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.

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

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

scholarly journals The Influence of Loop Heat Pipe Evaporator Porous Structure Parameters and Charge on Its Effectiveness for Ethanol and Water as Working Fluids

Materials ◽  
2021 ◽  
Vol 14 (22) ◽  
pp. 7029
Author(s):  
Krzysztof Blauciak ◽  
Pawel Szymanski ◽  
Dariusz Mikielewicz
Keyword(s):  
Porous Structure ◽  
Pore Size ◽  
Heat Pipe ◽  
Capillary Pressure ◽  
Pressure Difference ◽  
Working Fluid ◽  
Loop Heat Pipe ◽  
Working Fluids ◽  
Integral Characteristics ◽  
Sintered Stainless Steel

This paper presents the results of experiments carried out on a specially designed experimental rig designed for the study of capillary pressure generated in the Loop Heat Pipe (LHP) evaporator. The commercially available porous structure made of sintered stainless steel constitutes the wick. Three different geometries of the porous wicks were tested, featuring the pore radius of 1, 3 and 7 µm. Ethanol and water as two different working fluids were tested at three different evaporator temperatures and three different installation charges. The paper firstly presents distributions of generated pressure in the LHP, indicating that the capillary pressure difference is generated in the porous structure. When installing with a wick that has a pore size of 1 μm and water as a working fluid, the pressure difference can reach up to 2.5 kPa at the installation charge of 65 mL. When installing with a wick that has a pore size of 1 μm and ethanol as a working fluid, the pressure difference can reach up to 2.1 kPa at the installation charge of 65 mL. The integral characteristics of the LHP were developed, namely, the mass flow rate vs. applied heat flux for both fluids. The results show that water offers larger pressure differences for developing the capillary pressure effect in the installation in comparison to ethanol. Additionally, this research presents the feasibility of manufacturing inexpensive LHPs with filter medium as a wick material and its influence on the LHP’s thermal performance.

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 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.

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 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 Problems of sodium using in pulsating heat pipe made from fused silica

2018 ◽  
Vol 207 ◽  
pp. 04004
Author(s):  
Radovan Nosek ◽  
Tatiana Liptáková ◽  
Libor Trško ◽  
Zuzana Kolková ◽  
Milan Malcho ◽  
...  
Keyword(s):  
High Temperature ◽  
Heat Pipe ◽  
Alkali Metals ◽  
High Efficiency ◽  
Fused Silica ◽  
Operating Conditions ◽  
Liquid Sodium ◽  
Working Fluid ◽  
Pulsating Heat Pipe ◽  
High Temperature Reaction

You Heat pipe is a high efficiency heat transfer element, depends on the evaporation, condensation and circulation of inside working fluid. The working fluid of a high temperature pulsating heat pipe is generally alkali metals, and sodium heat pipe can operate in range of 500-1100°C. In order to investigate terminal velocity of working fluid, the glass pulsating heat pipe was produced for experimental purposes. The experiment was carried out, in order to simulate real operating conditions in range of 500-1100°C. Sudden boiling of liquid sodium (b.p. = 883°C at 1 atm) inside the all quartz-made heat pipe results in high-temperature reaction of sodium vapour with the inner wall surface. The reaction became more aggressive with increasing vapour temperature and resulted in heat pipe explosion. The evaluation of damage character is analysed in this paper.

Study on Heat Transfer Characteristics of Loop Heat Pipe for Solar Collector

2012 ◽  
Author(s):  
Shota Sato ◽  
Shigeki Hirasawa ◽  
Tsuyoshi Kawanami ◽  
Katsuaki Shirai
Keyword(s):  
Heat Transfer ◽  
Heat Pipe ◽  
Heat Transfer Rate ◽  
Solar Collector ◽  
Transfer Rate ◽  
Thermal Conductance ◽  
Filling Ratio ◽  
Working Fluid ◽  
Loop Heat Pipe ◽  
Single Tube

We experimentally study the thermal conductance of single-tube and loop heat pipes for a solar collector. The evaporator of the heat pipe is 1 m long, 6 mm in diameter and has 30° inclination. The thermal conductance is defined as the heat transfer rate divided by the temperature difference between the evaporator-wall and the condenser-wall. Effects of heat transfer rate, saturation temperature of the working fluid, liquid filling ratio, inclination angle, and position of the evaporator on the thermal conductance are examined. We found that the thermal conductance of the 30°-inclined loop heat pipe with an upper-evaporator is 40–50 (W/K), which is 1.8 times higher than that of the vertical loop type and 3 times higher than that of the single-tube type. Thus, the inclined loop heat pipe is preferable for a solar collector. There is an optimum liquid filling ratio. When the liquid filling ratio is too small, a dry-out portion appears in the evaporator. When the liquid filling ratio is too large, the liquid flows in the condenser to decrease heat transfer area. Also we numerically analyze the thermal conductance of a vertical loop heat pipe.

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