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.

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.

Experimental Study on Heat Transfer Capability of a Miniature Loop Heat Pipe

2016 ◽  
Author(s):  
Guohui Zhou ◽  
Ji Li ◽  
Lucang Lv
Keyword(s):  
Heat Pipe ◽  
Heat Load ◽  
Electronics Cooling ◽  
High Heat ◽  
Working Fluid ◽  
Loop Heat Pipe ◽  
Evaporator Temperature ◽  
Liquid Line ◽  
Horizontal Orientation ◽  
Flat Evaporator

In this paper, a miniature loop heat pipe (mLHP) with a flat evaporator is illustrated and investigated experimentally, with water as the working fluid. The mLHP can be applied for the mobile electronics cooling, such as tablet computers and laptop computers, with a 1.2 mm thick ultra-thin flat evaporator and a thickness of 1.0 mm for the vapor line, liquid line and condenser. A narrow sintered copper mesh in the liquid line and a part of the condenser as the secondary wick can promote the flow of the condensed working fluid back to the evaporator. The experimental results showed that the mLHP could start up successfully and operate stably at low heat load of 3 W in the horizontal orientation, and transport a high heat load of 12 W (the heat flux of 4 W/cm2) with the evaporator temperature below 100 °C in different test orientations by natural convection, showing good operational performance against gravity field. The minimum mLHP thermal resistance of 0.32 K/W was achieved at the input heat load of 12 W in the horizontal orientation.

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.

Thermal Performance of a Loop Heat Pipe Having Polypropylene Wick in a Flat Evaporator

2005 ◽  
Author(s):  
Joon Hong Boo ◽  
Won Bok Chung
Keyword(s):  
Heat Pipe ◽  
Thermal Performance ◽  
Thermal Load ◽  
Thermal Control ◽  
Working Fluid ◽  
Small Scale ◽  
Loop Heat Pipe ◽  
Horizontal Position ◽  
Condenser Temperature ◽  
Flat Evaporator

A small-scale loop heat pipe (LHP) with polypropylene (PP) wick was fabricated and tested for its thermal performance. The container and tubing of the system were made of stainless steel and several working fluids were used including methanol, ethanol, acetone, and ammonia. The heater and the evaporator were sized so that the system can be applied to a local thermal control including electronics cooling. The heating area was 35 mm × 35 mm and there were nine axial grooves in the flat evaporator (40 by 50 mm) to provide a vapor passage. The pore size of the polypropylene wick inside the evaporator was varied from 0.5 μm to 25 μm. The size of condenser was 40 mm (W) × 50 mm (L) in which ten coolant paths were provided. The inner diameters of liquid and vapor transport lines were 2.0 mm and 4.0 mm, respectively and the length of the two lines was 0.5 m each. The start-up transient as well as steady-state operation was investigated with maximum system operating temperature of 90°C, which was imposed to protect the PP from permanent deformation. The minimum thermal load of 10 W (0.8 W/cm2) and maximum thermal load of 80 W (6.5 W/cm2) were achieved using methanol as working fluid with the condenser temperature of 20°C at horizontal position. For a LHP with ammonia as working fluid, the minimum thermal load of 1 W and maximum thermal load of 87 W (7.1 W/cm2) were achieved for condenser temperature of 0°C at horizontal position. The minimum system thermal resistance was 0.65 K/W.

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.

Flat Miniature Heat Pipe With Composite Fibre Wick Structure for Cooling of Mobile Handheld Devices

2005 ◽  
Author(s):  
Randeep Singh ◽  
Aliakbar Akbarzadeh ◽  
Mastaka Mochizuki ◽  
Yuji Saito ◽  
Thang Nguyen ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Thermal Resistance ◽  
Heat Pipe ◽  
Thermal Control ◽  
Heat Fluxes ◽  
The Body ◽  
Handheld Devices ◽  
Working Fluid ◽  
Composite Fibre ◽  
Wick Structure

Heat pipe is a very reliable and efficient two phase heat transfer device that has been extensively investigated for applications in electronic cooling. In the past, different types of heat pipe have been developed for specific as well as general applications. With the development in technology and trend towards miniaturization, thermal control of electronic devices with compact structure and concentrated heat sources has really become a challenge. Miniature heat pipes can be considered as potential candidates to address these issues. In the present paper, experimental investigation of the Flat Miniature Heat Pipe (FMHP), with the characteristic thickness of 1.5 mm and new type of composite fibre wick structure (FB-G), has been done for the thermal management of the mobile handheld devices. The so called composite fibre structure consists of combination of copper fibres and axial grooves as a capillary wick along the inner wall of the heat pipe. The design configuration of the experimental FMHP comprised of L-shaped flat heat pipe with rectangular cross section (1.5 mm × 8 mm) and heat transfer length of 100 mm. The body of FMHP was made of copper with pure deionised water as the working fluid. FMHP was easily able to transfer required heat fluxes in the range of 1–6 W/cm2 given by mobile-handheld chipset. Thermal resistance of the heat pipe from evaporator to the condenser surface came out to be in the range of 0.25–0.45 °C/W. In order to highlight the performance of the FMHP with composite fibre wick, thermal resistance was compared to different prototypes with screen mesh and axial grooves. It can be concluded from the outcomes of the investigation that the composite fibre wick structure provides an optimum capillary head and permeability for better heat transfer capabilities and minimal end to end temperature gradient than the conventional type of wick structures. FMHPs with composite fibre wicks will find prospective applications in the cooling of the compact handheld devices like Palm PC, mobile phones and digital diaries.

