Simulation Study Of Heat Transfer Process Between Intumescent Fire Retardant Coating And Steel Substrate

Building fires cause huge casualties and property losses every year.As a mainstream building structural system,steel structures will rapidly reduce their strength and stiffness when they are attacked by fire,causing collapse accidents.Intumescent fire retardant coatings are the mainstream solution for protecting steel structures due to their ease of use and good thermal insulation performance.In order to realize the rapid evaluation of the coating thermal insulation performance,the heat transfer in the thermal protection process of the coating was studied,and a heat transfer model was constructed to deepen the understanding of the heat transfer mechanism.In this paper,an intumescent heat transfer model for intumescent fire retardant（IFR）coatings is developed,which enables rapid evaluation of the thermal insulation performance of intumescent coatings with different components.And the temperature calculation equation of the heat transfer model is simplified to reduce the input of temperature data.Finally,the MATLAB program is used to realize the visualization of the heat transfer simplified model.At the same time,the thermophysical parameters and external environmental conditions of the two IFR coatings are measured by cone calorimeter,thermogravimetric analyzer,differential scanning calorimeter,thermal conductivity meter and other instruments,and the relationship with temperature is explored to ensure the accuracy of the model input parameters.The results obtained are as follows:（1）Through the experimental measurement of the input parameters,it is found that the thermophysical parameters such as specific heat capacity,thermal conductivity and mass loss rate will change with the change of temperature.When adjusting the incident heat flux of the cone calorimeter to a stable value,it will be found that as the measured point is farther away from the radiation cone,the actual incident heat flux value will be smaller.It is also found that the change of the char layer height is affected by the coating mass loss rate.Once one of the values is inaccurate,it will affect the calculation of other values.Through the analysis of the experimental data,the variation laws of these thermophysical parameters are obtained.After fitting the corresponding functional relationship,the corresponding thermophysical model and pyrolysis model are constructed.（2）When studying the construction of the heat transfer model,the thermal protection process of the coating is divided into stages,which is divided into preheating stage,expansion into char stage and char heat transfer stage according to material changes,and the corresponding energy conservation equations are established.For the more complex expansion into char stage,the layering treatment is carried out,which is divided into the char layer,the swelling decomposition layer and the coating.When constructing the energy conservation equation of the char layer in the expansion into char stage,the influence of the expansion endothermic effect of the char layer is introduced,and the effect of the coating decomposition heat is introduced into the energy conservation equation of the swelling decomposition layer.The model quantifies the effect of heat absorption by gas in the pores of the char layer on heat conduction,and considers the energy more comprehensively.By analyzing the simulation results of temperature and height,the rationality of the heat transfer model is verified.（3）When studying the construction of the heat transfer simplified model,the internal temperature calculation equation is simplified.By integrating the energy conservation equations in different stages and different regions,the temperature change rate is obtained,and then the heat loss through the unit distance is quantified,and finally the establishment of the temperature equation is completed.The heat transfer simplified model greatly reduces the input of temperature data and improves computational efficiency.By analyzing the simulation results of temperature and height,it is found that the error generated by the heat transfer simplified model is small,which verifies the rationality of the heat transfer simplified model.The heat transfer simplified model is programmed by MATLAB program,and the visualization of the model is realized.The sensitivity analysis of the specific heat capacity and thermal conductivity of the coating is carried out using this program,and the results show that different thermophysical parameters have different effects on the simulation results.