• Nuclear Engineering and Technology
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• v.52 no.12
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• pp.2771-2788
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• 2020

Experiments are conducted to study bubble flow behavior during the instability of subcooled boiling under uniform and non-uniform transverse heating. The non-uniform heat distribution introduces nonuniform bubble generation and condensation rates on the heated surface, which is different from the uniform heating. These bubble generation and condensation characteristics introduce a non-uniform local pressure distribution in the transverse direction, which creates an extra non-uniform pressure on the flowing bubbles. Therefore, different bubble flow behavior can be observed between uniform and non-uniform heating conditions. In the uniform heating, bubble velocity fluctuations are low, and the bubbles travel straight along the axial direction. In the non-uniform heating, more fluctuation in the bubble velocity occurs at low mass flow rate and high subcooled inlet temperatures, and reverse flow is observed. Additionally, the bubbles show a zigzag trajectory when they pass through the channel, which indicates the existence of cross flow in the transverse direction.

• Transactions on Electrical and Electronic Materials
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• v.18 no.1
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• pp.51-54
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• 2017

TFTs (thin film transistors) were fabricated using a-SIZO (amorphous silicon-indium-zinc-oxide) channel by RF (radio frequency) magnetron sputtering at room temperature. We report the influence of various channel thickness on the electrical performances of a-SIZO TFTs and their stability, using TS (temperature stress) and NBTS (negative bias temperature stress). Channel thickness was controlled by changing the deposition time. As the channel thickness increased, the threshold voltage ($V_{TH}$) of a-SIZO changed to the negative direction, from 1.3 to -2.4 V. This is mainly due to the increase of carrier concentration. During TS and NBTS, the threshold voltage shift (${\Delta}V_{TH}$) increased steadily, with increasing channel thickness. These results can be explained by the total trap density ($N_T$) increase due to the increase of bulk trap density ($N_{Bulk}$) in a-SIZO channel layer.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.11 no.3
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• pp.321-331
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• 1999

A numerical study is carried out for increasing heat removal using indirect cooling system. Computation is performed for nine cases as variation of flow condition in the lower channel. As the result of this study, water is more effective than air at the same pressure loss in spite of the lower inlet velocity. In channel configuration, the vertical channel is more effective than horizontal channel because of the buoyancy effect. Under the condition that heat generation is the same, counter flow effectively decreases the temperature difference among blocks. Parallel flow is more effective than counter flow when average temperature of all blocks is considered. In the case of installing obstacles in the lower channel, it is desirable to install obstacles in the bottom of lower channel. Heat transfer rate increases as the height of obstacles increases.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.5
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• pp.1592-1596
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• 2010

According to the increase of the channel length with fixed width/length, characteristic curves of drain current as a function of gate bias voltage of indium gallium zinc oxide (IGZO) thin-film transistors moved to a positive direction of gate voltage, and field-effect mobility decreased. In case of fixed length and width of channel, field-effect mobility was lower and subthreshold slope was larger when drain bias voltage was higher. Due to large work function of IGZO, band bending at the junction region between IGZO channel and source/drain electrodes was expected to be in opposite direction to that between silicon and metal electrodes; this could explain the above results.

• Proceedings of the SAREK Conference
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• 2006.06a
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• pp.621-626
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• 2006

Regenerative evaporative cooling is known as an environment-friendly and energy efficient cooling method. A regenerative evaporative cooler (REC) consisting of dry and wet channels is able to cool down the air stream below the inlet wet-bulb temperature. In the regenerative evaporative cooler, the cooling effect is achieved by redirecting a portion of the air flown out of the dry channel into the wet channel and spraying water onto the redirected air. In this study, a horizontal regenerative cooler is considered. In the horizontal regenerative cooler, the flow direction of evaporating water has a right angle to the flow direction of supply air. This difference was investigated with visualization technique and simplified 2-module performance test was done in a thermo-environment chamber. Optimum design configuration is changed due to the wet channel which are easily fully covered with evaporating water and block the air flow inside the channel. Applying the optimized fin configuration design with the highly wetting surface treatment, a regenerative evaporative cooler was fabricated and tested to Identify the cooling performance improvement and operation characteristics. From the experimental results at the intake condition of $32^{\circ}C$ and 50% RH, the supply temperature was measured to be around $23.4^{\circ}C$. The cooling effectiveness based on the inlet dewpoint temperature was evaluated 73% which is almost close to the design expectation.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.18 no.7
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• pp.8-13
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• 2019

