2.7. Finite Element Analysis

The finite element calculation software ANSYS is used to verify the temperature rise test of the pouring conductive asphalt concrete, and the effect of the electrode layout optimization is further clarified. The finite element simulation of the melting ice and snow of the pouring conductive asphalt concrete is then carried out. In line with the indoor melting ice and snow test, the reliability of the finite element simulation of the melting ice effect of the pouring conductive asphalt concrete is verified, which reflects the effect of the electrode layout optimization scheme on the actual pavement melting ice.

The latent heat is often taken into account in the phase change analysis of ice. The enthalpy of ice at various temperatures is shown in Table 9, and the ANSYS finite element analysis parameters are selected as shown in Table 10.

Enthalpy values of ice at various temperatures.

Material parameter list.

Under the condition of temperature change and electric conduction, the resistivity of electrodes and castable conductive asphalt concrete will change to some extent. Contact resistance will also be generated, due to the contact tightness between electrodes and wires and between electrodes and castable conductive asphalt concrete, which will bring a huge amount of calculation to the model processing. In order to simplify the model and reduce the amount of calculation, the following assumptions are made according to the actual situation: (1) various materials used in the model are homogeneous and continuous materials. (2) Without considering the contact resistance between the electrode and the pouring conductive asphalt concrete, the contact between the two solids is close. (3) Without considering the contact thermal resistance between the electrode and the pouring conductive asphalt concrete, the contact between the two solids is close. (4) Each physical parameter does not change with the change of temperature, which is a fixed value and does not consider the influence of low temperature box radiation. (5) The ice layer is homogeneous and isotropic material, and the melting process of the ice layer is reflected by temperature, without considering the evaporation in the melting process of the ice layer. (6) The steel plate material is isotropic and the bonding between the structural layers is good.

The finite element thermal analysis environment temperature is set to −10 °C, and the pouring conductive asphalt concrete melting ice and snow model is shown in Figure 11. The SOLID226 thermoelectric analysis unit is selected for the cast conductive asphalt concrete layer and electrode, and the SOLID70 thermal analysis unit is selected for the ice layer and the stainless steel bottom plate. The convective heat transfer coefficient between the surface of the cast conductive asphalt concrete and the air is 6.02 W/m²·K, and the convective heat transfer coefficient between the stainless steel and the air is 10 W/m²·K when natural convection occurs. The latent heat of the melting process of the ice block is reflected in the enthalpy change value, without considering radiation.

Casting conductive asphalt concrete ice melting model.

In the finite element modeling with an insulation layer, because the bottom plate means that the insulation is good, the insulation adhesive layer and steel plate are omitted, and the conductive asphalt concrete layer and ice layer only are established. The convective heat transfer coefficient of ice and air is 34 W/m²·K. When there is no insulation analysis, the insulation layer is removed, and the convective heat transfer is applied to the outer surface of the model, without considering the thickness of the adhesive layer. After the parameter has been applied, the analysis model is established, and the unit properties are assigned after each part is bonded. The model is divided and then meshed, as shown in Figure 12.

Mesh division of the melting ice model. (a) Grid division with heat insulation model; (b) Meshing without heat insulation model.

Firstly, the initial temperature of the model is set to −10 °C. Secondly, the convective heat transfer and voltage are applied. The convective heat transfer is applied to the outer surface of the model in the form of surface load. Depending on the different materials, different convective heat transfer coefficients are set up. The ambient temperature is −10 °C. Zero V is applied on the electrode side and a given voltage is applied on the side. The solution is set to transient analysis. The solution time is set to 8 h (28,800 s). Because the temperature rises slowly without an insulation layer, the solution time is set to 20 h (72,000 s) without an insulation layer. The temperature field distribution nephogram solved is shown in Figure 13.

Cloud map of temperature field distribution in melting ice model. (a) Temperature field distribution nephogram with insulation layer; (b) Temperature field distribution cloud chart without insulation layer.

It can be seen from Figure 13 that the temperature distribution of the melting ice model with and without the heat insulation layer is as follows: the middle temperature at the bottom of the pouring conductive asphalt concrete layer is the highest, and the temperature distribution presents a water wave shape, which increases in turn from inside to out. In the case of the heat insulation layer, the heat is directly transmitted upward, making the temperature of the upper surface increase rapidly. In the case of no heat insulation layer, the heat is transmitted to the steel plate, and some heat is lost. Therefore, the heating rate of the pavement scheme with the insulation layer is faster, and the heating structure with the insulation layer is recommended.