The requirements for power density are increasing, resulting in smaller form factor devices, which produce more heat. A good thermal design is essential to ensuring the reliability and life of a product used in harsh military environments. Modern equipment is pushing to be smaller, use fewer moving parts and increase the density of chips and components. This means there is less room for the power supply and the systems that will cool it. The more extreme your requirements for space, operational temperature, or life span, the harder it becomes to properly power and cool that equipment.
Here’s an overview of the three most common ways a power supply is cooled, along with some considerations for each. We’ll touch on the most prevalent methods. Advanced Conversion Technology is able to implement these thermal design techniques and understand what the future of cooling will be.
Conduction cooling transfers heat from high temperature to lower temperature parts by direct contact. Heat sinks and cold plates are used to conduct heat away from hot components within the device. Conduction cooling can be attractive where electrical and audible noise is a concern but is limited when high power densities are required in a limited space. Conductive cooling allows you to seal your device from harsh environments and minimize electromagnetic interference.
Improving thermal resistance between heat dissipating components and their cooling device is very important and can be minimized with the proper surface finish and thermal interface materials. The proper thermal interface can significantly reduce the temperature of small, high-power components. In addition to more common materials, phase change or graphite thermal interface materials minimize the small air gaps between a component and its heat sink. Thermally conductive potting materials are used to improve conductive heat transfer to chassis, especially components with complex geometries.
Often, conduction is used in conjunction with liquid cooling in an overall design. Liquid cooling techniques have become prevalent in high power density designs. Heat is conducted to a liquid, which transfers the energy to another location to be dissipated. Heat pipes, vapor chambers, and liquid cold plates are very effective at removing large amounts of heat.
This involves the transfer of heat from a device to a fluid, such as air. Natural convection takes advantage of the buoyancy effects of heated air. Air is heated by the device, which becomes less dense, rises as a result, and transfers heat to the environment. Natural convection cooled devices depend on a supply of cool air surrounding the device. Although the rate of heat transfer is limited, the advantage of this method is that there are no electromechanical fans to deal with and the device can be sealed from more extreme environments, such as those encountered by the military.
Convection supplies often have specific requirements for testing and installation to ensure that it will operate properly during your specific type of operation. Air can behave in many different ways, understanding this flow and how it impacts the power supply is essential to ensuring a long life for your equipment.
One of the most common cooling methods is the use of fans or blowers to force air across the supply, moving heat away from the device and into the air stream. This method can be effective and economic but can have several disadvantages that need consideration. Fan and blower motors require space and also dissipate additional heat and produce unwanted noise. Internal fans mean that your device will require openings and therefore is exposed to the environment and other means of protecting internal components will need consideration.
This involves the transfer of heat by means of electromagnetic radiation, which moves, from a hot surface to a cooler surface. Radiation does not require a medium to transfer heat and can take place in a vacuum. An example of radiation is the heat you feel coming from a fire when you place your hands near the flame. The efficiency with radiant heat transfer takes place is dependent on the emissivity of a material’s surface, often times the surface is coated with a dark-colored finish, which provides a higher emissivity than a metal finish. Radiant heat transfer is less effective than conduction or convection but can reduce temperatures by up to 10%.
As there are several different ways a power supply can be cooled, Advanced Conversion Technology (ACT) can design a custom thermal solution that will meet your cooling and environmental requirements based on mounting, available space, and method of cooling. Using computational fluid dynamics (CFD) simulation software, we can determine the cooling method or combination of cooling methods to provide an overall solution to meet your needs and quickly determine if a change or modification will affect a design. Contact us today to see how we can help with your project.