Effect of heterogeneous wetting surface characteristics on flow boiling performance

2018 ◽  
Vol 70 ◽  
pp. 141-151 ◽  
Author(s):  
Jin Man Kim ◽  
TaeJoo Kim ◽  
Dong In Yu ◽  
Hyunwoo Noh ◽  
Moo Hwan Kim ◽  
...  
Author(s):  
Tamanna Alam ◽  
Wenming Li ◽  
Fanghao Yang ◽  
Jamil Khan ◽  
Chen Li

Flow boiling in Silicon Nanowire microchannel enhances heat transfer performance, CHF and reduces pressure drop compared to Plainwall microchannel. It is revealed by earlier studies that promoted nucleate boiling, liquid rewetting and enhanced thin film evaporation are the primary reasons behind these significant performance enchantments. Although flow regime plays a significant role to characterize the flow boiling Silicon Nanowire microchannel performances; surface characteristics, hydrodynamic phenomena, bubble contact angle and surface orientation are also some of the major influencing parameters in system performances. More importantly, effect of orientation (effect of gravity) draws a great attention in establishing the viability of flow boiling in microchannels in space applications. In this study, the effects of heating surface orientation in flow boiling Silicon Nanowire microchannels have been investigated to reveal the underlying heat transfer phenomena and also to discover the applicability of this system in space applications. Comparison between Nanowire and Plainwall microchannels have been performed by experimental and visual studies. Experiments were conducted in a forced convection loop with deionized water at mass flux range of 100kg/m2s – 600kg/m2s. Micro devices consist of five parallel straight microchannels with Nanowire and without Nanowire (Plainwall) (200μm × 250μm × 10mm) were used to investigate the effects of orientation. Two different orientations were used to perform the test: upward facing (0° Orientation) and downward facing (180° Orientation). Results for Plainwall show sensitivity to orientation and mass flux, whereas, little effects of mass flux and orientation have been observed for Nanowire configuration.


2021 ◽  
Author(s):  
Prasanna Jayaramu ◽  
Shashwat Jain ◽  
Sateesh Gedupudi ◽  
Sarit Kumar Das

Abstract Heat sinks and heat exchangers based on flow boiling in mini/micro-channels are expected to be more compact and efficient. One of the major challenges while using copper material for phase-change heat transfer application is the change in surface characteristics after prolonged usage due to the thermal oxidation of surface over time. The present study involves the repeated experimental runs of flow boiling of water in a 1 mm hydraulic diameter end-milled copper channel to verify the influence of ageing on the thermal and hydraulic performance. As it is difficult to measure the surface wettability in a mini/micro-channel, the present work makes use of the ageing and surface characterization study conducted on the dummy copper samples to infer the influence of ageing on mini/micro-channel surface characteristics and consequently its boiling performance. The test involves measuring over a period of time the wetting behaviors of the end-milled copper samples left in water at three different conditions, one in a constant temperature bath maintained at 60 oC and 1 atm and the remaining two in a pool of boiling water at 110 oC and 120 oC. The study compares the fresh sample and the aged sample for the surface oxidation, surface chemical composition and surface morphology, and discusses the changes in contact angle and surface morphology caused by copper ageing.


2021 ◽  
pp. 153269
Author(s):  
Rajnikant V. Umretiya ◽  
Donghwi Lee ◽  
Barret Elward ◽  
Mark Anderson ◽  
Raul B. Rebak ◽  
...  

1984 ◽  
Vol 51 (01) ◽  
pp. 075-078 ◽  
Author(s):  
R G Schaub ◽  
C A Simmons

SummaryTwenty-seven adult male New Zealand rabbits (3–4 kgs) were used in this study. Six rabbits received vehicle, 3 groups of 6 each received doses of 4,5-bis(p-methoxyphenyl)-2-(trifluoromethyl)- thiazole, (U-53,059), at 0.3 mg/kg, 3.0 mg/kg and 30.0 mg/kg/day respectively. Drug and vehicle doses were given orally each day starting 3 days before balloon injury and continuing for the entire 2 week time period. Three rabbits were used as nontreated sham controls. In the vehicle and U-53,059 treated groups aortae were denuded of endothelial cells by balloon catheter injury. Two weeks after injury platelet aggregation to collagen was measured and the aortae removed for analysis of surface characteristics by scanning electron microscopy and lesion size by morphometry. All doses of U-53,059 inhibited platelet aggregation. The 3.0 and 30.0 mg/kg groups had the greatest inhibitory effect. All balloon injured aortae had the same morphologic characteristics. All vessels had similar extent and intensity of Evan’s blue staining, similar areas of leukocyte/platelet adhesion, and a myointimal cell cover of transformed smooth muscle cells. The myointimal proliferative response was not inhibited at any of the drug doses studied.


MRS Advances ◽  
2020 ◽  
Vol 5 (61) ◽  
pp. 3141-3152
Author(s):  
Alma C. Chávez-Mejía ◽  
Génesis Villegas-Suárez ◽  
Paloma I. Zaragoza-Sánchez ◽  
Rafael Magaña-López ◽  
Julio C. Morales-Mejía ◽  
...  

AbstractSeveral photocatalysts, based on titanium dioxide, were synthesized by spark anodization techniques and anodic spark oxidation. Photocatalytic activity was determined by methylene blue oxidation and the catalytic activities of the catalysts were evaluated after 70 hours of reaction. Scanning Electron Microscopy and X Ray Diffraction analysis were used to characterize the catalysts. The photocatalyst prepared with a solution of sulfuric acid and 100 V presented the best performance in terms of oxidation of the dye (62%). The electric potential during the synthesis (10 V, low potential; 100 V, high potential) affected the surface characteristics: under low potential, catalyst presented smooth and homogeneous surfaces with spots (high TiO2 concentration) of amorphous solids; under low potential, catalyst presented porous surfaces with crystalline solids homogeneously distributed.


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