Passive heat pump, phase change to increase heat transport.
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The Heat Pipe - How it works (from Thermacore)
Heat pipes remove heat from the source in a two-phase process. As heat is generated, a liquid at one end of the pipe evaporates and releases the heat to a heat sink by condensation at the other end. The liquid is returned to start the process over through a wick structure on the inside of the heat pipe.
The Heat Pipe - How it works
Thermacore's Heat Pipe technology provides a cost effective solution for laptop cooling applications or for any other electronic cooling where minimal space and low maintenance requirements are involved.
Heat pipes are relatively simple devices. They passively transfer heat from the heat source to a heat sink where the heat is dissipated. The heat pipe itself is a vacuum-tight vessel that is evacuated and partially filled with a minute amount of water or other working fluid. As heat is directed into the device, the fluid is vaporized creating a pressure gradient in the pipe. This forces the vapor to flow along the pipe to the cooler section where it condenses, giving up its latent heat of vaporization. The working fluid is then returned to the evaporator by capillary forces developed in the heat pipe's porous wick structure, or by gravity. (See illustration)
The Thermacore Laptop Heat Pipe Solution
Thermacore has taken heat pipe technology originally used for space applications and applied it to laptop computer cooling. It is an ideal, cost effective solution. Its light weight (generally less than 40 grams), small, compact profile, and its passive operation, allow it to meet the demanding requirements of laptops.
Thermacore's HS-NB series of heat pipes is specifically designed for P-5 notebooks, but can also be adapted for other processors and component cooling. For an 8 watt CPU with an environmental temperature no greater than 40°C it provides a 6.25°C/watt thermal resistance, allowing the processor to run at full speed under any environmental condition by keeping the case temperature at 90°C or less.
One end of the heat pipe is attached to the processor with a thin, clip-on mounting plate. The other is attached to the heat sink, in this case, a specially designed keyboard RF shield. This approach uses existing parts to minimize weight and complexity. The heat pipe could also be attached to other physical components suitable as a heat sink to dissipate heat. (See photo of inside of laptop computer)
Thermacore's heat pipes provide a small profile without any interference to existing components and can be easily adapted to an existing package design. Because there are no moving parts, there is no maintenance and nothing to break. Some are concerned about the possibility of the fluid leaking from the heat pipe into the electronics. The amount of fluid in a heat pipe of this diameter is less than 1cc. In a properly designed heat pipe, the water is totally contained within the capillary wick structure and is at less than 1 atmosphere of pressure. If the integrity of the heat pipe vessel were ever compromised, air would leak into the heat pipe instead of the water leaking out. Then the fluid would slowly vaporize as it reaches its atmospheric boiling point. A heat pipe's MTTF is estimated to be over 100,000 hours of use.
The Cost Effectiveness of Heat Pipes
The flexibility of the Thermacore heat pipe solution provides an effective method for cooling processors in laptops. The cost of heat pipes designed for laptop use is very competitive compared to other alternatives. Cost is partially offset and justified by improved system reliability and the increased life of cooler running electronics. Heat pipes, in quantity, cost a few dollars each while an entire cooling system will cost between $5 - $10 in production quantities, depending on the final design. Standard design products are available to reduce cost even further.
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heat transport by mass flow
heat transport by conduction
heating / cooling
thermal mass, heat capacity