Biporous Sintered Copper for Closed Loop Heat Pipe Evaporator

2005 ◽  
Author(s):  
Tadej Semenic ◽  
Ying-Yu Lin ◽  
Ivan Catton
Keyword(s):  
Heat Flux ◽  
Heat Pipe ◽  
Atmospheric Pressure ◽  
Closed Loop ◽  
Working Fluid ◽  
Loop Heat Pipe ◽  
Copper Base ◽  
Sintered Copper ◽  
Wick Structure ◽  
Heat Loads

Parameters that determine a critical heat flux (CHF) inside a biporous evaporator (wick) for a closed loop heat pipe have been studied. In a present work, a biporous wick structure was sintered from copper powder 53–63μm diameter into clusters 500–710μm diameter; the clusters were then sintered into 20mm long and 3mm wide wicks with different wick thickness on copper bases with three different lengths (5mm, 7.5mm and 10mm). Total of six wicks were made and tested. Copper base(mm) to wick thickness(mm) ratios of the wicks tested are: 5/5, 7.5/5, 10/5, 5/3, 7.5/3 and 10/1.5. Narrow (3mm) wicks with different copper base lengths allowed sidewise observation of the boiling inside the wick at different heat loads. Best-performed 10/1.5 wick, second best was 5/3 and then following 7.5/3, 5/5, 7.5/5, 10/5. Tests were run at atmospheric pressure and absolute ethanol as working fluid.

Experimental Investigation of the Miniature Loop Heat Pipe With Flat Evaporator

2005 ◽  
Author(s):  
Randeep Singh ◽  
Aliakbar Akbarzadeh ◽  
Masataka Mochizuki ◽  
Thang Nguyen ◽  
Vijit Wuttijumnong
Keyword(s):  
Thermal Resistance ◽  
Heat Pipe ◽  
Thermal Control ◽  
Capillary Forces ◽  
High Heat ◽  
Working Fluid ◽  
Loop Heat Pipe ◽  
Wick Structure ◽  
Flat Evaporator ◽  
Heat Loads

Loop heat pipe (LHP) is a very versatile heat transfer device that uses capillary forces developed in the wick structure and latent heat of evaporation of the working fluid to carry high heat loads over considerable distances. Robust behaviour and temperature control capabilities of this device has enable it to score an edge over the traditional heat pipes. In the past, LHPs has been invariably assessed for electronic cooling at large scale. As the size of the thermal footprint and available space is going down drastically, miniature size of the LHP has to be developed. In this paper, results of the investigation on the miniature LHP (mLHP) for thermal control of electronic devices with heat dissipation capacity of up to 70 W have been discussed. Copper mLHP with disk-shaped flat evaporator 30 mm in diameter and 10 mm thickness was developed. Flat evaporators are easy to attach to the heat source without any need of cylinder-plane-reducer saddle that creates additional thermal resistance in the case of cylindrical evaporators. Wick structure made from sintered nickel powder with pore size of 3–5 μm was able to provide adequate capillary forces for the continuos circulation of the working fluid, and successfully transport heat load at the required distance of 60 mm. Heat was transferred using 3 mm ID copper tube with vapour and liquid lines of 60 mm and 200 mm length respectively. mLHP showed very reliable start up at different heat loads and was able to achieve steady state without any symptoms of wick dry-out. Tests were conducted on the mLHP with evaporator and condenser at the same level. Total thermal resistance, R total of the mLHP came out to be in the range of 1–4°C/W. It is concluded from the outcomes of the investigation that mLHP with flat evaporator can be effectively used for the thermal control of the electronic equipments with restricted space and high heat flux chipsets.

scholarly journals Distribution of heat flux by working fluid in loop heat pipe

2016 ◽  
Vol 114 ◽  
pp. 02081
Author(s):  
Patrik Nemec ◽  
Milan Malcho
Keyword(s):  
Heat Flux ◽  
Heat Pipe ◽  
Working Fluid ◽  
Loop Heat Pipe

