• 농업과학연구
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• 제45권4호
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• pp.811-821
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• 2018

This study focused on the improvement of blueberry delivery service using pre-cooled ice and $SO_2$ pads to prevent an increase in the fruit temperature as well as decay. To maintain the fruit quality during low temperature storage, the effect of a $SO_2$ pad and modified atmosphere packaging was also examined. Harvested blueberries were precooled at $15^{\circ}C$, sorted, and packaged. And the fruits were placed in a similar environment as that for the parcel service. Part of the fruits were stored at $0^{\circ}C$ for long term storage. The air temperature in the delivery box increased along with an increase in the simulated delivery time regardless of the treatment. However, the rate of temperature increase was lower in the ice pad treatment. No significant difference was not found after 48 h. The oxygen concentration in the box ranged between 10.5 - 14.5% in the ice pad treatment, which was higher than that of the untreated control (7.5 - 11.9%) whereas the $CO_2$ concentration was lower in the ice pad treatment. No differences were found in the occurrence of off-flavor, decay, and sensory quality loss during the 48 hours of the parcel service simulation. The combined treatment of the $SO_2$ pad and modified atmosphere packaging (MAP) using a perforated film increased the shelf-life of the blueberry fruits, the overall quality such as firmness, and the soluble solid content was not different between the treatments except for the decay incidence. No decayed fruit was found in the combined treatment. However, the percentage of decayed fruit in the control was 25% on day 15 of storage and 75% on day 33 of storage, respectively.

• 생물환경조절학회지
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• 제14권2호
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• pp.76-82
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• 2005

팬 앤 패드 시스템은 국내외적으로 온실냉방에서 많이 이용되고 있으며, 그 효율도 매우 높지만 온실 내부의 온도분포가 불균일하고 설치비와 유지비가 많이드는 단점이 있다. 본 연구에서는 팬 앤 패드 시스템의 설계를 위한 자료를 제공할 목적으로 팬 앤 패드시스템 설치온실의 온도분포를 예측하기 위한 CFD 모델을 개발하였다. 개발된 모델은 실험 데이터를 이용하여 검증한 결과 실험치와 예측치가 잘 일치하여 모델의 응용이 가능할 것으로 판단되었다. 개발된 모델을 이용하여 온실 외부의 풍속과 풍향, 팬과 패드의 높이, 환기율에 따른 실내유속, 차광율 및 온실의 길이가 팬 앤 패드 냉방온실의 실내 온도경사에 미치는 영향을 검토하였다. 실내 온도경사를 감소시키기 위하여는 온실 설치 지역의 주풍향을 고려하고 팬과 패드의 높이가 적절해야 할 것으로 판단되었다. 시뮬레이션 결과 높은 환기율과 차광율은 팬 앤 패드 냉방 온실의 온도경사를 감소시키는데 기여할 수 있는 것으로 나타났다. 팬 앤 패드 냉방 온실의 온도를 적정 수준으로 유지시키기 위해서는 외부기상조건, 차광 및 환기율에 따라 온실의 길이를 제한해야 할 것으로 판단되었다. 개발된 CFD모델은 다양한 조건에서 팬 앤 패드 냉방온실의 설계와 평가에 유용한 도구가 될 수 있을 것으로 판단된다.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2011년도 정기총회 및 추계학술대회 논문집
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• pp.975-985
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• 2011

Cu-Matrix sintered brake pads and low alloyed heat resistance steel are most applied to basic brake system for high energy moving machine. In this research, we analyzed tribological characteristics for influence of air velocity between disk and pad. At low brake pressure with air flow, friction stability was decreased due to no formation of tribofilm at disk surface. But there are no significant change of friction coefficient at all test conditions. Wear rate of friction materials were decreased with increasing of air flow velocity. In result, air flow velocity influenced friction stability, wear rate of friction materials and disk but not friction coefficient.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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• pp.469-474
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• 2002

Laser and hot air reflow soldering of PBGA solder ball was investigated. Experimental results showed that surface quality and shear strength of solder bumps reflowed by laser was superior than the solder bumps reflowed by hot air, and the microstructure inside the solder bumps reflowed by laser was much finer. Analysis on interfacial reaction showed that eutectic solder reacted with Au/Ni/Cu pad shortly after the solder was melted. Interface of solder bump reflowed by laser consists of a continuous AuSn$_4$ layer and remnant Au element. Needle-like AuSn$_4$ grew sidewise from interface, and then spread out to the entire interface region. A thin layer of Ni$_3$Sn$_4$ intermetallic compound was found at the interface of solder bump reflowed by hot air, AuSn$_4$ particles distributed inside the whole solder bump randomly. It is the combination effect of the continuous AuSn$_4$ layer and finer eutectic microstructure inside the solder bump reflowed by laser that resulted in higher shear strength.

