3D printed aluminum flat heat pipes with micro grooves for efficient thermal management of high power LEDs

AbstractAs the electronic technology becomes increasingly integrated and miniaturized, thermal management has become a major challenge for electronic device applications. A heat pipe is a highly efficient two-phase heat transfer device. Due to its simple structure, high thermal conductivity and good temperature uniformity, it has been used in many different industrial fields. A novel aluminum flat heat pipe, with micro-grooves, has in the present work been designed and fabricated by using a 3D printing technology. Aluminum powder was used as a raw material, which was selectively melted and solidified to form the shape of the heat pipe. The sintered aluminum powder increased the roughness of the inner surface of the heat pipe, and the designed micro-grooves further enhanced the capillary forces induced by the wick structure. The wettability, for the working fluid (acetone), was excellent and the capillary forces were sufficient for the working fluid to flow back in the pipe. The effects of working fluid filling ratio, on the heat transfer performance of the heat pipe, was also investigated. It was shown that a filling ratio of 10% gave the best heat transfer performance with the lowest thermal resistance. The 3D-printed flat heat pipe was, therefore, also tested for the thermal management of a LED. The temperature of the LED could be kept within 40 °C and its service life became prolonged.

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Experimental Study of the Heat-Transfer Performance of an Extra-Long Gravity-Assisted Heat Pipe Aiming at Geothermal Heat Exploitation

Sustainability ◽

10.3390/su132212481 ◽

2021 ◽

Vol 13 (22) ◽

pp. 12481

Author(s):

Jiwen Cen ◽

Feng Li ◽

Tingliang Li ◽

Wenbo Huang ◽

Juanwen Chen ◽

...

Keyword(s):

Heat Transfer ◽

Heat Pipe ◽

Heat Transfer Performance ◽

Water Flow Rate ◽

Cooling Water ◽

Filling Ratio ◽

Working Fluid ◽

Enhanced Geothermal Systems ◽

Transfer Performance ◽

Cooling Water Flow Rate

The installation and operation of enhanced geothermal systems (EGS) involves many challenges. These challenges include the high cost and high risk associated with the investment capital, potential large working-fluid leakage, corrosion of equipment, and subsiding land. A super-long heat pipe can be used for geothermal exploitation to avoid these problems. In this paper, a high aspect-ratio heat pipe (30 m long, 17 mm in inner diameter) is installed vertically. Experiments are then carried out to study its heat-transfer performance and characteristics using several filling ratios of deionized water, different heating powers, and various cooling-water flowrates. The results show that the optimal filling-ratio is about 40% of the volume of the vaporizing section of the heat pipe. Compared with a conventional short heat pipe, the extra-long heat pipe experiences significant thermal vibration. The oscillation frequency depends on the heating power and working-fluid filling ratio. With increasing cooling-water flow rate, the heat-transfer rate of the heat pipe increases before it reaches a plateau. In addition, we investigate the heat-transfer performance of the heat pipe for an extreme working-fluid filling ratio; the results indicate that the lower part of the heat pipe is filled with vapor, which reduces the heat-transfer to the top part. Based on the experimental data, guidelines for designing a heat pipe that can be really used for the exploitation of earth-deep geothermal energy are analyzed.

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Heat Transfer Characteristics of Oscillating Heat Pipe With Water and Ethanol as Working Fluids

Journal of Heat Transfer ◽

10.1115/1.4002366 ◽

2010 ◽

Vol 132 (12) ◽

Cited By ~ 17

Author(s):

Haizhen Xian ◽

Yongping Yang ◽

Dengying Liu ◽

Xiaoze Du

Keyword(s):

Heat Transfer ◽

Heat Pipe ◽

Inclination Angle ◽

Heat Transfer Performance ◽

Filling Ratio ◽

Working Fluid ◽

Transfer Performance ◽

Heat Transfer Characteristics ◽

Oscillating Heat Pipe ◽

Transfer Characteristics

In this paper, experiments were conducted to achieve a better understanding of the oscillating heat pipe (OHP) operating behavior with water and ethanol as working fluid. The experimental results showed that there existed a necessary temperature difference between the evaporator and the condenser section to keep the heat pipe working. The maximum effective conductivity of the water OHP reached up to 259 kW/m K, while that of the ethanol OHP is of 111 kW/m K. Not all the OHPs are operated in the horizontal operation mode. The heat transfer performance of the ethanol OHP was obviously affected by the filling ratio and the inclination angle but the influence law is irregular. The effect of the filling ratio and the inclination angle of the water OHP were smaller than that of the ethanol one. The heat transfer performance of the OHP was improved with increase of operating temperature. The startup characteristics of the OHP depended on the establishment of the integral oscillating process, which was determined by the operating factors. The startup temperature of the ethanol OHP varied from 40°C to 50°C and that of the water, OHP varied from 40°C to 60°C without considering the horizontal operating mode. The water OHP showed a better performance and more stable heat transfer characteristics than the ethanol OHP, which had no obvious advantages of the startup capability as well.

