n-butanol fuel.The axial temperature distribution and longitudinal temperature distribution of the oil surface were analyzed.According to the characteristics of temperature profile and velocity of spilling fire,the concurrent-flow spilling fire over horizontal steady flow n-butanol fuel can be divided into two stages:When discharge rate Q?141.5 ml/min,it can be called the low-discharge rate heat transfer dominant stage;when Q>141.5 ml/min,it can be called the high-discharge rate forced flow dominant stage.The low-discharge rate spilling fire spread depends on the coupled effects of the subsurface flow preheating and intrinsic dragging of flowing fuel,whereas the high-discharge rate concurrent spilling fire depends mainly on the dragging effect from the liquid surface non-slip boundary layer.The spilling fire spread experiments on the substrates with different thermal conductivities?thermal conductivity:stainless steel<brass<aluminum alloy?were conducted,which shows that,in the low-discharge rate stage,no matter whether it is in the opposed or concurrent flow,the velocity of spilling fire on the stainless steel is the fastest,followed by brass,and the velocity of spilling fire on the aluminum alloy is the slowest.This means that the velocity of spilling fire decreases with the increase of thermal conductivity of the substrate.In addition,the dimensionless velocity(u_x-u_alu)/u_alu decreases with the increase of discharge rate.At the stage of high-discharge rate,only in concurrent flow,the flame can spread,and the velocity of spilling fire is independent of the substrate.This means as the discharge rate increases,the effect of heat dissipation from the substrate is gradually weakened,and the effect of forced flow is gradually increased.The subsurface flow heat transfer model of horizontal spilling fire spread over steady flow n-butanol fuel was established.The research reveals that the subsurface flow length increases with the increase of the discharge rate whether it is in concurrent flow or opposed flow.In the oncurrent flow,the subsurface flow speed increases with the increase of discharge rate.However,in opposed flow,it decreases with the increase of discharge rate.The heat transfer model of the subsurface flow for spilling fire spread over steady flow n-butanol was established.The total heat flux inside the subsurface flow,the sensible heat of liquid temperature rise and the heat dissipation from substrate were quantitatively calculated.For small-scale spilling fire,the latent heat of liquid fuel evaporation is negligible.The calculation proves that the sum of sensible heat and convective heat loss accounts for more than 80%of the total heat flux inside the subsurface flow.