• Tribology and Lubricants
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• v.15 no.4
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• pp.321-327
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• 1999

An experimental study was performed to discover the effect of adsorbed moisture on the rolling resistance behavior of pure silver-coated 52100 bearing steel. Plasma surface modifications were performed on the silver-coated specimen to change the wetting characteristics. Experiments using a thrust ball bearing-type rolling test-rig were performed under vacuum, dry air and various humidity conditions. Results showed that the changes in the wetting characteristics influenced remarkably on the silver particle agglomeration and resulted in the different behavior of rolling resistance with humidity.

• 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.

• Journal of the Microelectronics and Packaging Society
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• v.7 no.4
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• pp.7-15
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• 2000

The purpose of this work is to evaluate the solderahility and characteristics of solder joints. Bridge defect of solder joint was examined in natural atmosphere and $N_2$ condition. Consequently, wettability was excellent for each of Sn-Pb plated Cu specimen, Sn plated Cu specimen, and Cu polished in $N_2$ condition. The wetting time in $N_2$ condition was shorter than that of natural atmosphere condition, showing the decreasing values of about 0.2~0.45 seconds. The max. wetting force under the $N_2$ condition was more increasing that of natural atmosphere condition, showing the increasing values of about 1.8~2.8 N. With the result of wetting balance test, the wetting time ($t_2$) and wetting farce according to increasing amount of $N_2$ from 10 1/min to 30 1/min, the wetting time ($t_2$) was reduced about 0.25 second and wetting force was increased about 2.3 N. In non-cleaning flux, when $N_2$ gas is applied, it is compensated to decrease of wettability. In the case of using the $N_2$ gas, the wettability was improved. The reason for improving wettability is due to preventing the formation of dross. The generation rate of bridge in $N_2$ condition decreased than that of natural atmosphere, and when the specimen had a fine pitch, the rate of bridge defects was considerably decreased in $N_2$ condition, showing the decreasing rate of 25~75%.

• Journal of The Korean Society of Agricultural Engineers
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• v.53 no.3
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• pp.83-91
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• 2011

This study aimed to investigate the engineering and environmental characteristics of phosphogypsum-cement-soil mixtures composed of phosphogypsum, soil, and a small amount of cement was analysed on the basis of the unconfined compression test, the tensile strength test, the freezing and thawing test, the wetting and drying test, SEM and EDS analysis, XRD analysis and Leaching test. The specimens were manufactured with soil, cement and phosphogypsum. The cement contents was 10 %, and the phosphogypsum contents was 10, 20, 30, and 40 % by the weight of total dry soil. Each specimen was manufactured after curing at constant temperature and humidity room for 3, 7 and 28 days, after which the engineering characteristics of phosphogypsum-cement-soil mixtures were investigated using the unconfined compression test, the tensile strength test, the freezing and thawing test, the wetting and drying test. The basic data were presented for the application of phosphogypsum-cement-soil mixtures as construction materials. To investigate the environmental characteristics, leaching test was performed and the leaching test results were far below than of regulatory requirement of Waste Management Act in Korea. Therefore the results show that phosphogypsum is environmentally safe and can be used as construction materials in environmental aspect.

• Proceedings of the KSME Conference
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• 2001.06d
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• pp.796-801
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• 2001

During cold operation period, fuel injection system directly contributes the unburned hydrocarbon formation in spark ignition engines. The relationship between injection parameters and HC emission behavior was investigated through a series of experiments. Spray behavior of port fuel injectors was characterized through a quantitative evaluation of mass concentration of liquid fuel by a patternator and PDA. 6-hole injector was found to produce finer spray than single hole one. Using a purpose-built test rig, the wall wetting fuel was measured, which was mostly affected by wall temperature. Varying coolant temperature($20{\sim}80^{\circ}C$), HC emissions were measured in a production engine. With respect to the different types of injectors, HC emission was also measured. In the 6-hole injector application, the engine produced less HC emission in low coolant temperature region. Though it produces much more amount of wetting fuel, it has the advantages of finer atomization quality. In high coolant temperature region, there was little effect between different types of injectors. The control schemes to reduce HC emissions during cold start could be suggested from the findings that the amount of fuel supply and HC emission could be reduced by utilizing fine spray and high intake wall temperature.

• Journal of computational fluids engineering
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• v.21 no.4
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• pp.90-95
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• 2016

Leidenfrost drops with ellipsoidal shaping can control the bouncing height by adjusting the aspect ratio(AR) of the shape at the moment of impact. In this work, we focus on the effect of the AR and the impact Weber number(We) on the non-axisymmetrical spreading dynamics of the drop, which plays an important role in the control of bouncing. To understand the impact dynamics, the numerical simulation is conducted for the ellipsoidal drop impact upon the perfect non-wetting solid surface by using volume of fluid method, which shows the characteristics of the spreading behavior in each principal axis. As the AR increases, the drop has a high degree of the alignment into one principal axis, which leads to the consequent suppression of bouncing height with shape oscillation. As the We increases, the maximum spreading diameters in the principal axes both increase whereas the contact time on the solid surface rarely depends on the impact velocity at the same AR. The comprehensive understanding of the ellipsoidal drop impact upon non-wetting surface will provide the way to control of drop deposition in applications, such as surface cleaning and spray cooling.

