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Although liquid and two phase are becoming more popular, air cooling is still the most common type of electronics cooling. Often equated with fans, air cooling encompasses both forced and natural convection. An extremely simple example of air cooling would be the use of a heat sink or heat spreader used on its own, where the heat sink conducts heat away from the heat source to the ambient air. More complex air cooled thermal solutions would include air movers such as fans, blowers, pulsejets, or even an air to air heat exchanger.
Lower power devices and heat densities can be cooled passively with natural convection. Heat conducts through the metal heat sink or spreader from the heat source into the ambient air, buoyancy then carries the hot air away from the device. Performance of these solutions relies heavily on geometric design to optimize the effects of conduction and buoyancy.
The construction and fabrication method of the heat sink depends on device type, placement, and heat load. Stamped heat sinks come in a wide range of shapes and sizes to accommodate specific devices with low heat loads. Devices with a higher heat load often require a larger heat sink constructed of a base and fins. Traditional base and fin heat sinks for natural convection are designed with wider fin gaps to optimize the effect of buoyancy and are constructed from a solid piece of metal (extruded or skived fabrications) for better conduction.
Fans and blowers for cooling electronics work in much the same way as any other fan or blower, but with specially engineered attributes that optimize them for cooling assemblies. They are designed to balance power consumption and flow capacity so that they can work efficiently within the device. This is a particular concern for battery powered applications.
Axial fans pull air in and blow it forward along the same axis while blowers pull air in and eject it through a nozzle in a different direction. This gives greater flexibility for fan placement as it can either be mounted on top of the fins of the heat sink for impinged flow or on the side for standard air flow. Blowers, on the other hand, provide for lower profile and hot spot cooling. Blowers also have a higher static pressure, allowing them to push air through the fins more forcefully. Heat sinks used for forced convection cooling with fans or blowers typically have higher fin densities.
Aavid PulseJets utilize unique patented synthetic jet technology where an oscillating diaphragm is used to emit quick pulses of air across a heat source or the fins of a heat sink. As the air blows quickly out of the opening, ambient air around the nozzle is entrained, increasing the overall airflow. This allows for greater air flow at a lower power consumption. Additionally, the puffs of air being consistently pushed across the heat sink fins creates turbulence and improves overall heat transfer.
PulseJets are frictionless air movers, they have no bearings, sleeves, or any other frictional parts that can cause the reliability issues seen with fans or blowers. This high reliability combined with low power consumption and low profiles make PulseJets ideal for small form factor cooling, RRUs, and LED cooling. The most popular line of PulseJets, Aavid SynJets, can be paired with specially engineered LED heat sinks for reliable, long lasting cooling at a fraction of the size and weight of natural convection cooling.
For more information on Air to Air Heat Exchangers and more complex systems, go to our Heat Exchanger section.