The focus is on the development and testing of heat pipes with variable thermal conductance in a. There are three sections of a basic heat pipe with a working fluid enclosed inside the pipe. Flanges can be added on the outer surface for easy integration with instruments or radiators the flange is an integral part of the extrusion. The conductivity has the dimension of a volume flow rate and is normally expressed in l s 1 or m 3 h 1.
Variable conductance heat pipes have two additions compared to a standard heat pipe. Cvchp stands for cascade variableconductance heat pipe. This is the ability to control the operating temperature of a given component against variations in the heat dissipation of the component and in the environmental thermal conditions. Experimental investigation of thermal performance of variable. Esdu 800 heat pipes general information on their use, operation, and design. A heat pipe is a heattransfer device that combines the principles of both thermal conductivity.
The activities presented in this paper demonstrate a new approach to provide passive thermal control using heat pipes, as demonstrated on the electronic unit of dlrs mascot lander, which embarked on the nea sample return mission hayabusa 2 jaxa. Experimental investigation of thermal performance of. Such a system is called a variable conductance heat pipe vchp. Freeconvection energy transport in variable conductance. Variable conductance heat pipes for variable thermal links. Design of a variable conductance vacuum insulation 940315 this paper describes one approach to the design of a variable conductance vacuum insulation. Pressure balance in heat pipes the fluid flow will induce a frictional pressure drop. Variable conductance heat pipe, rotating heat pipe, loop heat pipe, micro heat pipe, nanofluids 1. Variable conductance heat pipe cooling of stirling convertor and general purpose heat source. In this design, the vacuum insulation consists of a permanently sealed, thin sheet steel, evacuated envelope of whatever geom etry is required for the application. Ats engineering ebook advanced thermal solutions, inc. He defined a micro heat pipe as so small that the mean curvature of the liquidvapor interface is comparable in magnitude to the reciprocal of the hydraulic radius of the total flow channel. Heat pipe routines built into sindafluint provide fast systemlevel solutions to modeling heat pipes when a full twophase solution is not required.
Historically, lhps were considered primarily as candidates for high power, high adverse elevation and high heat flux applications such as deployable radiators for. Keywords variable conductance heat pipe, rotating heat pipe, loop heat pipe, micro heat pipe, nanofluids 1. The temperature transfer matrix was obtained for the air preheater that comprises several discrete heat transfer units with same or different heat transfer surface area in a parallel or counter flow mode. In a rechargable metal oxidehydrogen cell having an outer shell, an electrode stack within said shell having positive and negative electrodes positioned on an alignment member, positive and negative bus bars coupling respective positive and negative electrodes to like conductive terminals, the improvement comprising a variable conductance. Variable conductance heat pipes heat pipe manufacturer. Cascade variableconductance heat pipe how is cascade. Heat pipes with variable thermal conductance property for. Special types of heat pipe variable conductance heat pipes thermal diodes oscillating heat pipes capillary loop heat pipes microheat pipes rotating heat pipes miscellaneous data base working fluid. Gas flowing through piping produces a pressure differential. Variable conductance heat pipes vchps are used to passively maintain the temperature of the electronics being cooled as power and sink conditions change. The full range of heat pipe classifications, including rotating and revolving, micro, cryogenic, and variable conductance heat pipes, as well as thermal diodes and switches this book provides all the information and guidance you need to increase your understanding of these innovative devices and to begin to apply them to the thermal control of.
Heat pipe theory of operation and test data are presented along with a discussion of its applicability for nasas direct detection laser transceiver ddlt program. How is cascade variableconductance heat pipe abbreviated. Variable conductance heat pipes vchps have a unique feature that sets them apart from other types of heat pipe. The treatment has been comprehensi ve, involving theoreti sal andor experimental studies in hydrostatics, hydrodynamics, heat transfer into and out of the pipe, flid selection, and materials compatibility, in addi tior. When the stirling convertor is turned off, the vchp will activate when the temperatures rises 30 c above the setpoint temperature. May 31, 20 shows the action of noncondensable gas ncg blocking vapor flow to form a variable conductance effect inside a heat pipe. Variable conductance heat pipes vchps are a common. An alkalimetal variable conductance heat pipe vchp was designed to allow multiple. Development of a variableconductance heatpipe for a sodium. Advanced passive thermal experiment for hybrid variable.