Investigation of Loop Heat Pipe Startup Using Liquid Core Visualization

2008 ◽  
Author(s):  
B. P. d’Entremont ◽  
J. M. Ochterbeck
Keyword(s):  
Heat Pipe ◽  
Liquid Core ◽  
High Heat ◽  
Working Fluid ◽  
Loop Heat Pipe ◽  
Two Phase ◽  
Buoyancy Driven Flows ◽  
Compensation Chamber ◽  
Fill Level ◽  
Heat Loads

In this investigation, a Loop Heat Pipe (LHP) evaporator has been studied using a borescope inserted through the compensation chamber into the liquid core. This minimally intrusive technique allows liquid/vapor interactions to be observed throughout the liquid core and compensation chamber. A low conductivity ceramic was used for the wick and ammonia as the working fluid. Results indicate that buoyancy driven flows, both two-phase and single-phase, play essential roles in evacuating excess heat from the core, which explains the several differences in performance between horizontal and vertical orientations of the evaporator. This study also found no discernable effect of the pre-start fill level of the compensation chamber on thermal performance during startup at moderate and high heat loads.

scholarly journals Heat Removal from Bipolar Transistor by Loop Heat Pipe with Nickel and Copper Porous Structures

2014 ◽  
Vol 2014 ◽  
pp. 1-9 ◽  
Author(s):  
Patrik Nemec ◽  
Martin Smitka ◽  
Milan Malcho
Keyword(s):  
Grain Size ◽  
Heat Pipe ◽  
Nickel Powder ◽  
Heat Removal ◽  
Bipolar Transistor ◽  
Working Fluid ◽  
Loop Heat Pipe ◽  
Porous Structures ◽  
Porous Wick ◽  
Wick Structure

Loop heat pipes (LHPs) are used in many branches of industry, mainly for cooling of electrical elements and systems. The loop heat pipe is a vapour-liquid phase-change device that transfers heat from evaporator to condenser. One of the most important parts of the LHP is the porous wick structure. The wick structure provides capillary force to circulate the working fluid. To achieve good thermal performance of LHP, capillary wicks with high permeability and porosity and fine pore radius are expected. The aim of this work was to develop porous structures from copper and nickel powder with different grain sizes. For experiment copper powder with grain size of 50 and 100 μm and nickel powder with grain size of 10 and 25 μm were used. Analysis of these porous structures and LHP design are described in the paper. And the measurements’ influences of porous structures in LHP on heat removal from the insulated gate bipolar transistor (IGBT) have been made.

scholarly journals Performance Assessment of a Three-Dimensional Printed Porous Media Produced by Selective Laser Melting Technology for the Optimization of Loop Heat Pipe Wicks

2019 ◽  
Vol 9 (14) ◽  
pp. 2905 ◽  
Author(s):  
Jesús Esarte ◽  
Jesús M. Blanco ◽  
Angela Bernardini ◽  
Ramón Sancibrián
Keyword(s):  
Heat Pipe ◽  
Selective Laser Melting ◽  
Three Dimensional ◽  
Loop Heat Pipe ◽  
High Permeability ◽  
Laser Melting ◽  
Powder Sintering ◽  
Sintered Copper ◽  
Wick Structure ◽  
Better Than

The primary wick in a loop heat pipe device is a key component that is central to the operation of the device. Both high permeability and capillary pumping capacity, two properties highly dependent on wick structure, are strongly desirable for a satisfactory thermal performance. In this paper, selective laser melting (SLM), a three-dimensional (3D) printing technology, is used to create a primary wick for an 80 W heat transfer application. The permeability and capillarity values of this wick, experimentally measured, are compared with those built with the most widely used technologies nowadays, such as powder sintering and meshes. In this study, the SLM scaffold is shown to satisfy the minimum values required by the application in terms of capillarity and permeability: 0.031 mm/s and 4 × 10−12 m2, respectively. Our comparative study revealed that the wick produced with the SLM technology presented higher values of permeability, by two orders of magnitude, and slightly higher capillary figures than those corresponding to powder sintering for such application. However, it had capillary values well below those of a stainless-steel mesh. The hydraulic behavior of the SLM wick was better than that of the sintered copper powder, because it not only met the above-mentioned specifications, but it also improved its performance.