• 연구논문집
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• 통권34호
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• pp.101-112
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• 2004

In order to analyze the motion errors of the aerostatic stage, it is necessary to consider the influence of the moment variation occurredinside the pads. In this paper, a motion error anaysis method utilizing the transfer functions on the reaction force and moment is proposed, and general characteristics of the transfer functions are discussed. Calculated motion errors by the proposed method show good agreement with the ones calculated by Multi Pad Method, which is considered the entire table as an analysis object. Also, by the introduction of the transfer function of motion errors, which represent the relationship between the spatial frequency components of the rail form error and motion errors, motional characteristics of the porous aerostatic stage can be generalized. In detail, the influence of the spatial frequencies is analyzed quantatively, and the patterns of the insensitive frequencies which almost do not affect the linear motion error or angular motion error according to the rail length ratio and the number of the pad are verified. The relationship between the moment variation occurred inside the pads and the motion errors is also verified together.

• 한국유체기계학회 논문집
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• 제13권3호
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• pp.43-48
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• 2010

In this study rotordynamic characteristics of an air turbo-compressor (ATC) used in oxygen plant are analyzed and its operating-speed balancing is performed to solve the vibration trouble caused by rotor unbalance. Three dimensional model of the ATC rotor is completed and then analytical FE (finite element) model, which is verified by experimental modal testing, is developed. A rotordynamic analysis includes the critical map, Campbell diagram, and unbalance response, especially considering the pedestal housings supporting tilting pad bearings. A test run of operating-speed, using tilting-pad bearing of actual use, showed that the vibration level increased very sharply as approaching the rated speed. The operating-speed balancing specified by API 684 was carried out by using influence coefficient method. The results showed that the vibrations at the bearing pedestal housings represented good levels of 0.1 mm/s. From the test run and operating-speed balancing, the analytical results, that is, critical speeds are in good agreement with the test results and unbalance responses introducing the correction masses are similar to the as-is test responses in its aspect.

• 한국자동차공학회논문집
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• 제23권6호
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• pp.601-607
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• 2015

The friction material for automobile is manufactured by mixing several composites to stop the running vehicles. Friction characteristics are changed significantly according to the relative amount of the base materials. However, difference of friction coefficient is sometimes measured at the test for the same friction material. Nevertheless, the study for solving these problems is insufficient. In this paper, the friction tests were carried out by changing the external environment and processing condition when the main ingredients are fixed and also evaluated how the friction coefficient changes. The variables are cooling air speed, humidity (Relative humidity and Absolute humidity), scorching time, soaking time and pad area. And it is analytically considered which environmental factor mainly affects the characteristic of friction coefficient variation by experiment. It is expected that the results from this study can be very useful as a database for development of the friction material.

• 생물환경조절학회지
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• 제11권2호
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• pp.81-87
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• 2002

근권냉방 방식에 따른 냉방 효율과 토마토 생육 특성을 검토하고자 XL냉수순환, 라디에이타 냉풍, 패드냉풍 및 대조구를 처리한 결과는 다음과 같다. 근권부 냉방온도는 공급수온이 17.8$^{\circ}C$일 때 XL 냉수순환구는 18.$0^{\circ}C$ 라디에이타 냉풍구는 27.2$^{\circ}C$, 패드 냉풍구는 20.3$^{\circ}C$였다. 배지 깊이와 시간대별 평균온도는 XL냉수순환구 22.8~24.7$^{\circ}C$. 라디에이타 냉풍구 22.7~24.2$^{\circ}C$, 패드 냉풍구 20.5~23.2$^{\circ}C$, 대조구 25.9~29.6$^{\circ}C$를 나타내어 냉방처리구가 대조구에 비해 5~6$^{\circ}C$더 낮았다. 토마토의 생육에 있어 엽장. 엽폭은 대조구에 비해 컸으며, 생체중 및 건물중의 경우에서도 비슷한 경향이었다 근활력에 있어 대조구는 45.0ug/g에 비해 근권냉방 처리구는 58.5-62.8 ug/g으로 높았으나. 근권냉방 처리구간에는 큰 차이가 없었다.

• Tribology and Lubricants
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• 제17권5호
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• pp.358-364
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• 2001

Disk brake system transforms a large amount of kinetic energy to thermal energy in a short time. As the size and speed of automotive increases in recent years, the disk brakes absorbs more thermal energy. And this thermal energy can cause an unacceptable braking performance due to the high transient temperature, that is attained at the friction surface of brake disk and pad. Although these high temperatures are one of the biggest problems. In this study, the overall thermal behavior of ventilated disk brake system was investigated by numerical method. The 3-Dimensional unsteady model was simulated by using a general purpose software package “FLUENT” to obtain the temperature distributions of disk and pad. The model includes the more realistic braking method, which repeats braking and release. The effects of several parameters such as the repeated braking, inlet air velocity and thermal conductivity on the temperature distribution were investigated.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
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• pp.275-276
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• 2002

Active-head sliders with a unimorph piezoelectric actuator for flying height control were experimentally evaluated. It was found that the normalized stroke of the actuator is 5.2 to 6 nm/V/mm without flying over the disk. However, the normalized adjustment range of flying height is about 1.6 nm/V/mm when the active-head slider is flying over the disk. This value is smaller than the measured value when the slider is not flying, because of the air pressure generated at the active pad when the pad approaches the disk surface.