Annex C) Heat Exchangers, Microchannel, Capilliary, Spray Watercooling

NASA Radial Heat Exchanger For Watercooling : Engineers working for NASA have developed a new kind of Radial Flow Heat exchanger with a "thermal effectiveness of 0.99 with a mass of only 2.5 kg and a fractional pressure drop of only 6 percent." The device is produced by Creare, Inc. who specialize in fluid dynamics and heat transfer. It would be interesting to see if this kind of device is adaptable to PC cooling.

Wire Mesh Heatsinks: Screen-fin Technology Research : In this paper by Chen Li and R. A. Wirtz, entitled "Development of a High Performance Heat Sink Based on Screen-Fin Technology", a novel high-performance heat sink based on screen-fin technology is outlined and tested for effectiveness. The picture above shows top and side views of a simple screen-fin heat sink - a heatsink whose cooling fins are made from sections of copper screen soldered to a copper base plate. The heatsinks' fin structure consists of a screen-fin oriented perpendicular to the heat sink base, and laid out in a serpentine arrangement so there is a very big surface area and a reasonable pressure drop. "The tests show that coolant pressure drop and Stanton number are sensitive to the angle of incidence of the superficial mass velocity. The modified friction factor is found to increase rapidly as 0, while the modified Colburn -factor is observed to become small. As a consequence, configurations with 90 will maximize the heat transfer rate while they minimize coolant pressure drop. On the other hand, configurations having 90 generally present a minimum heat transfer surface area." "The design attributes of a air-cooled heat sink with a footprint of 76.2 mm 63.5 mm (3 2.5 ) and 38.1 mm (1.5 ) tall screen-fins deployed as multiple rows in a serpentine configuration is investigated. The design is optimized to operate at 62 Pa (0.25 in H O). The overall conductance is found to be 4.3 W C with 8 l/s coolant consumption." This is quite an interesting approach into a method of enhancing cooling fins I haven't seen commercially attempted before... you can find a listing of other papers by Richard A. Wirtz here that expand upon the theme of screen laminates, meshes, and lattices as heat exchanger surfaces.

Silicon loop heat pipe wicks: NASA: "The University of Cincinnati, along with Texas A & M, Thermacore, GRC and LaRC, has pioneered the macro-porous silicon wet-etching process, and has performed preliminary testing to demonstrate the concept of a silicon loop heat pipe wick. This ability to fabricate a loop heat pipe in silicon would allow a very small temperature drop between the die and the ultimate heat sink, the radiator. Current radiators for space applications typically operate at the box baseplate temperature, which is near 25 °C. If a space-based radiator could operate at a much higher temperature, say, at the temperature of a die (~ 125 °C), the radiator weight savings would be substantial, since thermal radiation heat transfer is a function of temperature to the fourth power."

Liquid Cooling Technique Uses Microfluidic Channels: GATECH: "A new technique for fabricating liquid cooling channels onto the backs of high-performance integrated circuits could allow denser packaging of chips while providing better temperature control and improved reliability. In addition to the cooling channels, the researchers have also built through-chip holes and polymer pipes that would allow the on-chip cooling system to be connected to embedded fluidic channels built into a printed wiring board. They have already demonstrated that the on-chip microfluidic channels can be connected at the same time the IC is connected electronically – using a conventional automated process known as flip-chip bonding."