Study On Characteristic Properties Of Compressed Air Foam And Flow Characteristics Of Pipe Network

With the rapid development of social economy,the number of high-rise/super high-rise buildings and the area of chemical parks are increasing,and the layout of the corresponding functional structure is showing complex characteristics,which increases the burden of fire fighting and rescue difficulties,and once a fire occurs,it will cause serious social impact.For the above fire scenarios,it is especially important to choose suitable fire extinguishing devices,and compressed air foam can help with the above scenarios with its superior fire extinguishing performance.However,in the process of promoting the application of compressed air foam,there are still problems such as the unknown mechanism of the influence of foam generation device parameters on the characteristic properties of foam and the unclear law of pipeline network transportation.In this paper,from the perspective of practical application,the following aspects of research are carried out for the characteristic properties of compressed air foam and the change law of pipe network transport:1.Through foam microscopic observation and liquid precipitation measurement experiments,the effects of foam type,mixing ratio and gas-liquid ratio on the particle size of compressed air foam and foam precipitation process were studied,and the prediction function of foam precipitation quality based on the effect of gas-liquid ratio was established.The results showed that the particle size distributions of AFFF and A type foam were similar at the initial moment,and with the increase of time,the particle size homogenization of AFFF foam was weakened,the number of large-sized bubbles increased,and the increase of foam particle size was 2.6 times of that of A type foam.30 min later,the number and average particle size of A type foam were about 4.9 times and 1/2 times of that of AFFF foam under the condition of gas-liquid ratio of 6.The effect of mixing ratio and gas-liquid ratio on the particle size of the foam is small.Under the same conditions,the maximum precipitation mass and precipitation rate decreased with the increase of gas-liquid ratio,and the maximum precipitation rate decreased slowly when the gas-liquid ratio was more than 12.The effects of different air-liquid ratios on the process of compressed air foam precipitation were analyzed comprehensively,and the prediction function of AFFF and class A foam precipitation quality based on the effects of air-liquid ratio was established.2.Numerical simulation of compressed air foam horizontal transport process was carried out by using simulation software,and the effects of foam liquid type,mixing ratio and pipe diameter on pressure decay in foam horizontal transport process were studied.It is found that:the pressure drop of pipeline is positively correlated with the viscosity of foam liquid,under the condition of 270 L/min mixing fluid flow rate and 1750 L/min gas flow rate,the pressure drop of high viscosity anti-soluble aqueous filmforming foam(AFFF/AR)of the same pipe diameter is 1.3 times of that of low viscosity class A and aqueous film-forming foam(AFFF);for the same type of foam,the influence of mixing ratio on the pressure drop of pipeline is smaller.The maximum pressure drop difference between different mixing ratios of 100 m pipe is 7.21 kPa.The influence of pipe diameter on pressure drop is larger,the pressure drop of 50 mm pipe diameter is 9.4 times of 80 mm pipe diameter under the same foam condition,and the pressure drop of 80 mm pipe diameter is 2.8 times of 100 mm pipe diameter,and the influence of different foams on pressure drop decreases gradually when the pipe diameter is larger than 80 mm.Combined with the theoretical analysis to establish the pressure decay prediction model in the process of compressed air foam horizontal transport,and carry out experiments of compressed air foam horizontal transport,the experimental value and the model prediction error is within 15%.3.Numerical simulation of vertical transport process was carried out by using simulation software,and the effects of gas-liquid ratio,mixing ratio and pipe diameter on the pressure decay in the process of vertical foam transport were studied,and the pressure decay prediction model of vertical foam pipeline network was proposed by comparing the selected cross-sectional gas content calculation model.The results show that the pressure drop of the pipeline is inversely proportional to the gas-liquid ratio under the condition that the total flow rate of foam is 3200 L/min,and the difference between the gas-liquid ratio of 7 and 31 in 80,100,125 and 150 mm pipe diameters is about 0.7 times of the pressure drop of gas-liquid ratio of 31.The pipe pressure drop decreases with the increase of pipe diameter,and the influence of pipe diameter on the pressure drop per unit height gradually weakens with the increase of gas-liquid ratio.The mixing ratio has less influence on the pressure drop of vertical pipeline.By comparing and analyzing the theoretical calculation models with different crosssectional air content,it is found that the calculated values of the variable density model are closer to the simulated values,and finally the compressed air foam pressure decay prediction model applicable to the vertical pipe network is proposed,and the previous experimental results are compared with the predicted values of the model,and the error between the two is within 10%.