The working principle of loop heat pipes is based on the application of a wick structure which allows a autonomous mode of operation. The first loop heat pipe working at liquid nitrogen temperatures cryogenic ohp was presented in 1991, and chandratilleke et al. Initially, the oph is evacuated and partially filled with the working fluid. The figures below illustrate the operating principles of a typical. The evaporator and absorber comprise the bottom most chamber. An introduction to pulsating heat pipes may 1, 2003 sameer khandekar heat pipes design, liquid cooling, number 2, php, pulsating heat pipe, volume 9 modern electronics thermal management faces considerable challenges in the wake of component miniaturization, which has led to higher demands on net heat flux dissipation. Gerner 2, eric golliher 3 1center for microelectronic sensors and mems, department of e lectrical computer engineering and computer science, university of cincinnati,cincinnati, ohio, 45221. Lhps are similar to heat pipes but have the advantage of being able to provide reliable operation over long distance and the ability to operate against gravity. Both are based on the same principle than heat pipes.
Introduction and working principle of cooling system. One of the main issues in spacecrafts such as satellites is their longlife. The main components of the absorption chiller are the condenser and the generator which comprise the top most chamber. Figure 1 crosssectional view of a typical wicked heat pipe 2 3. Act manufactured loop heat pipes provide highpower, passive twophase cooling for spacecraft thermal control and other applications. The heat dissipated from electronic devices is used to evaporate the working fluid. Twodegreeoffreedom heater control of a loop heat pipe. It is a twophase heat transfer device that utilizes the evaporation and condensation of a working fluid to transfer heat, and the capillary forces developed in fine porous wicks to circulate the fluid. A brief overview of loop heat pipes with respect to basic fundamentals, construction details, operating principles, and typical operating characteristics is presented in this paper. The loop heat pipe lhp is a passive twophase heat transport device that is gaining importance as a part of spacecraft thermal control systems and also in applications such as in avionics cooling and submarines. Content introduction working principle components of heat pipe type of heat pipe advantage of heat pipe application 3. Evaporative cooling is the process where warm water from an industrial process is pumped up to the top of the cooling tower where the water distribution system is.
In principle a heat pipe is operational for all temperatures between the melting point and the critical temperature of the working fluid. Understanding loop heat pipes advanced thermal solutions. The application of heat pipes should be considered when the thermal design is either conduction limited or when nonthermal goals such as weight cannot be achieved with other materials such as solid aluminum andor copper. Thermosiphoning is used for circulation of liquids and volatile gases in heating and cooling applications such as heat pumps, water heaters, boilers and furnaces. Loop heat pipe working medium was ethanol and capillary core was made by. A working fluid is encapsulated inside this closed loop as a coolant. Plate heat exchanger, how it works working principle hvac industrial engineering phx heat transfer duration. Fujitsu working on worlds first 1mm loop heat pipe. Safety in design of thermal fluid heat transfer systems tony ennis haztech consultants ltd. A brief overview of loop heat pipes with respect to basic fundamentals, construction details, operating principles, and typical operating. This work was conducted to confirm the working performance of multiple loop heat pipe under thermal vacuum ambience with the working fluid ammonia. The engine is the heat source of the whole system, the.
Lhps are similar to heat pipes but have the advantage of being able to provide reliable operation. Branch selectors are used with threepipe systems to perform the same functions as twopipe systems with the exception of separators. Loop heat pipes lhps are heat transfer devices whose operating principle is based on the evaporationcondensation of a working fluid, and which use the. When placed horizontally, this distance can extend to several tens of meters. The maximum amount of heat that can be transferred in a gravity heat pipe is limited by several effects. They are also passive systems and they present a huge advantage. The working principle, the fluid flow and heat transfer mechanism are similar in any heat pipe irrespective of the shape. Even the name is heat pipe,but working is very much different than the conventional heat pipes. Thermodynamics of the planar loop heat pipe the operating principle of the planar lhp is summarized as follows.
Loop heat pipe with multiple evaporators has the advantage of design flexibility for the cooling systems of many heating devices and it has been used for spacecraft applications 3, 4. Menisci, which are formed at the liquidvapor interface in the evaporator wick, are supported by capillary forces even though pressure forces push them down. Thermosiphon or thermosyphon is a method of passive heat exchange, based on natural convection, which circulates a fluid without the necessity of a mechanical pump. Loop is designed to prevent the pressure within the boiler from pushing liquid back up the line and thus starving the boiler causing overheating of the tube. Figure 1 is a schematic diagram illustrating the operating principles of one version of the heat pipe loop design. Steadystate modeling and analysis of a loop heat pipe. Kaya and goldak 5 reported the boiling limit of loop heat pipe obtained. Schematic of principle of operation of a loop heat pipe 1, 2. A compressor increases the pressure of the working fluid, which causes the temperature to rise.
Fujitsu develops thin cooling device for compact electronics. It can be vertically bore holes, or horizontally slinky loops, or even. It is a vacuum tight device consisting of an envelope, a working fluid, and a wick structure. Most cooling towers work based on the principle of evaporative cooling.
