Thermo-Wetting and Friction Reduction Characterization of Microtextured Superhydrophobic Surfaces

2012 ◽  
Vol 134 (11) ◽  
Author(s):  
Tae Jin Kim ◽  
Ravitej Kanapuram ◽  
Arnav Chhabra ◽  
Carlos Hidrovo
Keyword(s):  
Thermal Effects ◽  
Elevated Pressure ◽  
Friction Reduction ◽  
Superhydrophobic Surfaces ◽  
Microfluidic Channels ◽  
Pressure Drops ◽  
Cassie State ◽  
Heated Fluid ◽  
Gas Layer

Microtextured superhydrophobic surfaces have shown potential in friction reduction applications and could be poised to make a significant impact in thermal management applications. The purpose of this paper is to account for the thermal effects of the heated fluid flowing in superhydrophobic microfluidic channels. Through microscopic observation and flow rate measurements it was observed that (1) heating may prolong the Cassie state even under elevated pressure drops by increasing the temperature in the gas layer and that (2) excessive heating may pinch the microchannel flow due to the air layer invading into the liquid layer.

Thermo-Wetting and Friction Reduction Characterization of Microtextured Superhydrophobic Surfaces

2011 ◽  
Author(s):  
Tae Jin Kim ◽  
Phillip Glass ◽  
Carlos H. Hidrovo
Keyword(s):  
Thermal Management ◽  
Channel Flow ◽  
Liquid Layer ◽  
Microfluidic Channel ◽  
Friction Reduction ◽  
Superhydrophobic Surfaces ◽  
Microfluidic Channels ◽  
Textured Surface ◽  
Flow Measurements ◽  
Gas Layer

Microtextured superhydrophobic surfaces have become ubiquitous in a myriad of engineering applications. These surfaces have shown potential in friction reduction applications and could be poised to make a big impact in thermal management applications. For instance higher heat transfer rate with less pumping power might be achievable through the aid of superhydrophobic surfaces. However, past and current research on superhydrophobic surface has focused mainly on modifying either the chemical component or the roughness factors of such surfaces. The purpose of this paper is to account for the thermal effects of the heated fluid flowing in superhydrophobic microfluidic channels. Herein we characterize the wetting behavior as a function of temperature of microtextured superhydrophobic surfaces, for both active and passive thermal management applications. A series of PDMS microtextured samples were fabricated using micromachining and soft lithography techniques. Flow measurements were performed using the superhydrophobic microfluidic channel. The channel surface roughness was large enough to induce the Cassie-Baxter state, a phenomenon in which a liquid rests on top of a textured surface with a gas layer trapped underneath the liquid layer. This gas layer induces a two-phase flow, and friction reduction can be achieved for the liquid channel flow. With this channel, flow rates were measured by varying the equilibrium temperature of the substrate. The temperature in the constant pressure source was controlled by circulating the water through a water-bath. As the heating reached a certain threshold the curvature of the liquid-gas interface was reversed and dewetting of the penetrated liquid layer was observed. This result suggests that the Cassie state in fluid flow can be prolonged even under increased pressure drops by increasing the temperature in the gas layer.

Stability Analysis of Cassie-Baxter State Under Pressure Driven Flow

2010 ◽  
Author(s):  
Tae Jin Kim ◽  
Carlos H. Hidrovo
Keyword(s):  
Liquid Layer ◽  
Friction Reduction ◽  
Wetting Transition ◽  
Textured Surface ◽  
Microchannel Flow ◽  
Flow Conditions ◽  
Cassie State ◽  
The Stability ◽  
Gas Layer ◽  
Micro Cavity

The Cassie-Baxter state is a phenomenon in which a liquid rests on top of a textured surface with a gas layer trapped underneath the liquid layer. This gas layer introduces an effective shear free boundary that induces slip at the liquid-gas interface, allowing for friction reduction in liquid channel flows. Multiple studies have shown that different surface configurations result in different friction reduction characteristics, and most work is aimed at controlling the roughness factor and its shape in order to achieve an increased slip flow. This paper investigates the effects that different texturing geometries have on the stability of the Cassie state under pressurized microchannel flow conditions. To test the stability effects associated with the pressurized microchannel flow conditions, microfluidic channels with microstructures on the side walls were designed and fabricated. The microstructures were designed to induce the Cassie state with a liquid-air interface forming between the texturing trenches. The air trapped within the microstructure is treated as an ideal gas, with the compressibility induced pressure rise acting as a restrictive force against the Wenzel wetting transition. The model was validated against experimental flow data obtained using microchannel samples with microtextured boundaries. The microchannels were fabricated in PDMS (poly-dimethylsiloxane) using soft lithography and were baked on a hot plate to ensure the hydrophobicity of the microtexture. Pressure versus flow rate data was obtained using a constant gravitational pressure head setup and a flow meter. The liquid-gas interface layer in the microchannel was visualized using bright field microscopy that allowed measurement of the liquid penetration depth into the microtexturing throughout the microhannel. The experimental results indicate that air trapped in the pockets created by micro-cavity structures prevented the liquid layer from completely filling the void. As expected, the pressure drop in the micro-cavity textured channel showed a considerable decrease compared to that in the flat surfaced channel. These results also suggest that micro-cavities can maintain the Cassie state of a liquid meniscus, resting on top of the surface, in larger pressure ranges than open spaced micro-pillars arrays.

