Figure 4 Flame (a) and
appearances (b) at various concentration of R123 and flame appearances
height (c) and appearances (d) at various concentration of R125.
Figure 4 shows the evolution of the flame height after adding different
volume concentrations of two
extinguishing agents. With the
addition of R123 (Figure 4a and b),
the flame height occurred the process of rapid increase (0-2.21 %, 8 to
13.3 cm), slow increase (2.21-6.33 %, 13.3 to 17.2 cm) and slight
decrease (7.31 %, 17.2 to 16.9 cm). There is a reason for the increased
height that R123 can increase the O2 demand of
combustion system and make unfired gas buoyancy to burn with
O2[6, 30]. The density of the agent and its
decomposition products, and their heat-release all effect the buoyancy
forces, then may affect the flame height variations and flame
oscillations[9]. Furthermore,
after the R123 concentration
exceeded 6.33 %, the flame height
decreased from 17.2 to 16.9 cm. From Figure 4b, as the concentration of
R123 above 6.33 %, flame oscillation become more evident. The decreased
height and oscillation of flame mainly result from two theory. On one
hand, abundant fluorine-containing or chlorine-containing groups were
generated with plenty of R123 inhibiting combustion reactions, further
effectively inhibiting the combustion chain reactions[31].
On the other hand, R123 and
oxidizers was flowing on both sides of the nozzle, and they entered the
reaction zone from the root of flame, thus the reaction kernel would be
affected and weakened. Therefore, the reaction kernel is too weak to
maintain the flame stable, and the balance location of the reaction time
and the residence time becomes difficult to obtain. Eventually, the
flame oscillated violently, then blown out.
In comparison with R123, R125 made the flame height increase
continuously (0-8.91 %, 8 to 20 cm). Apart from the different changes
of flame height, the flame width did not have obvious change with the
addition of R125 (Figure 4c and d), but the flame was widened with the
addition of R123 (Figure 4a and b). For the co-flow diffusion flame in
cup burner, the flame width was wider, the combustion reaction was
slower[32], thus the addition of R123 made total combustion
reactions slow, which may accelerate the process of the fire
extinction[33]. Consistent with the results of the minimum fire
extinguishing concentration calculated earlier, the extinguishing
performance of R123 is better than that of R125.