Numerical and Experimental Investigation on Evaporation of Water Droplet on Surfaces With Mixed Wettability

Abstract Droplet evaporation is one of the most commonly observed phenomena and plays an important role in many applications such as in spray cooling, coating, and inkjet printing. Mechanisms such as dynamics of the contact line, evaporation-induced phase transitions, and formation of patterns on the substrate interact with each other in the evaporation of droplets. In this study, we investigated the effect of surface mixed wettability on water sessile droplet evaporation. The transient contact angle, center-height, contact radius, surface area, and droplet volume were experimentally measured and numerically estimated. Surfaces with mixed wettability consisting of hydrophilic islands surrounded by less hydrophilic area were fabricated. Visualization was conducted to capture droplet dynamics during evaporation using two high-speed cameras. According to the obtained results, there were three distinct stages in the water evaporation process: a constant contact radius mode, a constant contact angle mode, and a mixed-mode. The COMSOL 5.4 software was used for numerical analysis. According to the results, the receding contact angle and Marangoni instability in the droplet are two main factors that alter droplet dynamics and droplet evaporation.

Download Full-text

The Effects of Asymmetric Micro Ratchets on Dynamic Contact Angle and Pool Boiling Performance

Volume 7: Fluids and Heat Transfer, Parts A, B, C, and D ◽

10.1115/imece2012-87176 ◽

2012 ◽

Cited By ~ 1

Author(s):

Lance Austin Brumfield ◽

Sunggook Park

Keyword(s):

Contact Angle ◽

High Speed ◽

Pool Boiling ◽

Dynamic Contact Angle ◽

Dynamic Contact ◽

Contact Angles ◽

Equilibrium Contact Angle ◽

Droplet Impingement ◽

Receding Contact ◽

Receding Contact Angle

The dynamic advancing and receding contact angles of 5μl water droplets were experimentally measured via the droplet impingement technique on a polished brass surface, one brass symmetric micro ratchet, and five brass asymmetric micro ratchet samples of varying dimensions. Droplets were released from varying heights (Weber number) and the impacts studied via high speed camera. Equilibrium advancing and receding contact angles were measured by placing a water droplet on the surfaces and tilting it. Contact angle values were then compared to an existing pool boiling model which incorporates the dynamic receding contact angle, surface roughness ratio, and equilibrium contact angle.

Download Full-text

The Surface Modification with Fluorocarbon Thin Films for the Prevention of Stiction in Mems

MRS Proceedings ◽

10.1557/proc-518-143 ◽

1998 ◽

Vol 518 ◽

Cited By ~ 5

Author(s):

Sang-Ho Lee ◽

Myong-Jong Kwon ◽

Jin-Goo Park ◽

Yong-Kweon Kim ◽

Hyung-Jae Shin

Keyword(s):

Contact Angle ◽

Contact Angle Hysteresis ◽

Contact Angles ◽

Fluorocarbon Films ◽

Perfluorodecanoic Acid ◽

Large Hysteresis ◽

Static Contact ◽

Receding Contact ◽

Highly Hydrophobic ◽

Receding Contact Angle

AbstractHighly hydrophobic fluorocarbon films were prepared by the vapor phase (VP) deposition method in a vacuum chamber using both liquid (3M's FC40, FC722) and solid sources (perfluorodecanoic acid (CF3(CF2)8COOH), perfluorododecane (C12F26)) on Al, Si and oxide coated wafers. The highest static contact angles of water were measured on films deposited on aluminum substrate. But relatively lower contact angles were obtained on the films on Si and oxide wafers. The advancing and receding contact angle analysis using a captive drop method showed a large contact angle hysteresis (ΔH) on the VP deposited fluorocarbon films. AFM study showed poor film coverage on the surface with large hysteresis. FTIR-ATR analysis positively revealed the stretching band of CF2 groups on the VP deposited substrates. The thermal stability of films was measured at 150°C in air and nitrogen atmospheres as a function of time. The rapid decrease of contact angles was observed on VP deposited FC and PFDA films in air. However, no decrease of contact angle on them was observed in N2.

Download Full-text

FIG. 28 Critical condition for receding contact angle θ larger than

Surface and Interfacial Tension ◽

10.1201/9780203021262-127 ◽

2004 ◽

pp. 422-427

Keyword(s):

Contact Angle ◽

Critical Condition ◽

Receding Contact ◽

Receding Contact Angle

Download Full-text

FIG. 33 Comparison of contact angles measured by the proposed method using circular cylinder with those from a photograph: (a) advancing contact angle; (b) receding contact angle.

Surface and Interfacial Tension ◽

10.1201/9780203021262-128 ◽

2004 ◽

pp. 428-430

Keyword(s):

Contact Angle ◽

Circular Cylinder ◽

Contact Angles ◽

Receding Contact ◽

Advancing Contact Angle ◽

Receding Contact Angle

Download Full-text

A Superhydrophilic Aluminum Surface with Fast Water Evaporation Based on Anodic Alumina Bundle Structures via Anodizing in Pyrophosphoric Acid

Materials ◽

10.3390/ma12213497 ◽

2019 ◽

Vol 12 (21) ◽

pp. 3497 ◽

Cited By ~ 5

Author(s):

Daiki Nakajima ◽

Tatsuya Kikuchi ◽

Taiki Yoshioka ◽

Hisayoshi Matsushima ◽

Mikito Ueda ◽

...

