Heat Transfer Characteristics of Horizontal Nano-Structured Oscillating Heat Pipes

2019 ◽  
Author(s):  
Tingting Hao ◽  
Huiwen Yu ◽  
Xuehu Ma ◽  
Zhong Lan
Keyword(s):  
Heat Transfer ◽  
Heat Input ◽  
Capillary Force ◽  
Heat Transfer Performance ◽  
Filling Ratio ◽  
Water Evaporation ◽  
Working Fluid ◽  
Transfer Performance ◽  
Structured Surface ◽  
Inner Surface

Abstract Working fluid in the oscillating heat pipe (OHP) with low turn number (< 9) positioned in the horizontal heat mode could not easily backflow to the evaporator due to the absence of gravity. In this paper, copper OHP with superhydrophilic nano-structured inner surface by introducing additional capillary force was investigated through the visualization and thermal experiments. OHPs with 6 turns, charged with pure water as the working fluid, were fabricated with copper, and nano-structured inner surface and tested for comparison. Contact angles of water on the copper and superhydrophilic surface were 36.7 and 0 deg. The filling ratio of water was 50%, 65%, and 80%, respectively. Startup performance, thermal resistance, and liquid slug oscillation of OHPs were investigated experimentally at the heat input of 100–380 W. Experimental results showed that OHPs with the superhydrophilic nano-structured surface showed an enhanced heat transfer performance due to the nanostructure-induced capillary action for water in the horizontal direction. The optimum filling ratio was 65% in this work. Dryout was observed in the OHPs with the filling ratio of 50% at the heat input higher than 220 W. At the filling ratio of 80%, the working fluid was accumulated in the adiabatic and condensation section, and the driving force due to the water evaporation in evaporator was not high enough to activate the movements of liquid slugs. Heat transfer performance of OHP with nano-structured surface was higher than that of bare copper surface by introducing the additional capillary force.

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

2019 ◽  
Vol 141 (7) ◽  
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.

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

2020 ◽  
Vol 12 (6) ◽  
Author(s):  
Lilin Chu ◽  
Yulong Ji ◽  
Hongbin Ma ◽  
Yantao Li ◽  
Chao Chang ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Input ◽  
High Speed ◽  
Heat Transfer Performance ◽  
Power Input ◽  
Hydraulic Diameter ◽  
Working Fluid ◽  
Transfer Performance ◽  
Vertical Orientation ◽  
Oscillating Heat Pipe

Abstract In order to understand the heat transfer performance, startup, and fluid flow conditions of oscillating heat pipes (OHPs) with a hydraulic diameter far exceeding the maximum hydraulic diameter (MHD) defined by dh,max≤2σBo/(ρl−ρv)g, an experimental investigation on the OHP heat transfer performance and visualization was conducted. The effects of heat input, working fluid, and orientation on the oscillating motion and heat transfer performance of the investigated OHPs have been conducted. In addition, the detailed flow patterns of the tested OHPs were recorded by a high-speed camera from both vertical and horizontal orientations. Results show that the maximum hydraulic diameter, which can form a train of liquid plugs and vapor bubbles, which is essential for an OHP to function, depends on the heat input, working fluid, and orientation. At a power input of 1000 W, the OHP can still function well even when the tube diameter exceeds the MHD of 91.6%. This maximum hydraulic dimeter depends on the orientation. While the OHP with a dimeter far exceeding the MHD can still function, the heat transfer performance of the OHP in a vertical orientation is better than in a horizontal orientation.

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

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.

An Experimental Investigation of the Heat Transfer Performance of an Oscillating Heat Pipe With Copper Oxide (CuO) Microstructure Layer on the Inner Surface

2013 ◽  
Vol 135 (7) ◽  
Author(s):  
Yulong Ji ◽  
Chen Xu ◽  
Hongbin Ma ◽  
Pan Xinxiang
Keyword(s):  
Heat Transfer ◽  
Experimental Investigation ◽  
Copper Oxide ◽  
Heat Pipe ◽  
Heat Transfer Performance ◽  
Working Fluid ◽  
Transfer Performance ◽  
Oscillating Heat Pipe ◽  
Inner Surface ◽  
Copper Tubing

This paper presents an experimental investigation of whether heat transfer performance in an oscillating heat pipe (OHP) would improve if the inner surface of the heat pipe was coated with a layer of copper oxide (CuO). The OHP had six turns and three sections, i.e., evaporator, condenser, and adiabatic section with lengths of 40 mm, 64 mm, and 51 mm, respectively. The cleaned copper tubing was chemically treated with a chemical solution and heated in a furnace. A microstructure layer of CuO was formed in the inner surface of the OHP with K2S2O8 and KOH. The working fluid in this study was water with filling ratios ranging from 40% to 70%. The experimental results show that the CuO microstructure layer is superhydrophilic and can enhance the OHP heat transfer performance. The investigation results in a new way to enhance the heat transfer performance of an OHP.

