Quasi-Steady State Time Model of Fire Smoke Transmission in Long-Narrow Spaces

doi:10.16183/j.cnki.jsjtu.2021.062

Abstract

Abstract:

Transport time lag is a crucial characteristic of fire spreading in fire early stage, which determines the activation time of the fire detector. To clarify the quantitative relationship between the delay behavior and the quasi-steady state of smoke transmission in a long-narrow space, a time-varying spreadsheet is theoretically proposed to calculate the delay time of fire smoke transmission based on the theory of weak plume and the existing achievements concerned. Moreover, a theoretical model concerning the critical time for quasi-steady state assumption applicability is developed, where the method of calculating the critical time is also presented. The results of the case study show that due to the difference of smoke spreading velocity in long-narrow spaces and unconfined spaces for a case with the same conditions, the critical time for the smoke transmission to reach the quasi-steady state at a given radial distance on the ceiling in a long-narrow space is larger than that in the open space. For the open case, the thin ceiling plume, the small volume of entrained air, and the relatively high velocity of smoke lead to the longer delay time of smoke transmission in a long-narrow space than that in the open space under the same situations.

Key words: fire smoke, long-narrow space, lag, quasi-steady state model, critical time

CLC Number:

TU318
X 932

WANG Jinhui, HUANG Yijun, CUI Xin, ZHANG Shaogang, ZHANG Ruiqing. Quasi-Steady State Time Model of Fire Smoke Transmission in Long-Narrow Spaces[J]. Journal of Shanghai Jiao Tong University, 2022, 56(6): 746-753.

Figures/Tables 9

Fig.1

Tab.1

Time-varying spreadsheet method for calculating delay time of unsteady fire source smoke

计算量	t₁	…	t_i	…	t_n
$Q ·$ (t_i)/kW	$Q ·$ (t₁)	…	$Q ·$ (t_i)	…	$Q ·$ (t_n)
t_s( $Q ·$ (t_i))/s	t_s( $Q ·$ (t₁))	…	t_s( $Q ·$ (t_i))	…	t_s( $Q ·$ (t_n))
t_u( $Q ·$ (t_i))/s	t_u( $Q ·$ (t₁))	…	t_u( $Q ·$ (t_i))	…	t_u( $Q ·$ (t_n))
t_c( $Q ·$ (t_i))/s	t_c( $Q ·$ (t₁))	…	t_c( $Q ·$ (t_i))	…	t_c( $Q ·$ (t_n))
t_a( $Q ·$ (t_i))/s	t_a( $Q ·$ (t₁))	…	t_a( $Q ·$ (t_i))	…	t_a( $Q ·$ (t_n))
t_lag(t_i)/s	t₁+t_a( $Q ·$ (t₁))	…	t_i+t_a( $Q ·$ (t_i))	…	t_n+t_a( $Q ·$ (t_n))

Tab.1

Tab.2

Calculation of lag time in different fire scenarios

$Q · 0$ /kW	H/m	r/m	l_b/m	t_lag/s
0.2	3.9	4.8	0.8	43.9
0.5	2.5	3.1	0.5	18.3
0.7	3.7	4.5	0.8	26.3
0.8	2.6	3.3	0.6	16.3
1.2	3.2	4	0.7	18.7
1.3	3.4	4.2	0.7	19.3
1.5	3.7	8.6	1.2	43.8
1.0	3.4	7.8	1.1	43.8
0.8	2.1	4.8	0.7	25.0
0.6	3.2	7.5	1.0	49.2
1.1	3.9	12.4	1.8	79.1
0.9	3.5	11.1	1.6	72.8
0.8	3.6	11.5	1.6	80.5
1.4	2.6	5.2	1.3	25.6
0.7	3.3	6.6	1.7	44.7
0.8	1.9	3.8	1.0	20.2
0.2	3.1	6.2	1.6	61.8
0.7	2.7	6.3	1.4	40.5
0.3	2.9	6.9	1.6	61.0
2.1	3.5	8.3	1.9	40.7
0.2	2.6	6.2	1.4	61.2
0.9	3.1	7.3	1.7	46.6
0.2	2.5	6.0	1.4	57.8
2.0	3.4	8.0	1.8	39.4
0.7	2.2	5.3	1.2	32.4
1.1	2.2	2.8	0.9	12.7
0.2	2.2	2.8	0.9	22.4
0.9	2.2	2.8	0.9	13.8
0.4	2.2	2.8	0.9	18.6
1.5	2.2	2.8	0.9	11.4
0.7	2.2	2.8	0.9	14.7

Tab.2

Fig.2

Fig.3

Fig.4

Fig.5

Fig.6

Fig.7

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