## 3 Pavement Heat Transfer Theoretical Model and Solution  
### Theoretical Model Derivation  
This study analyzes the heat transfer process in airport pavement structures in saline environments. As shown in Figure 5, the pavement system is considered an integrated heat transfer system, with the heat transfer process primarily comprising two parts: heat exchange between the pavement and the external environment, and internal heat conduction within the pavement.  
Figure 4: Environmental simulation equipment and surface condition acquisition devices.  
1 Heat Exchange between Pavement and External Environment: The heat exchange between the pavement surface and the surrounding environment occurs in three main forms: solar radiation, convective heat transfer, and latent heat of phase change. By deriving the heat balance equation, we can quantitatively describe the effects of these heat exchange mechanisms on the pavement temperature field. For instance, the solar radiation formula calculates the net radiative heat absorbed by the pavement, while the convective heat transfer formula accounts for the influence of the wind speed and air temperature on the pavement temperature. The latent heat of the phase change involves the heat released or absorbed during the water-ice-salt phase transitions, which significantly affects the temperature variation of the pavement surface. Drawing on the studies by [PERSON] and [PERSON] [14; 20], the corresponding calculation formulas are as follows:  
* The net solar radiation \(Q_{sun}\) received by the runway is calculated as Equation (1): \[Q_{sun}=Q_{sun-in}-Q_{sun-out}=(1-\alpha_{ice})\big{(}1-\alpha_{p}\big{)}q_{sun }-\varepsilon\sigma T_{s}^{4}\] (1)
* The convective heat transfer \(Q_{wind}\) is calculated as Equation (2): \[Q_{wind}=\alpha_{wind}(T_{s}-T_{a})=\Big{(}10.4\omega_{wind}^{0.7}+2.2\Big{)}( T_{s}-T_{a})\] (2)
* The latent heat of phase change \(Q_{xup}\) is calculated as Equation (3): \[Q_{xup}=q_{fr}+q_{hy}=m_{fr}L_{fr}+m_{hy}L_{hy}\] (3)  
Definitions of the variables used in all the formulas throughout this paper are provided in Appendix A.  
2 Internal Heat Conduction within the Pavement: The internal heat conduction model focuses on the heat transfer between the different material layers of the pavement structure. From top to bottom, the pavement consists of an ice-water-salt layer, a concrete pavement layer, a gravel base layer, and a soil base layer. To ensure consistency between the model and the experimental results, the thickness and thermal properties of each layer in the model are based on the specific dimensions and materials of the pavement structural body previously described. Thus, the model is constructed as a realistic representation of an actual airport runway. We assume that the temperature field varies significantly along the  
Figure 5: Schematic diagram of energy exchange in pavement heat transfer system.  
vertical (longitudinal) direction and use the one-dimensional heat conduction equation to describe the temperature distribution and variation. The one-dimensional heat conduction follows [PERSON]'s law, as shown in Equation (4).  
\[\frac{\partial T}{\partial t}=\alpha\frac{\partial^{2}T}{\partial x^{2}} \tag{4}\]