Research On Dimensional Nonlinear Heat Transfer Model For Expansion Behavior Of Intumescent Coatings

In order to ensure that the steel structure building in the fire within the specified time to complete its intended function,usually the fireproof coating is painted on the surface of the steel structure,so as to isolate the high temperature of the fire site,prolong the fire resistance time of the steel structure,and ultimately reduce the damage effect of the fire.The thermal expansion of expansive fireproof coating under high temperature is a process of continuous physical and chemical changes,so it is necessary to explore the mechanism behind the coating expansion,reveal the change rule of coating fire performance,to provide more theoretical support for the fire protection design of steel structure in technology.In this paper,aiming at the thermal expansion process of expansive fireproof coatings under high temperature,a mathematical model based on the nonlinear change of expansion size was established,and compared with the existing experimental results,the change law of thermal physical property parameters in the model was analyzed.The results show that the model accurately describes the process of coating mass loss and expansion behavior of the coating.The maximum rate of coating expansion increases with the decrease of dry film thickness.The apparent thermal conductivity first decreases with the increase of porosity,and then increases after the coating is completely expanded due to the enhancement of convection and radiation heat transfer in the pores.On this basis,numerical modeling and verification of heat-transfer process of steel pipe coated with intumescent fireproof coating under high temperature field were carried out.The protective behavior and influencing factors of steel pipe coated under high temperature field were studied.In the working condition of this paper,although the ambient temperature presents an exponential rising trend,the rapid foaming expansion of the coating significantly delays the temperature rise effect of the steel tube,making the maximum temperature rise rate of the steel tube only 1.23 K·s^-1.Compared with bare steel tubes,the maximum fire temperature of coated steel tubes decreased by 798.8 K after the application of high temperature field for 2000 s.The fire resistance of the coating varies nonlinear with the thickness,so appropriate coating thickness should be selected according to the environmental field with different heating rate.Based on the semi-empirical formula,the pool flame characteristics of two typical fuels were obtained,and the radiation intensity of the pool flame to the petrochemical storage tank was obtained by solving the finite element model.The variation rule of the protective performance of the expansive fireproof coating on the tank wall under different radiation fluxes was analyzed,and the failure time of the storage tank under fire was determined.Calculation results show that the area closest to the flame on the wall of the tank receives the largest radiation flux,which decreases along both sides and below.The fourth order relationship between the radiation flux and temperature leads to a large difference in the heat radiation from the pool flame of different fuels to the adjacent tank.For the relatively low temperature gasoline fire,the protective performance of the coating can not be fully played.