Experimental study of the non-monotonous moisture effect on upward flame spread over cotton fabric

Abstract

The present paper studies the moisture effect on upward flame spread over cotton fabric by performing experiments using 0.245 mm thick, 180 cm tall and 10 cm wide sample sheets with moisture content ranging from 0% to 18%. As the moisture content increases, the flame height, pyrolysis height, burnout height, pyrolysis length and spread rate show the same trend, first increasing and then decreasing. The maximum value is observed in the case of the 2% moisture content samples. Furthermore, at an infinite length of fabric fuel, the upward flame propagation would reach an asymptotic steady state with constant pyrolysis length and spread rate. Finally, a higher moisture content corresponds to a lower flame temperature. For upward flame spread, the moisture content has the negative effects of increasing the thermal inertia parameters and reducing the flame temperature and heat feedback; simultaneously, the positive effect is that the moisture can enlarge the flame size and the effective preheating length. The combined effects of positive and negative effects result in the non-monotonous trend in the pyrolysis spread rate.

Experimental study of the width effects on self-induced buoyant blow off in upward flame spread over thin fabric fuels

“…To our knowledge, the flame spread over thermally thin materials is dominated by net heat flux to the unburned surface, which consists of a convective component and a radiative component. 2,3,39 The energy conservation can be expressed by the following equation where qf ″ is the net heat flux to the unburned surface and qr ″ and qc ″ are the radiation and convection heat flux from the flame, respectively. For upward flame spread over thin materials, the radiation fraction is 75–90% of the total heat feedback from the flame to the unburned surface.…”

“…For upward flame spread over thin materials, the radiation fraction is 75–90% of the total heat feedback from the flame to the unburned surface. 6,7,35,39 Based on the analysis mentioned above, the radiation heat flux clearly plays a primary role in upward flame spreading for test samples with a width larger than 3 cm. The radiation heat flux can be estimated by the following equation where ɛ denotes the emissivity,σ is the Stefan–Boltzmann constant (5.67×10-8W/m 2 k 2 ) and T represents the flame temperature.…”

“…To our knowledge, the flame spread over thermally thin materials is dominated by net heat flux to the unburned surface, which consists of a convective component and a radiative component. 2,3,39 The energy conservation can be expressed by the following equation…”

Effects of porosity and area density on upward flame spread characteristics over thin flax fabric

“…The flame front is quantitatively obtained by reading the gray images frame by frame, which is similar to the method in previous works. 18 Zhu et al 27 and Rangwala et al 33 successfully applied gray image processing technology to obtain the flame front and flame length. of the test samples.…”

“…Gollner et al, 9 Huang and Gollner 10 and Gao et al 11 investigated the upward flame spread characteristics over inclined solid fuel surfaces and proposed that the flame tilt angle and flame standoff distance could qualitatively describe the heat flux profiles in the preheating region. Moreover, the effects of ambient pressure, [12][13][14] oxygen concentration, [15][16][17] moisture content, [18][19][20] external flow velocity [21][22][23][24] and different configurations [25][26][27][28] on flame spread over solid fuel surfaces have been widely investigated by experimental measures and theoretical analyses.…”