Variable conductance heat pipes vchps are used to passively maintain the temperature. Vchp is defined as variable conductance heat pipe somewhat frequently. Cvchp cascade variableconductance heat pipe acronymfinder. However, in an actual application when a heat pipe is soldered or epoxied to the base of a heat sink, the effective thermal conductivity of the heat pipe may be drastically reduced due to the extra thermal resistances added by the bonding. The performance of the heat pipe is investigated at three different amounts of both. Amir faghri written to cover simple, intermediate, and advanced approaches to the theoretical and experimental analysis of heat pipes, this second edition emphasizes the physics and mathematics of heat pipes as well as the related technological and experimental issues. Pdf the heat pipe is one of the remarkable achievements of thermal. Heat pipe is a capillary twophase heat transfer device.
Gravitational effects on the operation of a variable. An experimental investigation is carried out to study the effects of nanofluid and mass of noncondensable gas on the thermal performance of variable conductance heat pipe by testing circular screen mesh wick heat pipe. Introduction a typical heat pipe consists of a sealed pipe or tube made of a material that is compatible with the working fluid such as copper for water heat pipes, or aluminium for ammonia heat pipes. The conductance between two points is defined as the gas flow rate flowing through a device divided by the pressure drop that is driving it. Variable conductance heat pipe cooling of stirling. Heat pipes seminar ppt with pdf report study mafia. The performance of the heat pipe is investigated at three different amounts of both heat input and mass of noncondensable gas air. By controlling the water inventory so that no free liquid is available, hik. An alkalimetal variable conductance heat pipe vchp has been designed to allow multiple stops and restarts of the stirling convertor in an advanced stirling radioisotope generator asrg. Pdf nak variable conductance heat pipe for radioisotope. Free convection energy transport in variable conductance heat pipes vchp. By using the temperature transfer matrix, the outlet fluid temperatures. The heat transfer analysis of variable conductance heat pipe air preheater was carried out. In this design, the vacuum insulation consists of a permanently sealed, thin sheet steel, evacuated envelope of whatever geometry is required for the application.
The performance of the heat pipe is investigated at three. The working fluid repeatedly vaporizes and condenses as a. Applications general heat recovery thermal control space miscellaneous 7. The temperature diff f th h t condenser heat sink evaporator heat source adiabatic section difference from the heat source to the heat sink is dominated by the much smaller thermal r ce temp. Neural network analysis of free convection around isothermal elliptic tube. A primer on variable conductance heat pipes vchps, discussing their operation and limitations, with an animated schematic. Gas generati on i n methanol istai nlesssteel heat pipes showi ng. Various fluids are used in heat pipes and the selected fluid is based upon its saturation temperature and the temperature at which the heat pipe will be functioning. Pdf basic principles of heat pipes and history researchgate. Variable conductance heat pipes vchps for spacecraft thermal control typically have a coldbiased reservoir for the noncondensable gas ncg at the end.
The total pressure drop over the length of the heat pipe is the sum of individual pressure drops. Applications for vchps include passively controlling temperature, providing over temperature protection, acting as a variable thermal link, and helping heat pipe startup from a frozen state. May 21, 2011 the heat transfer analysis of variable conductance heat pipe air preheater was carried out. Jul 25, 2017 the activities presented in this paper demonstrate a new approach to provide passive thermal control using heat pipes, as demonstrated on the electronic unit of dlrs mascot lander, which embarked on the nea sample return mission hayabusa 2 jaxa. Conductance has units of volumetric flow rate divided by pressure drop, expressed as liters per second. Special types of heat pipe variable conductance heat pipes thermal diodes oscillating heat pipes capillary loop heat pipes microheat pipes rotating heat pipes miscellaneous data base working fluid properties tabulated wallwick material basic properties. It applies the implied heat of the vaporized working fluid instead of the reasonable heat.
Jun 18, 20 types of heat pipes thermosyphon leading edge rotating and revolving cryogenic pumped loop heat pipe flat plate micro heat pipes variable conductance capillary pumped loop heat pipe 16. Introduction the basic heat pipe is a closed container which has evacuated all noncondensable gases and contains a capillary structure wick and a small amount of a vaporizable fluid 1. Variable conductance heat pipe cooling of stirling convertor. Metaloxidehydrogen cell with variable conductant heat pipe. Development of a variableconductance heatpipe for a. Pdf this dissertation investigated experimentally and theoretically the. Conductance heat pipe cchp, it is wise to start with the layout of a cchp. Variable conductance heat pipe technology for precise.
