• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2008년도 추계학술대회B
• /
• pp.2738-2743
• /
• 2008

We conducted a study by computational simulation about the effects of frost thickness on the pressure drop and heat transfer characteristics as whole heat exchanger configuration changes. In order to perform the analysis for validation, we assumed that frost properties have constant values and the frost layers that are formed on the fin and tube surfaces are uniform. In order to find the constant thermal conductivity of frost layer, a variety of frost thermal conductivities are performed in our work and compared with the results by Lee et al. [4] and Yang et al. [5] proposed many experimental data about the 2-rows and 2-columns finned tube heat exchanger. The numerical results agreed well with the experimental data when frost conductivity is 0.07W/mK. After the validation had performed, we applied this procedure to the finned tube heat exchanger of domestic refrigeration and investigated the thermo-hydraulic characteristic of the heat exchanger affected by frost thickness according to the inlet velocities and temperatures of air considering the configuration change such as fin pitch.

• Membrane and Water Treatment
• /
• 제6권6호
• /
• pp.489-499
• /
• 2015

In this work, treatment of real hypersaline refinery wastewater by hollow fiber membrane bioreactor coupled with reverse osmosis unit was studied. The ability of HF-MBR and RO developed in this work, was evaluated through examination of the effluent properties under various operating conditions including hydraulic retention time and flux. Arak refinery wastewater was employed as influent of the bioreactor which consists of an immersed ultrafiltation membrane. The HF-MBR/RO was run for 6 months. Average elimination performance of chemical oxygen demand, biological oxygen demand, total suspended solids, volatile suspended solids, total dissolved soild and turbidity were obtained 82%, 89%, 98%, 99%, 99% and 98% respectively. Highly removal performance of oily contaminant, TDS and the complete retention of suspends solids implies good potential of the HF-MBR/RO system for wastewater refinement.

• 한국재료학회지
• /
• 제18권3호
• /
• pp.117-122
• /
• 2008

Micro-sized bumps on a multi-layered build-up PCB were fabricated by pulse-reverse copper electroplating. The values of the current density and brightener content for the electroplating were optimized for suitable performance with maximum efficiency. The micro-bumps thus electroplated were characterized using a range of analytical tools that included an optical microscope, a scanning electron microscope, an atomic force microscope and a hydraulic bulge tester. The optical microscope and scanning electron microscope analyses results showed that the uniformity of the electroplating was viable in the current density range of $2-4\;A/dm^2$; however, the uniformity was slightly degraded as the current density increased. To study the effect of the brightener concentration, the concentration was varied from zero to 1.2 ml/L. The optimum concentration for micro-bump electroplating was found to be 0.6 ml/L based on an examination of the electroplating properties, including the roughness, yield strength and grain size.

• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 2006년도 추계 학술발표회 논문집
• /
• pp.501-504
• /
• 2006

Recycled aggregate mortar contains plenty of calcium hydroxide to improve the strength of blast furnace slag, although the surface mortar made of recycled aggregate deteriorates adhesion to cement paste and blast furnace slag has a low initial strength. Therefore, this study assumes that the combination with both recycled aggregate and blast furnace slag will produce a better performance. The results of the experiment show that dry mortar made of recycled aggregate provides with higher strength than wet mortar does at the 3-day and 7-day age, while lower at the 28-day age. It indicates that a large amount of cement mortar made of dry recycled aggregate has deteriorated adhesion strength. The mixes with 30% and 50% of blast furnace slag and 50% and 75% of recycled aggregate provide with much better strength at the 7-day age, although they usually have latent hydraulic property at the 28-day age. It indicates that calcium hydroxide($Ca(OH){_2}$) in recycled aggregate has affected ground granulated blast furnace slag.

• Journal of Mechanical Science and Technology
• /
• 제20권8호
• /
• pp.1266-1274
• /
• 2006

A numerical study is performed to investigate the effect of inner surface roughness and micro-particles on adiabatic single phase frictional pressure drop in a perfect square micro channel. With the variation of particles sizes (0.1 to $1{\mu}m$) and occupied volume ratio (0.01 to 10%) by particles, the Eulerian multi-phase model is applied to a $100{\mu}m$ hydraulic diameter perfect square micro channel in laminar flow region. Frictional pressure loss is affected significantly by particle size than occupied volume ratio by particles. The particle properties like density and coefficient of restitution are investigated with various particle materials and the density of particle is found as an influential factor. Roughness effect on pressure drop in the micro channel is investigated with the consideration of roughness height, pitch, and distribution. Additionally, the combination effect by particles and surface roughness are simulated. The pressure loss in microchannel with 2.5% relative roughness surface can be increased more than 20% by the addition of $0.5{\mu}m$ diameter particles.

