Heat transfer is critical to the performance and safety of mechanical components, and fins are a key technology for enhancing it. This article examines the role of fins and efficient cooling methods.
Long ago, in 2016, the Samsung Galaxy Note 7 explosion incident occurred, leading to a recommendation to discontinue its use due to the risk. This incident caused a major shock worldwide and sparked extensive discussions and research on the safety of electronic devices. Particularly, several issues related to battery technology safety were re-examined, prompting many companies to strive to ensure product safety. While the exact cause of the explosions remains unclear, the most likely culprit is battery overheating. Battery overheating occurs when heat transfer to the outside is insufficient. It is crucial to consider this heat transfer during the design and manufacturing of mechanical components. This article briefly introduces the fundamentals of heat transfer and fins, which are efficient for increasing heat transfer rates.
What is heat transfer? To answer this question, heat transfer refers to the movement of thermal energy due to temperature differences. In other words, heat is transferred when a temperature difference exists within or between media. There are three modes of heat transfer: conduction, convection, and radiation. Conduction is heat transfer that occurs through a stationary medium, such as a solid or liquid, when a temperature gradient exists within it. For example, heating one end of a metal rod causes heat to travel through the metal to the opposite end—this is conduction. Convection is heat transfer between surfaces of different temperatures and a moving fluid. For instance, when boiling water in a pot, heat is transferred through the circulation of the water—this is convection. Radiation is heat transfer between surfaces of different temperatures, occurring even without an intermediate medium. A prime example of radiation is solar energy being transmitted to Earth through space. To prevent overheating of machine components, efficient heat transfer between the component and the external fluid is essential. Next, we will examine heat transfer methods and their corresponding cooling methods from the perspective of machine component production. Among conduction, convection, and radiation, heat transfer via radiation is negligible compared to conduction and convection, so it need not be given significant attention. Therefore, its explanation will be omitted.
Conduction can be viewed as the transfer of energy from more active particles to less active particles within a material through particle-particle interactions. Fourier’s Law is the equation describing the heat transfer rate due to thermal conduction. This law states that the heat transfer rate due to conduction is proportional to the thermal conductivity, the cross-sectional area, and the temperature difference, and inversely proportional to the distance (in the direction of heat transfer).
Convection is energy transfer due to irregular molecular motion or diffusion. For example, in a heating system, warm air circulating through a room to transfer heat is also a type of convection. Similarly, Newton’s cooling law, the heat transfer rate equation for convective heat transfer, states that the heat transfer rate is proportional to the convective heat transfer coefficient, the cross-sectional area, and the temperature difference.
According to these two laws, there are three main methods to significantly increase the heat transfer rate for efficiently cooling overheated machine components. First, increase the thermal conductivity and convective heat transfer coefficient. Second, increase the temperature difference between the component and the external fluid. Third, increase the cross-sectional area. Since thermal conductivity and convective heat transfer coefficient are inherent material properties, improving them requires manufacturing the mechanical component from better materials. However, this faces the issue of cost. To increase the temperature difference between the component and the external fluid, the temperature of the external fluid must be lowered. Except in special cases, ambient temperature is constant, making this difficult as well. On the other hand, increasing the cross-sectional area can easily significantly boost the heat transfer rate. The expanded surface created in this way is called a fin.
Fins can be found in everyday objects. Consider the engine cases or radiator housings of motorcycles and lawnmowers. Fin shapes can be varied, broadly categorized into straight fins, annular fins, and finned fins (spine-type fins). The choice of fin shape is determined by volume, weight, manufacturing conditions, and cost. The most critical aspect of fins is their performance. Fins’ performance isn’t governed by a simple, easily formulaic law. Calculating fin performance involves considering various conditions at the fin tips, allowing trends to be inferred by synthesizing these calculations. Inference suggests that fins perform better when they are thinner and spaced closer together, within the range where they do not interfere with each other due to excessive proximity. Furthermore, considering the thermal conductivity, weight, and cost of the fins, aluminum alloys are most commonly used.
We have now covered the fundamentals of heat transfer and briefly introduced fins. Fins are predominantly used in manufacturing components where overheating could compromise functionality. They are particularly essential in various industries requiring efficient thermal management, such as aerospace, automotive, and electronics. Heat transfer is thus a critical factor in producing safe mechanical components. It is essential to consider how much a component can overheat and whether it can be sufficiently cooled to prevent malfunctions. While recent technological advancements have led to the development of diverse machinery, we must not be blinded by new features and technologies. Instead, we must prioritize fundamental safety considerations to prevent the recurrence of incidents like exploding smartphones. Furthermore, these technical challenges and the pursuit of safety will serve as important lessons for future technological development.