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

2010 ◽  
Vol 132 (12) ◽  
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.

Copper Oxide (CuO) Effect on Heat Transfer Performance in an Oscillating Heat Pipe

2012 ◽  
Author(s):  
Yulong Ji ◽  
Chen Xu ◽  
Hongbin Ma
Keyword(s):  
Heat Transfer ◽  
Copper Oxide ◽  
Heat Pipe ◽  
Heat Transfer Performance ◽  
Working Fluid ◽  
Transfer Performance ◽  
Oscillating Heat Pipe ◽  
Inner Surface ◽  
Copper Tubing ◽  
Adiabatic Section

An experimental investigation of an oscillating heat pipe (OHP) with an inner surface coated with a copper oxide (CuO) layer was conducted. The OHP has six turns and three sections: evaporator, condenser and adiabatic section with the lengths of 40 mm, 64 mm and 51 mm, respectively. The cleaned copper tubing was chemically treated with a chemical solution and heated in a furnace. A layer of CuO was formed in the inner surface of the OHP. A working fluid (water in this study) at filling ratios ranging from 40% to 70% was studied. The experimental results show that the CuO layer can enhance the heat transfer performance of the OHP. The investigation results in a new way to enhance the heat transfer performance of an OHP.

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

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Chao Chang ◽  
Zhaoyang Han ◽  
Xiaoyu He ◽  
Zongyu Wang ◽  
Yulong Ji
Keyword(s):  
Heat Transfer ◽  
Heat Pipe ◽  
Thermal Management ◽  
Aluminum Powder ◽  
Heat Transfer Performance ◽  
Filling Ratio ◽  
Working Fluid ◽  
Transfer Performance ◽  
3D Printed ◽  
Flat Heat Pipe

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.

EXPERIMENTAL STUDY ON THERMAL TRANSPORT PHENOMENON OF NANOFLUIDS AS WORKING FLUID IN HEAT EXCHANGER

2014 ◽  
Vol 22 (01) ◽  
pp. 1450005 ◽  
Author(s):  
SHUICHI TORII
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Performance ◽  
Pure Water ◽  
Horizontal Tube ◽  
Constant Heat Flux ◽  
Working Fluid ◽  
Transfer Performance ◽  
Nanoparticles Concentration ◽  
Transfer Behavior

This paper aims to study the convective heat transfer behavior of aqueous suspensions of nanoparticles flowing through a horizontal tube heated under constant heat flux condition. Consideration is given to the effects of particle concentration and Reynolds number on heat transfer enhancement and the possibility of nanofluids as the working fluid in various heat exchangers. It is found that (i) significant enhancement of heat transfer performance due to suspension of nanoparticles in the circular tube flow is observed in comparison with pure water as the working fluid, (ii) enhancement is intensified with an increase in the Reynolds number and the nanoparticles concentration, and (iii) substantial amplification of heat transfer performance is not attributed purely to the enhancement of thermal conductivity due to suspension of nanoparticles.

scholarly journals Numerical study of flow patterns and heat transfer in mini twisted oval tubes

2015 ◽  
Vol 26 (12) ◽  
pp. 1550140 ◽  
Author(s):  
Amin Ebrahimi ◽  
Ehsan Roohi
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Performance ◽  
Numerical Study ◽  
Critical Role ◽  
Reynolds Numbers ◽  
Flow Patterns ◽  
Working Fluid ◽  
Transfer Performance ◽  
Temperature Dependent ◽  
Overall Performance

Flow patterns and heat transfer inside mini twisted oval tubes (TOTs) heated by constant-temperature walls are numerically investigated. Different configurations of tubes are simulated using water as the working fluid with temperature-dependent thermo-physical properties at Reynolds numbers ranging between 500 and 1100. After validating the numerical method with the published correlations and available experimental results, the performance of TOTs is compared to a smooth circular tube. The overall performance of TOTs is evaluated by investigating the thermal-hydraulic performance and the results are analyzed in terms of the field synergy principle and entropy generation. Enhanced heat transfer performance for TOTs is observed at the expense of a higher pressure drop. Additionally, the secondary flow generated by the tube-wall twist is concluded to play a critical role in the augmentation of convective heat transfer, and consequently, better heat transfer performance. It is also observed that the improvement of synergy between velocity and temperature gradient and lower irreversibility cause heat transfer enhancement for TOTs.

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