Heat Pipe Test Research Articles

Experimental and Numerical Analysis of Thermal Performance in Heat Pipes

Heat pipes come handy now-a-days as they operate with highest heat conductance compared to any other mode of heat transfer and available over wide range of parameters. In the present study de-ionized water flow in the plain thermo-syphon, Sintered Copper wick and Helical grooved heat pipes with simultaneous evaporation, adiabatic and condensation phenomenon are studied using Heat pipe test equipment. In this equipment a heat pipe subjected to a predetermine heat load by a resistance heater at its evaporator end and water jacket with controlled flow of water is employed to dissipate the heat energy at the condenser end. All the temperatures are measured and the required calculations are carried out to get percentage efficiencies at varying flow rates and heat inputs. The performance of heat pipes and comparison between their efficiencies is done. The sintered copper wick structure pipe have been found efficient when compared to other two with heat inputs starting from 50 to 200 watts because of predominating Capillarity property. Even the helical grooved heat pipe can also be used efficiently at the lower flow rates for power input ranging from 100 to 200W. Whereas, the plain thermo-syphon has lower efficiency and also the relative difference between the evaporator and condenser temperature is also very high which makes it in-effective. The variations of evaporator and condenser surface temperatures are plotted for changing heat inputs and flow rate changes at condenser water jacket. ANSYS 15.0 software is used for computational analysis and the experimental results are in good agreement with the analysis.

Thermal Performance of a Cylindrical Heat Pipe for Different Heat Inputs and Inclination Angles

An experimental study on thermal performance of a copper heat pipe operated with sintered powder wick has been performed. A miniature cylindrical heat pipe with small outer diameter, Ø10 mm and 300 mm in length, has been chosen in the study. An attempt is also made to design, fabricate and assemble a heat pipe test rig to be used for the experiment. The performance of the heat pipe is investigated at various heat inputs and inclination angles (orientations). The aim of this study is to evaluate and compare the thermal performance of the heat pipe based on temperature differential between the evaporator and condenser sections, thermal resistance and thermal conductivity. The results show that the orientation and heat input have significant effects on the thermal performance of the cylindrical heat pipe. The Ø10 mm heat pipe operates with good thermal performance at the heat input of 70 W - 80 W and at the inclination angle of 30° - 60°.

Standards and Certification Schemes for Solar Thermal Collectors, Stores and Systems — An Overview about the Latest Developments

During the last decade the use of solar thermal products has grown drastically all over the world. One reason for this increase was the implementation and continuous further development of specific standards series like the EN 12975 [1], EN 12976 [2] and EN 12977 [3] as well as the European certification scheme Solar Keymark which has become the most important certification scheme worldwide. The Solar Keymark being the world wide largest certification program with approx. 1600 certificates is not only accepted basically throughout Europe but is also introduced in other regions such as Northern Africa or Latin America and other countries like Japan or Canada. With the latest revision of the EN 12977 series Solar Keymark can now also be granted for so-called custom built solar thermal systems as well as for solar thermal heat stores.In order to support the global solar thermal market further developments of the International Standards and the implementation of a global certification schemes are essential. The first steps have been taken in the field of the solar thermal collectors. In 2011 ISO TC 180 decided to join their efforts in the review of the EN 12975 series dedicated to solar thermal collectors with CEN TC 312 to come up with a joined standard. The FDIS/ISO 9806 is currently under enquiry and is expected to come in force as EN ISO 98096 by the end of 2013. This standard will pave the way towards a global certification scheme which is currently under discussion between the already existing schemes Solar Keymark and SRCC with the support of certification bodies (e.g. AENOR and DINCERTCO) and Research and Testing Centre for Solar Thermal Systems (TZS) at ITW, University of Stuttgart being one of the leading test laboratories worldwide. Apart from the well-known collector technologies the EN ISO 9806 will cover in addition concentrating and tracking collectors, air collectors and PVT collectors.Besides the harmonization of existing standards another important topic is the development of new test procedures in order to make the existing standards applicable for new developments and to reduce testing costs as well as the implementation of new standards. Just lately ITW/TZS developed an indoor test procedure for complete solar thermal domestic hot water systems which will help to reduce the testing time and development periods. Examples for new standards are standards for the absorber durability, the durability and performance testing of evacuated tubes and the durability and performance testing of heat pipes which are currently under development in cooperation of ISO TC 180 and CEN TC 312.Additional work is done in the project SpeedColl funded by the German Government. Here the project partners ITW/TZS and Fraunhofer ISE are developing test procedure for accelerating aging testing of complete solar collectors.This conference contribution will give an overview of the current international standards, the ones to come and new test procedures. In the field of product certification it will provide a review of the existing Solar Keymark certification and an outlook to the currently discussed global certification scheme. The advantages of a global certification scheme on the future development of the worldwide market for solar thermal products will be described as well as the roadmap towards its implementation.

