Critical Heat Flux Enhancement Through Improved Surface Wettability With Surface Oxides and Nanofluids

2007 ◽  
Author(s):  
Johnathan S. Coursey ◽  
Jungho Kim
Keyword(s):  
Heat Flux ◽  
Surface Energy ◽  
Critical Heat Flux ◽  
Surface Oxidation ◽  
Phase Contact ◽  
Surface Wetting ◽  
Three Phase ◽  
Surface Oxides ◽  
Water Based ◽  
Oxide Nanoparticle

Surface wetting characteristics have been shown to affect the critical heat flux (CHF) observed during boiling. Surface oxidation is known to improve the ability of the fluid to wet the surface thus enhancing CHF. Nanofluids have also shown potential to enhance CHF, but the mechanisms are poorly understood. This study is targeted towards investigating whether or not nanofluids improve CHF by altering the surface energy. The surface energy of a heater was altered by oxidizing the surface to varying degrees or depositing metal onto the surface, and was characterized by measuring the advancing three-phase contact angle. Boiling curves were determined for water and ethanol based nanofluids with aluminum oxide nanoparticle concentrations from 0.001 g/l to 0.5 g/l as well as pure fluids on surfaces of varying surface energy. A 2.7 cm2 copper heater (polished or oxidized) was used for the water-based measurements. A 1.1 cm2 thick-film heater coated with glass and/or gold was used for the ethanol-based measurements. Boiling curves obtained using these fluid/surface combinations are discussed.

Critical Heat Flux Enhancement in Water-Based Nanofluid With Honeycomb Porous Plate on Large Heated Surface

2016 ◽  
Author(s):  
Suazlan Mt Aznam ◽  
Shoji Mori ◽  
Kunito Okuyama
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Heated Surface ◽  
Porous Plate ◽  
High Heat ◽  
High Heat Flux ◽  
Heater Surface ◽  
Solid Structure ◽  
Water Based ◽  
Plain Surface

Heat removal through pool boiling is limited by the phenomena of critical heat flux (CHF). CHF enhancement is vitally important in order to satisfy demand for the cooling technology with high heat flux in In Vessel Retention (IVR). Various surface modifications of the boiling surface, e.g., integrated surface structures and coating of a micro-porous have been proven to effectively enhance the CHF in saturated pool boiling. We have been proposed a novel method of attaching a honeycomb structured porous plate on a considerably large heater surface. Previous results, by the authors in [1] reported that CHF has been enhanced experimentally up to more than approximately twice that of a plain surface (approximately 2.0 to 2.5 MW/m2) with a diameter of 30 mm heated surface. However, it is necessary to demonstrate the method together with infinite heater surface within laboratory scale. It is important that cooling techniques for IVR could be applicable to a large heated surface as well as remove high heat flux. Objective of this study is to investigate the CHF of honeycomb porous plate and metal solid structure in nanofluid boiling or water boiling on a large heated surface. Water-based nanofluid offers good wettability and capillarity. While metal solid structure is installed on honeycomb porous plate to increase the number of vapor jet. Experimental results of honeycomb porous plate and combination of honeycomb porous plate and metal solid structure in water-based nanofluid boiling shows that CHF is increased up to twice [2] and thrice, respectively compared to plain surface in water boiling. To the best of the author’s knowledge, the highest value (3.1 MW/m2) was obtained for a large heated surface having a diameter of 50 mm which is regarded as infinite heated surface. This demonstrates potential for general applicability to have more safety margin in IVR method.

Study on Nucleate Boiling Heat Transfer by Measuring Spatially Instantaneous Local Surface Temperature and Observing Instantaneous Bubble/Liquid Fluid Behavior

2013 ◽  
Author(s):  
Yasuo Koizumi ◽  
Kenta Hayashi
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Surface Temperature ◽  
Critical Heat Flux ◽  
Boiling Heat Transfer ◽  
Nucleate Boiling ◽  
Heat Transfer Surface ◽  
Bubble Generation ◽  
Three Phase ◽  
Nucleate Boiling Heat Transfer

Pool nucleate boiling heat transfer experiments were performed for water at 0.101 MPa to examine the elementary process of the nucleate boiling. Heat transfer surface was made from a copper printed circuit board. Direct current was supplied to heat it up. The Bakelite plate of the backside of a copper layer was taken off at the center portion of the heat transfer surface. The instantaneous variation of the backside temperature of the heat transfer surface was measured with an infrared radiation camera. Bubble behavior was recorded with a high speed video camera. In the isolated bubble region, surface temperature was uniform during waiting time. When boiling bubble generation started, a large dip in the surface temperature was formed under the bubble. After the bubble left from the heat transfer surface, the surface temperature returned to former uniform temperature distribution. Surface temperature was not affected by the bubble generation beyond 1.6 mm from the center of the bubble. In the isolated bubble region, a convection term was approximately 80 % in total heat transfer rate. The importance of the three-phase interface line in the heat transfer should be checked carefully. In the intermediate and high heat flux region, the variation of surface temperature and heat flux were small. Rather those were close to their average values even at critical heat flux condition. It seemed that the large part of the heat transfer surface was covered with water even at the critical heat flux condition. The heat flux at the area that appeared to be the three-phase contact line was not so high and close to the average heat flux.

scholarly journals Water-based lubrication of niobium nitride

Friction ◽  
2021 ◽  
Author(s):  
Kaifei Miao ◽  
Jia Wang ◽  
Qiang Zhao ◽  
Kaiwen Wang ◽  
Mao Wen ◽  
...  
Keyword(s):  
Friction And Wear ◽  
Colloidal Particles ◽  
Niobium Nitride ◽  
Material Research ◽  
Transition Metal Nitrides ◽  
Phase Contact ◽  
Low Friction ◽  
Three Phase ◽  
Water Based ◽  
Solid Water

AbstractWater-based lubrication has attracted wide attention as an oil-free lubrication method owing to its greener and cleaner lubrication means. However, due to operating in the water environment, most moving parts would inevitably suffer from abrasion, rusting, and aging problems. Developing a novel solid-water composite system with ultra-low friction and wear will open new possibilities for innovative lubrication material research and development. Here, we first revealed the water-based lubrication behavior of a high-hardness niobium nitride coating (NbN). In a three-phase contact environment (water, air, and NbN), oxidation and hydrolytic reactions of NbN result in the formation of “colloidal solutions”, containing Nb2O5 colloidal particles between the tribo-pairs. Utilizing the double electric layer repulsion and weak shear action of the “colloidal solution”, NbN achieves ultra-low friction and wear; the corresponding values are as low as 0.058 and 1.79 × 10−10 mm3·N−1·m−1, respectively. In addition, other VB transition metal nitrides (VB TMNs) exhibit the same low friction feature as NbN in the three-phase contact environment; the friction coefficients are even lower than those in an oil-based environment. The water-based lubrication of VB TMNs provides a new reliable scheme for optimizing solid-water composite lubrication systems without additives and is expected to be applied in environments with high humidity or insufficient water coverage.

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