As increasing demand for precise machining in advanced disciplines, especially in semi-conductor, aeronautical and automotive industries, the magnetic abrasive deburring(MAD) which is able to eliminate micro-sized burr on complex surface in less time has drawn the attention in the last decades. However, the performance of MAD is subject to shape and size of a tool. Therefore, this study aim to identify deburring behavior of MAD in U-type flow channel by measuring the length rate of burr removal in radial distance of the cylindrical tool under four process factors. In order to evaluate the deburring effect of MAD on the surface, finishing regions are divided based on center of the circular cutting tool. As a results, it was defined that the amount of burr removal in a downward direction moving toward flow channel from the top surface was higher than upward direction. This is because the magnetic abrasives were detached from magnetic lines of force due to geometrical shape.

• Journal of Korea Water Resources Association
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• v.48 no.8
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• pp.635-645
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• 2015

The objective of this study is to examine the three-dimensional turbulent flows occurring in the meandering channel with presence of a groyne. A series of laboratory experiments are carried out in a meandering channel with trapezoidal cross sections. The channel is a 24.4 m long, 1.5 m wide, and the bottom slope in the longitudinal direction is 0.02. Two cases with and without the groyne are considered in the experiment. Three-dimensional velocity fields are measured using an acoustic Doppler velocimetry (ADV) at approximately sixty locations in each cross section. The measured velocity fields are averaged in time, and the time-averaged flow revealed that the mean velocity magnitude along the outer bank of the channel was reduced significantly and the direction of the primary flow was directed toward the center of the channel due to the presence of the groyne.

• 한국정보디스플레이학회:학술대회논문집
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• 2007.08b
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• pp.1263-1265
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• 2007

The electrical characteristics of low temperature poly-Si (LTPS) thin-film transistors (TFT) with channel parallel and perpendicular to the direction of lateral growth were studied. The poly-Si film was crystallized using sequential lateral solidification (SLS) laser crystallization technique. The channel orientation dependent turn-on characteristics were investigated by using gated-diodes and capacitance-voltage measurements

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.8A
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• pp.752-759
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• 2006

In this paper, the performances of representative high resolution direction finding algorithms are evaluated and compared in wideband mobile environments. The angular spread phenomenon in mobile environments is first investigated and then a vector channel model for wideband OFDMA signals is derived. A direction finding system architecture for OFDMA smart antenna systems is proposed and finally the performances of high resolution direction finding algorithms are evaluated in wideband mobile environments by taking the WiBro system as a target system.

• Transactions of the Korean hydrogen and new energy society
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• v.19 no.4
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• pp.283-290
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• 2008

In this paper, experiments with an air-breathing proton exchange membrane fuel cell (PEMFC) for mobile devices were carried out according to cathode conditions. These conditions are defined by the cathode flow field plate type (the channel type, the open type) and the cathode surface direction. Single-cell and 6-cell stack were used in the experiments. The experimental results showed that the open-type cathode flow field plate gave a better performance than the small channel type. In the experiments related to the direction of the slits on the cathode flow field plate, the horizontal slit cell was better than the vertical one. With respect to the cathode surface direction, when the cathode surface is placed in the direction normal to the ground, the PEMFC generated more stable power in the mass transport loss region. Since stable power in the mass transport region is closely related to the air supply, computational fluid dynamics (CFD) analysis for air-breathing PEMFC of different cathode surface directions was performed.