Avionics Cooling Thermal Management Methods
Modern unmanned aerial vehicles (UAVs) and military aircraft carry advanced electronics and equipment critical to their successful operation. Innovation is carrying airborne technologies farther and higher than ever before, and current avionic cooling practices are evolving to keep up.
To accommodate the immense heat generated by modern UAV electronics, design engineers have several cooling options at their disposal.
While the method implemented often depends on design restrictions such as space and thermal load, each method has its own inherent advantages and disadvantages that should be considered.
Natural Air & Forced Air
Natural and forced air systems were the original avionics cooling method for early UAV’s, and are often the least costly option available.
Air provides thermal relief simply by flowing through the system either freely through vents in a natural air design or propelled via fans in forced air systems.
Despite the benefits of simple design and the abundance of coolant available in the Earth’s atmosphere, air-cooled systems are limited in their thermal management capabilities.
Air can only remove so much heat, therefore these systems’ cooling capabilities typically cannot compensate for the amount of heat generated by modern UAV electronics.
Cold plates use a metal plate to remove heat from a process by conduction. While typically a simple and compact avionics cooling method, cold plates must also be paired with an additional cooling method to remove heat from the plate (forced air, for example).
This reliance on a secondary cooling method may complicate designs and severely limit the cold plate’s thermal management capabilities in complex or enclosed systems.
Heat sinks, which are essentially cold plates with exhaust fins, are more efficient at removing heat due to their increased surface area.
The fins are exposed to a secondary cooling system, typically forced air, to facilitate thermal relief.
Due to heat sink size demands to accommodate both bulky fins and a forced air system, designs implementing this coolant method must often be larger in scale.
To accommodate the increasing thermal relief demands of modern electronics, design engineers have turned to liquid-cooled cold plates. In
these designs, a line of coolant runs through the cold plate, removing heat and releasing it through a heat exchanger.
Using this method, the cold plates are kept at a fairly even temperature, avoiding temperature spikes and allowing for effective thermal transfer.
Compact and efficient, liquid cooling is ideal for designs with space constrains and high thermal output, making them a good fit for many aircraft applications.
The downfall of this perfect match, however, comes in the form of increased pricing and complexity and the demand for more engineering hours.
Fixed vs. Thermostatic Liquid Cooling
With traditional fixed flow through a liquid cooling design, coolant continuously moves between the cold plate and the heat exchanger, regardless of the coolant’s actual temperature. This decreases cooling efficiency and increases coolant usage.
To remedy this design flaw, thermostatic valves are used to direct coolant flow either to the heat exchanger or back through the system, solely based on fluid temperature. This ensures efficient usage of coolant and reduces overall system wear, extending the life of system components over time.
Of course, each liquid cooling system has unique thermal needs. To accommodate a variety of designs, ThermOmegaTech offers thermostatic thermal bypass valves in a variety of sizes and temperature set-points.
Which Cooling Technique Is Best?
Selecting which cooling method to implement into a project will depend heavily on thermal load, space restrictions, and cost sensitivity.
For less complex systems, forced air and cold plates may satisfy meager thermal management needs. However, as UAV designs become more complex, design engineers are likely to continue turning to liquid cooling to keep up.