• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.662-665
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• 2008

We experimentally investigate the evaporation characteristics of water droplet on surfaces of various wettabilities in the range of contact angle from 30$^{circ}$ to 150$^{circ}$. When a liquid droplet on a solid surface evaporates, the contact angle generally decreases with time and the evaporation rate varies with the droplet geometry such as the contact angle and the radius of curvature. Experimental data on the contact angle as a function of the droplet volume obtained by digital image analysis techniques cannot be explained by the existing theories. By measuring the temporal evolutions of the droplet radius and contact angle, we find the qualitative difference between the evaporation patterns on the hydrophilic surfaces where the contact radius remains constant initially and those on the superhydrophobic surfaces where the contact angle remains constant. Also, the evaporation rate is observed to depend on the surface material although the currently available models assume that the rate is solely determined by the droplet geometry. Despite the fact that the theory to explain this dependence on the surface remains to be pursued by the future work, we give the empirical relations that can be used to predict the droplet volume evolution for each surface. It is expected that the present study will contribute to interpreting the effect of droplet geometry on the evaporation.

• Transactions on Electrical and Electronic Materials
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• v.7 no.1
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• pp.21-25
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• 2006

In this study, liquid crystal (LC) aligning properties for homeotropic alignment on the $SiO_x$ thin film by electron beam evaporation method with electron beam system in accordance with the evaporation angles were investigated. Also, the control of pretilt angles homeotropic aligned LC on $SiO_x$ thin film as the function of the evaporation angles were studied. The uniform vertical LC alignment on the $SiO_x$ thin film surfaces with electron beam evaporation was achieved with all of the thin film angle conditions. It is considerated that the LC alignment on the $SiO_x$ thin film by electron beam evaporation is attributed to elastic interaction between LC molecules and micro-grooves at the $SiO_x$ thin film surface created by evaporation. The values of the pretilt angles according to the evaporation angle were from about $0.7^{\circ}$ to about $3.4^{\circ}$. The highest pretilt angles of about $3.4^{\circ}$ in aligned NLC on the $SiO_x$ thin film surfaces by electron beam evaporation were measured under the condition of $45^{\circ}$. Also, good LC alignment states on the treated $SiO_x$ thin film layer by electron beam evaporation were observed at annealing temperature of $250^{\circ}C$. Consequently, the high pretilt angle and the good thermal stability of LC alignment on the $SiO_x$ thin film by electron beam evaporation can be achieved.

• Journal of ILASS-Korea
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• v.20 no.4
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• pp.236-240
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• 2015

This study aims to experimentally investigate the evaporation characteristics of nanofluid droplet on heated surface at boiling temperature of DI-water. In particular, textured surface was used to examine the effect of wettability on evaporation. At the initial stage of evaporation process, dynamic contact angle (DCA) of nanofluid droplet with 0.01 vol.% concentration on textured surface rapidly increased over its equilibrium contact angle by generated large bubble inside the droplet due to lower wettability. However, contact angle of nanofluid droplet with higher concentration on textured surface decreased with surface tension. In addition, total evaporation time of droplet on textured surface was considerably delayed due to reduction of contact area between droplet and solid surface. Thus, evaporation characteristics were highly affected by the nanofluid concentration and surface wettability.

• Transactions on Electrical and Electronic Materials
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• v.7 no.6
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• pp.305-308
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• 2006

We have studied liquid crystal (LC) aligning capabilities for homeotropic alignment and the control of tilt angles on the $SiO_{x}$ thin film by electron beam evaporation method. A high tilt angle of about $86.5^{\circ}$ was obtained, and also the suitable tilt angle of the NLC on the $SiO_{x}$ thin film at $20{\sim}50\;nm$ thickness with e-beam evaporation can be achieved. The uniform LC alignment on the $SiO_{x}$ thin film surfaces with electron beam evaporation can be achieved. It is considerated that the LC alignment on the $SiO_{x}$ thin film by electron beam evaporation is attributed to elastic interaction between LC molecules and micro-grooves at the $SiO_{x}$ thin film surface created by evaporation.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.6 s.261
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• pp.558-565
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• 2007

Many studies of microdroplet evaporation from solid surfaces were made with priority given to inkjet printing and dye painting techniques. The objective of these studies is how to evaporate a droplet quickly and uniformly. Also it is necessary to prevent evaporation of a droplet to observe cells in a droplet generated through cell-patterning. In general, an identical volume of a water droplet on hydrophobic surfaces evaporates slower than that on hydrophilic surfaces. In this study, we observe the evaporation process of a droplet on various hydrophobic surfaces and calculated the evaporation rate considering the droplet geometry such as contact angle and height. This study also proposes a new model based on the fact that evaporation mode at the edge of a droplet is different from that at the outer surface of a droplet as the contact angle changes during evaporation. Finally, we reveal the cause fur the increase of evaporation flux and show that the ratio of edge evaporation to total evaporation increases with time.

