Thermal Management Glossary

Thermal management and heat transfer technology terms and definitions. Click on a letter to jump to that section.

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Alkali Metal Heat Pipe
Heat pipe that uses alkali metal as working fluid. Alkali Metal Heat Pipes are typically used for high temperature (300°C to 2,000°C) applications.

Aluminum silicon carbide.

Advanced pyrolytic graphite.

Axially-Grooved Heat Pipe
Heat pipe that uses extruded axial grooves in the internal wall as the wick material.

Command, Control, Communications, Computers.

Computer-Aided-Design software programs.

Capillary Pumped Loop
Capillary action generated by fine porous wick material located only in the evaporator provides pressure head needed to circulate fluid through entire system. Vapor and liquid move in the same direction in a loop, rather than in counterflow, as in conventional heat pipes.

Cold Plate
A plate used to transfer heat and cool electronics. See Liquid Cold Plate.

Commercial Off The Shelf.

Coefficient of Thermal Expansion.

CTE Matching
Coefficient of Thermal Expansion (CTE) matching involves harmonizing the materials of a heat source and heat sink to ensure that as temperature changes the devices expand and contract such that mechanical stresses are not induced to cause failure.

Delta T or dT
Temperature difference between hot spot and heat sink.

Embedded Heat Pipe
Heat pipe that is integrated into a solid material such as copper or aluminum to enhance the effective thermal conductivity of the solid material.

Finite Element Method.

Flexible Heat Pipe
Heat pipe that includes a flexible section between the evaporator and condenser. The flexible section can be made of a bellows or other flexible structure.

Flux Density
Heat load per unit area (W/cm2).

Fuel Cell
A system that combines hydrogen and oxygen to produce electricity.

Graded Wick Structure
A wick structure that has spatially varying wick properties.

A mixture of water and propylene glycol, an antifreeze that lowers the freezing point of water.

Heat Exchanger
A device built for efficient heat transfer from one medium such as air or liquid to another, whether the media are separated by a solid wall so that they never mix, or the media are in direct contact. Heat exchangers are typically used for enclosure cooling and can be of the following type: air-to-air, liquid-to-air, or liquid-to-liquid.

Heat Pipe Heat Spreader
A plate that utilizes heat pipes to improve thermal conductivity and to move heat and cool electronics. Heat pipe spreaders are passive and increase the conductivity of the base material significantly.

Heat Pipe
A device that transports heat through the evaporation and condensation of a working fluid (i.e., two-phase cooling). Heat pipes are devices that have an extremely high effective thermal conductivity, typically 10 to 10,000 times more conductive than solid materials.

Heat Sink
A heat sink (or heatsink) is an environment or object that absorbs and dissipates heat from another object using thermal contact (either direct or radiant). Heat sinks are used in a wide range of applications wherever efficient heat dissipation is required; major examples include refrigeration, heat engines, cooling electronic devices, and lasers.

Heat Spreader
A heat spreader is a device having high thermal conductivity to move heat from a concentrated or high heat flux source (high heat flow per unit area), to a heat exchanger with a larger cross sectional area, surface area and volume. Heat spreaders can be solid conductors like copper or pyrolytic graphite, or they can be a two-phase device like heat pipes and vapor chamber heat pipes.

Heavy Rail
High passenger volume multi-car subway system.

Hybrid Electric
Engine drives a generator for electric propulsion.


Insulated Gate Bipolar Transistor.

Isothermal Furnace Liner (IFL)
An annular heat pipe that is typically operating at high temperature (>300°C) to keep the hot zone of a furnace at uniform temperature or isothermal. IFLs typically utilize alkali metals such as cesium, potassium, sodium or NaK as the working fluid. Typical applications include crystal growth, temperature calibration, etc.

k-Core with carbon fiber composite encapsulant.

Light Airborne Multipurpose System.

Light Rail
Street level two-car transit rail systems.

Liquid Cold Plate
A plate that utilizes pumped liquid to move heat and cool electronics. Liquid cold plates are often machined and/or vacuum brazed with connectors for the liquid inlet/outlet ports.

Liquid Cooling System
A system used to remove heat by circulating a single-phase liquid using a pump and liquid-to-air heat exchanger. As opposed to air cooling, a single-phase liquid is used as the medium for transferring the heat. A water-based coolant is commonly used for cooling electronics, internal combustion engines in automobiles and large electrical generators.

Loop Heat Pipe
A two-phase heat transfer device that uses capillary action to remove heat from a source and passively move it to a condenser or radiator. LHPs are similar to CPLs but have improved startup characteristics.

Nanoscale Wick
A wick that is constructed of nano-sized structures for improved capillary pressure generation.

Thermal expansion in parts per million per K (e.g. micron/meter/Kelvin).

Polyalphaolefin (PAO)
A highly purified ethylene derivative used as a cooling medium in liquid cooling systems.

Power Modules
Integrated modules of power switching devices.

Shock caused by explosive devices for space deployment.

Mounting a device on shock absorbers to limit loading.

Thermal mass or masses at the edge of thermal cores or spreaders.

Remote Dissipation
Moving heat from a concentrated heat source to a location where that heat can be dissipated and managed more effectively.

Silicon Carbide device.

Thermal Circuit
Thermal resistance path between heat load and sink.

Thermal Plane
A plate to cool electronics.

Thermosyphon/ Thermosiphon
A heat pipe that relies on gravitational forces to return the liquid back to the evaporator. Thermosiphons typically have no wick.

Thin Vapor Chamber
A vapor chamber with a thickness less than 3mm or 0.118 inches, basically the thickness of a credit card. See vapor chamber.

T/R Module
Transmitted/Receiver module for phased arrays.

Through-the-thickness conductivity.

Vapor Chamber
A flat or planar heat pipe that allows three-dimensional spreading of heat with an extremely high thermal conductivity. Vapor chambers are typically used as the base of a heat sink. Vapor chambers deliver higher thermal performance than a traditional heat sink by alleviating spreading resistance found in solid heat sink construction. Vapor chambers are typically constructed of stamped or machined plates with a hollow center for vapor flow.

Vapor Tower
A vapor tower heat pipe is a combination of a vapor chamber and vertical heat pipe. A vapor tower not only can spread heat like a vapor chamber in the x-y plane, but also transfers heat in the z-plane to heights much greater than 12mm or 0.5 inches.

Variable Conductance Heat Pipe (VCHP)
A variable conductance heat pipe is a heat pipe with a fixed charge of inert gas such as Argon or Helium used in applications requiring tight temperature control. Variable conductance heat pipes employ a large reservoir of inert non-condensable gas attached to the condensing section. The gas partially occupies the condenser as well, so changes in the pressure or temperature of the gas cause a change in its volume, allowing more or less condenser area to be active; this has a regulating effect on the operating temperature of the VCHP.

Standard commercial card format - IEEE 1101.2.

SI units for conductivity Watts/(meter·Kelvin).

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