Cooling System Design
Unlike processor coolers, designing cooling solutions for powerful graphics adapters doesn’t give you much room for engineering maneuvers. While the shape, size and weight of the former may vary within very wide range, the latter have these parameters set pretty strictly to ensure that the graphics accelerator will fit into the standard ATX system case and will not block more than one expansion slot on the mainboard. However, since the power consumption of contemporary GPUs is sometimes even higher than that of the fastest CPUs, they should feature extremely efficient cooling solutions. It is a hard task to fulfill considering the limitations mentioned above. Over the years of graphics card cooling systems evolution, the developers have checked out multiple designed and with the time both ATI/AMD and Nvidia have arrived at a more or less unified design of their graphics card coolers that ensured maximum efficiency with acceptable size and levels of generated noise.
This design implies a radial fan (the so-called blower or centrifugal), grabbing the air from the middle of the system case, pushing it through the heatsink dissipating heat from the GPU, memory and other components, and ousting the air outside the case through the slits in the dual-slot bracket in the rear panel of the case.
The interesting thing about radial fan is that is provides higher static airflow pressure and lower turbulence while its performance remains the same as that of the axial-flow fan.
So, a fan like that works better with long heatsinks with relatively small gap between the fins in the array, and these are exactly the type of heatsinks that are used in Nvidia GeForce 8800 GTX/GTS and AMD Radeon HD 2900 XT coolers.
Unlike Nvidia solution, this cooling system uses copper heatsink. It definitely has a positive cooling effect, but also increases the weight of the entire system quite noticeably. The heatsink array consists of 30 fins sitting on copper base that is pressed directly against the graphics processor die. For more even heat distribution there are two heatpipes connecting the heatsink to the copper base of the cooler. This heatsink is not as large as the one on GeForce 8800 GTS, but the use of copper instead of aluminum may definitely make up for the smaller heat dissipating surface area. The cooler base is connected to a steel frame that serves to fasten the cooler to the PCB with four screws. There is a resilient metal plate on the reverse side of the PCB that ensures tight contact between the cooler base and the GPU and protects the PCB against bending.
They use traditional dark-gray thermal grease between the die and the cooler base. The base of the cooler and the heatsink are not connected mechanically with the read aluminum part that cools the memory chips and other power elements on the PCB via the pink elastic thermal pads. This part of the cooler is fastened to the PCB with another 8 screws. The same screws press the black hear-spreader plate used for the memory chips to the reverse side of the PCB. The memory chips are covered with the pink thermal pads that ensure proper contact between the surfaces. Since the memory works at frequencies much lower than the nominal, this cooling is quite sufficient for it. The aluminum part is cased into semi-transparent red plastic with silverfish ornaments on it that symbolize flames.
Radeon HD 2900 XT uses a fan with pulse-width modulation method for the speed control connected to the board via a four-pin connector. It seems to be more powerful than the one on GeForce 8800 GTX/GTS and should produce a lot of noise at full speed. Taking into account smaller heatsink surface area and high power consumption of AMD R600, we can expect pretty noisy operation even in everyday routine work, but we will find out later if it is really so.
All in all, the cooling system of the new AMD Radeon HD 2900 XT uses the today’s most optimal design with radial fan, heatpipes and warm air redirect outside the system chassis. Hopefully, it will prove as efficient as the Nvidia cooling solution developed for GeForce 8800 GTX/GTS family.