Heat Pipes background
Heat pipes were rediscovered by George Grover in 1963. A heat pipe is a heat transfer apparatus that combines thermal conductivity and phase transition to efficiently transfer heat. The liquid, which surrounds the wick, is heated, causing the liquid to evaporate and fill in the capillary in the center. Due to gravitational forces, the hot gas travels to the cool side of the tube (the top) and the cool liquid travels to the hot part. By producing this cycle the cool water condenses the gas and then the water at the other side is heated up and turned into a gas again. This whole cycle repeats. Due to the evaporation and condensation taking place inside the heat pipe, they are classified as highly effective thermal conductors.
Extensive tests have been done to determine the compatible metals and fluids used for best results. Simply because some materials appear to be compatible does not mean they are. One example for this would be aluminium and water. These materials will develop large amount of non-condensable gas over a few hours or days. the aim of heat pipes is to operate for long periods of time, with few monitoring for problems such as: material transport, non-condensable gas generation and corrosion.
Most common material mixture used:
-Copper and Water. (This is the most common type of heat pipe.)
-Copper or Steel and Refrigerant.
-Aluminium and Ammonia
-Superalloy and an alkali metal.
-Stainless steel and nitrogen/oxygen/neon/hydrogen or helium. (At a temperature below 100 K)
It is worth to mention that heat pipes using water must operate below water's boiling point, which is 100 degrees Celsius.
Types of Heat Pipes:
There are various types of heat pipes. Some of them are:
-Vapor Chambers: Used for flux transformation and isothermalization of surfaces.
-Variable Conductance Heat pipes: Used as non-condensable gas to change the heat pipe effective thermal conductivity as power or the heat sink conditions change.
-Pressure Controlled Heat Pipes: Where the volume of the reservoir or the mass of the gas can be changed, for a more precise temperature control.
-Diode Heat Pipes: Has a high thermal conductivity in the forward direction and a low thermal conductivity in the reverse direction.
-Thermosyphons: These are heat pipes where the liquid is returned to the evaporator by gravitational forces.
-Rotating Heat Pipes: These heat pipes are characterized by the liquid being returned to the evaporator by centrifugal forces.
Limitations:
-Heat pipes must be adjusted to a certain cooling conditions.
-The effective thermal conductivity varies with heat pipe length.
-The pipe's material and size, apart from the coolant, all have an effect upon the optimal temperature at which the heat pipe works.
-Fact: Most manufactures can't make a traditional heat pipe smaller than 3 mm in diameter, due to the material limitations.
Useful Videos:
https://www.youtube.com/watch?v=2vk5B6Gga10
https://www.youtube.com/watch?v=60PctdoRHd0
Extensive tests have been done to determine the compatible metals and fluids used for best results. Simply because some materials appear to be compatible does not mean they are. One example for this would be aluminium and water. These materials will develop large amount of non-condensable gas over a few hours or days. the aim of heat pipes is to operate for long periods of time, with few monitoring for problems such as: material transport, non-condensable gas generation and corrosion.
Most common material mixture used:
-Copper and Water. (This is the most common type of heat pipe.)
-Copper or Steel and Refrigerant.
-Aluminium and Ammonia
-Superalloy and an alkali metal.
-Stainless steel and nitrogen/oxygen/neon/hydrogen or helium. (At a temperature below 100 K)
It is worth to mention that heat pipes using water must operate below water's boiling point, which is 100 degrees Celsius.
Types of Heat Pipes:
There are various types of heat pipes. Some of them are:
-Vapor Chambers: Used for flux transformation and isothermalization of surfaces.
-Variable Conductance Heat pipes: Used as non-condensable gas to change the heat pipe effective thermal conductivity as power or the heat sink conditions change.
-Pressure Controlled Heat Pipes: Where the volume of the reservoir or the mass of the gas can be changed, for a more precise temperature control.
-Diode Heat Pipes: Has a high thermal conductivity in the forward direction and a low thermal conductivity in the reverse direction.
-Thermosyphons: These are heat pipes where the liquid is returned to the evaporator by gravitational forces.
-Rotating Heat Pipes: These heat pipes are characterized by the liquid being returned to the evaporator by centrifugal forces.
Limitations:
-Heat pipes must be adjusted to a certain cooling conditions.
-The effective thermal conductivity varies with heat pipe length.
-The pipe's material and size, apart from the coolant, all have an effect upon the optimal temperature at which the heat pipe works.
-Fact: Most manufactures can't make a traditional heat pipe smaller than 3 mm in diameter, due to the material limitations.
Useful Videos:
https://www.youtube.com/watch?v=2vk5B6Gga10
https://www.youtube.com/watch?v=60PctdoRHd0
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