Combined Conduction and Convection Heat Transfer in Heat Sinks

Key Takeaways

• In combined conduction and convection heat transfer, the conduction process transfers heat generated to the surface of the component and convection establishes heat transfer to the surroundings.

• Combined conduction and convection heat transfers require a medium for thermal transport.

• Fin arrangement is crucial for achieving effective combined conduction and convection heat transfer rates in heat sinks.

Electronics cooling using heat sinks is an example of combined conduction and convection heat transfer

Electronic heat transfer processes have gained attention with the increasing demand for high power density and complex and reliable circuits. Heat transfer processes--conduction, convection, and radiation--allow electronic components to maintain their temperature below the failure threshold. To prevent failures in electronics, cooling is employed in critical circuits. In most cases, electronics cooling is a combined process. For example, the thermal management in an electronics circuit can be a three-in-one heat transfer clubbing conduction, convection, and radiation or it can be combined conduction and convection heat transfer, but never conduction vs convection heat transfer. Radiation and radiant heat is rarely combined with convection and conduction, but is still a vital process to understand for thermal conduction as well as with electromagnetic radiation calculations.

Conduction and convection heat transfer processes seldom occur individually. This co-existence makes combined conduction and convection heat transfer a common phenomenon in any thermal management system. Thermal energy and hot air each utilize vapor, heat loss, and kinetic energy to determine the energy output and management of an electronic system. Let's explore combined conduction and convection heat transfer and how the fin arrangement in heat sinks influences the combined heat transfer rate.

Combined Conduction and Convection Heat Transfer

Electronics cooling is a thermal management method that utilizes various techniques or props for heat transfer from critical components. The heat transfer process accounts for the spatial distribution of heat losses generated in the critical components present in electronic circuits. As energy transfer from a heating element requires a finite understanding of temperature difference, thermal radiation, heat conduction and convection heating, you will want to know the style of heat flow to resolve your thermal conductivity. The heat transfer process employs different modes, such as conduction, convection, and radiation, for heat dissipation from the circuit. In combined conduction and convection heat transfer, the conduction process transfers heat generated to the surface of the component and convection establishes heat transfer to the surroundings.

Convection heat transfers can be either natural or forced. Natural convection doesn’t require any external stimuli for initiating the heat transfer process. The temperature of the critical component induces density variation in surrounding fluids, causing fluid flow, which results in natural convection. In forced convection, external forces such as pumps, fans, or wind induce fluid flow. 

Medium Requirements in Combined Conduction and Convection 

Conduction and convection heat transfer processes are entirely different in characteristics except for the fact that they transfer heat from a hot to a cold body. Fluids are the medium in convection, whereas solids function as the medium in conduction. Due to the differences in heat transfer mediums, the equations defining conduction and convection are totally different. Fourier’s law of conduction governs the thermal conduction process, whereas Newton’s law of cooling is typically used to mathematically represent convection. To mathematically express combined conduction and convection heat transfer, Fourier’s law of conduction and Newton’s law of cooling are rearranged depending on how the two heat transfers are taking place.

Combined conduction and convection heat transfer can take place either in series or in parallel. Irrespective of the series or parallel occurrence, combined conduction and convection heat transfer require a medium for thermal transport. There is no combined conduction and convection heat transfer possible in a vacuum, only radiation establishes heat dissipation without a medium.

Let’s look at an example of electronic cooling where combined conduction and convection co-exist.

Combined Conduction and Convection in Heat Transfer

A heat sink is one of the main thermal management devices used for electronics cooling. Heat sinks are passive heat exchangers that utilize conduction and convection heat transfer modes for heat dissipation from electronic circuits. They transfer heat from critical components to the surrounding medium using conduction and convection, thus helping to regulate the component temperature below the failure thermal limit.

The absence of moving parts is an important factor that directs the dissipation of heat energy from electronic components to heat sinks. The internal distribution of heat energy from the critical component to its surface takes place via conduction. The heat sink attached to the critical component surface transfers heat from the component surface to the heat sink surface also via conduction. At the heat sink surface, extensions, called fins, are arranged for enhancing the heat transfer beyond the plain surface. The heat sinks often come with different fin arrangements such as plain fins, extruded fins, bonded fins, brazed fins, etc. It is the fin arrangement that initiates convective heat transfer around heat sink boundaries.

Characteristics of heat sink fins influence the convective heat transfer process. The fin-shape, material, temperature distribution, type of fin tips, etc. affect convective heat loss in heat sink-based thermal management systems. In the combined conduction and convection heat transfer process that takes place in heat sinks, convective losses from fins affect the conduction rate along the fins.

It can be concluded that fin arrangements are crucial for achieving effective combined conduction and convection heat transfer rates in heat sinks. Celsius Thermal Solver or Future Facilities software can help you in designing your heat sinks for electronics cooling.

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