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February 2014

Thermacore Highlight on Heat Pipe Assemblies


heat pipe assemblies from thermacore mean that thermal engineers can count on innovative, best-in-class thermal management solutions that offer industry-leading thermal performance, help control energy costs and maximize system life and reliability even under harsh conditions.  efficient, cost-effective cooling from compact-size thermal solutions - even where space is limited - can be realized through a range of proven thermacore heat pipe assembly systems. these thermal technologies give engineers effective means to move heat for remote heat dissipation, low thermal resistance heat spreading from concentrated heat sources or isolated cooling to protect sensitive computer components, consumer electronics devices, transportation control systems and military systems, among many other applications.

heat pipes are composed of three basic parts, all of which thermacore has extensive experience in developing and delivering to the industry
:

  • a vacuum tight, sealed containment shell or vessel
  • working fluid
  • capillary wick structure

what are the containment vessels?

 

heat pipes can be constructed from a variety of different materials. thermacore has constructed heat pipes from aluminum, copper, titanium, monel, stainless steel, inconel and tungsten. the most common for electronics cooling applications is copper. the choice of heat pipe containment material is largely dependent on the compatibility with the working fluid.

 

thermacore-heat-pipe_330

 

how many kinds of working fluids are used?

 

 

thermacore has designed, developed and manufactured heat pipes using over 27 different working fluids. the heat pipe working fluid chosen depends on the operating temperature range of the application. working fluids range from liquid helium for extremely low temperature applications (-271°c) to silver (>2,000°c) for extremely high temperatures. the most common heat pipe working fluid is water for an operating temperature range from 1°c to 325°c. low temperature heat pipes use fluids like ammonia and nitrogen. high temperature heat pipes utilize cesium, potassium, nak and sodium (873–1,473°k).

 

heat pipe working fluidoperating temperature range (°c)heat pipe shell material
low temperature or cryogenic heat pipe working fluids
carbon dioxide -50 to 30 aluminum, stainless steel, titanium
helium -271 to -269 stainless steel, titanium
hydrogen -260 to -230 stainless steel
methane -180 to -100 stainless steel
neon -240 to -230 stainless steel
nitrogen -200 to -160 stainless steel
oxygen -210 to -130 aluminum, titanium
mid range heat pipe working fluids
acetone -48 to 125 aluminum, stainless steel
ammonia -75 to 125 aluminum, stainless steel
ethane -150 to 25 aluminum
methanol -75 to 120 copper, stainless steel
methylamine -90 to 125 aluminum
pentane -125 to 125 aluminum, stainless steel
propylene -150 to 60 aluminum, stainless steel
water 1 to 325 copper, monel, nickel, titanium
high temperature heat pipe fluids
cesium 350 to 925 stainless steel, inconel, haynes
nak 425 to 825 stainless steel, inconel, haynes
potassium 400 to 1,025 stainless steel, inconel, haynes
sodium 500 to 1,225 stainless steel, inconel, haynes
lithium 925 to 1,825 tungsten, niobium
silver 1,625 to 2,025 tungsten, molybdenum

 

how do the capillary wick structures work and what does thermacore offer?


a wick structure or a specific envelope shape enables efficient capillarity. heat applied to the evaporator section by an external source is conducted through the pipe wall and wick structure where it vaporizes the working fluid. the resulting vapor pressure drives the vapor through the adiabatic section to the condenser, where it condenses, releasing its latent heat of vaporization to the heat sink. the capillary force created by the menisci in the wick pumps the condensed fluid back to the evaporator section. this provides the driving force for liquid in the heat pipe. the operating principle as described here is shown in the followin schematic:

 

cooling_zone_wick_structure_508

thermacore manufactures all of the common wick structures, as well as the advanced wick structures. however, thermacore specializes in a "sintered powder metal" wick structure that allows the heat pipe to provide the highest heat flux capability, greatest degree of gravitational orientation insensitivity and freeze/thaw tolerance.

 

click here to learn more about thermacore heat pipe technology

 

click here to visit thermacore's main web site

a wick structure or a specific envelope shape enables efficient capillarity. heat applied to the evaporator section by an external source is conducted through the pipe wall and wick structure where it vaporizes the working fluid. the resulting vapor pressure drives the vapor through the adiabatic section to the condenser, where it condenses, releasing its latent heat of vaporization to the heat sink. the capillary force created by the menisci in the wick pumps the condensed fluid back to the evaporator section. this provides the driving force for liquid in the heat pipe. the operating principle as described here is shown schematically in figure 1.

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