Study of droplet dynamics and condensation heat transfer on superhydrophobic copper surface

Yuvaraj, R.; Senthkil, D Kumar

doi:10.2298/tsci190126089y

Cited by 4 publications

(3 citation statements)

References 22 publications

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“…When higher saturation temperature for vapor is assumed, a minor increase in heat transfer performance is predicted by the Nusselt theory for comparable subcooling temperature. This is mostly attributed to the larger driving temperature difference between the surface of the wall and the vapor [30]. Subsequent to electrochemical treatment of all surfaces (see example in Figure 18b1), the contact angle increased as shown exemplarily in Figure 18b2 at all surfaces.…”

Section: Manufacturing Of Nano-micro-structured 7075 Aluminum Substratesmentioning

confidence: 83%

“…Compared to the surface modifications that require a mechanical manufacturing method, coatings are relatively inexpensive and can be made by simply dipping, spraying, or steaming. One possible way to obtain superhydrophobic copper surfaces for instance having a maximum contact angle of 168° can be achieved by the so-called thermo solution immersion technique [30]. As solution, ethanol and tetradecanoic acid is used, while a heat treatment at 45°C for about 4 hours is necessary.…”

Section: Figure 2 Equation For Surface Energy and Contact Angle According To Young Lawmentioning

confidence: 99%

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confidence: 99%

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Conceptualization, Thermal Analysis, and Manufacturing of Nano-Textured Micro-Structured Surfaces for Enhanced Condensation Heat Transfer

Budaklı

2021

Journal of Thermal Engineering

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In the present study, nano-micro-structured surfaces have been systematically designed and manufactured in order to generate controlled dropwise condensation mode for enhanced heat transfer during phase-change from vapor to liquid. The conceptualization of micro-structures was conducted by using thermal modelling of an individual droplet pinned at a single micro-hexagonal cavity. By varying droplet radius, resulting contact angles and geometric dimensions of micro-structure, threshold values have been determined for the later manufacturing process. According to the calculations for instance at contact angles of 150°, a subcooling of 1 K and a maximum droplet radius of 100 µm, the edge length and the depth of the micro-structures should be kept below 50 µm and 25 µm, respectively. Ensuring these parameters, a roughly 100 % larger heat transfer coefficient would result compared to that predicted by the classical Nusselt theory for filmwise condensation. Taking into account the mathematical analysis, laser ablation technique was adopted on 7075 aluminum samples to emboss hexagonal structures with respect to the predicted dimensions. After this step, the samples were electrochemically etched in order to achieve contact angles of more than 150° to ensure superhydrophobic solid-liquid interaction at the surface. Measurements with a high-precision microscope show that most of the structure dimensions and geometric shape were precisely manufactured. The Tensiometer results disclosed that the surface topography at all samples exhibit contact angles larger than 150° for a sessile droplet with a radius of 100 µm pinned on an individual micro-hexagon.

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Section: Manufacturing Of Nano-micro-structured 7075 Aluminum Substratesmentioning

confidence: 83%

Section: Figure 2 Equation For Surface Energy and Contact Angle According To Young Lawmentioning

confidence: 99%

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Conceptualization, Thermal Analysis, and Manufacturing of Nano-Textured Micro-Structured Surfaces for Enhanced Condensation Heat Transfer

Budaklı

2021

Journal of Thermal Engineering

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Heat transfer model for dropwise condensation on hydrophobic and superhydrophobic interfaces

YUVARAJ,

SENTHILKUMAR

2023

Journal of Thermal Engineering

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Heat transfer models for condensation on hydrophobic and superhydrophobic interfaces are broadly available based on thermal resistance correlations. In the previous studies, very few models are presented based on the scaling factor or Nusselt number, and no model is available that directly correlates Biot number. This study develops a heat transfer model for dropwise condensation underneath a horizontal surface. The present model correlates with the Biot number to predict the heat transfer, temperature variation at the interfaces, solid-liquid, and liquid-vapor, and the growth rate of droplet condensate on the hydrophobic and superhydro-phobic interfaces by using Archimedes’ hat-box theorem. The present model is validated with analytical and experimental results against hydrophobic and superhydrophobic contact angles of similar working parameters made excellent agreements. The analytical model for dropwise condensation produces inaccurate results due to discrepancies and discontinuities due to mul-tiple correlations in the modeling. The present model is modified to obtain a continuous result using experimental data. The modified model is used for analyzing heat transfer by varying Biot numbers from 0.0001 to 1000 using Python 3.6.1 with an accuracy of 10-4. Simulation of the present model results in constant heat transfer at Bi = 4, irrespective of the contact angle. A negligible amount of coating resistance and interface resistance when Bi > 0.1, curvature effect when Bi > 0.04, droplet resistance when Bi < 0.02, the maximum liquid-vapor interface tem-perature at Bi ≈ 10, and maximum solid-liquid interface temperature at Bi ≈ 5, are presented.

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Kinetic characterization of low velocity positive collision of double droplets

Ma,

Sun,

Tian

et al. 2024

THERM SCI

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Droplet positive collision is a complex process involving heat transfer in gas-liquid-solid three-phase flow and droplet collide dynamics. In order to study the kinetic behavior of droplets under positive collision in low velocity (v<2 m/s), this paper focuses on the spreading, vibration and fracture characteristics of double droplets by numerical simulation. First, the accuracy of the model is verified by experimental comparison. The effects of droplet diameters, collision velocities and wall contact angles on the spreading process are analyzed, and the spreading factor curves are plotted. Then, the droplet rebound vibration after collision fusion is equated to a single-degree-of-freedom damped vibration system, and the peak vibration height variation curve of the fused droplet is obtained by nonlinear fitting. Considering the droplet phase change, the influence law of different conditions on the vibration damping factor and vibration time of the fused droplet is studied. Finally, it is found that rebound fracture and spreading fracture occur after the fusion of double droplets under positive collision, and the critical values of collide velocity required for the occurrence of the above phenomenon are found. To provide a reliable theoretical basis for the study of heat and mass transfer processes after multiple droplets collide the wall.

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Study of droplet dynamics and condensation heat transfer on superhydrophobic copper surface

Cited by 4 publications

References 22 publications

Conceptualization, Thermal Analysis, and Manufacturing of Nano-Textured Micro-Structured Surfaces for Enhanced Condensation Heat Transfer

Conceptualization, Thermal Analysis, and Manufacturing of Nano-Textured Micro-Structured Surfaces for Enhanced Condensation Heat Transfer

Heat transfer model for dropwise condensation on hydrophobic and superhydrophobic interfaces

Kinetic characterization of low velocity positive collision of double droplets

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