Although the tiny Single Board Computer called the Raspberry Pi (RBPi) is mainly to teach the young kids how to code, several people are now hooked onto it and are executing extraordinary projects with it. Like other CPUs in regular computers, the RBPi can as well be overclocked and run in a turbo mode. Last year, the Pi Foundation, originators of the SBC, added the turbo mode and clarified that this will not void the warranty. Therefore, you can safely apply turbo mode when the RBPi is busy, limit turbo when the core of the RBPi (the BCM2835) reaches 85°C. By doing so, you will not be reducing the lifetime of your SBC.
Phame, from London, wanted to use more of the turbo mode without limiting the RBPi in any way. His immediate concern was to keep the BCM2835 cool. His motivation came in the form of a competition for building a new case for RBPi. That set him on the path of water-cooling the RBPi using a carefully designed case suitable for the purpose.
Phame went on to make a water block that sits on top of the RBPi’s CPU, LAN controller and some of the other components. Two pipes lead from the water block to a radiator filled with a coolant, circulated with a tiny British micropump. The radiator is a large aluminum tank, roughly 98x70x17 mm, containing more of the coolant. The entire rig sits in a frame and the pump draws its power from the RBPi. Phame custom made the frame, water block and the radiator, including the custom etching of the Pi logo on its interior.
The contraption works via convection, the process by which hot liquid rises to the top, to be replaced by colder parts of the liquid. As the CPU and other parts of the RBPi start to get hotter when run in turbo mode, the temperature of the coolant inside the water block that is in contact with the chips also rises. The hot liquid moves towards the upper part of the water block, and colder liquid flows in from the radiator below. By itself, this process would have sufficed to keep the temperature of the hot parts in check, but Phame added a pump to accelerate the coolant flow.
The micropump circulates the coolant between the radiator and the water block. Therefore, hot coolant from the water block moves on and colder liquid replaces it, thereby effectively removing the heat from the CPU and other parts. The hot liquid passes into the radiator, where it transfers the heat it is carrying into the aluminum. As a large surface of the aluminum radiator is in contact with the air outside, the heat is radiated into the ambient. Phame has gold-plated the internal surface of the aluminum radiator, so that the coolant in contact cannot corrode the surface.
You can see the rig in operation in this video. The only thing that Phame has not declared is whether he has operated the RBPi with the water cooler in place. It would be nice to have some temperature readings.