scholarly journals Hydrophilic and Hydrophobic Nanostructured Copper Surfaces for Efficient Pool Boiling Heat Transfer with Water, Water/Butanol Mixtures and Novec 649

Nanomaterials ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 3216
Author(s):  
Matic Može ◽  
Viktor Vajc ◽  
Matevž Zupančič ◽  
Iztok Golobič
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Heat Dissipation ◽  
Pool Boiling ◽  
Chemical Oxidation ◽  
Dielectric Fluid ◽  
Surface Stability ◽  
Copper Surfaces ◽  
Functionalized Surfaces ◽  
Fluorinated Silane

Increasing heat dissipation requirements of small and miniature devices demands advanced cooling methods, such as application of immersion cooling via boiling heat transfer. In this study, functionalized copper surfaces for enhanced heat transfer are developed and evaluated. Samples are functionalized using a chemical oxidation treatment with subsequent hydrophobization of selected surfaces with a fluorinated silane. Pool boiling tests with water, water/1-butanol mixture with self-rewetting properties and a novel dielectric fluid with low GWP (Novec™ 649) are conducted to evaluate the boiling performance of individual surfaces. The results show that hydrophobized functionalized surfaces covered by microcavities with diameters between 40 nm and 2 µm exhibit increased heat transfer coefficient (HTC; enhancements up to 120%) and critical heat flux (CHF; enhancements up to 64%) values in comparison with the untreated reference surface, complemented by favorable fabrication repeatability. Positive surface stability is observed in contact with water, while both the self-rewetting fluids and Novec™ 649 gradually degrade the boiling performance and in some cases also the surface itself. The use of water/1-butanol mixtures in particular results in surface chemistry and morphology changes, as observed using SEM imaging and Raman spectroscopy. This seems to be neglected in the available literature and should be focused on in further studies.

Pool Boiling Heat Transfer of Water on Hydrophilic Surfaces With Different Wettability

2016 ◽  
Author(s):  
Adam R. Girard ◽  
Jinsub Kim ◽  
Seung M. You
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Copper Surface ◽  
Contact Angles ◽  
Copper Surfaces ◽  
Nanoscale Structures ◽  
Flat Surfaces ◽  
Hydrophilic Surfaces ◽  
Alkali Solutions

The effect of wettability on boiling heat transfer (BHT) coefficient and critical heat flux (CHF) in pool boiling of water on hydrophilic surfaces having different contact angles was investigated. Hot alkali solutions were utilized to promote cupric and cuprous oxide growth which exhibited micro and nanoscale structures on copper surfaces, with thicknesses on the order of a couple of micrometers. These structure and surface energy variations result in different levels of wettability and roughness while maintaining the effusivity of the bare copper surface. The study showed that the BHT coefficient has an inverse relationship to wettability; the BHT coefficient decreases as wettability increases. Furthermore, it was shown that this dependency between BHT coefficient and wettability is more significant than the relationship between BHT coefficient and surface roughness. The CHF was also found to increase with increases in wettability and roughness. For the most hydrophilic surface tested in this study, CHF values were recorded near the 2,000 kW/m2 mark. This value is compared with maximum values reported in literature for water on non-structured flat surfaces without area enhancements. Based on these results it is postulated that there exists a true hydrodynamic CHF limit for pool boiling with water on flat surfaces, very near 2,000 kW/m2, independent of heater material, representing an 80% increase in the limit suggested by Zuber [1].

Influence of Copper Oxide on Femtosecond Laser Surface Processed Copper Pool Boiling Heat Transfer Surfaces

2019 ◽  
Vol 141 (5) ◽  
Author(s):  
Corey Kruse ◽  
Alfred Tsubaki ◽  
Craig Zuhlke ◽  
Dennis Alexander ◽  
Mark Anderson ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Oxide Layer ◽  
Boiling Heat Transfer ◽  
Heat Transfer Performance ◽  
Pool Boiling ◽  
Laser Surface ◽  
Transfer Performance ◽  
Reference Surface ◽  
Copper Surfaces ◽  
Pool Boiling Heat Transfer

Pool boiling heat transfer with the use of femtosecond laser surface processing (FLSP) on copper surfaces has been studied. FLSP creates a self-organized micro/nanostructured surface. In the previous pool boiling heat transfer studies with stainless steel FLSP surfaces, enhancements in critical heat flux (CHF) and heat transfer coefficients (HTCs) were observed compared to the polished reference surface. However, this study shows that copper FLSP surfaces exhibit reductions in both CHF and HTCs consistently. This reduction in heat transfer performance is a result of an oxide layer that covers the surface of the microstructures and acts as an insulator due to its low thermal conductivity. The oxide layer was observed and measured with the use of a focused ion beam milling process and found to have thickness of a few microns. The thickness of this oxide layer was found to be related to the laser fluence parameter. As the fluence increased, the oxide layer thickness increased and the heat transfer performance decreased. For a specific test surface, the oxide layer was selectively removed by a chemical etching process. The removal of the oxide layer resulted in an enhancement in the HTC compared to the polished reference surface. Although the original FLSP copper surfaces were unable to outperform the polished reference curve, this experiment illustrates how an oxide layer can significantly affect heat transfer results and dominate other surface characteristics (such as increased surface area and wicking) that typically lead to heat transfer enhancement.

Pool Boiling Heat Transfer Enhancement With Structured Surfaces

2016 ◽  
Author(s):  
Birce Dikici ◽  
Basim Q. A. Al-Sukaini
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Boiling Heat Transfer ◽  
Heat Dissipation ◽  
Pool Boiling ◽  
Base Temperature ◽  
Excess Temperature ◽  
Structured Surfaces ◽  
Plain Surface

With the increasing power of electronic devices in recent years, thermal management has become an obstacle in scaling down chip designs. Direct liquid cooling is a great option for heat dissipation from high powered electronic systems due to its ability to remove large amounts of heat [1–2]. The aim of this study is to investigate pool boiling performance of water under atmospheric pressure by using structured surfaces. Surfaces with rectangular channels, holes, and mushroom fins are manufactured and tested. The results showed that boiling heat transfer can be enhanced by macroscopically structured surfaces. Heat transfer coefficient (h) enhancement ranged between 23–44% for structured surfaces compared to plain surface. Heat flux is varied in the range of 16–18kW/m2. The maximum enhancement in heat transfer coefficient is ranged between 39–44.4% measured by 405 holed surface compared to the plain surface. The measured excess temperature drops ranged between 12–34% for different surfaces compared to plain surface. The excess temperature dropped around 29–34% for 405-holed surface compared to the plain surface. As the spacing between channels or holes is decreased, the heat transfer coefficient is increased. Base temperature measurements are carried out using an Infrared Camera. A digital camera was used to record pool boiling phenomena and evaluate bubble dynamics. The bubbles with holed surfaces and mushroomed surface observed to have almost spherical shape, while in plain and grooved surfaces they have an irregular shape.

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