• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.1
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• pp.31-36
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• 2021

Recently, automobile air conditioning systems have applied an alternative refrigerant that can replace the high GWP refrigerant R134a due to the global warming problem. This study simulated the performance of an automobile climate control system with an internal heat exchanger and TXV. Refrigerant R1234yf was applied as the working fluid. Amesim, a commercial software program, was used to model the main components of the compressor, condenser, TXV, evaporator, and internal heat exchanger. As the outside temperature increased from 30℃ to 40℃, the cooling capacity of the system decreased by 3.1%, and the power consumption of the compressor increased by 17.1%. In addition, The performance characteristics of the refrigeration cycle were simulated by increasing the fin pitch of the condenser from 0.8 mm to 1.4 mm. When the fin pitch was larger than 1.0 mm, the condenser capacity decreased, and the system COP was lowered by 5.9%. When the fin pitch of the condenser was 0.8 mm, which was smaller than 1.0 mm, there was no significant change in the system performance. Hence, the optimal performance was observed at a fin pitch of 1.0 mm.

• Current Applied Physics
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• v.18 no.12
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• pp.1605-1608
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• 2018

$Gd_{1-x}Ho_xNi$ melt-spun ribbons were fabricated by a single-roller melt spinning method. All the compounds crystallize in an orthorhombic CrB-type structure. The Curie temperature ($T_C$) was tuned between 46 and 99 K by varying the concentration of Gd and Ho. A spin reorientation (SRO) transition is observed around 13 K. Different from $T_C$, the SRO transition temperature is almost invariable for all compounds. Two peaks of magnetic entropy change (${\Delta}S_M$) were found. One at the higher temperature range was originated from the paramagnet-ferromagnet phase transition and the other at the lower temperature range was caused by the SRO transition. The maximum of ${\Delta}S_M$ around $T_C$ is almost same. The other maximum of ${\Delta}S_M$ around SRO transition, however, had significantly positive relationship with x. It reached a maximum about $8.2J\;kg^{-1}\;K^{-1}$ for x = 0.8. Thus double large ${\Delta}S_M$ peaks were obtained in $Gd_{1-x}Ho_xNi$ melt-spun ribbons with the high Ho concentration. And the refrigerant capacity power reached a maximum of $622J\;kg^{-1}$ for x = 0.6. $Gd_{1-x}Ho_xNi$ ribbons could be good candidate for magnetic refrigerant working in the low temperature especially near the liquid nitrogen temperature range.

• Journal of Convergence for Information Technology
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• v.12 no.4
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• pp.338-344
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• 2022

It is necessarily required in developing Si-based anode materials for lithium ion batteries, and the related researches are actively working especially in Si-carbon composite material. On the other hand, the photovoltaic and semiconductor industries discard huge amount of Si resources, facing the environmental issue. In this study, recycled Si resource is adopted to obtain Si-carbon composite for LIB(Lithium-Ion Batteries). In order to improve high-capacity retention characteristics and cycle stability of a Si anode material for the LIB, two differenct composites having a mass ratio of silicon and pitch of 1:1 and 2:1 are synthesized and electrochemical characteristics of the anode material manufactured by simple self-assembly method. This result in excellent initial capacity with stable cycle life, and confirming the potential use of recycled Si material for LIB.

• Journal of agriculture & life science
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• v.50 no.5
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• pp.217-224
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• 2016

In this study, performance of a developed automatic punching machine considering the planting density of soybeans was evaluated in the case of the operation speed of 0.18-0.28 m/s. The performance demonstrated a rate of 320-500 ㎡/h, 260-400 ㎡/h, and 210-330 ㎡/h for the 0.20 m, 0.25 m, and 0.30 m soybean planting density, respectively. One hundred percent punching capacity was confirmed in 30 mm distance between the ground and the blade. Additionally, in the 50 mm distance condition, the performance of round, square, and hexagonal blades were observed in the range of 16.7-25.2%, 33.0-42.3%, and 54.5-100.0%, respectively. Above all, the hexagonal blade with a 60° edge angle had the most superior cutting quality demonstrating a smooth and soft cutting plane of the plastic.

• Applied Chemistry for Engineering
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• v.35 no.3
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• pp.255-259
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• 2024

In this study, an aqueous-based redox flow battery (RFB) was constructed using tungstosilic acid (TSA), which is a kind of polyoxometalate, as the negative electrode active material and iron chloride (FeCl3) as the positive electrode active material in a sulfuric acid (H₂SO₄) supporting electrolyte. As a result of the cell's performance, it exhibited capacity fading and low energy efficiency. To address these issues, malic acid (MA), an organic additive, was introduced to the positive electrode active material and then tested for electrochemical properties and single cell performance. The malic acid in the iron chloride aqueous solution is working as a chelate agent, and two carboxyl groups are effectively coordinated with iron ions. It was found that MA reduced the electrolyte resistance of the positive electrode active material, leading to chemical stabilization and an increase in capacity and energy efficiency.