Safety in design of thermal fluid heat transfer systems. In otec, the ammonia picks up heat from the hot, surface ocean waters just as the coolant chemical picks. Outline from heat pipe to loop heat pipe and capillary pumped loop lhp operating principleslhp operating principles lhp components sizing and fluid inventory lhp operating temperature control lhp startup lhp shutdown lhp analytical modelinganalytical modeling recent lhp technology developments introduction to lhp ku 2015 tfaws 2. There are many different types of cooling towers but the cooling tower working principles stay pretty much the same. Heat pipes a novel cooling principle for generator. To make liquid and vapour plugs to exist diameter of tube must be small. Design considerations when using heat pipes electronics. The loop heat pipe lhp was invented in russia in the early 1980s. Finally, the paper presents the current developments in modeling of thermohydraulics and design methodologies of lhps. Startup of the lhp was performed in flight and ground testing. It should be stable and resist deterioration over the working life of.
It is a member of wickless heat pipes the oscillation of working fluid and phase change phenomina in capillary tube is basic principle. A heat pipe heat exchanger is a simple device which is made use of to transfer heat from one location to another, using an evaporationcondensation cycle. Loop heat pipe design flexible heating pipe tech two. Loop heat pipes lhps are twophase heattransfer devices with capillary pumping of a working fluid. Closedloop heatsyncs are typically much larger and often require components to pump the liquid around the system, neither of which make existing designs. The technology was invented in the former soviet union in the 1980s for spacecraft thermal control. They possess all the main advantages of conventional heat pipes, but owing to the original design and special properties of the capillary structure are capable of transferring heat efficiency for distances up to several meters at any orientation in the gravity field, or to several tens of. An introduction to pulsating heat pipes electronics cooling. Lhps can transfer heat efficiently up to several meters at any orientation in the gravity field. A heat pipe is a heattransfer device that combines the principles of both thermal conductivity and phase transition to effectively transfer heat between two solid interfaces. The principle of a heat loop pipe is quite simple collect the heat at one end, move the heat to a dissipater via a fluid and then cycle back the cooled liquid to collect more heat. Loop heat pipes and capillary pumped loops ntrs nasa.
Loop heat pipes lhps are effective and efficient twophase heat transfer devices that utilize the evaporation and condensation of a working fluid to transfer heat, and the capillary forces developed in fine porous wicks to circulate the working fluid1, 2. The principle is that the air compressor acts as a gas source to. A loop heat pipe model was built with the following mesh characteristics. Threepipe systems, which are configured with a heating pipe, a cooling pipe, and a return pipe see figure 3. Loop heat pipes and capillary pumped loops an applications perspective dan butler, jentung ku, theodore swanson nasagsfc, code 545, greenbelt, md 20771. Heat enters the evaporator and vaporizes the working fluid at the wick outer surface. Loop heat pipe design flexible heating pipe tech two phase. Various works on the heat transfer performance of loop heat pipes have been reported. They can transport a large heat load over a long distance with a small temperature difference. The cooling air passes through intercooler, radiator, fan and engine and takes away the heat generated by the engine. Cylindrical heat pipes vapor chamber or flat heat pipes variable conductance heat pipes vchps diode heat pipes loop heat pipe 9. Asmall multiple loop heat pipe with two evaporators and two ra diators was designed and fabricated.
Because of heat pipes closed loop design, heat pipes works continuously and passively. Thermal performance of closed loop pulsating heat pipe. Test cell for a novel planar mems loop heat pipe based on coherent porous silicon debra cytrynowicz 1, mohammed hamdan 2, praveen medis 1 h. From heat pipe to loop heat pipe and capillary pumped. An evaporator ground loop heat exchanger transfers the heat from the ground into the fluid circulating in the loop. Cooling water loop includes engine, water pipe, thermostat, radiator and cooling water pump. Heat pipe is generally selfheat recovery devices that is used to transfer heat from one end heat injection to another destination with minimum temperature differences and also to pass the heat across internal surface. Loop heat pipe has high heat transfer capacity and be able to transport large heat load over a long distance, up to 1 to 2 meters with low thermal resistance. Niobium, zirconium and tungsten were the container materials used. Test cell for a novel planar mems loop heat pipe based on. At the hot interface of a heat pipe a liquid in contact with a thermally conductive solid surface turns into a vapor by absorbing heat from that surface.
The maximum heat loss from insulated pipe should not exceed 1 kcal per hour per square m per o c. The vapor flows down a system of grooves and headers in the evaporator and the vapor line toward the condenser, where it condenses as heat is removed by the cold plate or radiator. At this point the energy in the ground loop transfers through the evaporator within the heat pump and into a cfc free refrigerant. The present study is based on a detailed experimental and numerical thermal characterization of the loop heat pipe. Experimental investigation of loop heat pipe with two. Heat transfer and flow analysis in loop heat pipe with. Introduction loop heat pipes lhp were firstly conceived in russia in the mid 70s to address some of the heat transfer issues present on board spacecrafts 17. A loop heat pipe lhp is a twophase heat transfer device that uses capillary action to remove heat from a source and passively move it to a condenser or radiator. An experimental package was constructed to operate a loop heat pipe lhp in microgravity aboard nasas kc5 aircraft. Its the two phase heat transfer device suitable for low power applications such as electronic cooling. A ground source heat pump or geothermal system is nothing more than a series of interconnecting loops that work on the principle of the 2nd law of thermodynamics heat moves to cold ground loop this loop consists of piping buried in the ground in some manner. Looped heat pipes lhps are twophase heat transfer devices that employ the same capillary pumping of a working fluid as used in conventional heat pipes. Heat pipes are referred to as the superconductors of heat due to their. The loop heat pipe for ams02 politecnico di milano.
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