# Heat Transfer Optimization of an Electronic Control Unit Immersed in Forced Liquid Coolant
## 1 Introduction
[23] concluded that direct liquid cooling of base plates produced the best results, and stacked liquid-cooled modules enabled switching high power in a small volume. GRC Electrosafe [24], a hydrocarbon-based fluid, was shown to have significantly better heat transfer than an air-cooled solution. [PERSON] et al. [25] discovered that direct liquid cooling could reduce the thermal resistance of a junction to a heat sink by more than 50% due to the elimination of the thermal grease layer. As a result, active and passive temperature fluctuations are significantly reduced, which can improve module reliability and life. Spray cooling, a promising cooling solution that uses a direct coolant and has applications on high-performance computers and data centers, aerospace and spacecraft, or hybrid electrical vehicles [26; 27], has a 409.3% better heat transfer coefficient than forced air, according to an investigation on battery thermal management by [PERSON] et al. [28]. The disadvantages identified by [PERSON] et al. [26], which include the complexity of the nozzles structural design, long-term corrosion and blockage of the nozzles, and the complicated interrelationship between all parameters considered for the system, including spray parameters, working fluid type, surface modification, and environmental parameters to obtain a good system performance, all lead to the conclusion that the use of spray cooling in a vehicle ECU appears to be challenging. Immersion cooling, which employs dielectric fluids, has emerged as one of the most promising methods of removing heat from high power densities compared to indirect cooling, according to [PERSON]'s classification [29]. SLIC technology is widely used in data centers, and liquids are recirculated to improve thermal management. Mineral oil outperformed silicone oil, synthetic esters, and natural esters in terms of thermal performance. Because of its low cost, toxicity, and wide operating temperature range, mineral oil is an excellent choice for battery immersion cooling systems and data centers [30; 31; 32; 33; 34]. It also has no impact on the reliability of electronic devices or the increasing corrosion rates [35]. A study with perfluorocarbon-structured refrigerant (Fluorimet) demonstrated that it can be used as an immersion coolant with natural convection in a data center [36]. Immersion cooling, which immerses the battery in a dielectric fluid, has the potential to increase heat transfer rate by 10,000 times over passive air cooling, as recently reported by [PERSON] et al. [37]. To investigate additional thermal solutions for electric vehicle batteries, many studies use hydrofluoroether [38; 39] or natural and synthetic esters [31; 40; 41]. There is an effort to demonstrate that by enhancing their properties with nanoparticles, biodegradable materials can match the properties of mineral oil [42; 43]. In comparison to their basic conventional fluids, nanofluids were shown to have much enhanced thermal properties, particularly thermal conductivity and convective as well as boiling heat transfer features. These novel fluids not only possess desirable high thermal properties but also have several advantages and applications in other fields, including electronics [44; 45]. Novec 3283, Novec 43, 50 cSt silicone oil, 20 cSt silicone oil, and soybean oil were tested as single-phase immersion coolants [46]. Because of its lower viscosity, the 20 cSt silicone oil performs better in natural convection than the 50 cSt silicone oil. The viscosity of the fluid is critical to pumping efficiency. When compared to existing mineral base oils used in driveline formulations, synthetic fluids such as PAO have a wider range of viscosities and can go to much lower viscosities (2 cSt, KV 100 \({}^{\circ}\)C). This implies that synthetic fluids with lower viscosity can provide better pumping efficiency and possibly better heat transfer efficiency in the system. On the other hand, immersing electronic components in viscous coolants provides a slight mechanical advantage.