Self-rewetting carbon nanofluid as working fluid for space and terrestrial heat pipes

Thermal management is very important in modern electronic systems. Recent researches have been dedicated to the study of the heat transfer performances of binary heat transfer fluids with peculiar surface tension properties and in particular to that of “self-rewetting fluids”, i.e., liquids with a surface tension increasing with temperature and concentration. Since in the course of liquid/vapor-phase change, self-rewetting fluids behavior induces a rather strong liquid inflow (caused by both temperature and concentration gradients) from the cold region (where liquid condensates) to the hot evaporator region, this fluids have been proposed and investigated as new heat transfer fluids for advanced heat transfer devices, e.g., heat pipes or heat spreaders for terrestrial and space applications (Savino et al. in Space Technol 25(1):59–61, 2009). The present work is dedicated to the study of the thermophysical properties of a new class of heat transfer fluids based on water/alcohol solutions with suspended carbon nanostructures, in particular single-wall carbon nanohorns (SWNH), synthesized by a homemade apparatus with an AC arc discharge in open air (Mirabile Gattia et al. in Nanotechnology 18:255604, 2007). SWNHs are cone-shaped nanoparticles with diameters between 1 and 5 nm and lengths in the range of 20–100 nm. SWNHs could be found in the form of quite-spherical aggregates with diameters ranging from 20 to 100 nm. The paper also discusses the results of these investigations and laboratory characterization tests of different heat pipes, including reference ordinary heat pipes and innovative pipes filled with self-rewetting fluids and self-rewetting nanofluids. The potential interest of the proposed studies stems from the large number of possible industrial applications, including space technologies and terrestrial applications, such as cooling of electronic components.

Fabrication and Testing of SOG Structure Flat Heat Pipes with Triangle Grooves

A new kind of charging and sealing method for SOG (silicon on glass) structure micro heat pipe with triangular grooves is investigated. MHP (micro heat pipe) is fully charged in a vacuum atmosphere which is useful for preventing air intermingle. Experimental results shows that when the fill ration of working fluid is about 35%, thermal conductivity of MHP with ethanol as its working fluid has an improvement of 19% compared to empty MHP.

Self-rewetting heat transfer fluids and nanobrines for space heat pipes

This paper summarizes the main activities in preparation of microgravity experiments dedicated to performances characterization of innovative heat pipes systems based on “self-rewetting fluids”, i.e. fluid mixtures with a non-linear dependence of the surface tension with temperature. In preparation of the flight experiments, laboratory researches have been carried out to identify potential heat transfer fluids. The activities include measurements of surface tensions, contact angles and thermal conductivities for a number of multicomponent solutions, including self-rewetting alcohol solutions, brines and nanofluids. A non-linear surface tension dependence with temperature was found not only in binary mixtures but also in brines and nanofluids with small concentrations of butanol or heptanol. A number of figures of merit are introduced and evaluated on the basis of several fluid properties, including surface tension, contact angle, viscosity, freezing point, thermal conductivity. The paper discusses the results of these investigations and laboratory characterization tests of different heat pipes, including reference ordinary heat pipes and innovative pipes filled with self-rewetting fluids, brines and nanofluids.

