| While the electrical energy meets the needs of our lives,it also increases the risk of electrical fires.Cable conductors are the main source of ignition for electrical fires.Polyethylene cables are widely used in social life due to their good insulation properties and low cost.In this paper,theoretical research,experimental research and numerical simulation research are carried out on the fire spread law of inclined polyethylene cable,and the effects of inclination angle and fire source location on the fire spread and melt dripping behavior of polyethylene cables are explored.The main research results are as follows:(1)According to the ignition theory of combustible solids,solid combustion propagation theory and fire propagation control mechanism,the inclined cable combustion area is divided into three parts: combustion area,pyrolysis area,and preheating area.Three characteristic lengths that can characterize the rate of fire spread are defined,and the calculation formula of the inclined cable fire spread rate is analyzed and a simplified heat transfer analysis model is established.(2)The polyethylene cable cone calorimetry experiment and the polyethylene insulation sheath thermogravimetric analysis experiment are carried out to explore the combustion characteristics of the polyethylene cable.The heat release rate and the concentration of combustion products when the cable is burned under different radiation intensities are analyzed.Through the TG and DTG curves of polyethylene insulating sheath under different heating rates and air atmosphere,the activation energy,reaction order and frequency factor of the pyrolysis reaction of polyethylene insulating sheath under different experimental conditions are analyzed.(3)The influence of factors such as inclination angle on the fire spread process of polyethylene cable is analyzed.The three characteristic lengths show the same trend with the increase of the dip angle.Comparing the experimentally measured values of wire core temperature and fire spread rate with the model calculated values,it is found that the two are in good agreement,which verifies the rationality of the model.(4)The influence of the fire source location and other factors on the droplet behavior of the cable is revealed.There is a nonlinear relationship between the dripping frequency and the inclination angle.For downstream fire spread,part of the droplets slide down and fall in the combustion zone and are consumed after pyrolysis,and the remaining part of the unconsumed droplets will drip after reaching the critical volume.For countercurrent fire spread,the molten droplets slide down and enter the preheating zone,and part of the molten material will solidify on the outer surface of the cable insulation layer in the unburned area without dripping,and after the rest of the melt droplets reach the critical volume will drip in the unburned area of the cable.(5)The numerical simulation study of the fire spread of a single inclined polyethylene cable is carried out,and the influence of the inclination angle and the position of the fire source on the fire spread process of the cable is explored.When the inclination angle increases,the time interval for the adjacent temperature measurement points to reach the peak value decreases.Compared with the spread of downstream fire,the time of the temperature peak at each temperature measurement point is relatively lagging when the countercurrent fire spreads,which indirectly reflects that when other conditions remain unchanged,the spread rate of downstream fire is greater than that of countercurrent fire.There are 61 figures,12 tables,and 99 references. |
