The Experts below are selected from a list of 276 Experts worldwide ranked by ideXlab platform
Wei Qu - One of the best experts on this subject based on the ideXlab platform.
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theoretical analysis of startup of a pulsating Heat Pipe
International Journal of Heat and Mass Transfer, 2007Co-Authors: Wei QuAbstract:A theoretical analysis is conducted to determine the primary factors affecting the startup characteristics of a pulsating Heat Pipe. It is found that the wall surface condition, evaporation in the Heating section, superHeat, bubble growth, and vapor bubbles trapped in cavities at the capillary inner wall affect the startup of oscillating motion in the pulsating Heat Pipe. The required superHeat and Heat flux level for the startup of oscillating motions in a pulsating Heat Pipe depend on the cavity size of the inner wall surface and the naturally-formed vapor bubbles and their shapes. When the capillary inner surface is coated or fabricated with cavities or roughness, the pulsating Heat Pipe can be readily started up. And it is found that the working fluid significantly affects the startup characteristics of a pulsating Heat Pipe. The results presented here can result in a better understanding of the startup operation of a pulsating Heat Pipe.
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Frequency Analysis on Pulsating Heat Pipe
ASME 2007 InterPACK Conference Volume 1, 2007Co-Authors: Wei Qu, Yuhua Li, Tongze MaAbstract:The pulsating Heat Pipe should have one eigen frequency based on the temperature visualization of pulsating Heat Pipe. The preliminary model of pulsating Heat Pipe is established by the force balance between the driving force, the inertial force and the frictional force. The results show that different structural parameter of pulsating Heat Pipe influences the eigen frequency differently. If a pulsating Heat Pipe has less turning number, or has micro or mini capillary, or has higher filling ratio, then the eigen frequency will change quickly. The frequency stands for the springiness of the system. The results can explain why some pulsating Heat Pipes with less turning number are hard to operate.
Amir Faghri - One of the best experts on this subject based on the ideXlab platform.
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Is a non-phase change Heat Pipe a new Heat Pipe?
International Journal of Heat and Mass Transfer, 2019Co-Authors: Sara Kloczko, Amir Faghri, Yuhua LiAbstract:Abstract A Non-phase change Heat Pipe (NPCHP) with no wick was proposed recently as a new Heat Pipe which is not dependent on a wick or phase change at steady state operation and where Heat transfer is driven by the pressure response to a Heat input, rather than phase change. The NPCHP is not a new device as suggested but is a loop thermosyphon with very high fill ratio. This effort focuses on proving the NPCHP, as an overfilled loop thermosyphon, is an effective Heat transfer device through experiments and numerical simulations. An analysis of the operation and effectiveness of the device is performed, and it is shown to exhibit several Heat transfer characteristics of a Heat Pipe, including high thermal conductivity and a fast thermal response time. Depending upon the initial fill ratio of the NPCHP, the device is shown to either operate as an overfilled two-phase loop thermosyphon or a single-phase loop thermosyphon. The NPCHP exhibits characteristics of a loop thermosyphon and can be classified as such.
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Entropy generation in a Heat Pipe system
Applied Thermal Engineering, 1999Co-Authors: H. Khalkhali, Amir FaghriAbstract:Abstract A thermodynamic model of conventional cylindrical Heat Pipes is developed based on the second law of thermodynamics. Entropy generation, an important parameter of the Heat Pipe performance, is caused by the temperature difference between the hot and cold reservoirs, the frictional losses in the working fluid flows, and the vapor temperature/pressure drop along the Heat Pipe. The ambient temperature in the condenser section and the convection Heat transfer coefficient in the transport section can be adjusted to minimize entropy generation in the Heat Pipe system. A detailed parametric analysis is presented in which the effects of various Heat Pipe parameters on entropy generation are examined.
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A network thermodynamic analysis of the Heat Pipe
International Journal of Heat and Mass Transfer, 1998Co-Authors: Amir FaghriAbstract:Abstract This work provides a unique view into the physics behind the Heat Pipe operation which was considered a thermal network of various components. Transient Heat Pipe behavior was described by first-order, linear, ordinary differential equations. The working fluid undergoes a thermodynamic cycle which was analyzed by T-s diagrams. The Heat Pipe dimensions must be “thermally compatible” with the Heat Pipe materials to establish the thermodynamic cycle. This was illustrated by a dimensionless number proposed here for the first time. Validated by comparisons with previous experimental and numerical studies, the present thermodynamic theory may lead to simplified Heat Pipe design schemes.
