# Heat Transfer Optimization of an Electronic Control Unit Immersed in Forced Liquid Coolant
## 1 Introduction  
ECUs are widely used in the automotive industry. The number of functions that these ECUs must complete has steadily increased in recent years. New requirements and the latest technologies have created numerous opportunities and possibilities for the development of new applications and functions for automobiles that users can connect with. As part of the IoT (Internet of Things), vehicle modernization will result in the integration of ECUs into standardized High-Performance Computers (HPC). Because of the trend toward centralized computation with dynamic resource allocation, the focus markets of this cluster may overlap with other automotive controller and infotainment applications. Autonomous car applications will dominate the automotive AI (artificial intelligence) market, and computing will dominate the HW costs. By 2028, the computing HW market will be worth $13 billion, accounting for roughly 10% of total electronic control unit markets. The second-most common HPC-HW application in automotive is infotainment. By 2028, AI computing for infotainment will be worth $0.8 billion [1; 2]. Memory is another important IC (integrated circuit) market in the automotive sector, with $2.5 billion in 2017 and averagegrowth of 20% expected in the near future [3]. The exponentially increasing data volumes and rates, both in the wired and wireless domains, are a major industry trend. End-users in automotive interior electronics are increasingly expecting the same innovative features found in consumer electronics, such as curved and flat displays, haptic feedback, and so on. Introducing these technologies into automotive markets while maintaining long-term reliability is a difficult task, where materials and methods for PCB (Printed Circuit Board) assembly play a critical role. These are the factors that increase the power of the vehicle's ECUs. To compete in the market and meet customer demands, machine manufacturers must provide these features and services. Because of the large amount of power required to perform functions, the cooling of electronic components in the automotive industry has begun to be limited. A scalable \"add-on\" cooling solution for electronics is an interesting and appealing addition to the product/solution, appealing not only for HPC but also for growing markets of battery/hybrid vehicles [4; 5] and TCUs (Telematic Controls Units) or lidar and radar products, where the trend is to pack more powerful chips into a more compact space, passive cooling is reaching its limits, and new solutions are sought. Currently, heat transfer systems for ECUs in conventional cars are overly conservative, with thermal paste, metal housings, or fan cooling solutions being the most common [6]. The benefits of these technologies are that they are inexpensive, but numerous air-filled spaces can be found inside the module due to design restrictions on housing production. Air has no effect on the heat transmission of electrical components because it is an insulating medium. Indirect contact cold plate cooling using an ethylene glycol/water mixture or R134a as working fluids has been used in recent years [7], but it has drawbacks such as being influenced by the thermal resistances of the materials used in between, having poor temperature uniformity, low stability for temperature control, and the heat dissipation capacity being highly dependent on the flow rate. Air cooling has the advantages of simplicity and low cost. It does away with the need for cooling loops and any worries about liquid leaking into the electronics. The most significant disadvantage of air cooling is its inefficiency. Even with high-powered blowers, air cooling cannot transport as much heat as a liquid system [8]. This has caused issues for EVs (electric vehicles) in hot climates, and blower noise can also be a problem. The acoustic behavior, however, depends strongly on the size of the fan used at a particular airflow [9]. Nonetheless, air cooling solutions serve a purpose and provide value.