Fractal Loop Heat Pipe Heat Flux and Operational Performance Testing

2009 ◽  
Author(s):  
Eric A. Silk ◽  
David Myre
Keyword(s):  
Heat Flux ◽  
Heat Pipe ◽  
Performance Testing ◽  
Working Fluid ◽  
Thermal Engineering ◽  
Loop Heat Pipe ◽  
Intimate Contact ◽  
Cross Sectional ◽  
Nasa Goddard Space ◽  
Start Ups

This study investigates heat flux performance for a LHP that includes a fractal based evaporator design. The prototype Fractal Loop Heat Pipe (FLHP) was designed and manufactured by Mikros Manufacturing Inc. and validation tested at NASA Goddard Space Flight Center’s Thermal Engineering Branch laboratory. Heat input to the FLHP was supplied via cartridge heaters mounted in a copper block. The copper heater block was placed in intimate contact with the evaporator. The evaporator had a circular cross-sectional area of 0.877 cm2. Twice distilled, deionized water was used as the working fluid. Thermal performance data was obtained for three different Condenser/Subcooler temperature combinations under degassed conditions (Psat = 25.3 kPa at 22°C). The FLHP demonstrated successful start-ups in each of the test cases performed. Test results show that the highest heat flux demonstrated was 75 W/cm2.

Study of Nickel Wick Structure Applied to Loop Heat Pipe with Flat Evaporator

2016 ◽  
Vol 723 ◽  
pp. 282-287 ◽  
Author(s):  
Shen Chun Wu ◽  
Shih Hsuan Yen ◽  
Wei Chen Lo ◽  
Chen Yu Chung ◽  
Shen Jwu Su
Keyword(s):  
Heat Transfer ◽  
Surface Tension ◽  
Heat Pipe ◽  
Heat Transfer Performance ◽  
Working Fluid ◽  
Loop Heat Pipe ◽  
Transfer Performance ◽  
Total Thermal Resistance ◽  
Wick Structure ◽  
Flat Evaporator

This study investigated the use of sintered Nickel powder as the wick material of Loop heat pipe with flat evaporator (Flat loop heat pipe, FLHP) and its effect on the heat transfer performance. Add the 1-heptanol into water and form Self-rewetting Fluid (SRF), resulting in the Marangoni effect. The colder liquid can be transport to the heating surface, delaying the occurrence of dry-out and increasing the critical heat load. This paper use Surface tension measurements to measure the change of 1-heptanol SRF, then it was apply to nickel wick FLHP as working fluid to investigate its effect on the heat transfer performance. This study successfully established production process of Nickel wick structure. Results of wick structure for the effective pore radius of 2.6 μm, porosity of 62%, permeability of 5.7 × 10-13m2. Results of Surface tension measurements show that 1-heptanol aqueous solution’s surface tension increases with increasing temperature, Results from applying 0.1% 1-heptanol aqueous solution to FLHP as working fluid. For performance testing show that the critical heat load was 240 W and the total thermal resistance was 0.77 ° C/W. Compared with FLHP with pure water, SRF raised the maximum heat flux of 70%, the total thermal resistance of the system reduces 40%, SRF has the potential to enhance the heat transfer performance of FLHP.

