## 3 Results and Discussion
### Temperature Difference Between the Left and Right Sides of the Fracture
This indicates that the middle part of the fracture significantly affects the heat transfer of granite, while the upper right corner of the fracture presents a relatively minor hindrance to granite's heat transfer. From the perspective of the heat transfer path and the heating rate, it can be seen that in the middle of the fracture, the heat reaching the left monitoring point 31# of the fracture must go through a longer heat transfer path and overcome greater thermal resistance, resulting in a significantly lower heating rate at monitoring point 31# compared to monitoring point 33#. This ultimately leads to the maximum temperature difference between the two monitoring points, 33# and 31#. In the right upper part of the fracture, although monitoring point 51# has a longer heat transfer path, as the distance from the monitoring point to the heat source increases, the extent of heat loss also increases, and heat attenuation is obvious, which makes the heating rates of the monitoring points 53# and 51# lower, eventually leading to the smallest temperature difference between the left and right monitoring points in the right upper part of the fracture. The maximum temperature difference between the left and right monitoring points at different positions of the fracture at different heat source temperatures is shown in Figure 11.  
As seen from Figure 11, in the range of a heat source temperature from 60 \({}^{\circ}\)C to 90 \({}^{\circ}\)C, the sizes of maximum temperature differences between the left and right monitoring points of the fracture are ranked as follows: 33#-31# > 23#-21# > 43#-41# > 13#-11# > 53#-51#. As the temperature of the heating source increases, the maximum temperature difference between the two monitoring points exhibits a significant growth trend. Specifically, the  
Figure 11: The maximum temperature difference between the left and right monitoring points of the fracture at different heat source temperatures. maximum temperature difference between monitoring points 33# and 31# increases from 6.4 \({}^{\circ}\)C at 60 \({}^{\circ}\)C to 7.2 \({}^{\circ}\)C at 70 \({}^{\circ}\)C, marking a 12.50% rise. There is a further increase from 7.2 \({}^{\circ}\)C at 70 \({}^{\circ}\)C to 10.5 \({}^{\circ}\)C at 80 \({}^{\circ}\)C, an increase of 45.83%. This indicates that in the temperature interval from 60 \({}^{\circ}\)C to 80 \({}^{\circ}\)C, there is a difference in the degree of influence of the fracture on the heat transfer of granite for every 10 \({}^{\circ}\)C increase in temperature. In addition, when the heat source temperature increases from 80 \({}^{\circ}\)C to 90 \({}^{\circ}\)C, the maximum temperature difference between the two monitoring points remains essentially unchanged. It is worth noting that when the heat source temperature reaches 100 \({}^{\circ}\)C, the maximum temperature difference between the left and right monitoring points at different positions of the fracture becomes 43#-41# > 53#-51# > 33#-31# > 23#-21# > 13#-11#, which demonstrates that the impact of the fracture on natural convection heat transfer (60 \({}^{\circ}\)C, 70 \({}^{\circ}\)C, 80 \({}^{\circ}\)C, 90 \({}^{\circ}\)C) and boiling heat transfer (100 \({}^{\circ}\)C) is different. According to the principle of heat transfer, during boiling heat transfer, the formation and growth of bubbles, as well as the flow disturbance generated by their detachment from the heating wall surface, significantly enhance heat transfer efficiency. In this process, the formation and release of bubbles promote the effective exchange and transfer of heat, which makes the temperature of the heating wall surface of granite rise rapidly, leading to a different effect of the existence of the fracture on the heat transfer of the granite.