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Heat Pipe turbine vane cooling
1995Co-Authors: L. Langston, Amir FaghriAbstract:The applicability of using Heat Pipe principles to cool gas turbine vanes is addressed in this beginning program. This innovative concept involves fitting out the vane interior as a Heat Pipe and extending the vane into an adjacent Heat sink, thus transferring the vane incident Heat transfer through the Heat Pipe to Heat sink. This design provides an extremely high Heat transfer rate and a uniform temperature along the vane due to the internal change of phase of the Heat Pipe working fluid. Furthermore, this technology can also eliminate hot spots at the vane leading and trailing edges and increase the vane life by preventing thermal fatigue cracking. There is also the possibility of requiring no bleed air from the compressor, and therefore eliminating engine performance losses resulting from the diversion of compressor discharge air. Significant improvement in gas turbine performance can be achieved by using Heat Pipe technology in place of conventional air cooled vanes. A detailed numerical analysis of a Heat Pipe vane will be made and an experimental model will be designed in the first year of this new program.
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Heat Pipe science and technology
1995Co-Authors: Amir FaghriAbstract: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
Chien-chih Chen - One of the best experts on this subject based on the ideXlab platform.
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Developing the Coaxial Dual-Pipe Heat Pipe for Applications on Heat Pipe Cooler
Journal of Heat Transfer-transactions of The Asme, 2011Co-Authors: Chen-ching Ting, Chien-chih ChenAbstract:This article presents significant experimental data about the coaxial dual-Pipe Heat Pipe which is invented by our CCT laboratory. The coaxial dual-Pipe Heat Pipe is built-in an inner Pipe in the adiabatic section of a common Heat Pipe. A common Heat Pipe is composed of three sections: the evaporator section at the one end; the condenser section at the other end; and the adiabatic section in between. The vapor and the liquid phases of the working fluid flow in opposite directions through the core and the wick, respectively. This special Heat transfer behavior causes a common Heat Pipe to yield the discrete Heat transfer property. In process, the vapor directly brings large amounts of Heat from Heat source and rapidly flows through the adiabatic section to the condenser section. This intelligent Heat transfer technique lets the Heat Pipe yield extremely large thermal conductivity. Unfortunately, a Heat Pipe integrated with cooling fin in the adiabatic section has changed its original Heat transfer property. The integrated cooling fin in the adiabatic section has in advance taken Heat of the vapor away and caused the vapor to be condensed in the adiabatic section. Therefore, the vapor cannot reach the condenser section and the condenser section hence loses its cooling capability. In other words, the effective cooling length of a common Heat Pipe which is integrated with cooling fin in the adiabatic section is shortened. The coaxial dual-Pipe Heat Pipe is built-in an inner Pipe in the adiabatic section of a common Heat Pipe to avoid Heat of the vapor to be earlier taken away and even condensed in the adiabatic section. Experimental study in this work first built a home-made square coaxial dual-Pipe Heat Pipe integrated with outside isothermal cycling cooling water as the coaxial dual-Pipe Heat Pipe cooler. The home-made square coaxial dual-Pipe Heat Pipe has an observation window. It is convenient to observe change of the two-phase flow inside the Heat Pipe influenced by the outside cooling water. The results show that the new developed coaxial dual-Pipe Heat Pipe cooler has kept the original Heat transfer property of the bare Heat Pipe. The vapor has reached the condenser section.
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Thermal efficiency of Heat Pipe with alumina nanofluid
Journal of Alloys and Compounds, 2010Co-Authors: Tun Ping Teng, Huai En Mo, Chien-chih ChenAbstract:Abstract The study presents the enhancement of thermal efficiency of Heat Pipe charged with nanofluid. The Al 2 O 3 /water nanofluid produced by direct synthesis method is used as the working fluid of experimental Heat Pipes with three different concentrations (0.5, 1.0 and 3.0 wt.%). The Heat Pipe is a straight copper tube with inner diameter and length of 8 and 600 mm, respectively. The Heat Pipes charged with distilled water and nanofluids are tested, respectively. The study discusses about the effects of charge amount of working fluid, tilt angle of Heat Pipe and weight fraction of nanoparticles on the thermal efficiency of Heat Pipe. According to the experimental results, the optimum condition of Heat Pipe is when nanoparticles being at 1.0 wt.%. Under this condition, the thermal efficiency is 16.8%, which is higher than that of Heat Pipe charged with distilled water. The charge amount can be decreased from 60% to 20%.