Performance Testing of Loop Heat Pipes with Vapor Chamber in the Evaporator

This work develops a loop heat pipes (LHP) with the advantages of long distance (2050 mm) transport capability and high heat removal capacity (up to 300W). The evaporator of LHP is constructed by vapor chamber (VC) and compensation chamber (CC), which is separated by a 3 mm-thick sinter layer. The experiment incorporates five parameters, including as vapor channel layout, orientation, filling ratio (F.R.), wick material and heat capacity. The study results demonstrate that flow resistance is successfully used to design the vapor channel layout. The LHP has better thermal performance in the verticality, and the optimal F.R. is 80%. A wick material with low thermal conductivity prevents the residual heat to leak into the CC, and hence the boiling efficiency and thermal cycle is enhanced. The minimum thermal resistance of LHP with radial channel layout is 0.212℃/W when the heat load is 200W. Therefore, the equilibrium between boiling and condensation established at 200W.

Development and tests of ammonia Miniature Loop Heat Pipes with cylindrical evaporators

Miniature Loop Heat Pipes (MLHPs) are an attractive object for development and investigation as quite a promising means for cooling powerful electronics operating in the temperature range from 50 to 100 °C. The paper generalizes and presents the results of development and tests of 15 different variants of ammonia MLHPs with cylindrical evaporators 5 and 6 mm in diameter, which have an active zone length of 20 mm and are equipped with titanium and nickel wicks. As a result of successive efforts aimed at increasing the MLHPs efficiency, it was possible to achieve values of the heat-transfer coefficient close to 162,000 W/m 2 °C at a value of the heat flux of about 100 × 10 4 W/m 2. A maximum heat flux value of about 135 × 10 4 W/m 2 was achieved at the heat-transfer coefficient equal approximately to 75,000 W/m 2 °C.

Experimental Study of a Curved Rotating Heat Pipe

A curved rotating heat pipe for use in motor and generator applications is studied experimentally. The heat pipe is built so that both the condenser and evaporator sections are parallel to the axis of rotation. The condenser section is close to the axis of rotation while the evaporator section can be placed in contact with off-axis heat sources in the rotating machine. The geometry is achieved by incorporating an S-shaped curve between the on-axis rotating condenser section and the off-axis revolving evaporator section. The curved rotating heat pipe allows for a direct coupling of the rotating condenser section to an on-axis stationary refrigeration system, while allowing the revolving evaporator section to intercept off-axis heat sources in the rotating machine. An experimental rotating heat pipe test apparatus was built and operated. The test data indicate that the working fluid continued to circulate, resulting in heat transfer with a high effective thermal conductivity, with the curved rotating heat pipe operating under the influence of centrifugal accelerations approaching 400g. Furthermore, the experimental results were used to validate a heat pipe thermal model that can be used in the design of rotating machines that rely on the curved rotating heat pipe as part of the thermal management system.

Design and fabrication of hybrid bi-modal wick structure for heat pipe application

A new hybrid bi-modal wick structure was designed and fabricated in this study with the objective to simultaneously enhance performance in capillary pumping, permeability and evaporative heat transfer. Utilizing substrates with large pores and sintered powders, a highly integrated bi-modal wick structure was created with small pores lining the walls of the large pores. This unique structure can be tailored to a number of different configurations, including uniform, radial and axially varied pore morphologies. Tests of heat pipes containing the bi-modal wick structure in various configurations revealed increases in effective thermal conductivity by as much as 400% as compared to baseline heat pipes containing monolithic wick materials such as copper mesh.

Hysteresis phenomena in loop heat pipes

Testing of loop heat pipes (LHPs) has shown that the heat-load dependence of the operating temperature is not always unambiguous. It may have a hysteresis nature. It has been found that temperature hysteresis is connected with changes in the liquid distribution between the compensation chamber (CC) and the condenser. Analysis makes it possible to distinguish three types of temperature hysteresis. In the first case this redistribution is caused by the change in the amount of the parasitic heat flow that penetrates into the CC, which in its turn is a result of heat-transfer hysteresis in the evaporation zone. In the second, temperature hysteresis is connected with the liquid metastable state, which leads to a delay of formation of the vapor phase in the compensation chamber. The reason for hysteresis of the third type is the change of the initial liquid distribution in an LHP during a start-up.

