scholarly journals Techniques for the Fabrication of Super-Hydrophobic Surfaces and Their Heat Transfer Applications

2018 ◽  
Author(s):  
Hafiz Muhammad Ali ◽  
Muhammad Arslan Qasim ◽  
Sullahuddin Malik ◽  
Ghulam Murtaza
Keyword(s):  
Heat Transfer ◽  
Hydrophobic Surfaces

Droplet Impingement and Vapor Layer Formation on Hot Hydrophobic Surfaces

2014 ◽  
Vol 136 (9) ◽  
Author(s):  
Ji Yong Park ◽  
Andrew Gardner ◽  
William P. King ◽  
David G. Cahill
Keyword(s):  
Heat Transfer ◽  
Residence Time ◽  
High Speed ◽  
Hydrophobic Surface ◽  
Vapor Layer ◽  
Si Substrate ◽  
Hydrophobic Surfaces ◽  
High Speed Imaging ◽  
Temperature Range ◽  
The Impact

We use pump–probe thermal transport measurements and high speed imaging to study the residence time and heat transfer of small (360 μm diameter) water droplets that bounce from hydrophobic surfaces whose temperature exceeds the boiling point. The structure of the hydrophobic surface is a 10 nm thick fluorocarbon coating on a Si substrate; the Si substrate is also patterned with micron-scale ridges using photolithography to further increase the contact angle. The residence time determined by high-speed imaging is constant at ≈1 ms over the temperature range of our study, 110 < T < 210 °C. Measurements of the thermal conductance of the interface show that the time of intimate contact between liquid water and the hydrophobic surface is reduced by the rapid formation of a vapor layer and reaches a minimum value of ≈0.025 ms at T > 190 °C. We tentatively associate this time-scale with a ∼1 m s − 1 velocity of the liquid/vapor/solid contact line. The amount of heat transferred during the impact, normalized by the droplet volume, ranges from 0.028 J mm − 3 to 0.048 J mm − 3 in the temperature range 110 < T < 210 °C. This amount of heat transfer is ≈1–2% of the latent heat of evaporation.

Heat Transfer Enhancement for Heat Exchanger Applications: Use of Surface Hydrophobicity

2016 ◽  
Author(s):  
S. T. Kafarakis ◽  
M. E. Mastrokalos ◽  
C. I. Papadopoulos ◽  
L. Kaiktsis
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Heat Transfer Enhancement ◽  
Slip Length ◽  
Convection Heat Transfer ◽  
Solid Boundary ◽  
Convection Heat ◽  
Transfer Enhancement ◽  
Hydrophobic Surfaces ◽  
Enhancement Of Heat Transfer

Hydrophobic surfaces, enabling flow slip past a solid boundary, can potentially be effective for heat transfer enhancement in heat exchanger applications. The scope of the present work is the computational study of forced convection heat transfer in flow past a hydrophobic cylinder, maintained at constant surface temperature. Hydrophobic surfaces are applied in flow control applications, since they enable flow slip past a solid boundary; as a result, they can contribute to flow stabilization. At the same time, hydrophobic surfaces are a potential means for heat transfer enhancement. In the present study, a computational investigation of forced convection heat transfer in cross-flow past a circular hydrophobic cylinder is performed by means of Computational Fluid Dynamics; the effects of hydrophobicity on flow stability and forces are also quantified. Here, low Reynolds number values, Re, are considered, whereas the Prandtl number, Pr, is maintained constant, equal to unity. Hydrophobicity is modelled by means of the Navier model. For slip conditions applied on the entire cylinder surface, the present results demonstrate that the stabilizing effect of increasing the non-dimensional slip length, b* = b/D, b being the slip length and D the cylinder diameter, is accompanied by a simultaneous enhancement of heat transfer. In particular, the time-averaged mean Nusselt number, Num, is found to be an increasing function of both b* and Re. Further, it is shown that, for the same levels of b*, an equivalent heat transfer rate can be achieved by substantially reducing the extent of the hydrophobic region, in particular by excluding the rear stagnation point region, i.e. at a significantly reduced cost. Overall, the present results illustrate that implementing partial hydrophobicity results in a substantial enhancement of heat transfer rates and a simultaneous (partial or full) suppression of the wake unsteadiness.

Biotemplated Superhydrophobic Surfaces for Enhanced Dropwise Condensation

2012 ◽  
Author(s):  
Emre Olceroglu ◽  
Stephen M. King ◽  
Md. Mahamudur Rahman ◽  
Matthew McCarthy
Keyword(s):  
Heat Transfer ◽  
Large Scale ◽  
Electronics Cooling ◽  
High Heat ◽  
The Self ◽  
High Heat Flux ◽  
Dropwise Condensation ◽  
Large Area ◽  
Hydrophobic Surfaces ◽  
Structured Surfaces

The increased heat transfer achieved through dropwise condensation, as compared to filmwise condensation, has the potential to substantially impact a variety of applications including high-heat flux thermal management systems, integrated electronics cooling, and various industrial and chemical processes. Here, we report stable dropwise condensation onto biotemplated nanostructured super-hydrophobic surfaces. We have demonstrated continuous droplet coalescence and ejection at diameters of less than 20 μm and compared directly with flat hydrophobic surfaces. The self-ejection mechanism characteristic of dropwise condensation has been shown using a simple bio-nano-fabrication technique based on the self-assembly and mineralization of the Tobacco mosaic virus (TMV). This process is extendable to commercially relevant nanomanufacturing of both microscale electronics devices as well as large-scale large-area industrial equipment. This manufacturing flexibility is unique as compared to many other micro/nano-structured surfaces fabricated to demonstrate similar increases in condensation heat transfer.

scholarly journals Numerical simulation of dropwise condensation over hydrophobic surfaces using vapor-diffusion model

2021 ◽  
Vol 2116 (1) ◽  
pp. 012011
Author(s):  
N Suzzi ◽  
G Croce
Keyword(s):  
Heat Transfer ◽  
Diffusion Model ◽  
Lagrangian Model ◽  
Dropwise Condensation ◽  
Velocity Range ◽  
Air Velocity ◽  
Hydrophobic Surfaces ◽  
Vapor Diffusion ◽  
Condensation Model ◽  
Hydrophilic And Hydrophobic Surfaces

Abstract Dropwise condensation of humid air over hydrophilic and hydrophobic surfaces is numerically investigated using a phenomenological, Lagrangian model. Mass flux through droplets free surface is predicted via a vapor-diffusion model. Validation with literature experimental data is successfully conducted at different air humidities and air velocities. The accuracy of the implemented condensation model is compared with a standard analogy between convective heat and mass transfer, showing that the latter is not able to predict heat transfer performances in the investigated air velocity range.

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