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Lecture 11: Heat Transport

Heat Pipes:

Passive heat pump, phase change to increase heat transport.

Thermacore:  http://www.thermacore.com/

Swales and Associated: http://www.swales.com/products/index.html

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 40C it provides a 6.25C/watt thermal resistance, allowing the processor to run at full speed under any environmental condition by keeping the case temperature at 90C 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.

check here for information:  http://www.thermacore.com/

What's the most cost effective way to dissipate heat?

The Swales Heat Pipe
Our heat pipes improve performance and extend equipment life, while they dissipate heat. The pipe can be made of flexible material or in a variety of shapes and sizes. This allows it to accommodate design constraints, yet still efficiently transport unwanted heat to an available heat sink.

The Swales heat pipe features:
High thermal conductivity
Lightweight compact construction
Temperature uniformity
No need for external power
Reliable, no-maintenance design
Silent, vibration free operation
Quick thermal response
Ability to operate in extreme environments
Variety of shapes and sizes
Allows heat sink to be located away from heat source

How a Heat Pipe Works

A heat pipe is a passive device that transports heat efficiently from one point to another. It is made of a sealed container with a working fluid and wick, or grooves, inside. As heat is applied to the evaporator section, the working fluid vaporizes and flows to the cool or condenser section of the heat pipe. There the working fluid condenses, releasing the heat of vaporization.


Heat Pipe Applications

The uses of heat pipes are virtually unlimited. Here are a few examples:
Electronic enclosures
Motor controllers
Heat pipe heat exchangers
Industrial drives
Manufacturing processes
Traction drives
De-icing
RF modules
Computers

Swales can design and manufacture heat pipes in the size, shape and power rating you require. Our applications engineers are experienced, knowledgeable and available to assist you in optimizing a heat pipe system that will satisfy your needs.

This info from Swales (http://www.swales.com/products/heatpipe.html)


 

Thermal Gradients:

heat transport by mass flow

heat transport by conduction

Thermal Transients:

heating / cooling

thermal mass, heat capacity


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