Thermal conductivity of heat pipe container and wick materials. The second figure shows a typical grooved aluminiumammonia variable conductance heat pipe vchp for spacecraft thermal control. The thermal control range for this system is much greater than other variable conductance heat pipes. Constant conductance heat pipe cchp variable conductance heat pipe vchp di d h t pidiode heat pipe heat input wick heat output vapor flow evaporator condenser liquid return introduction to heat pipes ku 2015 tfaws. Thermal performance of a miniature variable conductance loop. The nanofluid used is waterbased cuonanofluid with the volume fraction of 1, 3 and 5 vol. Introduction a typical heat pipe consists of a sealed pipe or tube made of a material that is compatible with the working fluid. This paper describes one approach to the design of a variable conductance vacuum insulation. This is its ability to maintain a device mounted at the evaporator at a near constant temperature, independent of the amount of power being generated by. Shows the action of noncondensable gas ncg blocking vapor flow to form a variable conductance effect inside a heat pipe. Vchps have two additions compared to a standard heat pipe. At the time, there was no good method for sealing a refractory metal heat pipe, so a lower temperature valve was left on condenser end of the heat pipe. Cascade variableconductance heat pipe how is cascade variableconductance heat pipe abbreviated.
Efficient heat transferefficient heat transfer boiling and condensationboiling and condensation small temperature difference between the heat source and. Advantages of heat pipes may reduce or eliminate the need fir reheat, allow cost effective manner to accommodate newventilation standards, requires no. Cascade variableconductance heat pipe listed as cvchp. An alkalimetal variable conductance heat pipe vchp is under development to allow multiple stops and restarts of the stirling convertor. Analysis and application of variable conductance heat pipe. Science, technology, applications what is a heat pipe. The status of the ongoing effort in developing this. Investigation of the performance of a gasloaded variable. An introductory guide to variable conductance heat pipe.
Micro heat pipes the theory of micro heat pipe was introduced by cotter in 1984. Nov 11, 2015 such a system is called a variable conductance heat pipe vchp. A noncondensable gas ncg added to the heat pipe, in addition to the working fluid. This last category encompasses the following micro heat pipe structures 8 91011. In this aspect, heat pipes with variable conductance properties such as the. Thermal performance of a miniature variable conductance. The heat pipe is an aluminium extrusion, similar to that shown in the first figure. Above the evaporator, the flange is machined off to allow the adiabatic section to be bent. A heat pipe is a device that effortlessly transports thermal energy from its one point to the other. Pdf variable conductance heat pipes for radioisotope. A rule of thumb for the effective thermal conductivity of a heat pipe is 4000 wmk.
Thermal performance of a miniature variable conductance loop heat pipe 2000012490 loop heat pipes lhp of different designs are currently used in aerospace applications worldwide. By using the temperature transfer matrix, the outlet fluid temperatures could be easily calculated. Nas 25503, design, fabrication and testing of a variable conductance. Types of heat pipes thermosyphon leading edge rotating and revolving cryogenic pumped loop heat pipe flat plate micro heat pipes variable conductance capillary pumped loop heat pipe 16. Experimental investigation into the feasibility of using a. Variable conductance heat pipe animation video youtube. Transports heat from a heat source to a heat sink works as an isothermalizer why twophase thermal system. Both constant conductance cchp, also called fchp, with or without noncondensible gas ncg, and variable conductance vchp pipes can easily be simulated. Variable conductance heat pipes vchp differ from other heat pipe types by its thermal control capability. Heat flow path the thermal conductance is very high for the fluid flow wick container. The time required to draw a vacuum depends on the pumping speed. The particular application of hps is the removal of heat. The variable conductance heat pipe vchp, sometimes called a specific variant the gascontrolled or gasloaded heat pipe, has a unique feature that sets it apart from other types of heat pipe. The steel envelope is suppoted internally against the atmospheric pressure loads by an array of discrete, lowconductance, ceramic.
Heat pipe science and technology, second edition by dr. Freeconvection energy transport in variable conductance heat. Nasa glenn steadystate heat pipe code users manual, dos input. This page contains heat pipes seminar and ppt with pdf report.
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