• 한국마린엔지니어링학회:학술대회논문집
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• 한국마린엔지니어링학회 2005년도 전기학술대회논문집
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• pp.216-221
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• 2005

The heat transfer coefficient and pressure drop during gas cooling process of carbon dioxide in a helically coiled tube were investigated experimentally. The experiments were conducted without oil in the refrigerant loop. The main components of the refrigerant loop are a receiver, a variable speed pump, a mass flowmeter, a pre-heater, a gas cooler(test section) and an isothermal tank. The test section is a double pipe type heat exchanger with refrigerant flowing in the inner tube and water flowing in the annulus. It was made of a copper tube with the inner diameter of 4.85 [mm], the outer diameter of 6.35 [mm] and length of 10000 [mm]. The refrigerant mass fluxes were 200${\sim}$600 [kg/$m^2$s] and the average pressure varied from 7.5 [MPa] to 10.0 [MPa]. The main results were summarized as follows: The heat transfer coefficient of supercritical $CO_2$ increases, as the cooling pressure of gas cooler decreases. And the heat transfer coefficient increases with the increase of the refrigerant mass flux. The pressure drop decreases in increase of the gas cooler pressure and increases with increase the refrigerant mass flux.

• 대한기계학회논문집B
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• 제28권11호
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• pp.1390-1397
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• 2004

This study is concerned with the thermal analysis during the cool-down period of 135,000㎥ class GT-96 membrane type LNG carrier under IMO and USCG design condition. During the cool-down period, the spraying rate for the NG cooling decreases as the temperature of NG falls down from -4$0^{\circ}C$ to -l3$0^{\circ}C$, and the spraying rate for the cooling of the insulation wall increases as the temperature gradient of the insulation wall is large. It was confirmed that there existed the largest temperature decrease at the first barrier and the first insulation, which are among the insulation wall, especially in the top side of the insulation wall under IMO and USCG design condition. Also, as the NG temperature distribution is fixed, the outer temperature condition under the design condition has influence on the temperature variation at the insulation. By the 3-D numerical calculation about the cargo tank and the cofferdam during the cool-down period, the temperature variation in hulls and insulations is precisely predicted under IMO and USCG design condition. From the comparison between two conditions; IMO design condition shows more severe temperature gradient than USCG design condition, therefore, it provides the conservative estimation of the BOG.

• Structural Engineering and Mechanics
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• 제77권6호
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• pp.753-763
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• 2021

Feasibility studies of a reinforced concrete (RC) deep pile foundation system with the compressed air energy storage (CAES) technology were conducted in previous studies. However, those studies showed some technical limitations in its serviceability and durability performances. To overcome such drawbacks of the conventional RC energy pile system, various steel-concrete composite pile foundations are addressed in this study to be utilized as a dual functional system for an energy storage medium and load-resistant foundation. This study conducts finite element analyses to examine the applicability of various composite energy pile foundation systems considering the combined effects of structural loading, soil boundary forces, and internal air pressures induced by the thermos-dynamic cycle of compressed air. On this basis, it was clearly confirmed that the role of inner and outer tubes is essential in terms of reliable storage tank and better constructability of pile, respectively, and the steel tubes in the composite pile foundation can also ensure improved serviceability and durability performances compared to the conventional RC pile system.

• 한국식품위생안전성학회지
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• 제22권3호
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• pp.192-198
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• 2007

김치는 우리나라의 대표적인 전통 식품이며 참살이(well-being) 식품으로 인정되고 있지만, 최근 김치를 수입 농산물로 만들거나 완전 제조한 상태로 수입되고 있어 이에 대한 안전성 확보가 요구된다. 따라서 안전한 김치 제조를 위해서는 김치 재료의 생물학적 위해요소 제거가 필수적이다. 본 연구는 김치의 주재료인 배추를 대상으로 배추에 존재할 수 있는 생물학적 위해 요소, 특히 기생충 오염을 제거 위하여, 기생충란 오염 배추 모델을 이용하여 배추의 효과적 세척 방법을 평가한 결과 다음과 같은 결론을 얻었다. 배추에 붙어 있는 흙을 없애고, 뿌리 및 오염된 잎을 제거한 다음, 3단계 이상으로 분리된 세척조로 분리 급수하면서(유속 0.8 m/sec 이상 유지) 소금에 절인 배추를 각 세척조에서 다음과 같이 수세한다. 손가락으로 배추의 뿌리부분과 잎 사이를 골고루 벌려 잡고, 배추를 물속에 넣은 후 물속에서 상하로 20cm 이상 넣었다 빼는 것을 3회 이상 반복 후 다시 좌우로 30cm 이상 3회 이상 흔들어 세척한다. 이때 세척 횟수 및 세척수의 유속을 증가시키거나 야채용 세제(제1종 세제)을 첨가시 세척효과는 더 증가하였다.