Research, development and industrial application of heat pipe technology in China

This paper introduces some typical cases of industrial applications, which include the equipment for the waste heat recovery and the industrial process equipment. Carbon steel–water heat pipe technology, applied to air preheater and waste heat boiler, has been successfully used in many fields, such as waste heat recovery, energy conservation and environmental protection. Liquid metal high-temperature heat pipe technology has been extensively employed in the process equipment, for example, high-temperature hot air generators and heat extractors. Heat pipe technology also finds its use in chemical reactors including ammonia converters. The success of applications is founded on the basis of fundamental research of heat pipe technology, which includes the theoretical and experimental researches on the vapor–liquid two-phase flow and heat transfer inside the heat pipe, the heat transfer limits of heat pipes, the heat transfer enhancement with heat pipes, and researches on the material compatibility and life tests of heat pipes. Hi-efficient heat pipe heat and mass transfer equipment is going to play a more and more important role in the various industrial fields.

Roadmap for developing heat pipes for ALCATEL SPACE’s satellites

Heat pipe has become a common thermal control component on satellites since the beginning of its industrial development in 1970s. ALCATEL SPACE develops and manufactures its own axially grooved heat pipes made of aluminium and with ammonia as working fluid. After a quick overview of heat pipe development for space applications worldwide, the present paper will give an outlook of ALCATEL SPACE’s heat pipes and their thermal performances. The Research & Development activities are strongly concerned with new heat pipe developments. Indeed there is a need for an upgraded technology to meet the future thermal control requirements on telecommunication and scientific satellites. A roadmap gives the objectives to reach and the technical challenges to overcome. The main technical characteristics that need to be addressed are: • an increase in heat transport capability, • a higher heat flux density, • an extension of the operational temperature range, • a characterisation of the reflux mode for ground testing. To develop such an upgraded heat pipe, it is necessary to gain understanding on the physical processes which rule heat pipes. A three year Ph.D. research work is on going with experiments on a heat pipe testing apparatus at the University laboratory LET (Laboratoire d’Etudes Thermiques), Poitiers. Modelling studies are also being developed. The outcome of these studies will be useful to design optimised heat pipe profiles.

Fabrication and Testing of Mo-Re Heat Pipes Embedded in Carbon/Carbon

Refractory-composite/heat-pipe-cooled wing and tail leading edges are being considered for use on hypersonic vehicles to limit maximum temperatures to values below material reuse limits and to eliminate the need to actively cool the leading edges. The development of a refractory-composite/heat-pipe-cooled leading edge has evolved from the design stage to the fabrication and testing of heat pipes embedded in carbon/carbon (C/C). A three-foot-long, molybdenum-rhenium heat pipe with a lithium working fluid was fabricated and tested at an operating temperature of 2460 degrees F to verify the individual heat-pipe design. Following the fabrication of this heat pipe, three additional heat pipes were fabricated and embedded in C/C. The C/C heat-pipe test article was successfully tested using quartz lamps in a vacuum chamber in both a horizontal and vertical orientation. Start up and steady state data are presented for the C/C heat pipe test article. Radiography and eddy current evaluations were performed on the test article.

Experimental study of a refrigerant charged solar collector

The performance of a heat-pipe solar collector was investigated experimentally using refrigerants R11 as the working fluid. The unit is fabricated locally and its performance is evaluated under Beirut Solar conditions. The heat transfer from the heat pipes to the hot-water storage tank took place through a circular end condenser section of the heat-pipe integrated within the collector frame. Tests of single heat pipes showed that the thermal performance of the heat pipe were dependent on its tilt angle, condenser section length and configuration, and type of internal wick used. A circular condenser end of the heat-pipe performed better than a straight condenser due to increased surface area for heat transfer. The R11-charged solar collector with integrated condenser for secondary cooling of water had an efficiency in early operation hours that reached values higher than 60% for the forced circulation mode. The instantaneous system efficiencies varied from 60 to 20%, which are in the range of conventional water solar collectors. System response was fast and sensitive to the incident solar radiation. The thermosyphonic mode of the system operation generated build up of stored energy in the condenser, resulting in oscillating-type flow thus reducing system efficiency below values obtained with forced circulation. © 1998 John Wiley & Sons, Ltd.