• Journal of the Korea institute for structural maintenance and inspection
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• v.11 no.4
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• pp.89-98
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• 2007

The purpose of this study is to experimentally evaluate the structural behavior of built-up type column consisted of angles and y-shape steel sheet forms for filling concrete. This column for minimizing form working and reinforcement placing is able to improve capacity of construction and reduce the term of works. Thirteen 1/3 scaled columns were fabricated. The main variables are 1) effect of angles and y-shape steel sheets of fabricated columns, 2) slenderness of column, 3) eccentricity of column. The results show that the experimental capacity of built-up type column is similar to theoretical one by reinforcement concrete design code. The maximum loads increase according to the rate of angle to cross section of column.

• Journal of the Korean Society of Marine Environment & Safety
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• v.23 no.5
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• pp.595-602
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• 2017

In Korea, much research and development have occurred to enhance the technological competitiveness of tuna purse seining fisheries. Due to these efforts, fishing efficiency has been improved with the development of radar, sonar and global positioning systems for fish detection and revisions to the hull forms of tuna purse seiners. However, for skiff boats, net boats and speed boats, which are auxiliary working boats mounted on tuna purse seiners, technology has lagged behind relative to the modernization of the main vessel. In this study, the hull of an existing propeller-based net boat with steel wire net to protect tuna was changed to the hull of a water jet propulsion vehicle to reduce resistance and improve maneuverability. As a result, a prototype of a water jet propulsion option was produced according to the aluminum structure strength standards specified by the Ministry of Oceans and Fisheries, and safety was confirmed by performing a drop test. Moreover, through a sea trial test, an existing net boat was shown to have a speed of 12.0knots and a towing force of 2,545 kgf at 2,500 RPM. The prototype had a speed of 26.7 knots and a towing force of 2,011 kgf at 3,200 RPM, which satisfied the towing capacity standards of auxiliary working boats mounted on tuna purse seiners.

• Journal of the Korean GEO-environmental Society
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• v.7 no.6
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• pp.101-111
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• 2006

In case of drilled shafts installed by drilling through soft overburden onto a strong rock, the piles can be regarded as end-bearing elements and their working load is determined by the safe working stress on the pile shaft at the point of minimum cross-section or by code of practice requirements. Drilled shafts drilled down for some depth into weak or weathered rocks and terminated within these rocks act partly as friction and partly as end-bearing piles. The base resistance component can contribute significantly to the ultimate capacity of the pile. However, the shaft resistance is typically mobilized at considerably smaller pile movements than that of the base. In addition, the base response can be adversely affected by any debris that is left in the bottom of the socket. The reliability of base response therefore depends on the use of a construction and inspection technique which leaves the socket free of debris. This may be difficult and costly to achieve, particularly in deep sockets, which are often drilled under water or drilling slurry. As a consequence of these factors, shaft resistance generally dominates pile performance at working loads. The efforts to improve the prediction of drilled shaft pile performance are therefore primarily concerned with the complex mechanisms of shaft resistance development. In this study, the numerical analyses are carried out to investigate the behavior characteristics of side of rock socketed drilled shafts varying the loading condition at the pile head. The difference of behavior characteristics of side resistance is also evaluated with the effects of modelling of asperity.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.1969-1973
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• 2007

The purpose of this study is to investigate the performance of a sea water heat source cascade heat pump system. R717(Ammonia) is used for a low-stage working fluid while R134a is for a high-stage. In order to gain a high temperature supply water in winter season, the system is designed to perform a cascade cycle. In this study, two experiments were carried out. One is a system starting test from the low load temperature of $10^{\circ}C$. The other is a system performance investigation over the R717 compressor capacity changes. Experimental results show that when it starts from the low load temperature, the suction temperature of the low-stage compressor is higher than that of a high-stage. The system performance increases when a water source temperature or a low-stage compressor rotational frequency goes higher.

• Journal of Power Electronics
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• v.15 no.3
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• pp.775-785
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• 2015

Many equalization circuits have been proposed to improve pack performance and reduce imbalance. Although bidirectional equalization topologies are promising in these methods, pre-equalization global equalization strategy is lacking. This study proposes a novel state-of-charge (SoC) equalization algorithm for bidirectional equalizer based on particle swarm optimization (PSO), which is employed to find optimal equalization time and steps. The working principle of bidirectional equalization topologies is analyzed, and the reason behind the application of SoC as a balancing criterion is explained. To verify the performance of the proposed algorithm, a pack with 12 LiFePO4 batteries is applied in the experiment. Results show that the maximum SoC gap is within 2% after equalization, and the available pack capacity is enhanced by 13.2%. Furthermore, a comparison between previously used methods and the proposed PSO equalization algorithm is presented. Experimental tests are performed, and results show that the proposed PSO equalization algorithm requires fewer steps and is superior to traditional methods in terms of equalization time, energy loss, and balancing performance.