• 지질공학
• /
• 제1권1호
• /
• pp.137-145
• /
• 1991

열극암반에서의 유동특성은 석유산업, 지열수탐사, 지하수의 오염문제, 지하 동굴건설 등 많은 공학적 분야에서 선결되어야 하는 중요성을 갖고 있다. 암반을 통한 지하수의 유동은 연속체 개념과 불연속열극 개념에 의하여 수치모형화 되고 또한 해석되고 있다. 불연속 열극체계 개념은 국지적인 각 열극의 특성을 강조하는 반면, 다공성매질 개념은 수리학적 파라메타의 평균값을 쓰기 때문에 각 열극의 특성은 무시하게 된다. 지하동굴에서 관찰된 지하수 유입특성에 의하면, 지하수는 channel 형태로 유동한다고 해석되어지고 있다. 이러한 channel 현상은 복합적인 열극의 기하학적 특성에 따른 열극틈의 변화에 의하여 이루어 진다.

• 한국의류학회지
• /
• 제31권1호
• /
• pp.77-84
• /
• 2007

The purpose of this study was to investigate and to compare the performances of silicone laminated materials sold for swimming cap in market, to get the basic data for product development. We selected 4 specimens and tested their air permeability, waterproofness and breathability. We also tested the physical and mechanical properties of the specimens using KES system. Silicone-laminated material was not bursted on high hydraulic pressure since silicone membrane gave waterproofness while PU/Polyester substrate gave elasticity. It didn't have air permeability and breathability at all. Any toxic materials such as Formaldehyde, Deldrin, PCP, Amin, TDBPP were not detected in silicone-laminated material and other materials. Silicone-laminated material had higher stretchability with the low force but it had lower elastic recovery and shape stability comparing to PU laminated material. It had lower flexibility than PU laminated material. It had lower unrecoverable amount in shearing direction. Friction coefficient was higher in silicone-laminated material than PU laminated material due to its surface stickiness. It was compressed easily and its compression resiliency was higher with compared to PU laminated material.

• 한국자동차공학회논문집
• /
• 제21권2호
• /
• pp.17-25
• /
• 2013

Performance of DI diesel engine with high fuel injection method is directly related to the emission characteristics and fuel consumption. At present, diesel injection system with piezo element is replacing conventional solenoid type due to their faster electro-mechanical properties. In this study, it was investigated the sensitivity characteristics regarding internal hydraulic modeling based on the AMESim environment of piezo-driven injector The analytic parameter for this study defined such as In/Out orifice, injection hole's diameter and driven voltage on piezo stack. As the results, it was shown that these parameter influence on a fast response characteristics of piezo-driven injector. Also we found fuel pressure recovery time is faster about 0.1 ms due to larger IN orifice diameter. And larger OUT orifice diameter occurs maximum pressure drop with faster its timing of about 0.2 ms.

• Advances in nano research
• /
• 제8권1호
• /
• pp.37-47
• /
• 2020

This work focuses on the behavior of non-local shear deformation beam theory for the vibration of functionally graded (FG) nanobeams with porosities that may occur inside the functionally graded materials (FG) during their fabrication, using the non-local differential constitutive relations of Eringen. For this purpose, the developed theory accounts for the higher-order variation of transverse shear strain through the depth of the nanobeam. The material properties of the FG nanobeam are assumed to vary in the thickness direction. The equations of motion are derived from Hamilton's principle. Analytical solutions are presented for a simply supported FG nanobeam with porosities. The validity of this theory is verified by comparing some of the present results with other higher-order theories reported in the literature, the influence of material parameters, the volume fraction of porosity and the thickness ratio on the behavior mechanical P-FGM beam are represented by numerical examples.

• Geomechanics and Engineering
• /
• 제19권2호
• /
• pp.193-199
• /
• 2019

A frozen fringe plays a key role in frost heave development in soils. Previous studies have focused on the physical and mechanical properties of the frozen fringe, such as overall hydraulic conductivity, water content and pore pressure. It has been proposed that the thickness of the frozen fringe controls frost heave behavior, but this effect has not been thoroughly evaluated. This study used a temperature-controllable cell to investigate the impact of frozen fringe thickness on the characteristics of frost heave. A series of laboratory tests was performed with various temperature boundary conditions and specimen heights, revealing that: (1) the amount and rate of development of frost heave are dependent on the frozen fringe thickness; (2) the thicker the frozen fringe, the thinner the resulting ice lens; and (3) care must be taken when using the frost heave ratio to characterize frost heave and evaluate frost susceptibility because the frost heave ratio is not a normalized factor but a specimen height-dependent factor.