科研之友
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摘要
Tests in model tunnel (1:20) were performed and analyzed in order to study the effects of tunnel cross section (width and height) together with ventilation velocity on ceiling flame length in case of large heat release rate. Test results show that in tests with the same fuel and ventilation velocity, the flame length tends to decrease with increasing tunnel cross-sectional area, due to different restriction degrees of air entrainment into the flame plume by the tunnel ceiling and sidewalls. For wood crib under the same tunnel cross-sectional area, the flame length evidently decreases with the increasing ventilation velocity, due to that a larger ventilation velocity provides more air for the combustion, and thus, the combustible gas evaporating from the fuel does not need to spread a longer distance with generating a larger flame length. In order to build an integral model of flame length considering the effect of both tunnel cross section and ventilation velocity, a dimensionless form of ventilation velocity including the hydraulic diameter of tunnel is introduced. The global model of flame length can correlate well with the data from both large- and model-scale tests.