• Journal of the Korean Geotechnical Society
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• v.28 no.3
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• pp.55-66
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• 2012

To investigate the hysteresis of the suction stress in unsaturated weathered mudstone soils (CL), matric suction and volumetric water content were measured in both drying and wetting processes using Automated Soil-Water Characteristics Curve Apparatus. The drying and wetting processes in unsaturated soils were reproduced in the test; the drying process means to load matric suction to spill pore water from the soils, and the wetting process means to unload matric suction to inject pore water into the soils. Based on the measured result, Soil Water Characteristic Curve(SWCC)s were estimated by van Genuchten model (1980). SWCCs have nonlinear relationship between effective degree of saturation and matric suction. The hysteresis in SWCCs between drying and wetting processes occurred. As a result of estimating Suction Stress Characteristic Curve(SSCC) using Lu and Likos model (2006), the suction stress rapidly increased in the low level of matric suction and then increased slightly. Also, the hysteresis in SSCCs between drying and wetting processes occurred. In order to design geo-structures and check its stability considering unsaturated soil mechanics, therefore, it is more reasonable that the SSCC of drying process should be applied in the condition of rainfall infiltration and the SSCC of wetting process in the condition of evaporation or drainage.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.6
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• pp.2369-2379
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• 2013

The Soil-Water Characteristics Curve (SWCC) is affected by the initial density of soil under unsaturated condition. Also, the characteristic of hydraulic conductivity is changed by the initial density of soil. To study the effect of initial density of unsaturated soil, SWCC and the Hydraulic Conductivity Function (HCF) of Jumoonjin sand with various relative densities, 40%, 60% and 75% were measured in both drying and wetting processes. As the results of SWCC estimated by van Genuchten (1980) model, the parameter related to Air Entry Value(AEV), ${\alpha}$ in the wetting process is larger than that in drying process, but the parameters related to the SWCC slope, n and the residual water content, m are larger than those in wetting process. The AEV is increased or Water Entry Value (WEV) is decreased with increasing the relative density of sand. The AEV is larger than the WEV at the same relative density of sand. As the results of HCF estimated by van Genuchten (1980) model which is one of the parameter estimation methods, the unsaturated hydraulic conductivity maintained at a saturated one in the low level of matric suctions and then suddenly decreased just before the AEV or the WEV. The saturated hydraulic conductivity in drying process is larger than that in wetting process. The saturated hydraulic conductivity is decreased with increasing the relative density of sand in both drying and wetting processes. Also, the hysteresis in unsaturated HCFs between drying and wetting process was occurred like the hysteresis in SWCCs. According to the test results, the AEV on SWCC is decreased and the saturated hydraulic conductivity is increased with increasing the initial density. It means that SWCC and HCF are affected by the initial density in the unsaturated soil.

• The Journal of Engineering Geology
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• v.20 no.3
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• pp.281-295
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• 2010

A new, automated apparatus is proposed for calculating the Soil-Water Characteristic Curve (SWCC), representing a simple and easily applied testing device for continuous measurements of the volumetric water content and suction of unsaturated soils. The use of this apparatus helps to avoid the errors that arise when performing experiments. Consequently, the apparatus provides greater accuracy in calculating the SWCC of unsaturated soils. The apparatus is composed of a pressure panel, flow cell, water reservoir, air bubble trap, balance, sample-preparation accessories, and measurement system, among other components. The air pressure can attain 300 kPa, and a general test can be completed in a short time. The apparatus can simply control the drying process and wetting process. The changes in volumetric water content that occur during the drying and wetting processes are shown directly in the SWRC program, in real time. As a case study, we performed an SWCC test of Joomunjin sand (75% relative density) to measure matric suction and volumetric water content during both the drying and wetting processes. The test revealed hysteresis behavior, whereby the water content on the wetting curve is always lower than that on the drying curve for a specific matric suction, during the wetting and drying processes. Based on the test results, SWCCs were estimated using the Brooks and Corey, van Genuchten, and Fredlund and Xing models. The van Genuchten model performed best for the given soil conditions, as it yielded the highest coefficient of determination.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2001.11a
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• pp.35-42
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• 2001

Nanotribological characteristics between a Si$_3$N$_4$ AFM tip and hydrophobic thin films were experimentally studied. Tests were performed to measure the nano adhesion and friction in both AFM(atomic force microscope) and LFM(lateral force microscope) modes in various ranges of normal load. Plasma-modified thin polymeric films were deposited on Si-wafer (100). Results showed that wetting angle of plasma-modified thin polymeric film increased with the treating time, which resulted in the hydrophobic surface and the decrease of adhesion and friction. Nanotribological characteristics of these surfaces were compared with those of other hydrophobic surfaces, such as DLC, OTS and IBAD-Ag coated surfaces. Those of OTS coated surface was superior to those of others, though wetting angle of plasma-modified thin polymeric film is higher.