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Developing the Coaxial Dual-Pipe Heat Pipe for Applications of Heat Pipe Cooler
Volume 7: Fluid Flow Heat Transfer and Thermal Systems Parts A and B, 2010Co-Authors: Chien-chih Chen, Chen-ching TingAbstract:This article presents significant experimental data about the coaxial dual-Pipe Heat Pipe which is new developed for applications of the Heat Pipe cooler in our CCT laboratory. It’s well known that Heat Pipe integrated with cooling plates has changed the Heat transfer property of the Heat Pipe to be similar to copper Pipe, where the Heat transfer property of the bare Heat Pipe is discrete and the copper Pipe is continuous. The integrated cooling plates cause the original Heat transfer property of the Heat Pipe to be destroyed. For recovery of the original Heat transfer property of the Heat Pipe in a Heat Pipe cooler, the coaxial dual-Pipe Heat Pipe built a coaxial Pipe inside the Heat Pipe in the thermal insulating section to avoid the Heat of vapor being earlier taken away in the thermal insulating section. Experimental study in this work first built a home-made square coaxial dual-Pipe Heat Pipe integrated with outside isothermal cycling cooling water. The home-made square coaxial dual-Pipe Heat Pipe has an observation window and is convenient to observe the change of two-phase flow inside the Heat Pipe influenced by the outside cooling water. The results show that the new developed dual-Pipe Heat Pipe cooler has kept the original Heat transfer property of the bare Heat Pipe and therefore increases its cooling efficiency clearly.Copyright © 2010 by ASME
Pichai Assadamongkol - One of the best experts on this subject based on the ideXlab platform.
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Heat Pipe efficiency enhancement with refrigerant nanoparticles mixtures
Energy Conversion and Management, 2009Co-Authors: Paisarn Naphon, Dithapong Thongkum, Pichai AssadamongkolAbstract:Abstract In the present study, the enhancement of Heat Pipe efficiency with refrigerant–nanoparticles mixtures is presented. The Heat Pipe is fabricated from the straight copper tube with the outer diameter and length of 15, 600 mm, respectively. The refrigerant (R11) is used as a base working fluid while the nanoparticles used in the present study are the titanium nanoparticles with diameter of 21 nm. The mixtures of refrigerant and nanoparticles are prepared using an ultrasonic homogenizer. Effects of the charge amount of working fluid, Heat Pipe tilt angle on the efficiency of Heat Pipe are considered. For the used pure refrigerant as working fluid, the Heat Pipe at the tilt angle of 60°, working fluid charge amount of 50% gives the highest efficiency. At the optimum condition for the pure refrigerant, the Heat Pipe with 0.1% nanoparticles concentration gives efficiency 1.40 times higher than that with pure refrigerant.
Arsalan Razani - One of the best experts on this subject based on the ideXlab platform.
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Experimental Study of a Curved Rotating Heat Pipe
Journal of Heat Transfer-transactions of The Asme, 2008Co-Authors: Todd A. Jankowski, F. C. Prenger, Arsalan RazaniAbstract: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.
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A ROTATING Heat Pipe FOR COOLING OF SUPERCONDUCTING MACHINES
AIP Conference Proceedings, 2008Co-Authors: Todd A. Jankowski, F. C. Prenger, Eric N. Schmierer, Arsalan RazaniAbstract:A curved rotating Heat Pipe for use in superconducting motor and generator applications is introduced here. The Heat Pipe shown here is built so that both the condenser and evaporator sections are parallel to the axis of rotation. The condenser section is concentric with 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. We show that because the Heat Pipe is a sealed, passive Heat transfer device with nearly isothermal operation, the Heat Pipe concept may be advantageous when considering the overall refrigeration system used with the superconducting machine. High-speed, room temperature test data with this Heat Pipe geometry indicate that the working fluid in the Heat Pipe continued to circulate, resulting in Heat transfer with a high effective thermal conductivity, with the Heat...
