Heat Pipes

A pin heat pipe or heat is the heat transfer device that combines the principles of both the thermal conductivity and phase transition to efficiently manage the transfer of heat between two solid interfaces. At the interface of heat in the heat pipe, which is usually at very low pressure, the liquid in contact with the thermally conductive solid surface turned into steam by absorbing heat from the surface. vapor that condenses back to liquid at the cold interface, releasing latent heat. The liquid then returns to the heat interfaces either through capillary action or the action of gravity in which evaporated once again and repeat the cycle. In addition, the heat pipe internal pressure can be adjusted or adapted to facilitate a phase change depending on the demands of working conditions of thermal systems are managed.

A typical heat pipe consists of sealed pipe or tube made of material with high thermal conductivity such as copper or aluminum at both ends of heat and cold. A vacuum pump used to remove the air all of the heat pipe is empty, and then pipe filled with a fraction of the percent by volume of working fluid (or cooling) is selected in accordance with the operating temperature. Examples of fluids include water, ethanol, acetone, sodium, or mercury. Because the partial vacuum that is near or below the vapor pressure of liquid, some liquid will be in the liquid phase and some will be in the gas phase. The use of vacuum gas eliminates the need to work to spread through other gases so that the transfer of most of the steam into the cold end of heat pipe at the speed of moving molecules. In this sense, the only practical limit heat transfer rate is the speed with which gas can be condensed into a liquid at the end of the cold. [1] Inside the pipe wall that, optional wick structure to provide a capillary pressure on liquid phase of the working fluid. This is usually a sintered metal powder or a series of grooves parallel to the axis of the pipe, but there might be a material capable of providing capillary pressure on the viscous liquid to wick back into the heated end. Heat pipe may not need a wick structure if gravity or some other source of acceleration is sufficient to overcome surface tension and causes the viscous fluid to flow back into the heated end. [Citation needed] A heat pipe is not termosipon, because there is no siphon. Thermosiphons heat transfer by convection one phase. (See also: Perkins tube, after Jacob Perkins.) heat pipe does not contain mechanical moving parts and usually require no treatment, although non-condensing gas (which is spread through the pipe wall, resulting from the breakup of the working fluid, or exist as impurities in the material) can eventually reduce the effectiveness of heat transfer pipes . This is important when the vapor pressure of the working fluid is low. [Citation needed] The material chosen depends on the temperature conditions in which the heat pipe must operate, with cooling from liquid helium for extremely low temperature applications (2-4 K) for mercury (523-923 K) and sodium (873-1473 K) and even indium (2000-3000 K) to very high temperatures. Most of the heat pipes for low temperature applications use some combination of ammonia (213-373 K), alcohol (methanol (283-403 K) or ethanol (273-403 K)) or water (303-473 K) as the working fluid. Because the heat pipe contains a vacuum, the working fluid will boil and thereby take away the latent heat below the boiling point at atmospheric pressure. Water, for example, will boil at just above 273 K (0 degrees Celsius) and so it can begin to effectively transfer the latent heat at low temperature. [Citation needed] The advantage of the heat pipe heat dissipation mechanism more-other is their great efficiency in transferring heat. They are conductors of heat, which is basically better than solid-copper equivalent cross-section (heat sink itself, though simple in design and construction, do not take advantage of the principle of the phase transition material.) Some of the heat pipe heat flux has shown more than 230 MW / m [2]. Active control of heat flux can be done by adding a variable volume fluid reservoir to the evaporator. Variable conductance heat pipe employs a large reservoir of gas mixed with inert attached to the condensation. Varying the gas reservoir pressure change of gas volume are charged to the condenser which in turn limit the area available for condensation of steam. So the larger the heat flux and temperature gradients can be accommodated with a single design. A modified heat pipes with capillary reservoir had no connection to the heat pipe axis at the end of the evaporator can also be used as a thermal diode. Heat pipes will transfer heat in one direction, acts as an insulator to another. [Citation needed] [edit] Chamber or Flat heat pipe steam Thin planar heat pipe (heat spreader) has the same main components such as heat pipe tube. These components are hermetically sealed hollow vessel, a working fluid, and closed-loop recirculation system of capillaries. Compared with a one-dimensional tubular heat pipe, heat pipes the width of two-dimensional cross-section sufficient to allow heat flow even with a very thin device. This thin planar heat pipes find their way into the "height-sensitive" applications, such as notebook computers, and surface mount circuit board cores. It is possible to produce flat heat pipes as thin as 0.5 mm (thinner than a credit card).

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