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Cooling System

Now let’s have a look at the cooler installed on the GeForce 8800 GTX card. Obviously, it is expected to dissipate the same amount of heat as today’s CPU coolers do, yet keep rather compact. As opposed to the CPU cooler, the graphics cooler has little room for growth as it is limited to the dimensions of the graphics card. How did Nvidia solve that riddle?

It has already become clear that the cooling system of a modern graphics card must exhaust hot air out of the system case. The extra 120-150 watts of heat inside the system case would make the thermal conditions there unbearable, especially if the system features a top-end CPU. ATI Technologies has been using such coolers since the Radeon X850, but Nvidia has only partially followed this concept until now (if you don’t count in the notorious cooling system of the GeForce FX 5800 Ultra). As you know from our reviews, the cooler of the GeForce 7900 GTX exhausts only a portion of hot air out of the case whereas the cooler of the GeForce 7950 GX2 doesn’t do even that due to the dual-PCB design of that graphics card. Developing the new cooling system for the GeForce 8800 series, Nvidia tried to address the older flaws and get rid of them where possible. Here’s what they have come up with in the end:

The new cooler resembles the device that was installed on the GeForce 6800 Ultra, but larger and turned around by 180 degrees so that the hot air was exhausted through the slits in the graphics card’s mounting bracket rather than into the system case. Of course, the cooler is more sophisticated than the one installed on the GeForce 6800 Ultra because the G80 generates more heat than the NV40. To our surprise, Nvidia didn’t use a copper heatsink as ATI did on its cards. You can see it through the slits in the casing that the heatsink, as before, consists of thin aluminum plates. We removed the cooler’s casing to see the following picture:

We can see the same component layout as in the ATI Radeon X1950 XTX cooler: the heat generated by the GPU is transferred to the massive copper base and is evenly distributed in the heatsink by means of a heat pipe, which greatly facilitates the transfer of heat.

The base, the heatsink and the fan are installed on a light aluminum frame that has protrusions opposite to the memory chips, to the chip containing TMDS transmitters and RAMDAC, and to the switching MOS transistors in the power circuit. In every case, there are traditional thermal pads made from some non-organic fiber and soaked in white thermal grease that serve as the thermal interface. There’s a layer of dark-gray thick thermal paste between the copper sole and the GPU cap. The frame has rectangular slits near the fan which helps improve the cooling of the power elements and the PCB by taking air in through those slits.

The heatsink is cooled with a blower whose airflow is directed perpendicular to the axis of its blades. The static pressure of the stream of air is higher than with the classic axial fans of the same wattage. A blower is the optimal choice for this cooling system design as it can effectively blow through the long densely-ribbed heatsink with high aerodynamic resistance.

The 5.8W fan employed by Nvidia has an input current of 0.48A at 12V voltage. At its highest speed the fan must be unbearably loud, but we hope the fan speed management system of the GeForce 8800 GTX will do its job well.

The cooling system of the Nvidia GeForce 8800 GTX card seems to be a logical, complete solution that is quite capable of cooling such a powerful chip as the G80. The use of aluminum instead of copper in the main heatsink is somewhat alarming – this may require the fan to rotate at a high speed and, accordingly, to produce more noise. We’ll check this out in the next section.

 
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