A majority of unmanned aerial vehicles (UAVs) and military aircraft are equipped with advanced electronics and equipment that is integral to their optimal functionality. As electronic devices produce excess heat, they necessitate thermal management systems to improve their reliability. Typically, the amount of heat output is equal to the power input as long as there are no additional energy interactions. As such, selecting the proper thermal relief system should correspond to the amount of heat that must be expelled.
To accommodate for the immense heat generated in UAV electronics, engineers have developed several cooling systems, such as heat sinks, forced air systems and fans, heat pipes, and various others. For the most part, the implementation of such thermal management systems depends on design restrictions like space and thermal loads. As each method of thermal management comes with its own advantages and disadvantages, this blog will go over each briefly.
Natural & Forced Air Convection
Often considered the original cooling method for early UAVs, natural and forced air convection systems are the least costly option available. Thermal relief is provided as air flows through the system via vents in a natural convection design or propelled via fans in forced convection systems. To facilitate heat transfer, heat sinks can be implemented alongside a heat producing device.
Despite their benefits and ease of use, air-cooled systems have limited thermal management capabilities. Air can only remove a limited amount of heat, meaning that these systems cannot compensate for the amount of heat generated by modern UAV electronics. Additionally, the use of unfiltered air can pose complications in applications where maintaining isolation from the external environment is pertinent.
Radiant heat sinks consist of metal cold plates with cooling fins that remove heat due to their increased surface area being exposed to a secondary cooling system, such as forced air convection. Generally, heat sinks feature a metallic object that comes into contact with an electronic component’s hot surface. In such instances, a thin thermal interface material (TIM) like thermal transfer paste is coated between the two surfaces to maximize the thermal transfer rate. For heat sinks that need to accommodate both fins and a forced air system, they can be designed to be large in scale.
Liquid Cooling Systems
In liquid cooling systems, coolant runs through the cold plate, removing heat and releasing it through a heat exchanger. With this method, the cold plates are maintained at an even temperature, allowing for effective thermal transfer. This also applies to systems exposed to cryogenic temperatures where heated fluid passses through plates to keep the electronic system within an acceptable operating temperature range.
In this method, the heat source is cooled under a thick, cold plate which improves heat transfer between the heat source and the cooling fluid by conducting the heat current in an optimal manner. Between the interfaces, a TIM is utilized to maximize energy transfer. The biggest benefit to this method is that no additional heat transfer surface area is required.
As modern electronics have increasing thermal relief demands, engineers have opted for liquid-cooled cold plates. Typically, cold plates use a metal plate to remove heat from power electronics. Electronic devices are positioned onto the metal, enabling heat to transfer through a cooling fluid that runs through the cold plate. It is important to note that cold plates must be paired with an additional cooling method to remove heat from the cooling fluid. However, the need for an extra cooling method often complicates the overall design and limits the cold plate’s thermal management capabilities.
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