• Nuclear Engineering and Technology
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• v.53 no.6
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• pp.1786-1795
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• 2021

Printed Circuit Heat Exchanger (PCHE) is a widely used heat exchanger in the supercritical carbon dioxide (sCO₂) Brayton cycle because it can work under high temperature and pressure, and has been a hot topic in Next Generation Nuclear Plant (NGNP) projects for use as recuperators and condensers. Most previous studies focused on channel structures or shapes. However, no clear advancement has so far been seen in the allover size of the PCHE. In this paper, we proposed an optimal size of the PCHE with a fixed volume. Two boundary conditions of PCHE were simulated, respectively. When the volume of PCHE was fixed, the heat transfer rate and pressure loss were picked as the optimization objectives. The Pareto front was obtained by the Multi-objective optimization procedure. We got the optimized number of PCHE channels under two different boundary conditions from the Pareto front. The comprehensive performance can be increased by 5.3% while holding in the same volume. The numerical results from this study can be used to improve the design of PCHE with straight channels.

• Journal of IKEEE
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• v.27 no.4
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• pp.411-417
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• 2023

Unmanned aerial vehicle (UAV)-assisted relay has the advantages of ease of deployment, good communication channels, and mobility over traditional terrestrial relay, which greatly improves wireless connectivity. In this paper, we design a UAV-enabled relay network that can utilize radio frequency bands to harvest energy from sources and utilize terahertz (THz) bands to transmit information between secondary transmitters and receivers. Next, we solve the optimal position of the UAV that maximizes the relay channel capacity, and propose an algorithm to design two trajectories of UAV (a straight and an elliptical trajectory) using the derived solution. Numerical results show that the straight trajectory is better in terms of harvested energy and channel capacity.

• Journal of Physiology & Pathology in Korean Medicine
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• v.18 no.2
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• pp.571-574
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• 2004

Effects of the Cheonggansoyo-san added Injinwiryeong-tang on recovery from damaged-liver and mental-faculty improvement in alcoholism were studied using male Sprague-Dawley rats, The rats were assigned into 4 groups; normal, control and CIX group. Control group administered ethanol(25 v/v %) at a dose 3 g/kg, while CIX group administered the water extract of Cheonggansoyo-san added Injinwiryeong-tang (CIX) 30 min before treating same dose of ethanol as control group for 10 days, orally. The GOT and GPT activities of rats were checked by Reitman & Frankel method, and all groups were subjected to trials of straight channel on the 1 st day and to those of multiple T-maze during the following 3 days. The GOT and GPT activities were increased in control group, but decreased in CIX group significantly. The time required in normal group for the straight channel of the 2nd and 3rd trials was significantly shorter than that of the 1 st, while the control group showed no significance. In the time required for the multiple T-maze trials, the control group showed no significance. But in the straight or T-maze trials, the CIX group showed significant decrease in the time required against the control group.

• Journal of Wetlands Research
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• v.22 no.2
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• pp.121-129
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• 2020

This paper described a laboratory investigation of micro hydropower at lower head water in a free vortex flow. The vortex height, turbine rotation and torque for straight blade with inner curved edge, twisted blade and curved blade were investigated at the flow rate of 0.0069 ㎥/s in the inlet channel. The results showed that the optimum vortex strength occurred within the range of the diameter of basin to the outlet diameter ratios of 0.17~18.5. The power output and efficiency of straight blade were higher as compared to other blades. The highest amount of generated energy was 12.33 W, the torque was 0.91 N·m and the highest efficiency by considering effective head was 29.5 %, whereas the highest efficiency by considering vortex height was 80.5 % at the rotational speed of 132 rpm. The water vortex velocity of straight blade was about 2.8 times larger than the mean velocity in the inlet channel.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.1894-1899
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• 2007

This paper presents the thermal characteristics for micro heat exchanger with different micro-channel shapes. The shapes of micro-channel has been manufactured sheet metal by chemical etching for the I shape of straight channel and V and W shapes of chevron feature and fabricated micro plated heat exchangers using the vacuum brazing of bonding technology. The experimental study has been performed on heat transfer and pressure drop characteristics with various Reynolds number for water to water at the counter flows. The average heat transfer rate of V and W shapes has been showed about 1.5${\sim}$1.6 times large than those of I shape. For the comparison of Nusselt number, it is known that the convective heat transfer of V and W shapes represent more effect than I shape. The pressure drops of V and W shapes are about 1.2${\sim}$1.7 times lager than those of I shape.