scholarly journals A Novel Analytical Modeling of a Loop Heat Pipe Employing Thin-Film Theory: Part II—Experimental Validation

Energies ◽  
2019 ◽  
Vol 12 (12) ◽  
pp. 2403 ◽  
Author(s):  
Eui Guk Jung ◽  
Joon Hong Boo
Keyword(s):  
Steady State ◽  
Heat Pipe ◽  
Film Theory ◽  
Design Parameters ◽  
Working Fluid ◽  
Coolant Temperature ◽  
Loop Heat Pipe ◽  
Analysis Model ◽  
Proposed Model ◽  
Flat Evaporator

Part I of this study introduced a mathematical model capable of predicting the steady-state performance of a loop heat pipe (LHP) with enhanced rationality and accuracy. Additionally, investigation of the effect of design parameters on the LHP thermal performance was also reported in Part I. The objective of Part II is to experimentally verify the utility of the steady-state analytical model proposed in Part I. To this end, an experimental device comprising a flat-evaporator LHP (FLHP) was designed and fabricated. Methanol was used as the working fluid, and stainless steel as the wall and tubing-system material. The capillary structure in the evaporator was made of polypropylene wick of porosity 47%. To provide vapor removal passages, axial grooves with inverted trapezoidal cross-section were machined at the inner wall of the flat evaporator. Both the evaporator and condenser components measure 40 × 50 mm (W × L). The inner diameters of the tubes constituting the liquid- and vapor-transport lines measure 2 mm and 4 mm, respectively, and the lengths of these lines are 0.5 m. The maximum input thermal load was 90 W in the horizontal alignment with a coolant temperature of 10 °C. Validity of the said steady-state analysis model was verified for both the flat and cylindrical evaporator LHP (CLHP) models in the light of experimental results. The observed difference in temperature values between the proposed model and experiment was less than 4% based on the absolute temperature. Correspondingly, a maximum error of 6% was observed with regard to thermal resistance. The proposed model is considered capable of providing more accurate performance prediction of an LHP.

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.

Thermal Characteristics of a Cylindrical Heat Pipe using Multi-Layer Screen Mesh Wick

2018 ◽  
Vol 10 (5) ◽  
Author(s):  
R. Sankar Rao ◽  
S. Bhanu Prakash
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Thermal Resistance ◽  
Transfer Coefficient ◽  
Heat Pipe ◽  
Thermal Characteristics ◽  
Wire Mesh ◽  
Working Fluid ◽  
Wick Structure ◽  
Screen Mesh

Heat pipe is the most widely used heat exchanging device in removal of heat from any given system at a faster rate. The thermal characteristics of heat pipe with single and multi-layered screen mesh wicks have been observed with two working fluids water and acetone. Heat pipe of length 250 mm and 12.7 mm outer diameter, made of copper material is used in all the trials of with and without wick structure. A 100 mesh stainless steel screen wire mesh is chosen as wick structure. Experiments were conducted at different heat loads and various inclinations with 100% fill ratio in evaporator. The performance is measured based on total thermal resistance and overall heat transfer coefficient. The heat pipe is found effective at 60o inclination with acetone as a working fluid and with four layered screen mesh wick. Uncertainty in thermal resistance and heat transfer coefficient is calculated for a heat input of 10W at 0 and 60 inclinations.

scholarly journals Visualization Experimental Study on Silicon-Based Ultra-Thin Loop Heat Pipe Using Deionized Water as Working Fluid

Micromachines ◽  
2021 ◽  
Vol 12 (9) ◽  
pp. 1080
Author(s):  
Wenzhe Song ◽  
Yanfeng Xu ◽  
Lihong Xue ◽  
Huajie Li ◽  
Chunsheng Guo
Keyword(s):  
Heat Pipe ◽  
Heat Dissipation ◽  
Experimental System ◽  
High Heat ◽  
Deionized Water ◽  
Working Fluid ◽  
Stable Operation ◽  
High Heat Flux ◽  
Loop Heat Pipe ◽  
Silicon Based

As a type of micro flat loop heat pipe, s-UTLHP (silicon-based ultra-thin loop heat pipe) is of great significance in the field of micro-scale heat dissipation. To prove the feasibility of s-UTLHP with high heat flux in a narrow space, it is necessary to study its heat transfer mechanism visually. In this paper, a structural design of s-UTLHP was proposed, and then, to realize the working fluid charging and visual experiment, an experimental system including a holding module, heating module, cooling module, data acquisition module, and vacuum chamber was proposed. Deionized water was selected as a working fluid in the experiment. The overall and micro phenomena of s-UTLHP during startup, as well as the evaporation and condensation phenomena of s-UTLHP during stable operation, were observed and analyzed. Finally, the failure phenomenon of s-UTLHP was analyzed, and several solutions were proposed. The observed phenomena and experimental conclusions can provide references for further related experimental research.

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