• Transactions on Electrical and Electronic Materials
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• v.8 no.6
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• pp.274-277
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• 2007

In this study, liquid crystal(LC) aligning capabilities for homeotropic alignment on the $SiO_x$ thin film by electron beam evaporation method were investigated. Also, the control of pretilt angles and thermal stabilities of the nematic liquid crystal(NLC) treated on $SiO_x$ thin film were investigated. A high pretilt angle of about $86.5^{\circ}$ was obtained, and also the suitable pretilt angle of the NLC on the $SiO_x$ thin film at $10{\sim}50nm$ thickness with e-beam evaporation can be achieved. The uniform LC alignment and good thermal stabilities on the $SiO_x$ thin film surfaces with electron beam evaporation can be achieved. It is considered that the LC alignment on the $SiO_x$ thin film by electron beam evaporation is attributed to elastic interaction between LC molecules and micro-grooves at the $SiO_x$ thin film surface created by evaporation.

• ETRI Journal
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• v.31 no.4
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• pp.351-356
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• 2009

We present a simple semiconductor process to fabricate nanogap arrays for application in molecular electronics and nano-bio electronics using a combination of freestanding silicon nanowires and angle evaporation. The gap distance is modulated using the height of the silicon dioxide, the width of the Si nanowires, and the evaporation angle. In addition, we fabricate and apply the nanogap arrays in single-electron transistors using DNA-linked Au nanoparticles for the detection of DNA hybridization.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.4
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• pp.424-431
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• 2003

The evaporation cooling phenomenon of a droplet containing a surfactant on a heated surface has been studied experimentally. The two kinds of heater modules made of brass and Teflon$^{TM}$ were tested to investigate the cooling characteristics of droplet. Solutions of water containing Sodium Lauryl Sulfate(0 ppm, 100 ppm, 1000 ppm) were tested in the experiments. The results showed that the contact angle decrease as the concentration of surfactant increases. The tendency did not very with different heated solid materials. As initial temperature of the heated surface becomes high, time averaged heat flux increases and evaporation time decreases with the denser concentration of surfactant. Therefore, water with denser concentration of surfactant could be effective to cool flammable materials. However, the effect of surfactant becomes low as the material temperature is higher than the boiling temperature of water.

• Proceedings of the KSME Conference
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• 2001.06d
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• pp.272-279
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• 2001

The objective of this paper is the investigation of the relationships between the surface roughness and film evaporative characteristics of the surface. For example, when the droplet of liquid is in contact with the solid surface, its behavior strongly depends on the surface characteristics. The material properties and geometry - profile shape, waviness, roughness - of the surfaces have strongly influenced on the wettability of the droplet. To investigate the effect of the surface roughness on the film evaporation, firstly, the characteristics of wettabilities were studied according to contact angle and surface tree energy of specimens with various roughness heights. Secondly, the experimental test were carried out on capacities of the tubes diversly roughened by using different kinds of emery papers. Finally, the relationships between the film evaporation characteristics and surface roughness were explained by means of the correlation of contact angle and surface free energy with surface roughness and the influences of surface tree energy on the heat transfer performance.

• Progress in Superconductivity and Cryogenics
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• v.10 no.2
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• pp.16-19
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• 2008

Angular dependence of critical current density of SmBCO coated conductor fabricated by co-evaporation method was investigated. For comparison, three samples were fabricated by a co-evaporation method and one sample was fabricated by a pulsed laser deposition process. The deposition system, named EDDC (Evaporation using Drum in Dual Chambers), is a batch type co-evaporation system, which is composed of reaction chamber and evaporation chamber. The normalized critical current density ratio ($I_c/I_c$(H//ab-plane)) of EDDC-SmBCO samples was found to be higher than that of PLD-YBCO sample in the whole range of angle. While the EDDC-SmBCO samples evidently had a peak at the angle of H//c-axis in the plot of the angular dependence of critical current, the normalized critical current of PLD-YBCO sample decreased monotonically without any peak as angle increased. The field dependence of critical current under the magnetic field parallel to the normal direction of those samples showed similar aspect in the range of $0\;G{\sim}5000\;G$.