• Transactions of the Korean Society of Automotive Engineers
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• v.5 no.6
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• pp.167-174
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• 1997

The penetration depth and the size distribution of the droplets of fuel sprays are important in the operation of spark-ignition MPI engines. A fluorescence/scattering image technique for droplet sizing was applied to measure th edroplet size distribution in non-evaporating gasoline sprays. The fluorescence and scattering lights were imaged simultaneously by the two-dimensional visualization system composed of a laser sheet, a doubling prism, optical filters, and a CCD camera. Quantitative droplet size distributions were extracted from evaluating the ratio of the two light densities. The mean droplet size measured by the fluorescence/scattering technique was compared with the result obtained by the enlarged photographs of droplets. The fluorescence/scattering image technique also gives the useful information of the characteristics of droplet impingement in a inclined wall.

• Journal of the Korean Society of Visualization
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• v.15 no.2
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• pp.21-25
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• 2017

If a liquid droplet evaporates on a solid substrate, when it completely dries, it leaves a peculiar pattern, which depends on the composition of the liquid. Not only a single component liquid but also complex liquids are studied for a different purpose. In particular, a binary mixture droplet has been widely studied and used for an ink-jet printing technology. In this study, we focus on investigating to visualize the internal flow field of an ethanol-water mixture by varying a concentration ratio between two liquids. We measure the in-plane velocity vector fields and vorticities. We believe that this fundamental study about the internal flow field provides a basic idea to understand the dried pattern of the binary mixture droplet.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.1
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• pp.69-81
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• 1999

In this research computational methods for the droplet atomization and spray wall impingement are studied for the non-evaporating diesel fuel spray. The TAB(Taylor Analogy Breakup) model and Wave model are compared with experiments in order to describe droplet atomization process. The Watkins model and O'Rourke model are compared to simulate the spray wall impingement. As a result, It is found that the application of the Wave model has a good agreement with the experimental data in the case of high pressure injection. With regard to wall Impingement phenomena, it is found that the Watkins model is appropriate to the high temperature cylinder wall condition, while the O'Rourke model is appropriate to cold starting problem.

• Journal of the Korean Society of Visualization
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• v.15 no.1
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• pp.25-31
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• 2017

This study aims to visualize the Marangoni flow inside a droplet placed on heated hydrophobic surface and to measure its internal velocity field. The experimental result shows that the internal velocity increases with the increase of the plate temperature. In addition, the temperature difference induces the initial flow and drives the Marangoni circulation inside the droplet as soon as the evaporation starts (i.e. the thermal Marangoni flow). The fluorescence particles in the droplet trace two large-scale counter-rotating vortex pairs yielding the downwards flow along the vertical central axis. These vortex pairs gradually become small and move towards the contact line as time goes by, and this Marangoni flow sustains only for a half of the total evaporation time.

• Journal of ILASS-Korea
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• v.17 no.1
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• pp.9-13
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• 2012

This study investigates experimentally evaporation characteristics of nanofluid droplets containing 50 nm alumina($Al_2O_3$) particles and the wettability changes on a hydrophilic glass surfaces. From the captured digital images by using a CMOS camera and a magnifying lens, we examined the effect of particle concentration on droplet evaporation rate which can be indirectly deduced from the measured droplet volumes varying with time. In particular, with the use of a digital image analysis technique, the present study measured droplet perimeters and the contact angles to study the wetting dynamics during evaporating process. In addition, we compared the measured total evaporation time with theoretically estimated values. It was found that as the volume fractions of nanofluid increased, the total evaporation time and the initial contact angles decreased, while the droplet perimeters increased.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.11 s.254
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• pp.1107-1116
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• 2006

The droplet ejection process driven by an evaporating bubble in a thermal inkjet printhead is investigated by numerically solving the conservation equations for mass, momentum and energy. The phase interfaces are tracked by a level set method which is modified to include the effect of phase change at the interface and extended for multiphase flows with irregular solid boundaries. The compressibility effect of a bubble is also included in the analysis to appropriately describe the bubble expansion behaviour associated with the high pressure caused by bubble nucleation. The whole process of bubble growth and collapse as well as droplet ejection during thermal inkjet printing is simulated without employing a simplified semi-empirical bubble growth model. Based on the numerical results, the jet breaking and droplet formation behaviour is observed to depend strongly on the bubble growth and collapse pattern. Also, the effects of liquid viscosity, surface tension and nozzle geometry are quantified from the calculated bubble growth rate and ink droplet ejection distance.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.9
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• pp.764-771
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• 2007

The objective of the present work is to evaluate the evaporation heat flux of deposited droplet on the hot surface by using of inverse heat transfer technique. On the basis of measured temperature, a integral form solution is determined for the transient temperatures beyond the two positions by using Green's function technique. This method first approximates the temperature data with a half polynomial series of time. we compared this result with constant radius model in single phase regime, nucleate boiling regime, film boiling regime respectively. this paper performed the experiments as following conditions: (a)the surface temperature is within the range between $80^{\circ}C\;and\;160^{\circ}C$ in the conduction, (b) droplet diameter are 2.4 and 3.0mm. (c) surface roughness is $0.18{\mu}m$.

• Journal of ILASS-Korea
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• v.26 no.1
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• pp.1-8
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• 2021

Droplet evaporation has been known as a common phenomenon in daily life, and it has been widely used for many applications. In particular, the influence of the different heated substrates on evaporation flux and flow characteristics is essential in understanding heat and mass transfer of evaporating droplets. This study aims to simulate the droplet evaporation process by considering variation of thermal property depending on the substrates and the surface temperature. The commercial program of ANSYS Fluent (V.17.2) is used for simulating the conjugated heat transfer in the solid-liquid-vapor domains. Moreover, we adopt the diffusion-limited model to predict the evaporation flux on the different heated substrates. It is found that the evaporation rate significantly changes with the increase in substrate temperature. The evaporation rate substantially varies with different substrates because of variation of thermal property. Also, the droplet evaporates more rapidly as the surface temperature increases owing to an increase in saturation vapor pressure as well as the free convection effect caused by the density gradient.

• Journal of the Korean Society of Visualization
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• v.15 no.2
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• pp.16-20
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• 2017

A coffee-ring effect is from capillary flow by different evaporation rate across the droplet. The capillary flow tends particles to accumulate at the edges of the droplet and makes the ring-shaped stain pattern. These coffee-ring formation and suppression of coffee-ring have been a critical role in printing and coating technologies. In this study, we present the experimental study on coffee-ring effect of silver nanowire inside the evaporating sessile droplet. Size and concentration effect of nanowires at coffee-ring effect has been investigated. From the coffee-ring, we observed the regimes of connected rings and disconnected ones and measure the resistivity of single ring pattern with different nanowire length.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.7 s.250
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• pp.663-670
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• 2006

The presented study aims to investigate the colloidal droplet deposition caused by evaporation of the liquid. In the numerical analysis, the evaporation is carried out by using different evaporation function intended to obtain different shape of solute deposition. In the experiment, the colloidal droplets of different solvents are placed on a glass plate and the surface profiles are measured after drying the solvents of the droplets to investigate the effect of the solvent evaporation on the final deposition profile. Comparing the surface profiles obtained under different conditions, the optimum drying conditions of colloidal droplets are, determined to obtain uniform surface profiles. The numerical results showed that ring-shaped deposition of solute was formed at the edge of the droplet due to the coffee stain effect and the height of the ring was reduced at the lower evaporation rate. The experiments showed that the boiling point of a solvent was critical to the surface uniformity of the deposition profile and the mixture of solvents with different boiling points influenced the uniformity as well.