Development of a Closed-Loop Heat-Pipe for Heat Recovery With Mini-Channels Enhancing Evaporation

2008 ◽  
Author(s):  
Bruno Duarte Rocha ◽  
Rene´ Reyes Mazzoco
Keyword(s):  
Heat Transfer ◽  
Heat Pipe ◽  
Surface Area ◽  
Heat Recovery ◽  
Closed Loop ◽  
Heat Removal ◽  
Working Fluid ◽  
Loop Heat Pipe ◽  
Vast Number ◽  
Mini Channels

A vast number of industrial processes require the addition and removal of heat at different stages of the same process. To accomplish heat recovery there are several technological options with specific characteristics. Thermal integration has been the focus of recent industrial developments to reduce variable costs through new investments when using fossil fuels for thermal energy generation. The conventional equipment for heat recovery uses conduction and convection heat transfer mechanisms and high surface area of a metal wall (normally subjected to corrosion and fouling) for the contact of the cold and hot fluids. Heat pipes are an option for heat recovery with less metal surface area (and therefore lower tendency to corrosion and fouling) because of their higher thermal conductivity, but have been used mostly for heat removal in electronic equipment. This study develops a closed-loop heat pipe configuration for heat recovery in industrial operations starting with a configuration for desalination. The variables of the heat pipe operation that were considered include the mini-channels structures associated to the evaporator section, the effect of the inclination of condenser to evaporator, the working fluids (ethanol-water mixtures, acetone, methanol, and isopropanol), and the internal pressure of the heat pipe (atmospheric and vacuum). The highest heat flux values (3.2 W/cm2) were obtained with a single layer mini-channels structure, 90° of inclination between the condenser and the evaporator, and a mixture of 16% ethanol in water as working fluid in the loop-heat-pipe because this mixture had the highest heat transfer parameter (that describes the capacity of the fluid to perform in a heat pipe) among the fluids tested and corresponded to the highest heat transfer rate measured.

USAGE OF A DIATOMITE-CONTAINING NANOFLUID AS THE WORKING FLUID IN A WICKLESS LOOP HEAT PIPE: EXPERIMENTAL AND NUMERICAL STUDY

2018 ◽  
Vol 49 (17) ◽  
pp. 1721-1744 ◽  
Author(s):  
Adnan Sözen ◽  
Erdem Çiftçi ◽  
Selçuk Keçel ◽  
Metin Gürü ◽  
Halil Ibrahim Variyenli ◽  
...  
Keyword(s):  
Heat Pipe ◽  
Numerical Study ◽  
Working Fluid ◽  
Loop Heat Pipe

Device Packaging Techniques for Implementing a Novel Thermal Flux Method for Fluid Degassing and Charging of a Planar Microscale Loop Heat Pipe

2011 ◽  
Author(s):  
Navdeep S. Dhillon ◽  
Jim C. Cheng ◽  
Albert P. Pisano
Keyword(s):  
High Temperature ◽  
Heat Pipe ◽  
Thermal Flux ◽  
Anodic Bonding ◽  
Working Fluid ◽  
Loop Heat Pipe ◽  
Pressure Gradients ◽  
Flux Method ◽  
Double Compression ◽  
Plastic Package

A novel two-port thermal flux method is implemented for degassing a microscale loop heat pipe (mLHP) and charging it with a working fluid. The mLHP is fabricated on a silicon wafer using standard MEMS micro-fabrication techniques, and capped by a Pyrex wafer, using anodic bonding. For these devices, small volumes and large capillary forces render conventional vacuum pump-based methods quite impractical. Instead, we employ thermally generated pressure gradients to purge non-condensible gases from the device, by vapor convection. Three different, high-temperature-compatible, MEMS device packaging techniques have been studied and implemented, in order to evaluate their effectiveness and reliability. The first approach uses O-rings in a mechanically sealed plastic package. The second approach uses an aluminum double compression fitting assembly for alignment, and soldering for establishing the chip-to-tube interconnects. The third approach uses a high temperature epoxy to hermetically embed the device in a machined plastic base package. Using water as the working fluid, degassing and filling experiments are conducted to verify the effectiveness of the thermal flux method.

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