Study on the flame shape of gas-solid jet diffusion

doi:10.11949/0438-1157.20201426

Abstract

Abstract:

This study investigates the flame geometrical features of the gas-solid jet diffusion flame (GSJDF). A new facility is designed and built using the Venturi effect, by which the jet diffusion flame can entrain the micron-sized solid particles at constantrate. The uniform white quartz sands of 147 μm and 178 μm in diameters were used for test, respectively. In particular, the gas jet diffusion flame (gas jet fire) formed by closing the side sand inlet is compared with it. Theoretical analysis and experimental result make sense that the addition of sand reduces the flame temperature, and then increases the flame height and the lift-off height by increasing the flame Froude number and decreasing the flame burning speed, respectively. The GSJDF of 147 μm sand has a higher flame height and lift-off height than that of 178 μm sand, for the total mass of 147 μm sand entrained into the flame is larger and so leads to a less flame temperature. In addition, the GSJDF holds a larger trend to produce the lift-off phenomena and a higher flame height than the jet diffusion flame, which also indicates the role of sand in the flame temperature reduction.

Key words: gas-solid mixtures, jet diffusion flame, flame temperature, lift-off height, flame height

摘要：

利用文丘里效应，自行设计气固射流扩散火焰（气固喷射火）实验装置，分别采用147 μm和178 μm两种粒径均匀的白色石英砂以近似恒定速率卷吸入火焰中，来研究固体颗粒对火焰形态的影响，特别地，通过关闭侧面进砂口所形成的气态射流扩散火焰（气态喷射火）与之相比较。理论分析和实验结果表明，砂子进入火焰中会降低火焰温度，并且粒径为147 μm的砂子进入火焰的质量大于178 μm砂子，导致小粒径气固喷射火具有更低的火焰温度，从而具有更低的层流燃烧速度和更大的火焰Froude数，最终使其具有更高的推举高度和火焰高度。对比分析气固喷射火和气态喷射火实验结果，也表明固体颗粒对火焰温度的冷却作用导致气固喷射火更容易产生推举现象并具有更高的火焰高度。

关键词: 气固混合物, 喷射火, 火焰温度, 火焰高度, 推举高度

CLC Number:

X 931

NIE Xuan, ZHOU Kuibin, WU Yueqiong, HUANG Mengyuan, JIANG Juncheng. Study on the flame shape of gas-solid jet diffusion[J]. CIESC Journal, 2021, 72(5): 2878-2886.

聂璇, 周魁斌, 吴月琼, 黄梦源, 蒋军成. 气固射流扩散火焰形态研究[J]. 化工学报, 2021, 72(5): 2878-2886.

Figures/Tables 13

Fig.1 Schematic diagram of the gas-solid jet diffusion flame (a) and sand entrainment process (b)

Table 1 Test conditions and experimental data summary

$d 0$ /μm	$m c$ /(g/s)	$m s$ /(g/s)	Fr_f	H/m	h/m
0	0.12~0.40	0	0.014~0.045	0.45~0.80	0
147	0.12~0.40	0.11~4.63	0.014~0.053	0.41~1.13	0~0.33
178	0.12~0.40	0.0~5.51	0.014~0.050	0.44~1.05	0~0.25

Table 1 Test conditions and experimental data summary

$d 0$ /μm	$m c$ /(g/s)	$m s$ /(g/s)	Fr_f	H/m	h/m
0	0.12~0.40	0	0.014~0.045	0.45~0.80	0
147	0.12~0.40	0.11~4.63	0.014~0.053	0.41~1.13	0~0.33
178	0.12~0.40	0.0~5.51	0.014~0.050	0.44~1.05	0~0.25

Fig.2 Variation of sand entrainment rate with gas mass flow rate

Fig.3 The test repeatability justified by the comparisons of parameters while size of sand is 147 μm

Fig.4 Schematic of the lift-off height appearance probability contour

Fig.5 Instantaneous images showing sand injection with a size of 178 μm

Fig.6 Typical experimental photos of gas-solid jet diffusion flame

Fig.7 Typical experimental photos of gas jet diffusion flame

Table 2 Characteristics of mixture[26]

物质	298 K下生成焓 $h ˉ 0 f$ / (kJ/mol)	比定压热容c_p/(kJ/(kg·K))
CH₄	-103847	—
CO₂	-393546	56.21
H₂O	-241845	43.87
N₂	0	33.71
O₂	0	—

Table 2 Characteristics of mixture[26]

物质	298 K下生成焓 $h ˉ 0 f$ / (kJ/mol)	比定压热容c_p/(kJ/(kg·K))
CH₄	-103847	—
CO₂	-393546	56.21
H₂O	-241845	43.87
N₂	0	33.71
O₂	0	—

Table 3 The influence of adiabatic flame temperature on laminar flame velocity calculated by Eq. (7)

状况	T_u/K	T_ad,g/K	S_L/S_L,A
A	300	2267	1
B	300	2100	0.69
C	300	2000	0.54
D	300	1900	0.41
E	300	1800	0.31
F	300	1700	0.22

Fig.8 Variation of lift-off height with propane mass flow rate for gas-solid jet diffusion flame

Fig.9 Variation of flame height with propane flow rate for gas-solid jet diffusion flame and jet diffusion flame

Table 4 The calculated physicochemical parameters of gas-solid jet diffusion flame

粒径/μm	m_s/(g/s)	L/m	$L - h L$	m_s,f / (g/s)	u_e,gs/ (m/s)	T_ad,gs/K	Fr_f
147	2.51	0.17	0.12	0.30	1.93	2061	0.033
	3.32	0.31	0.20	0.66	2.46	1930	0.044
	4.09	0.42	0.32	1.31	2.87	1766	0.054
	4.63	0.49	0.34	1.57	3.09	1727	0.059
178	4.97	0.24	0.14	0.69	2.17	1967	0.039
	5.51	0.29	0.16	0.90	2.38	1917	0.043

Table 4 The calculated physicochemical parameters of gas-solid jet diffusion flame

粒径/μm	m_s/(g/s)	L/m	$L - h L$	m_s,f / (g/s)	u_e,gs/ (m/s)	T_ad,gs/K	Fr_f
147	2.51	0.17	0.12	0.30	1.93	2061	0.033
	3.32	0.31	0.20	0.66	2.46	1930	0.044
	4.09	0.42	0.32	1.31	2.87	1766	0.054
	4.63	0.49	0.34	1.57	3.09	1727	0.059
178	4.97	0.24	0.14	0.69	2.17	1967	0.039
	5.51	0.29	0.16	0.90	2.38	1917	0.043

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