# Numerical Study of Coolant Flow Phenomena and Heat Transfer at the Cutting-Edge of Twist Drill
## 4 Results and Discussion
The highest inlet pressure, reaching 40 bar, is observed in the standard drill model (without a notch), explaining the corresponding higher coolant flow velocity at the borehole area. Conversely, the profile model drill with a notch exhibits the lowest inlet pressure, approaching 13 bar, approximately one-third of the pressure observed in the standard model drill without a notch. In contrast, both drills, standard model with a notch and the profile model without a notch, demonstrate relatively similar pressure difference profiles, approximately 22 bar and 19 bar, respectively, at a flow rate of 5.5 It/min. These observations highlight the influence of drill geometry and notch presence on the pressure characteristics within the system. Figure 4: _Cont._  
Figure 3: Velocity distribution profile for the given drill models at flow rate of 5.5 It/min. Note: the colour legend is in m/s. Numerical observations further indicate that the temperature is higher at the outer radius of the modified drill models. Notably, the standard model drill without a notch demonstrates effective heat dissipation, maintaining an average surface temperature of the cutting-edge area at around 196 \({}^{\circ}\)C, the lowest among all models. In contrast, the cutting-edge surface of the profile model drill with a notch experiences notably high thermal stress, resulting in an average fluid temperature of about 350 \({}^{\circ}\)C in the vicinity of the cutting zone. The temperature distribution over the cutting-edge surface can be explained by the analysing the fluid velocity profile shown in Figure 3. The standard model drill exhibits a higher fluid flow rate at the cutting-edge area and a relatively smaller dead zone. This configuration enables the cooling agent to reach much closer to the cutting region, actively dissipating heat, and thereby, reducing thermal stress on the cutting-edges. Consequently, the standard model drill without a notch achieves a lower local fluid temperature distribution over the cutting-edge area. The temperature distribution on the surface of the cutting-edge in the standard model drill with notch is almost same as the standard model without notch, except for a slightly higher temperature at the outer edge of the drill, which, in fact, explains the presence of the notch and its effect on the fluid flow. However, in the case of the profile model drills, despite achieving a homogeneous fluid distribution around the borehole area, the fluid flow at the cutting-edge is insufficient. The lack of coolant motion results in slow heat transfer, causing the cutting-edge area to undergo very high thermal stress. This observation emphasizes the impact of the fluid velocity profile on the temperature distribution. The examination of fluid motion, pressure distribution, and temperature patterns discussed above signifies the impact of the presence of a notch at the exit of the coolant channel on fluid flow, and thereby, heat dissipation. It is evident from the analysis that the presence of a notch at the exit provides an easy escape passage for the cooling agent from the coolant channel exit to the flute. However, this excess passage limits the coolant flow reaching the complex restricted region of the cutting-edge by decreasing the flow velocity. Consequently, the cooling agent bypasses the hot cutting zone without efficiently performing its intended function. Furthermore, in the case of the profile model drills, the triangular shape with elliptical corners leads to an increased exit area of the coolant channels. As a result, this design element provides the cooling agent with additional space, allowing it to escape easily to the flute instead of engaging in heat dissipation at the cutting-edge area. After analysing the numerical results under a constant velocity inlet condition (5.5 lt/min) it becomes apparent that the performance of the three modified drill models (the standard with notch, the profile without notch, and the profile with notch) is not better than the standard twist drill model.