Heat sinks are thermally conductive, usually metallic components or devices that absorb and dissipate heat generated by electronic components such as computers. Common heat sink materials include aluminum, copper, and steel. Larger heat sinks hold more heat than smaller heat sinks because of the relationship between surface area and the ability to dissipate heat radiantly. To help increase surface area, some heat sinks include integrated fans that use directed fins to achieve specific airflow geometries. These active heat sinks or fan sinks are typically used in CPUs as coolers and may be designed for specific processors. Passive heat sinks, such as thermal pads, do not contain integrated fans or other electronic components. Heat sinks include liquid coolers, which use a liquid medium such as water or liquid nitrogen to remove heat from components, and thermo-electric coolers, which use an electric element to pump heat from the element’s hot side to its cool side and transfer heat from the component to the environment. Vapor coolers or phase change coolers are similar to air conditioning or refrigeration systems, but evaporate a refrigerant in a small block mounted directly on the component.
Heat sinks vary in terms of length, width, height, and weight; fan airflow, speed, and noise level; DC voltage; and heat sink fin style. Round pins or elliptical fins offer a high surface area to weight ratio and provide multiple airflow paths. Straight fins use extruded and sometimes complex shapes to maximize the heat dissipation surface area. Stamped metal heat sinks are manufactured in standard configurations, and according to application-specific geometry and thickness requirements. Machined plate heat sinks conform to exact tolerances and are free of burrs and other irregularities. Heat sinks with folded fins include a continuous strip of convoluted or corrugated sheet metal stamping that is formed to a specified height, while heat sinks with bonded fins include a stamped or pre-fabricated plate bonded to a channel on a heat sink base plate. Heat pipes are evacuated vessels that are with back-filled with a small quantity of working fluid.
Important considerations when selecting heat sinks include component materials and thermal resistance. Heat sinks that are made of mixed materials typically include aluminum, copper, and steel in varying amounts. The central performance specification for heat sinks, thermal resistance or thermal sensitivity is typically expressed in Celsius (°C) as the temperature increase per watt of heat handled. For catalog and comparison ratings, thermal resistance is a nominal specification. Factors that affect this specification include increased airflow, water-cooling, and ambient temperatures. Frequently, thermal resistance is presented as a performance curve.
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CPU fans and coolers are integrated fans and heat sink assemblies packaged to provide optimum cooling performance, often for specific processors.