## 4 Thermal Management of Heat Transfer in 5G Networks Technology
[PERSON] et al., 2025 [85], developed an advanced topology design method for the optimal design of extruded fins in a 3D turbulent natural convection system to improve the cooling efficiency of chips within a 5G active antenna unit. They employed three-dimensional fluid flow modeling with standard \(k\)-\(\epsilon\) turbulence model. Their findings showed that the hollowed center and the heterogeneous distribution of pillars are two critical optimized features in the multi-finned thermal design problem, contributing nearly 30% to the overall enhancement of heat transfer. Applied to two 20 Watts chips, they revealed how their design method, with a fin volume fraction of 5%, can reduce the maximum temperature by over 10 K (and increase the Nusselt number by at least 14.6%) when compared to conventional pin and plate fins at the same value of volume fraction. [PERSON] et al., 2025 [86], developed a new phase-change device (called the roll-bond flat heat pipe (RBFHP)) that is easy to fabricate and apply on large surfaces for cooling base stations. The authors studied multi-heat-source scenarios under natural-air-cooling conditions, investigating the thermal performances and power distribution modes. Their findings revealed how their new device provides a better thermal performance compared to traditional devices. [PERSON] et al., 2024 [87], developed a parallel hybrid cooling system of thermosyphon and vapor compression to cool down 5G base stations. Their research findings revealed that operational parameters, including the set points for return air temperature and the speeds of the evaporator and condenser fans, can significantly influence the utilization ratio of the natural cooling source in the hybrid cooling system, thereby impacting the system's energy efficiency ratio (EER). They illustrated, for example, that when the outdoor temperature falls below 20 \({}^{\circ}\)C, the local variations in the evaporator fan speed notably affect the system's operating mode. Thus, by selecting an optimal evaporator fan speed, one may reduce the compressor's operating time to 0%. Moreover, at a temperature of 15 \({}^{\circ}\)C outdoors, a fine-tuning of the evaporator and condenser fan speeds can enhance, respectively, the EER by about 60% and 52%. If the outdoor temperature is above 25 \({}^{\circ}\)C, the system can operate in air-conditioning mode, leading to minimal influence of fan speeds on the EER. [PERSON] et al., 2024 [87] explained that, by optimizing both the evaporator fan speed and the set point temperature, the EER can be increased up to 17.19. [PERSON] et al., 2024 [88], proposed a new heat sink solution based on a microchannel thermosyphon array with air cooling; this was an attempt to optimize the design of 5G heat-dissipation devices. Their experimental measurements focused on the temperature uniformity across various filling ratios, heating power levels, and wind speeds. Their research findings revealed that the optimal filling ratio for the microchannel thermosyphon array is about 20%. The latter had a heating power of 80 W. They showed that the thermosyphon exhibits a thermal resistance of about 0.28 \({}^{\circ}\)C/W. Moreover, [PERSON] et al., 2024 [88], explained that, if one increases the input power, then one can facilitate the startup process and thus promote a transition into a stable fluid flow and heat transfer phase. They showed that the microchannel thermosyphon array has a power limit of 40 W under natural convection conditions; however, at a wind speed of 6 m/s, the power limit increases to 140 W, inducing a thermal resistance of less than 0.4 \({}^{\circ}\)C/W; here, the temperature does not exceed a value of 74.3 \({}^{\circ}\)C. These research findings offer valuable insights for the optimization of 5G heat-dissipation device designs. Many authors have been trying over the years to develop enhanced liquid-based coolers of base transceiver stations [89].