Apple files patent for liquid-cooled portable computer
Posted by Dennis Sellers 
Dec 1, 2008 at 8:00am
An Apple patent (number 20080291629) for a liquid-cooled portable computer has appeared at the US Patent & Trademark Office. The invention relates to heat-transfer techniques. More specifically, the present invention relates to the use of liquid coolants to transport heat in computer systems.
According to Apple, embodiments of a computer system are described. This computer system includes a power source that is coupled to a heat pipe, where the power source includes an integrated circuit. This heat pipe may contain a liquid coolant that has a density greater than a first pre-determined value at room temperature.
Here’s Apple’s summary of the invention: “The computational performance of electronic devices has increased significantly in recent years. This increased performance has been accompanied by an increase in power consumption and associated heat generation. Furthermore, this additional heat generation has made it harder to maintain acceptable internal and external operational temperatures in these devices.
“Portable devices, such as laptop computers (notebook PCs), cellular telephones, and personal digital assistants have additional design constraints which make it even harder to manage thermal load. In particular, size and weight limitations in such devices can make it difficult to achieve desired operational temperatures. For example, in many portable devices the size and weight of metal heat sinks may be prohibitive. Furthermore, battery life constraints in such devices may limit the available power for active cooling mechanisms, such as fans.
“Hence what is needed are cooling mechanisms that overcome the problems listed above.
“One embodiment of the present invention provides a computer system that includes a power source that is coupled to a heat pipe, where the power source includes an integrated circuit. This heat pipe may contain a liquid coolant that has a density greater than a first pre-determined value at room temperature. A pump is coupled to the heat pipe is configured to circulate the liquid coolant through the heat pipe. Furthermore, a heat exchanger coupled to the heat pipe is configured to transfer heat from the heat pipe to an environment external to the computer system.
”In some embodiments, the integrated circuit includes a processor. In some embodiments, the liquid coolant includes: water, a coolant in an R133 group of coolants, and/or a coolant in an R134 group of coolants. Furthermore, in some embodiments the liquid coolant includes two phases of matter. For example, the two phases may include a gaseous phase in bubbles, and nucleation of the bubbles may be used to increase the heat-transfer coefficient of the liquid coolant. In another example, latent heat may be used to increase the heat-transfer coefficient of the liquid coolant. And in some embodiments the liquid coolant includes metal particles to increase the heat-transfer coefficient of the liquid coolant.
“In some embodiments, the liquid coolant has a thermal conductivity greater than a second pre-determined value. In some embodiments, the pump includes a mechanical pump and/or an electrostatic pump. Furthermore, in some embodiments the pump is configured to circulate the liquid coolant using mechanical vibration of a membrane.
“In some embodiments, the computer system includes a laptop computer. In some embodiments, the heat exchanger includes a forced-fluid driver and a heat coupling-mechanism coupled to the forced-fluid driver. This forced-fluid driver may be configured to pump heat from inside the computer system to the environment. Furthermore, in some embodiments the heat coupling-mechanism includes convective-cooling fins.
‘In some embodiments, the computer system includes a cold plate coupled to the power source and the heat pipe. This cold plate includes channels which increase a surface area wetted by the liquid coolant, thereby increasing a heat-transfer coefficient of the cold plate.
“Another embodiment provides a method for cooling a portable computer system. During this method, the liquid coolant is circulated in the heat pipe. Then, heat is transferred from the heat pipe to an environment external to the portable computer system using the heat exchanger. Note that the heat is generated by an integrated circuit in the portable computer system.”
The inventor is Ihab A. Ali. The graphic below is a block diagram illustrating a computer system in accordance with an embodiment of the present invention.
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Contributor
Dennis Sellers
Dennis has been a newspaper editor/reporter (seven years) and teacher (seven years). He has over 4,000 magazine, newspaper and online articles to his credit. He has also covered the Mac and tech industries for over a decade for such online publications as MacCentral, MacMinute and now MacsimumNews.