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Heat Transfer Performance of a Flexible Looped Heat Pipe Using R134a as a Working Fluid. A Proposal of a Method for Predicting the Maximum Heat Transfer Rate of FLHP.

TRANSACTIONS OF THE JAPAN SOCIETY OF MECHANICAL ENGINEERS Series B ◽

10.1299/kikaib.66.1440 ◽

2000 ◽

Vol 66 (645) ◽

pp. 1440-1446 ◽

Cited By ~ 4

Author(s):

Takashi KOBAYASHI ◽

Tetsuro OGUSHI ◽

Seiji HAGA ◽

Eiichi OZAKI ◽

Masao FUJII

Keyword(s):

Heat Transfer ◽

Heat Pipe ◽

Heat Transfer Rate ◽

Transfer Rate ◽

Heat Transfer Performance ◽

Working Fluid ◽

Transfer Performance ◽

Maximum Heat ◽

Maximum Heat Transfer

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Study on Periodic Thermal-Switching Behavior of Flat Heat Pipe

Volume 8B: Heat Transfer and Thermal Engineering ◽

10.1115/imece2015-50158 ◽

2015 ◽

Author(s):

Shigeki Hirasawa ◽

Tatsuya Nakamu ◽

Tsuyoshi Kawanami ◽

Katsuaki Shirai

Keyword(s):

Heat Transfer ◽

Heat Source ◽

Heat Pipe ◽

Heat Transfer Performance ◽

Switching Behavior ◽

Transfer Performance ◽

Unsteady Heat Transfer ◽

Cold Energy ◽

Thermal Switching ◽

Flat Heat Pipe

The coupling of the electrocaloric effect in thin films with thermal switches has the potential to be used for efficient refrigeration. We studied the unsteady heat transfer performance and periodic thermal-switching behavior of a flat heat pipe to transfer cold energy from a changing heat source. The condenser of the flat heat pipe was the changing heat source and changed from −20 W to +20 W every 5 s. The temperature of the condenser surface changed in accordance with the heat generation of the heat source. The evaporator was a plate with a mesh wick attached to a water-flow pipe. Cold energy transferred from the condenser surface to the evaporator surface only when the temperature of the condenser surface was lower than that of the evaporator surface. We analyzed the unsteady temperature change and heat transfer performance of the flat heat pipe by numerical simulation. The analytical results showed that it was necessary to have two thermal switches to separate the heat energy and cold energy of the changing heat source. Also, it was important to reduce the thermal resistance and heat capacity of the evaporator surface to improve the unsteady heat transfer performance of the heat pipe. Next, we measured the unsteady heat transfer performance of the flat heat pipe experimentally. The experimental results showed that the thermal-switching behavior was observed when the heat generation of the heat source changed every 5 s.

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Combined effect of nanofluid concentration and filling ratio on heat transfer performance of pulsating heat pipe

IOP Conference Series Earth and Environmental Science ◽

10.1088/1755-1315/199/3/032020 ◽

2018 ◽

Vol 199 ◽

pp. 032020

Author(s):

Lina Bai ◽

Xinjun Su ◽

Wenhao Ren ◽

Wenzhe Yang

Keyword(s):

Heat Transfer ◽

Heat Pipe ◽

Heat Transfer Performance ◽

Filling Ratio ◽

Combined Effect ◽

Transfer Performance ◽

Pulsating Heat Pipe

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Effect of working fluid on heat transfer performance of the anti-gravity loop-shaped heat pipe

Applied Thermal Engineering ◽

10.1016/j.applthermaleng.2014.09.056 ◽

2015 ◽

Vol 88 ◽

pp. 391-397 ◽

Cited By ~ 7

Author(s):

Hui Li ◽

Bo Zhou ◽

Yong Tang ◽

Rui Zhou ◽

Zhongshan Liu ◽

...

Keyword(s):

Heat Transfer ◽

Heat Pipe ◽

Heat Transfer Performance ◽

Working Fluid ◽

Transfer Performance

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Experimental Study on Oscillating Heat Pipe With Hydraulic Diameter Far Exceeding the Maximum Hydraulic Diameter

ASME 2019 6th International Conference on Micro/Nanoscale Heat and Mass Transfer ◽

10.1115/mnhmt2019-4092 ◽

2019 ◽

Author(s):

Lilin Chu ◽

Yulong Ji ◽

Chunrong Yu ◽

Yantao Li ◽

Hongbin Ma ◽

...

