Modeling of Heat Transfer in Intumescent Fire-Retardant Coating Under High Radiant Heat Source and Parametric Study on Coating Thermal Response

In this study, a new model for intumescent coatings is developed including the radiation transfer equation. So, one of the important features of this model is to give the insight of the radiative heat transfer in intumescent coating during expansion. In addition, the model equations are derived into a new coordinate system by introducing the expansion effect into the corresponding parameters. Consequently, the numerical results can be carried out by using a fixed grid system. The numerical results show that the radiative heat transfer near the exposed coating surface cannot be well simulated by the model of thermal radiation conductivity, which is widely used in the previous studies. So, it is suggested that the radiative heat transfer in the expanded char region should be formulated by a more considerate model. In addition, several parameters of coating thermal properties (thermal conductivity, extinction coefficient, and albedo) are tested and investigated under a radiant heat source. In addition to the transient response, the effects of these coating properties on the quasi steady results are also discussed. It is found that the thermal conductivity and the extinction coefficient in the expanded char region both dominate the coating performance. For the thermal properties of virgin coating, the thermal conductivity may have significant effect when the coating has large incomplete pyrolysis (expansion) region, while the extinction coefficient has little influence. Besides, the thermal conductivity and the albedo of virgin coating both alter the heating time to initial expansion but in different mechanisms.