Electronic Design

Hot Applications Warm Up To Liquid Cooling

Gamer PCs, high-end projectors, LED displays, and other applications with high power densities have maxed out the ability of conventional cooling methods to keep system thermal levels within acceptable operating limits, indicating the need for a "next-generation" approach. Multiple heat pipes, vapor chamber/fan heatsink hybrids, and other optimized cooling methods, including the use of new multicore, low-power processors, can only delay the inevitable need for more efficient cooling as higher-performance applications continue to generate greater levels of thermal energy.

One such alternative, liquid cooling, is available today to fill that role. While liquid cooling systems (LCS) have been around for several years, leakage and other reliability problems that prevented general market acceptance dogged early designs. But now, tens of thousands of LCS have experienced up to several years of operation with zero field failures. This dramatic illustration of a cooling technology whose time has come is driving growing market acceptance of a cooling technique once considered questionable, but no longer deemed so by growing numbers of system designers and OEMs.

The crux of the problem driving renewed interest in LCS is higher total chip power, higher local heat flux in chip hotspots, and smaller system enclosures. These three compounding trends underscore the challenge facing conventional cooling systems and their growing inability to:

* Efficiently dissipate heat with high average heat density above 100 W/cm²

* Maintain consistent die temperature in the presence of local hot spot zones of 1 to 2 mm², with power densities of 500 W/cm² or above

* Decrease system noise caused by high-volume airflow

* Sustain reliability due to increased numbers of high-speed fans

Alternatively, the latest closed-loop microstructure LCS designs are a viable alternative for cooling high-power-density processors up to 1000 W/cm². This highly flexible concept is readily adaptable to single-CPU configurations, racks, servers, graphics chips, high-output LEDs, voltage regulators, insulated gate bipolar transistors (IGBTs), power semiconductors, and field effect transistors (FETs).

Performance & Reliability

The cooling solution used by most gamer PCs, a card-level heat-pipe heatsink with a fan, is generally limited to a total cooling power of only 120 W per card in a standard multicard configuration. Alternatively, LCS have demonstrated the ability to cool up to 450 W, or 150 W each for each the system's CPU and dual graphics processor chips.

Accompanied by extremely quiet fan operation, outstanding thermal performance is obtained from a very low combined airflow of only 60 cfm for all three system fans. Further, benchmark test results have shown a GPU case temperature of only 37°C at ambient room temperature—a significant thermal performance improvement over commercially available air-cooled solutions used in similar applications.

Cost of Ownership

In high-power/brightness LED display applications, the superior thermal performance of a well-designed LCS enhances projection system performance with a continuously bright light source and dramatically longer service life. Another consideration, as many as 10 or more 1000- to 2000-hour-rated arc lamps that cost hundreds of dollars each, may be required over the normal service life of one liquid-cooled LED device—representing a significantly higher cost of ownership versus the LCS solution.

As a technical challenge, the tremendous heat generated by LED power densities approaching 1000 W/cm² will require an aggressive thermal-management solution. At this stage of the game, liquid cooling is the most viable candidate in terms of reliability, scalability, and adequate thermal performance for the foreseeable future.

TAGS: Components
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