Modeling, Fabrication, and Testing of Micro Heat Pipes: An Update

In 1992, an overview was presented which summarized the status and progress made in the development of very small, “micro” heat pipes, manufactured as stand alone devices or fabricated as an integral part of silicon wafers. Since that initial review, significant advances have been made in the analysis, fabrication and testing of these devices, for use in a wide variety of applications. Following, is a review of the more recent work in this rapidly emerging field. Included is a summary of the analytical techniques developed, the various proposed methods of fabrication, and a summary of the most current test results achieved to date. Because the fundamental operating characteristics of micro heat pipes larger than 1 mm in diameter are similar to that of conventional heat pipes, this review focuses on the analysis, fabrication, and testing of micro heat pipes with characteristic dimensions of less than 500 μm. Particular emphasis is placed on research, related to the development of arrays of micro heat pipes and flat plate micro heat pipes fabricated as an integral part of semiconductor devices.

A stable microcomputer-controlled heat pipe furnace and test of new noble metal thermocouples

A highly stable sodium heat pipe furnace was developed for comparing a high-temperature platinum resistance thermometer (HTPRT) and noble metal thermocouples at the millikelvin level. In the range of 660–962°C, the short-term stability of the furnace was better than ±5 mK for 30 minutes and long-term stability was within approximately ±35 mK for 12 hours. The Au Pt and Au Pd thermocouples were compared with the calibrated HTPRT based on the ITS-90 using the heat pipe furnace system, and the thermoelectric properties of these thermocouples were characterized.

95/03996 Heat pipe science and technology

Preface Nomenclature 1.Introduction 2.Solid-Liquid-Vapor Phenomena, Driving Forces and Interfacial Heat and Mass Transfer 3.Steady Hydrodynamic and Thermal Characteristics 4.Heat Transfer Limitations 5.Continuum Transient and Frozen Startup Behavior of Heat Pipes 6.Two-Phase Closed Thermosyphons 7.Rotating and Revolving Heat Pipes 8.Variable Conductance Heat Pipes 9.Capillary Pumped Loop and Loop Heat Pipe Systems 10.Micro/Miniature Heat Pipe Characteristics and Operating Limitations 11.Heat Pipe Heat Exchangers 12.Analysis of Nonconventional Heat Pipes 13.Special Effects on Heat Pipes 14.Heat Pipe Fabrication, Processing, and Testing Appendix A:Thermophysical Properties Appedix B:Experimental Heat Pipe Results Index

The Design and Heat Pipe Tests for a Line Focus Solar Stirling Domestic Generation system

This paper outlines the methodology used in the design of a line focus solar Stirling power generation system for remote locations. Tests of potential working fluids for the heat pipes, used to transport energy from the solar concentrator focus to the Stirling engine heater heads, are also described. At the optimum achievable solar absorber temperature, very few heat pipe working fluids are available. Those tested were a sulphur iodine system, the organic fluid dioctyl phthalate and mercury These were designed to deliver energy to an already developed compact hermetically sealed Stirling engine battery charger of 200 W electrical power output. The only fluid to show promising performance was mercury, but safety considerations may rule mercury out for application in numerous dispersed small domestic systems. The line focus system efficiency tends to be low because of the low Stirling engine heater head temperature at optimum system conditions and the greater losses associated with a larger focal area than that used in a point focus system of similar power output. Predicted system efficiency was 4.9 per cent for the prototype 200 W generator and 12.5 per cent for a 3 kW full-scale system on which better insulation of the heat pipe is possible. The size and cost of the 200 W unit in relation to output are likely to be too high to be economically attractive, but development of the 3 kW system may still be viable if alternator efficiency can be maximized and heat pipe thermal losses kept to a minimum.

First international conference on aerospace heat exchanger technology: February 15–17, 1993 Palo Alto, California, U.S.A.

LeRC has designed a heat pipe test facility which will be used to provide data for validating heat pipe computer codes. A heat pipe test chamber that uses helium gas for enhancing heat transfer was investigated. The conceptual design employs the technique of guarded heating and guarded cooling to facilitate accurate measurements of heat transfer rates to the evaporator and from the condenser. The design parameters are selected for a baseline heat pipe made of stainless steel with an inner diameter of 38.10 mm and a wall thickness of 1.016 mm. The heat pipe operates at a design temperature of 1000 K with an evaporator radial heat flux of 53 W/sq. cm.