• Journal of the Korean Society of Visualization
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• v.19 no.3
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• pp.69-76
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• 2021

Printed circuit heat exchanger (PCHE) is a compact heat exchanger with good heat transfer performance, high structure integrity, and reliability over a wide range of temperatures and pressures. Instead of the traditional zigzag and straight shape channel, the sinusoidal shape channel was adopted in this study to investigate the relation of thermal-hydraulic performance and waviness factors (period and amplitude). The local flow characteristics and the heat flux distribution were compared to verify the effects of period and amplitude on heat transfer performance. As the period of channel becomes shorter, the rapid change of the flow direction can produce high flow separation around the corner leading to the disturbance of the boundary layer opposite wall. The nonuniform distribution of flow velocity appeared around the corner positions can promote fluid mixing and lead to higher thermal performance. An evaluation index was used to compare the comprehensive performance of PCHE considering the Nusselt number and Fanning factor. Based on the simulation results, the optimal design parameters of PCHE channel shape were found that the channel with an equivalent bending angle of 15° offers the highest heat flux capacity.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.5B
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• pp.469-479
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• 2006

In order to investigate characteristics of the primary flow and the secondary currents in meandering channels, the laboratory experiments were conducted in S-curved channels with angle of bend, $150^{\circ}$, and sinuosity of 1.52. The experimental conditions was decided varying average depth and velocity. Under these experimental conditions, spatial variations of the secondary currents in multiple bends were observed. The experimental results revealed that the distribution of primary flow in straight section is symmetric without respect to the experimental condition and the maximum velocity line of the primary flow occurs along the shortest path in experimental channel, supporting the result of previous works. The secondary currents in second bend became more developed than those in first bend. Particularly, the outer bank cell developed distinctively and the secondary current intensity was low at the straight section and high at the bends, periodically. Also, the secondary current intensity at the bends was as twice to three times as that at the straight section, and has its maximum value at the second bend. The turbulent flow characteristics of meandering channel was investigated with turbulent intensity of the primary flow and Reynolds shear stress. It was observed that the turbulent intensity is increasing when the velocity deviation of the primary flow is large whereas Reynolds shear stress increases when both the velocity deviation of the primary flow and the secondary current are large.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.11
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• pp.1497-1505
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• 2000

A numerical study is made on the ice-formation for a laminar flow in a curved channel. When the water flows through the curved channel with the walls specified below the freezing temperature, the ice layer has been formed on the curved surface, different from that of a straight channel. The fluctuation of ice layer has been predicted, considering the variation of velocity and temperature near the curved portion of channel. The study also takes into account the interaction existing between the laminar flow and the curved channel. In the solution strategy, the present study is substantially different from the existing works in that the complete set of governing equations in both the solid and liquid regions are resolved. The results from this study have been mainly presented, focusing on the variation of ice layer close to the curved portion. Numerical results have been obtained parametrically by varying the curved angle and the radius of curvature of channel, in addition to the variation of Reynolds numbers and wall temperatures of channel. The results show that the curved shape of channel has the great effect on the thickness of the solidification layer. The wave of ice layer thickness appears in the vicinity of curved portion. This behavior of ice layer has been amplified as is the increasing of curved angle and the radius of curvature of channel. In addition, the ice layer becomes thin as Reynolds numbers in increasing. And also, as the wall temperature of channel increases, the width of channel becomes to be shrunk due to the growth of ice layers in the upper and lower wall of channel.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.12 s.255
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• pp.1228-1235
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• 2006

PEMFC(Proton Exchange Membrane Fuel Cell) is a low temperature fuel cell and has many probabilities of commercial use. However, water management is one of the serious technical problems for commercialization. It is necessary to understand the relationship between operation conditions and water behavior in PEMFC channel because it affects fuel cell performance. In this paper, the distribution of current density according to inlet humidity condition is mainly observed and discussed. If the anode inlet is well humidified, electro-osmotic drag is very active. For this reason, current density is very high at inlet side and the distribution is non-uniform.

• Journal of the Korean GEO-environmental Society
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• v.14 no.11
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• pp.5-12
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• 2013

The purpose of this study is to estimate the behavior and the mechanism of debris flow at the end of mountain side when a berm was set on the inclined plane. The numerical model was performed by using the Finite Difference Method(FDM) based on the equation for the mass conservation and momentum conservation. In order to measure the behavior of the debris flow, the debris flow of a straight channel slope and the debris flow of channel slope with 3 types of berms were compared. First, the flow discharge and the sediment volume concentration at the downstream of the channel slope, depending on the various berm width and the different inflow discharges at the upstream of the channel were analyzed. The longer the berm width, the flow discharge at the downstream of the channel was decreased and the high flow fluctuation was reduced by a berm. And it means that a berm can effect for the delay of the debris flow. Through Root Mean Square ratio(RMS) comparison, the flow discharge of the channel slope with a berm was lower than that of a straight channel slope. The longer the berm width, for the sediment volume concentration, an inflection point did not show but mild curve. Because the low sediment concentration with water mixture by a berm continuously flow at the downstream end, it will be effect for reducing the disaster caused by debris flow. The results of this study will provide useful information in predicting and preventing disaster caused by the debris flow.