Keyword(s):

Heat Transfer ◽

Heat Pipe ◽

Heat Transfer Performance ◽

Hydraulic Diameter ◽

Working Fluid ◽

Transfer Performance ◽

Vertical Orientation ◽

Oscillating Heat Pipe ◽

Horizontal Orientation ◽

Small Bubbles

Abstract In order to understand the heat transfer performance, startup and fluid flow condition of oscillating heat pipe (OHP) with hydraulic diameter far exceeding the maximum hydraulic diameter (MHD), an experimental investigation on heat transfer performance and visualization was conducted. From the experimental performance, it is found that the OHP can still work well with ethanol as the working fluid when the tube diameter has exceeded the MHD of 91.6%. In addition, the detailed flow patterns of the OHP were recorded by a highspeed camera for vertical and horizontal orientation to understand its physical mechanism. In the vertical orientation, initially working fluid generates small bubbles, and then the small bubbles coalesce and grow to vapor plugs, the vapor plugs finally pushes the liquid slugs to oscillate in the tube. In the horizontal orientation, the working fluid surface fluctuates due to the vapors flow from the evaporator to the condenser and bubbles burst in the evaporator. When the peak of liquid wave reaches the upper surface of tube, a liquid slug has been formed, and then the steam flow pushes the liquid slugs to oscillate in the tube.

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Experimental Investigation of Oscillating Heat Pipe With Hybrid Fluids of Liquid Metal and Water

Journal of Heat Transfer ◽

10.1115/1.4043620 ◽

2019 ◽

Vol 141 (7) ◽

Cited By ~ 2

Author(s):

Tingting Hao ◽

Hongbin Ma ◽

Xuehu Ma

Keyword(s):

Heat Transfer ◽

Liquid Metal ◽

Heat Pipe ◽

Heat Input ◽

Heat Transfer Performance ◽

Pure Water ◽

Experimental Results ◽

Working Fluid ◽

Transfer Performance ◽

Oscillating Heat Pipe

A new oscillating heat pipe (OHP) charged with hybrid fluids can improve thermal performance. The key difference in this OHP is that it uses room temperature liquid metal (Galinstan consisting of gallium, indium, and tin) and water as the working fluid. The OHP was fabricated on a copper plate with six turns and a 3 × 3 mm2 cross section. The OHP with hybrid fluids as the working fluid was investigated through visual observation and thermal measurement. Liquid metal was successfully driven to flow through the OHP by the pressure difference between the evaporator and the condenser without external force. Experimental results show that while added liquid metal can increase the heat transport capability, liquid metal oscillation amplitude decreases as the filling ratio of liquid metal increases. Visualization of experimental results show that liquid metal oscillation position and velocity increase as the heat input increases. Oscillating motion of liquid metal in the OHP significantly increases the heat transfer performance at high heat input. The lowest thermal resistance of 0.076 °C/W was achieved in the hybrid fluids-filled OHP with a heat input of 420 W. We experimentally demonstrated a 13% higher heat transfer performance using liquid metal as the working fluid compared to an OHP charged with pure water.

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Working Fluid Inventory Effect on Heat Transfer Performance of a Grooved Micro Heat Pipe

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.589-590.559 ◽

2013 ◽

Vol 589-590 ◽

pp. 559-564

Author(s):

Xi Bing Li ◽

Yun Shi Ma ◽

Xun Wang ◽

Ming Li

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Heat Pipe ◽

Heat Transfer Performance ◽

Mathematic Model ◽

High Heat ◽

Working Fluid ◽

High Heat Flux ◽

Transfer Performance ◽

Flux Concentration

As a highly efficient heat transfer component, a micro heat pipe (MHP) has been widely applied to the situations with high heat flux concentration. However, a MHPs heat transfer performance is affected by many factors, among which, working fluid inventory has great influence on the security, reliability and frost resistance of its heat transfer performance. In order to determine the appropriate working fluid inventory for grooved MHPs, this paper first analyzed the working principle, major heat transfer limits and heat flux distribution law of grooved MHPs in electronic chips with high heat flux concentration, then established a mathematic model for the working fluid inventory in grooved MHPs. Finally, with distilled water being the working fluid, a series of experimental investigations were conducted at different temperatures to test the heat transfer performances of grooved MHPs, which were perfused with different inventories and with different adiabatic section lengths. The experimental results show that when the value of α is roughly within 0.40±0.05, a grooved MHP can acquire its best heat transfer performance, and the working fluid inventory can be determined by the proposed mathematic model. Therefore this study solves the complicated problem of determining appropriate working fluid inventory for grooved MHPs.

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