Critical mechanical pressure rise for preventing buoyancy-dominated flow pattern in inclined tunnel fire with longitudinal ventilation

doi:10.16265/j.cnki.issn1003-3033.2022.05.0938

Abstract

Abstract:

In order to prevent uncertainly of smoke flow in inclined tunnel fire with longitudinal ventilation, firstly, a theoretical model of critical fan-induced pressure corresponded to only existence of buoyancy-dominated flow pattern P_j_,min and only existence of fan-dominated flow pattern P_j_,max was proposed through potential function analysis. Then, small-scale experiments were carried out to validate the model's scientificity and effectiveness, and the magnitude of P_j_,c, which met critical velocity, were compared with the above P_j_,min and P_j_,max. The results show that P_j_,max is always larger than P_j_,c. If P_j_,c is adopted in a longitudinally ventilated inclined tunnel, there are two possible flow patterns caused by different fan activation time, one is the pattern that critical velocity is achieved and all of the smoke is exhausted downward, while the other is that buoyancy overwhelms fan-induced pressure rise, and thus part of smoke spreads upstream. If P_j_,max is adopted, effective longitudinal ventilation can be finally achieved under any fan activation time.

Key words: inclined tunnel fire, smoke flow, buoyancy-dominated flow pattern, critical fan-induced pressure rise, small-scale experiment, fan-dominated flow pattern

YANG Dong, LI Ping. Critical mechanical pressure rise for preventing buoyancy-dominated flow pattern in inclined tunnel fire with longitudinal ventilation[J]. China Safety Science Journal, 2022, 32(5): 41-47.

Figures/Tables 10

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References 13

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工况	火源位置	模型火源功率/ kW	风机开启时间/s	上游入口处风速/ (m·s^-1)	上游入口处静压值/Pa	工况	火源位置	模型火源功率/ kW	风机开启时间/s	上游入口处风速/ (m·s^-1)	上游入口处静压值/Pa
1	A	0.833	0	0.40	0	19	B	1.190	0	0.85	0.1
2	A	0.833	600	0.40	0	20	B	1.190	600	0.85	0.1
3	A	0.833	0	0.80	0.1	21	B	1.488	0	0.82	0.1
4	A	0.833	600	0.80	0.1	22	B	1.488	600	0.82	0.1
5	A	1.190	0	0.44	0	23	B	1.488	0	0.98	0.2
6	A	1.190	600	0.44	0	24	B	1.488	600	0.98	0.2
7	A	1.190	0	0.85	0.1	25	C	0.833	0	0.72	0
8	A	1.190	600	0.85	0.1	26	C	0.833	600	0.72	0
9	A	1.488	0	0.47	0	27	C	0.833	0	0.80	0.1
10	A	1.488	600	0.47	0	28	C	0.833	600	0.80	0.1
11	A	1.488	0	0.95	0.1	29	C	1.190	0	0.86	0.1
12	A	1.488	600	0.95	0.1	30	C	1.190	600	0.86	0.1
13	B	0.833	0	0.65	0	31	C	1.190	0	0.90	0.1
14	B	0.833	600	0.65	0	32	C	1.190	600	0.90	0.1
15	B	0.833	0	0.78	0.1	33	C	1.488	0	0.96	0.1
16	B	0.833	600	0.78	0.1	34	C	1.488	600	0.96	0.1
17	B	1.190	0	0.75	0	35	C	1.488	0	0.98	0.2
18	B	1.190	600	0.75	0	36	C	1.488	600	0.98	0.2

工况	理论值P_j_,min/Pa	试验值P_j_,min/Pa	工况	理论值P_j_,max/Pa	试验值P_j_,max/Pa	P_j_,c/Pa
1	2.01	1.92	4	11.52	7.68	3.29
13	5.75	5.07	16	11.52	9.30	5.30
25	6.98	6.22	28	11.52	9.68	6.04
5	2.53	2.32	8	14.45	10.67	4.18
17	7.21	6.75	20	14.45	10.67	7.02
29	8.76	10.88	32	14.45	11.72	8.38
9	2.86	2.65	12	16.38	10.83	4.82
21	8.17	8.07	24	16.38	11.52	8.29
33	9.92	11.06	36	16.38	11.52	10.20