New Dual G5 2.5GHz Liquid Cooling System

Nice n simple. The heatpipes cool the surrounding areas to the rear of the processor whilst the LCS cools the cores. As there is VERY little airflow over the mainboard, any excess ambient heat must also be removed to prevent overheating on other aspects of the system due to high ambient temps. The heatpipes cover this task. Every electronical component generates heat, and an excess of heat is always a bad thing no matter what the component... whether it be Mosfets, CPUs, bridging ASICs, SDRam, VPU, APU... Having an excess of cooling within a system is always a good thing. Apple is merely using a variant of the PC Watercooling Systems that enthusiasts have been running for YEARS with great success. To combat the reduced airflow of not having fans blowing down onto the mainboard surface, additional heatpipes have been added. S'not a new thing particularly. I've watercooled many PCs both on the core and rear of the CPU simultaneously to offer the best cooling performance.

A heat pipe is a two phase system that is sealed. The fluid in the sealed pipe (non-serviceable) is heated on one end and the vapor travels to the cold end where it is condensed. The condensed fluid is then wicked back to the hot end (via a wick system) and the process repeats. My big question with Apple's design is that they seem to be using BOTH a LCS and heat pipes. I can't figure out what the heat pipes are cooling (you can see them in the above figure). They long pipes that come from the area where the red circles with "cross outs" are located. Other figures on the net are showing that the processors are heat sunk to the cold plate system (LCS), but I can't figure out why they are using the heat pipes on the other end of the card. By the way, heat pipes have been used by Apple in the eMacs for quite a while.

Yeah, to my understanding, the G5's cooling system has a pump. All Liquid-Cooling computer systems have pumps...how else would the liquid get around?

I agree that the liquid contained in the new G5, being a water and propylene glycol mixture is essentially identical to the traditionaly water-cooled system in a car. But the car has a pump to move the liquid around. The G5 has the liquid moving by thermal differences which I thought was more closely associated with heat pipe technology. I assume there is an official, technical definition of a heat pipe, but I don't know what it is. Perhaps as you note, being a liquid-to-gas-to-liquid methodology such is used in home heat pumps and refrigerators is all that is required to be defined as a heat pipe.

No, this is liquid cooling technology, not a heat pipe approach. Heat pipes work in an entirely different fashion and consist of a tube (with one hot end and one cool end) containing a wick (or capillary tube) and a some liquid that vaporizes at low temperature. In operation, the heat source causes the liquid in the hot end to evaporate and the vapor migrates to the cool end, carrying the heat with it. At the cool end the vapor is condensed (giving up the heat to the cold sink) and the liquid is piped back to the hot end by flowing up the wick or through the capillary tube. Heat pipes have not mechanical pump, as the liquid is moved by capillary action. Heat pipes are attractive due to their simplicity, but they are expensive for the amount of heat removed and there is no way to control them. The G5 has a pure liquid cooling system pretty much identical to what you would find under the hood of your car.

In no way do I consider myself even remotely knowledgeable in these matters, but wouldn't this cooling system be more correctly described as "heat pipe" technology rather than what is traditionally considered "liquid cooling"?