Keyword(s):

Contact Angle ◽

Oxide Film ◽

High Speed ◽

Porous Alumina ◽

Aluminum Surface ◽

Water Evaporation ◽

Water Contact ◽

Initial Stage ◽

Angle Measuring ◽

Pyrophosphoric Acid

A superhydrophilic aluminum surface with fast water evaporation based on nanostructured aluminum oxide was fabricated via anodizing in pyrophosphoric acid. Anodizing aluminum in pyrophosphoric acid caused the successive formation of a barrier oxide film, a porous oxide film, pyramidal bundle structures with alumina nanofibers, and completely bent nanofibers. During the water contact angle measurements at 1 s after the water droplet was placed on the anodized surface, the contact angle rapidly decreased to less than 10°, and superhydrophilic behavior with the lowest contact angle measuring 2.0° was exhibited on the surface covered with the pyramidal bundle structures. As the measurement time of the contact angle decreased to 200–33 ms after the water placement, although the contact angle slightly increased in the initial stage due to the formation of porous alumina, at 33 ms after the water placement, the contact angle was 9.8°, indicating that superhydrophilicity with fast water evaporation was successfully obtained on the surface covered with the pyramidal bundle structures. We found that the shape of the pyramidal bundle structures was maintained in water without separation by in situ high-speed atomic force microscopy measurements.

Download Full-text

The effect of contact line dynamics and drop formation on measured values of receding contact angle at very low capillary numbers

Colloids and Surfaces A Physicochemical and Engineering Aspects ◽

10.1016/j.colsurfa.2012.04.012 ◽

2012 ◽

Vol 404 ◽

pp. 63-69 ◽

Cited By ~ 17

Author(s):

Carmen L. Moraila-Martínez ◽

Francisco J. Montes Ruiz-Cabello ◽

Miguel A. Cabrerizo-Vílchez ◽

Miguel A. Rodríguez-Valverde

Keyword(s):

Contact Angle ◽

Contact Line ◽

Drop Formation ◽

Receding Contact ◽

Receding Contact Angle ◽

Contact Line Dynamics

Download Full-text

Dynamics of Droplet Motion Induced by Electrowetting

Volume 1: Heat Transfer in Energy Systems; Thermophysical Properties; Theory and Fundamentals in Heat Transfer; Nanoscale Thermal Transport; Heat Transfer in Equipment; Heat Transfer in Fire and Combustion; Transport Processes in Fuel Cells and Heat Pipes; Boiling and Condensation in Macro, Micro and Nanosystems ◽

10.1115/ht2016-7331 ◽

2016 ◽

Author(s):

Yi Lu ◽

Aritra Sur ◽

Dong Liu ◽

Carmen Pascente ◽

Paul Ruchhoeft

Keyword(s):

Contact Angle ◽

High Speed ◽

Numerical Models ◽

Dynamic Contact Angle ◽

Dynamic Contact ◽

High Speed Photography ◽

Droplet Dynamics ◽

Droplet Shape ◽

Moving Contact Line ◽

Moving Contact

Electrowetting has drawn significant interests due to the potential applications in electronic displays, lab-on-a-chip devices and electro-optical switches, etc. Current understanding of electrowetting-induced droplet dynamics is hindered by the inadequacy of available numerical and theoretical models in properly handling the dynamic contact angle at the moving contact line. A combined numerical and experimental approach was employed in this work to study the spatiotemporal responses of a droplet subject to EW with both direct current and alternating current actuating signals. The time evolution of the droplet shape was measured using high-speed photography. Computational fluid dynamics models were developed by using the Volume of Fluid-Continuous Surface Force method in conjunction with a selected dynamic contact angle model. It was found that the numerical models were able to accurately predict the key parameters of the electrowetting-induced droplet dynamics.

Download Full-text

Evaporative Particle Deposition on Superhydrophobic Surfaces

Volume 10: Micro- and Nano-Systems Engineering and Packaging ◽

10.1115/imece2013-63928 ◽

2013 ◽

Author(s):

Mercy Dicuangco ◽

Susmita Dash ◽

Justin A. Weibel ◽

Suresh V. Garimella

Keyword(s):

Contact Angle ◽

Particle Deposition ◽

Contact Angle Hysteresis ◽

Droplet Evaporation ◽

Superhydrophobic Surfaces ◽

Contact Radius ◽

Droplet Shape ◽

Substrate Heating ◽

Solid Liquid ◽

Constant Contact Angle

The ability to control the size, shape, and location of particulate deposits is important in patterning, nanowire growth, sorting biological samples, and many other industrial and scientific applications. It is therefore of interest to understand the fundamentals of particle deposition via droplet evaporation. In the present study, we experimentally probe the assembly of particles on superhydrophobic surfaces by the evaporation of sessile water droplets containing suspended latex particles. Superhydrophobic surfaces are known to result in a significant decrease in the solid-liquid contact area of a droplet placed on such a substrate, thereby increasing the droplet contact angle and reducing the contact angle hysteresis. We conduct experiments on superhydrophobic surfaces of different geometric parameters that are maintained at different surface temperatures. The transient droplet shape and wetting behavior during evaporation are analyzed as a function of substrate temperature as well as surface morphology. During the evaporation process, the droplet exhibits a constant contact radius mode, a constant contact angle mode, or a mixed mode in which the contact angle and contact radius change simultaneously. The evaporation time of a droplet can be significantly reduced with substrate heating as compared to room-temperature evaporation. To describe the spatial distribution of the particle residues left on the surfaces, qualitative and quantitative evaluations of the deposits are presented. The results show that droplet evaporation on superhydrophobic surfaces, driven by mass diffusion under isothermal conditions or by substrate heating, suppresses particle deposition at the contact line. This preempts the so-called coffee-ring and allows active control of the location of particle deposition.

Download Full-text