Cavitation Experiments on Turbopump Inducers and Hydrofoils at Alta/Centrospazio: Overview and Future Activities

2005 ◽  
Author(s):  
Angelo Cervone ◽  
Cristina Bramanti ◽  
Emilio Rapposelli ◽  
Luca d’Agostino
Keyword(s):  
Thermal Effects ◽  
Cavity Length ◽  
Rocket Engine ◽  
Pressure Coefficient ◽  
Suction Side ◽  
Test Facility ◽  
Final Part ◽  
Cloud Cavitation ◽  
Naca 0015

The aim of the present paper is to provide some highlights about the most interesting experimental activities carried out during the years 2000–2004 through the CPRTF (Cavitating Pump Rotordynamic Test Facility) at Centrospazio/Alta S.p.A. After a brief description of the facility, the experimental activities carried out on a NACA 0015 hydrofoil for the characterization of the pressure coefficient on the suction side and evaluation the cavity length and oscillations are presented. Then, the results obtained to characterize the performance and the cavitation instabilities on three different axial inducers are showed: in particular, a commercial three-bladed inducer, the four-bladed inducer installed in the LOX turbopump of the Ariane Vulcain MK1 rocket engine and the “FAST2”, a two-bladed one manufactured by Avio S.p.A. using the criteria followed for the VINCI180 LOX inducer. The most interesting results are related to the effects of the temperature on the cavitation instabilities on hydrofoils and inducers. Experiments showed that some instabilities, like the cloud cavitation on hydrofoils and the surge on inducers, are strongly affected by the temperature, while others seem not to be influenced by the thermal effects. In the final part of this paper, some indications of the main experimental activities scheduled for the next future are provided.

Cassie-State Stability of Metallic Superhydrophobic Surfaces with Various Micro/Nanostructures Produced by a Femtosecond Laser

Langmuir ◽  
2016 ◽  
Vol 32 (4) ◽  
pp. 1065-1072 ◽  
Author(s):  
Jiangyou Long ◽  
Lin Pan ◽  
Peixun Fan ◽  
Dingwei Gong ◽  
Dafa Jiang ◽  
...  
Keyword(s):  
Femtosecond Laser ◽  
Superhydrophobic Surfaces ◽  
Cassie State

scholarly journals Experimental and Computational Investigation of binary drop collisions under elevated pressure

2017 ◽  
Author(s):  
Jan Breitenbach ◽  
Louis Maximilian Reitter ◽  
Muyuan Liu ◽  
Kuan-Ling Huang ◽  
Dieter Bothe ◽  
...  
Keyword(s):  
Relative Velocity ◽  
Computational Study ◽  
Ambient Pressure ◽  
Experimental System ◽  
Elevated Pressure ◽  
Computational Investigation ◽  
Ambient Conditions ◽  
Influencing Parameters ◽  
Gas Layer ◽  
The Impact

Spray systems often operate under extreme ambient conditions like high pressure, which can have a significant influence on important spray phenomena. One of these phenomena is binary drop collisions. Such collisions, depending on the relative velocity and the impact parameter (eccentricity of the collision), can lead to drop bouncing, coalescence or breakup. This experimental and computational study is focused on the description of the phenomenon of drop bouncing, which is caused by a thin gas layer preventing the drops coalescence. To identify the main influencing parameters of this phenomenon, experiments on binary drop collisions are performed in a pressure chamber. This experimental system allows us to investigate the effect of an ambient pressure (namely the density and viscosity of the surrounding gas) on the bouncing/coalescence threshold.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4758

Characterization of Microfluidic Channels using DVD Pick-up Fluorescent Scanner

2008 ◽  
Vol 32 (12) ◽  
pp. 1102-1106
Author(s):  
Vit Yim ◽  
Jae-Hyun Kim ◽  
Seung-Yop Lee ◽  
Jung-Yul Park
Keyword(s):  
Microfluidic Channels
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