Heat pipe is a very efficient way to transfer thermal energy from one end to another. It works on the principles of thermal conductivity and phase transfer. The High thermal conductivity enables a heat pipe to transfer and dissipate heat to the desired location through a “capillary action”. This effect is similar to placing a paper tissue in a fluid and observes the fluid rise up the paper towel.
Heat pipes were invented by Los Alamos National Laboratory in 1963 by George Grover to supply heat to and remove waste heat from energy conversion system.
Actual working of a Heat Pipe
A heat pipe is a copper tube with an internal wick structure that is sealed on both the ends with a small amount of water or ammonia liquid inside. The wick is used to transport the liquid from one end to other. As heat is applied to the hotter side of a pipe, the water will boil and turn to a gas which then travels with the thermal energy to the colder end of the heat pipe where it condenses back to a liquid. This process is known as capillary action. This cycle is repeated continuously to remove heat from a system.
Modern heat pipes are able to transfer heat several hundred times faster than a solid copper rod. Based on material used to design and area of application there are various types of heat pipes are available in the market.
Types of Heat Pipes
• Vapor chamber or flat heat pipes
• Variable conductance heat pipe
• Diode heat pipes
• Thermos phones
• Loop heat pipes

Applications of Heat Pipes
Today, Heat pipes are used in a variety of applications from space to handheld devices that fit in your packet. Some applications are listed below
• Spacecraft
• Computer systems
• Solar thermal
• Permafrost cooling
• Cooking appliances
• Ventilations and heat recovery nuclear power conversation

Benefits of a Heat Pipe
• High conductivity effective thermal
Transfers heat over long distance with minimal temperature drop.
• Passive operation
No energy input is required to operate the heat pipe. There are no moving parts.
• Long life with minimum maintenance
There is nothing in heat pipes that wear out heat pipes are passive. Since there are no moving parts the only maintenance recommended is periodic cleaning
• Cost efficient
By lowering the operating temperature, these devices can increase the Mean Time between Failure for electronic assemblies. In turn this lowers the maintenance and replacement costs.
• Flexible size
Heat recovery heat pipes can adjusted in less space than other heat recovery systems. They can be manufactured in custom sizes to fit in user requirements.


Frequently Asked Questions
Are heat pipes reliable?
Yes, mainly because they have no moving parts. They are ideal for applications such as aerospace where maintenance is not feasible. The main cause of heat pipe failures is gas generation in the heat pipe, but this can be completely avoided by proper cleaning and assembly procedures
Can heat pipes work against gravity?
Yes, this occurs whenever the evaporator is located above the condenser. In these applications the working fluid must be pumped against gravity back to the evaporator. This occurs through wick structures that pump working fluid through capillary pressure developed in the porous wick. The finer the pore radius of a wick structure, the higher against gravity the heat pipe can operate.
What materials can be used to construct a heat pipe?
The heat pipe wall or shell material selection is driven by compatibility of the working fluid. The heat pipe working fluid is selected based on the operating temperature range of the application. After a working fluid is selected, the heat pipe wall or shell material is selected based on its chemical compatibility with the working fluid to prevent corrosion or chemical reaction between the fluid and the heat pipe wall or shell material. A chemical compatibility problem between the working fluid and wall material within a heat pipe can create a chemical reaction that produces a non-condensable gas. Non-condensable gases within a heat pipe can cause operational failure.

What fluids are used in heat pipes?
Heat pipe working fluids range from helium and nitrogen for cryogenic heat pipe applications, to liquid metals like sodium and potassium for high-temperature heat dissipation. Some of the more common heat pipe fluids used for electronics cooling operations are ammonia, water, acetone and methanol.
Can heat pipes freeze?
Yes, heat pipe working fluids, including water, maintain their normal freezing point. Heat pipes will not operate until the temperature rises above the freezing temperature of the fluid. Properly designed heat pipes, however, will not be damaged by freezing or thawing of the working fluid.

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