• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.12
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• pp.1062-1070
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• 2016

The heat transfer and flow characteristics of gas turbine blade tip were investigated in this paper by using the conjugate heat transfer analysis. The rotor inlet boundary condition profile which was taken from the first stage nozzle outlet was used to analyse. The profile contained the velocity and temperature information. This study presents the influence of tip clearance about aerodynamic loss, heat transfer coefficient and film cooling effectiveness with the squealer tip designed blade model which tip clearance variation range from 1% to 2.5% of span. Results showed that the aerodynamic loss and the heat transfer coefficient were increased when the tip clearance was increased. Especially when the tip clearance was 2% of the span, the average heat transfer coefficient on the tip region was increased obviously. The film cooling effectiveness of tip region was increasing with decreasing of the tip clearance. There was high film cooling effectiveness at cavity and near tip hole region.

• Journal of Bio-Environment Control
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• v.22 no.3
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• pp.270-278
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• 2013

The objective of the present study is to provide data needed to decide covering method to be able to increase the thermal insulation and light transmittance efficiency of commercial greenhouse. The thermal insulation effect, PPF transmittance and quantity of condensation water were estimated in experimental tomato greenhouses covered with three types of coverings of single layer, air inflated and conventional double layers covering. The overall heat flow of air inflated double layers greenhouse was similar to that of conventional double layers greenhouse, but the temperature between covering material and thermal screen in air inflated double layers greenhouse was lower than that in conventional double layers greenhouse at the same outside temperature condition due to air leakage through the gap of roof vent. The overall heat transfer coefficients acquired by experiment that was performed in single layer and conventional double layers greenhouses were close to those obtained from model experiment. Even though the PPF transmittance of air inflated double layers greenhouse was lower than that of single layer greenhouse, which was greater than that of conventional double layers greenhouse. The quantity of condensation water on covering surface of single layer greenhouse was greater than that of air inflated double layers greenhouse due to lower covering surface temperature.

• Korean Chemical Engineering Research
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• v.61 no.3
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• pp.446-455
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• 2023

A mathematical model for predicting the liquid circulation velocity in an airlift reactor was developed based on the mechanical energy balance of the fluid circulation loop. The model considered the energy loss due to a 90° turn, the energy loss due to friction, and the energy loss due to the change in cross-sectional area at each part of the reactor. The model that separately considered the loss coefficients related to friction, direction change, and cross-sectional area change was able to predict the liquid circulation velocity better than the previous model using lumped parameters. The liquid circulation velocity was measured by the tracer pulse method. Most of our experimental results obtained in external-loop airlift reactors, which had the top and bottom connecting pipes, as well as other investigators' results obtained in various types of airlift reactors, were well predicted by the developed model with an error within 20%. Useful empirical equations for the loss coefficient related to the 90° turn of the circulating fluid were obtained in external and internal-loop airlift reactors and used to predict the liquid circulation velocity.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1991.04a
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• pp.133-138
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• 1991

일반적으로 고무를 비롯한 점탄성재료는 형상 및 크기를 적절히 조절함으로 써 한 방향 이상으로의 원하는 스프링상수를 얻을 수 있으며, 금속에 비하여 내부 마찰에 의한 에너지 발산이 매우 크기 때문에 강제 진동시의 진폭저감 및 충격에 따른 자유진동의 감쇠에 널리 이용되고 있다. 이와 같은 진동감쇠 에 점탄성재료를 효과적으로 사용하기 위해서는 복소탄성계수 즉, 탄성계수 와 손실계수를 정확하게 알아내는 것이 필요하다. 점탄성재료의 복소탄성계 수는 주파수, 온도 및 변형률등에 따라 변하므로 이와 같은 사용조건의 함수 로 구해야 한다. 복소탄성계수를 실험적으로 구하는 방법은 여러가지가 있으 며 실험의 용이성과 관심대상에 따라 적절한 방법을 선택하게 된다. 본 연구 에서는 주파수변화에 따른 복소탄성계수를 임피던스법으로 집중질량 모형을 이용하여 구하려고 할 때, 실험데이타로부터 보다 정확한 결과를 얻기 위하 여 적절한 시편의 크기를 결정하는 방법을 제시하고자 한다. 이를 위해서 시 편내의 파동전달효과와 포아송비와 관련된 양단제한효과 그리고 정하중시 압축변형에 대한 시편의 좌굴등을 고려하여 이론적으로 해석하였으며 실험 적으로도 검증하였다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.4
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• pp.377-383
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• 2012

The temperature distribution of an asymmetric trapezoidal fin with various upper lateral surface slopes is investigated by using the two-dimensional analytic method. For this asymmetric fin, convection from the inner fluid to the inner wall, conduction from the inner wall to the fin base and conduction through the fin base are considered simultaneously. The temperature profile with the variation of dimensionless fin length and height coordinates is shown. Also, the temperature variation at the bottom tip of the fin is presented as a function of the fin shape factor. Heat losses through the fin base and from each side are compared for variations in fin length. One of the results shows that temperature at the fin bottom tip decreases linearly as the fin shape factor increases.

