## 4 Thermal Management of Heat Transfer in 5G Networks Technology  
With the emergence of 5G networks, thermal management has become a critical aspect of device design; this is especially the case when it comes to the ongoing increase in the density of large-scale integration circuits. This is due to the changes in device behavior and the elevated local temperatures [51, 52, 53, 54, 55], even with involving renewable energy sources such photovoltaic solar cells and panels. It is worth noting that the efficiency of photovoltaic cells usually decreases at higher operating temperatures [56, 57]. Heat transfer in 5G networks occurs through convection, conduction, and radiation mechanisms. It takes place in many forms of equipment and devices such as antennas, chips, processors, and power amplifiers. Thermal management strategies are vital in overcoming the challenges posed by the overheating of these devices. It is important to ensure the correct functioning of the 5G network overall, as it is transitioning rapidly towards a 6G technology network. Today, we thus need more advanced solutions, such as innovative cooling techniques and AI-based thermal optimization, to sustain the effective performance of future mobile telecommunication technologies. The utilization of cryogenically cooled amplifiers is well established in the field of radio astronomy [58; 59; 60]; this started around 2008, ad has become economically viable in application in 3G technology system base stations (BSs). A detailed review of cryogenic receivers in commercial wireless applications can be found in [61]. [PERSON] et al., 2008 [62], introduced a cryogenic receiver front-end operating in the 2 GHz band; it features HTSFs and a cryogenically cooled low-noise amplifier. The progress in wireless BSs utilizing cryogenic technologies are discussed in the literature [63; 64; 65], with receiver front-ends having applications in their extension into LTE networks [66]. [PERSON] et al., 2019 [67] addressed a fully passive cooling approach using double-sided printed circuit board (PCB) configuration for antenna arrays. In comparison to conventional structures, their research findings indicated that utilizing a thicker ground plane leads to a better thermal performance. Employing a passive fin heat sink for heat dissipation, [PERSON] et al., 2022 [68], conducted a numerical analysis to quantify the cooling efficiencies of a 5G active antenna unit (AAU). Their works illustrated that the cooling efficiency improves with an increase in the number of fins. With their relatively low heat transfer rates that present a significant limitation, passive cooling techniques are commonly used in base stations [69] which require further optimization [70] for 5G and 6G systems. Currently, the majority of research concerning heat dissipation in 5G base stations is primarily focusing on passive cooling methods. Today, there is a clear gap in the literature in terms of research investigations that tend to quantify the temperature performances in 5G electronic devices. It is important to note that an effective thermal management system is crucial in ensuring the good operational efficiency of 5G equipment [71]. Phase-change materials (PCMs) are recognized for their ability to handle superior temperature control within a well-defined time period. Thus, their integration with heat sinks can be a promising approach for enhancing the thermal performance of electronic devices [72]. The advantage of PCMs over other materials is that, by controlling their volume fraction, in combination with heat sinks integration, their operating time to reach a set point temperature (SPT) can be controlled (see [PERSON] et al., 2020 [73]). As an example, [PERSON] et al., 2010 [74] conducted an experimental analysis to quantify the cooling efficiency of portable electronic devices employing a PCM-based heat sink with fins.