Flame behavior of jet fire confined by the tank wall

doi:10.11949/0438-1157.20201574

Abstract

Abstract:

Leakage of high-pressure gas storage tanks is very easy to induce jet fire. By building a jet fire experiment device with different jet angles under the restriction of the tank wall, the jet fire with restricted flow field near the nozzle was systematically studied, and the test repeatability of the device was verified. Experimental results show that the lift-off height of confined jet fire is less than that of the free jet. Numerical simulation confirms the effect of tank wall on the air entrainment that dominates the lift-off. The flame length of vertical free jet is less than that of vertical confined jet, but the flame length decreases with the increase of the inclined angle for both free and confined jet fires. The critical Froude number to distinguish the buoyancy and momentum-dominated jet fire, is constant despite the jet angle and the restriction condition of space. The study also found that the blocking effect of tank wall will reduce the liftoff velocity and increase the blowout velocity of the jet flame, as compared to the free jet.

Key words: jet angle, jet flame, lift-off height, flame length, tank wall, safety, instability, fluid mechanics

摘要：

高压燃气储罐泄漏极易诱发喷射火。通过搭建储罐壁面限制条件下不同喷射角度的喷射火实验装置，对近喷口流场受限的喷射火进行了系统研究，并验证了装置测试的可重复性。实验结果表明，储罐壁面限制条件下推举高度小于自由射流的推举高度，并通过数值模拟分析了两种空间条件下空气卷吸流场的差异性，从而物理解释了储罐壁面限制条件对推举高度的影响。两种空间条件下火焰长度都随喷射角度的增加而减小，但自由垂直射流的火焰长度小于储罐壁面限制条件下的火焰长度。火焰行为由浮力控制转为动量控制的临界Froude数与喷射角度和空间限制条件无关。研究还发现，与自由射流相比，储罐壁面的阻塞效应会降低火焰的推举速度，提高火焰的吹熄速度。

关键词: 喷射角度, 喷射火, 推举高度, 火焰长度, 储罐壁面, 安全, 不稳定性, 流体力学

CLC Number:

X 931

WU Yueqiong, ZHOU Kuibin, HUANG Mengyuan, ZHOU Mengya. Flame behavior of jet fire confined by the tank wall[J]. CIESC Journal, 2021, 72(5): 2896-2904.

吴月琼, 周魁斌, 黄梦源, 周梦雅. 储罐壁面限制条件下喷射火火焰行为[J]. 化工学报, 2021, 72(5): 2896-2904.

Figures/Tables 16

Fig.1 Schematic diagram of experimental setup

Table 1 Experimental conditions

倾斜角度θ /(°)	流速U_e/(m/s)	Fr= $U e 2$ /(gd)
0	8.96~75.45	2.7×10³~1.9×10⁵
30	8.49~75.45	2.5×10³~1.9×10⁵
45	8.72~75.45	2.6×10³~1.9×10⁵
60	8.25~75.45	2.3×10³~1.9×10⁵

Table 1 Experimental conditions

倾斜角度θ /(°)	流速U_e/(m/s)	Fr= $U e 2$ /(gd)
0	8.96~75.45	2.7×10³~1.9×10⁵
30	8.49~75.45	2.5×10³~1.9×10⁵
45	8.72~75.45	2.6×10³~1.9×10⁵
60	8.25~75.45	2.3×10³~1.9×10⁵

Fig.2 Flame length measurements under the exit velocity of 56.69 m/s

Fig.4 Schematic diagram of 2D geometric model

Fig.3 Test repeatability justified by the comparison of two repeatable tests under the jet angle of 0° and the exit velocity of 56.69 m/s

Fig.5 Velocity vector field near the exit under the jet angle of 45° and the exit velocity of 18.86 m/s

Fig.6 Lift-off height versus the exit velocity of different jet angles

Fig.7 Air entrainment rate versus vertical height under the exit velocity of 18.86 m/s

Fig.8 Variation of dimensionless lift-off height with dimensionless exit velocity for different jet angles

Fig.9 Variation of flame length with exit velocity for different jet angles under the tank wall restriction

Fig.10 Comparison of flame length between free and confined jets

Fig.11 Variation of dimensionless flame length with nozzle exit Froude number for different jet angles

Fig.13 Liftoff velocity ratio of confined jet to free jet versus the jet angle

Fig.12 Typical photos of attached flame, lifted flame and flame to reach blowout under the jet angle of 0°

Fig.14 Blowout velocity versus the jet angle

Fig.15 Blowout and quench boundary of propane jet flame（vertical dashed line indicates the critical pressure ratio condition）

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