• Composites Research
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• v.16 no.5
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• pp.39-44
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• 2003

Embedding viscoelastic-damping materials into composites can greatly increase the damping properties of composite structures. Usually viscoelastic-damping materials behave isotropically so that their damping properties are the same in all directions. In these days, there is a desire to develop viscoelastic-damping materials that behave orthotropically so that damping properties vary with material orientation. These orthotropic damping materials can be made by embedding rows of thin wires within the viscoelastic materials. These wires add significant directional stiffness to the damping materials. where the stiffness variation with wire orientation follows classical lamination theory. In this paper, the loss factor of composite laminate was evaluated based on Ni and Adams' theory. To investigate the effect of directional damping material, the low-velociy impact response analysis was also performed. The present analysis results show that directional damping material has a great influence on vibration and damping characteristic of composite laminate.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.11a
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• pp.199-202
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• 2008

This paper presents a mathematical-physical model to predict the performance of a gas pusher used as a separation system powered by a gas generator. The empirical coefficients of heat loss and friction were determined from experiments. Based on the grain configuration of the gas generator, the analytical approach of combustion, flow and movement of a piston inside the chamber of a gas generator and a gas pusher was simulated by numerical method. The prediction method developed can be usefully applied to the design of separation mechanism systems.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.110-110
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• 2009

Aerosol deposition method(ADM)는 상온에서 에어로졸화된 고상의 원료분말을 노즐을 통해 분사시켜 소결과정을 거치지 않고도 상온에서 고밀도 후막을 제조할 수 있는 공정으로서, 다양한 재료의 코팅이 가능하고, 코팅층의 조성 및 화학 양론비의 제어가 용이한 특징을 갖는다. 본 연구에서는 ADM을 이용하여 큰 유전상수, 압전계수, 초전계수, 탄성계수를 갖는 $BaTiO_3$ 분말을 원료로 하여 압전소자, 커패시터, 고전압용 유전체 등에 응용이 가능한 세라믹 층 형성에 관한 연구를 진행하였다. 또한 $BaTiO_3$ 같은 강유전체 세라믹을 이용하여 여러 가지 소자를 제조하는 경우 소자의 미세조직에 따라 물성이 영향을 받는 것으로 확인되어져 있다. 이에 본 연구에서는 세라믹 분말보다 상대적으로 탄성이 큰 polymer 분말을 첨가하여 후막 내부의 결정립의 크기가 20 nm 의 평균 결정립을 갖는 세라믹 후막에 비해 최대 10 배 정도까지 증가하는 것을 확인할 수 있었으며, 이에 따라 후막에서의 유전율 및 유전손실율의 전기적 특성 변화를 확인할 수 있었고, 이러한 물성변화에 대한 원인 고찰을 위하여 후막의 미세구조 및 화학조성 등에 대한 다양한 분석이 이루어 졌으며, 상온에서 성막되는 후막의 세라믹 층의 응용을 위한 최적의 공정조건을 제시하고자 한다.

• Korean Journal of Optics and Photonics
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• v.6 no.2
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• pp.130-134
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• 1995

A small signal gain coefficient of Nd:glass was measured and a cavity-dumped laser was constructed. To measure the small signal gain coefficient, we constructed a resonator consisting of Nd:glass, Pockels cell, polarizing beam splitter. The measured small signal gain coefficient was $0.088 cm_{-1}$ when the input energy was 100 J and the round-trip internal loss of the resonator was 56%. The cavity-dumped laser was constructed using Nd:glass. 2 m radius of curvature HR-mirrors, Pockels cell, polarizinig beam splitter and $\lambda/4$ plate. The output energy of cavity-dumped laser was 0.85 J at 140 J input energy and the laser pulse width was 8 ns.s 8 ns.

• Korean Journal of Food Science and Technology
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• v.47 no.5
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• pp.645-651
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• 2015

Sucrose in chiffon cakes was replaced with different levels of sorbitol (0, 30, 50, 70, and 100%), and the effects on the physical properties and storage stability of the cakes were measured. The specific gravity and viscosity of the batter, as well as the volume and moisture content of the cakes, decreased with increasing sorbitol content. The hardness of the cakes slightly decreased as the amount of sorbitol increased, whereas the lowest cohesiveness was observed in the cakes with equal amounts of sucrose and sorbitol. Storage for one day slightly increased the hardness of the cakes and decreased their cohesiveness. Although the amount of mold and total microbial count increased with increasing storage days at room temperature, the replacement of sucrose with 70 or 100% sorbitol was effective in suppressing microbial growth. In sensory tests, the formulation with 70% sorbitol substitution in the chiffon cakes was the most acceptable.