| Ships play an increasingly important role in the contemporary world for the civilian and military purposes. The ceiling vented enclosure has been widely existed in the ship cabins. The horizontal vent flow has the obvious distinction with the vertical vent flow due to the characteristic of the horizontal opening. The vent flow through the vertical opening will develop the stable layered flow, and which will cause the complicated irregular oscillatory flow through the horizontal opening. Hence, understanding the horizontal vent flow behavior and mechanism induced by fire is a significant aspect of ship fire safety, and can provide essential data and a theoretical basis for ship fire prevention and ventilation system design. In order to investigate the fire induced vent flow behavior coupled with fire behavior, experimental and theoretical studies of the vent flow behavior induced by fire, the fire behavior under the ceiling vented enclosure and the interaction between fire and vent flow considering a number of configurations characterized by different pool diameters and different ceiling vent sizes have been investigated. Then, the fire induced vent flow model has been proposed. The principle conclusions obtained from our experiments under the tested conditions are as follows:The horizontal vent flow behavior induced by fire, i.e. the flow pattern and the oscillatory behavior, was investigated. The flow pattern is the one important factor to indicate the vented flow regularity, and three vent flow patterns was observed during the tests by video camera and laser technique, namely the unidirectional flow, the bidirectional flow and the compound flow. Cooper’s and Chow’s theories based upon the salt water experiments and numerical calculations, respectively, were also introduced to predict the vent flow pattern in the real fire scenario. Good agreement results indicated that these theories also could be used in the prediction of vent flow pattern with some modification. A fire source area ratio (area ratio of horizontal opening and fuel) was proposed to distinguish the three flow patterns with correlating to Buoyancy number, as well as the flow area ratio. The vent flow oscillatory behavior was observed with the smoke visualization measurement. Smoke gas area and smoke temperature were adopted to characterize the vent flow oscillation frequency. The oscillation frequency of the smoke gas area decreased with the horizontal opening size rising, and smoke temperature oscillation frequency presented a rise trend with increasing the heat release rate. The empirical equations on oscillation frequency of smoke gas temperature in the opening were also verified. Fire behavior with the influence of the vent flow was studied in the confined enclosure with a horizontal opening. The influence of horizontal opening on the pool fire pulsation behavior was studied with considering a number of configurations characterized by different pool diameters and different ceiling vent sizes, ranging from well-ventilated to under-ventilated conditions. The mean flame height presented the binomial distribution with increasing the horizontal opening size, and the ratio of mean flame height and diameter correlated well with the horizontal ventilation parameter. The results are consistent with the usual dependence of unstable frequency with pool diameter but also reveal an unexpected dependence of unstable frequency with ceiling vent size. A new correlation between Strouhal number and Froude number is proposed that incorporates enclosure effects on the rate of fuel evaporation. The influence of the horizontal opening on the enclosure fire parameters was taken into account, such as the average MLR values, the oxygen concentration value at extinction time, the average rate of gas temperature rise, enclosure pressure in the closed and confined enclosure. The dimensionless horizontal ventilation parameter coupling horizontal opening and fuel areas was proposed with theoretical simplified method based upon the energy and oxygen conservations to analyze these fire parameters. The comprehensive frequency correlation aimed to reveal the interactions between fire and vent flow. It could be easier to obtain the vent flow frequency on account of the stable product of the flame pulsation frequency and the vent flow oscillation frequency with varying the horizontal opening, which depended on the pool fire parameters.Fire induced vent flow model through the horizontal opening based upon the multilayer concept with considering the interactions between fire and vent flow have been proposed. The fire induced flow process and the flow mechanism were discussed with considering the opening configuration and the flow pattern. The different flow transport processes were presented for the unidirectional flow and bidirectional flow, as well as the flow mechanism with the force analysis of the outflow and inflow. The vent flow model induced by fire for the unidirectional flow and bidirectional flow was established based upon the multilayer zone model. A new method to obtain the mass flow rate through the horizontal opening experimentally was presented. The mass outflow and inflow rates for the unidirectional flow and the bidirectional flow were obtained based on the laser technique and the pitot tube. A comparison between the theoretical and the experimental results was made to verify the feasibility of vent flow model. |
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