## 4 Results and Discussion
### Heat Transfer
Thus, even though the average heat transfer intensity (represented by \(Nu\)) generally increases with Re, this improvement is accompanied by significant fluctuations, indicating an unsteady, possibly chaotic regime. Figure 9: Time variation of global Nusselt number for different Reynolds Number values, \(Ra=5\times 10^{7}\). time* denotes dimensionless time, as defined in the nomenclature. Figure 10 clearly illustrates the influence of the Reynolds number (\(Re\)) on the efficiency of heat transfer within the cavity equipped with thermal dissipators. At a lower Reynolds number, specifically \(Ra=10^{3}\), the flow is largely governed by natural convection. This is confirmed by the stream function, which shows two large Rayleigh-Benard-type convection cells occupying the upper half of the cavity. In this regime, the forced airflow remains weak and bypasses the convection cells along a long path, limiting its direct interaction with the surfaces of the dissipators. As a result, heat transfer remains relatively modest, with the global Nusselt number stabilizing around 100 after the initial transient phase. As \(Re\) increases to \(1.5\times 10^{3}\), the flow becomes more complex. The right-side convection cell splits, with one part pushed toward the upper right corner of the cavity and the other descending into the micro-cavity (space between the heat sinks). This change reflects a growing influence of the forced jet on the overall flow structure, enhancing the penetration of cooler air into regions near the dissipators. This promotes better surface cooling, thins the thermal boundary layers, and leads to a noticeable increase in the Nusselt number. At higher Reynolds numbers, \(Re=2\times 10^{3}\) and \(2.5\times 10^{3}\), the forced jet becomes the dominant mechanism driving the flow. It suppresses the natural convection cells, pushing them upward, while also penetrating the space between the dissipators. This leads to the streamlines aligning more closely with the surfaces of the dissipators an effect that promotes strong convective heat transfer, with the Nusselt number exceeding 150. However, this strong jet also gives rise to small entrainment cells between the main airflow and the surfaces of the dissipators. These localized recirculations can temporarily reduce the heat transfer in specific regions, which explains the oscillations observed in the Nusselt number at higher \(Re\). Overall, the combined analysis of the Nusselt number and the stream function reveals a clear transition from a natural convection-dominated regime to one where forced convection prevails. This shift leads to a significant improvement in heat transfer performance due to the enhanced interaction between the airflow and the dissipator surfaces, despite the presence of small-scale flow instabilities at higher Reynolds numbers. To really highlight the sensitivity of the heat exchange between the hot block faces and the fresh air, an average value of \(Nu_{g}\) was defined and denoted as \(Nu_{g}^{m}\) representing the  
Figure 10: Time variation of global Nusselt number for different Reynolds Number values, \(Ra=5\times 10^{8}\). time* denotes dimensionless time, as defined in the nomenclature. average between the maximum and the minimum of \(Nu_{g}\) from a time \(\tau\) chosen according to the \(Re\) value. The average value of the global Nusselt number \(Nu_{g}^{m}\) was examined as a function of the Reynolds number for \(Ra=5\times 10^{7}\). As reported in Table 4, \(Nu_{g}^{m}\) increases from 76 to 86 across the investigated Re range, indicating a clear influence of forced convection on the overall heat transfer. This trend suggests that the flow intensification promotes more effective convective transport, even in the presence of significant buoyancy effects. The confidence interval associated with the slope of the fitted correlation, [0.00274, 0.00358], is relatively narrow, which reflects a consistent and statistically reliable relationship between \(Nu_{g}^{m}\) and \(Re\).