• Composites Research
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• 제18권4호
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• pp.1-7
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• 2005

삽입된 광섬유 브래그 격자(fiber Bragg grating, FBG) 센서를 이용하여 수압시험 동안에 필라멘트 와인딩 된 복합재료 압력탱크의 실시간 구조 건전성 모니터링을 수행하였다. 일반적으로 압력탱크의 내부와 외부의 유한요소해석 결과는 변형률과 응력 모두 큰 차이를 보인다. 그러므로, 압력탱크의 건전성을 검증하기 위해서는 운용 중 탱크 내부의 변형률 값을 정확하게 측정해야 한다. 여러 광섬유 센서 중 FBG 센서는 변형률 게이지에 비해 구조물에 삽입이 용이하고 많은 수의 센서를 한 가닥의 광섬유에 파장 분할 다중화(wavelength division multiplexing, WDM) 기법을 통해 쉽게 다중화 할 수 있다. 본 연구에서는 다중화 된 FBG 센서를 삽입한 표준압력용기(standard testing and evaluation bottle, STEB)를 제작하고 수압시험을 수행하였다. 삽입된 센서의 생존율을 높이기 위해 격자 부분에 대한 보강법을 포함한 새로운 삽입 적용 기법을 고안하였다. 제작된 탱크에 대한 수압 시험을 통해 FBG 센서가 필라멘트 와인딩 된 복합재 압력탱크의 건전성 모니터링을 위해 성공적으로 삽입 적용될 수 있음을 확인하였다.

• 대한기계학회논문집B
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• 제28권3호
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• pp.289-295
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• 2004

The heat transfer coefficient and pressure drop during gas cooling process of carbon dioxide in a horizontal tube were investigated. The experiments were conducted without oil in the refrigerant loop. The main components of the refrigerant loop are a receiver, a variable-speed pump, a mass flowmeter, an evaporator, and a gas cooler(test section). The main components of the water loop consist of a variable-speed pump, an isothermal tank, and a flowmeter. The gas cooler is a counterflow heat exchanger with refrigerant flowing in the inner tube and water flowing in the annulus. The test section consists of smooth, horizontal stainless steel tube of the outer diameter of 9.53mm and of the inner diameter of 7.75mm. The length of the test section is 6m. The refrigerant mass fluxes were 200∼300kg/(m2$.$s) and the inlet pressure of the gas cooler varied from 7.5㎫ to 8.5㎫. The main results were summarized as follows : Pressure drop of CO2 increases with increasing gas cooler pressure. The friction factors of CO2 in a horizontal tube show a relatively good agreement with the correlation by Blasius. The heat transfer coefficient of CO2 in transcritical region increases with decreasing gas cooler pressure and decreasing mass flux of CO2. Most of correlations proposed in a transcritical region showed significant deviations with experimental data except for those predicted by Gnielinski.

• 대한기계학회논문집B
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• 제25권2호
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• pp.180-186
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• 2001

The condensation heat transfer coefficients of pure refrigerants R-22, R-134a, and a binary refrigerant mixture R-410A flowing in a small diameter tube were investigated. The experiment apparatus consists of a refrigerant loop and a water loop. The main components of the refrigerant loop consist of a variable-speed pump, a mass flowmeter, an evaporator, and a condenser(test section). The water loop consists of a variable-speed pump, an isothermal tank, and a flowmeter. The condenser is a counterflow heat exchanger with refrigerant flowing in the inner tube and water flowing in the annulus. The test section consists of smooth, horizontal copper tube of 3.38mm outer diameter and 1.77mm inner diameter. The length of test section is 1220mm. The refrigerant mass fluxes varied from 450 to 1050kg/(㎡$.$s) and the average inlet and outlet qualities were 0.05 and 0.95, respectively. The main results were summarized as follows ; in the case of single-phase flow, the heat transfer coefficients increase with increasing mass flux. The heat transfer coefficient of R-410A was higher than that of R-22 and R-134a, and the heat transfer for small diameter tubes were about 20% to 27% higher than those predicted by Gnielinski. In the case of two-phase flow, the heat transfer coefficients also increase with increasing mass flux and quality. The condensation heat transfer coefficient of R-410A was slightly higher than that of R-22 and R-134a. Most of correlations proposed in the large diameter tube showed significant deviations with experimental data except for the ranges of low quality and low mass flux.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2005년도 동계학술발표대회 논문집
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• pp.353-358
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• 2005

The heat transfer and pressure drop of supercritical $CO_2$ cooled in a helically coiled tube was investigated experimentally. The experiments were conducted without oil in the refrigerant loop. The experimental apparatus of the refrigerant loop consist of receiver, a variable speed pump, a mass flowmeter, a pre-heater, a gas cooler(test section) and an isothermal tank. The test section is a helically coiled tube in tube counter flow heat exchanger with $CO_2$ flowed inside the inner tube and coolant( water) flowed along the outside annular passage, It was made of it copper tube with the inner diameter of 4.55[mm]. the outer diameter of 6.35 [mm] and length of 10000 [mm]. The refrigerant mass fluxes were $200^{\sim}600$ [kg/m2s] and the inlet pressure of gas cooler varied from 7.5 [MPa] to 10.0 [MPa]. The main results are summarized as follows : The heat transfer coefficient of supercritical $CO_2$ increases, as the cooling pressure of gas cooler decreases. And the heat transfer coefficient increases with the increase of the refrigerant mass flux. The pressure drop decreases in increase of the gas cooler pressure and increases with increase the refrigerant mass flux.

• 한국마린엔지니어링학회:학술대회논문집
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• 한국마린엔지니어링학회 2001년도 춘계학술대회 논문집
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• pp.106-111
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• 2001

The performance characteristics of heat pump system using the new refrigerant subcooling system were investigated. The new heat pump system has the ice storage tank to accumulate the latent heat of the refrigerant during the night-time. The heat is released to subcool the saturated refrigerant liquid at the outlet of a condenser in the daytime. The experimental apparatus is a well-instrumented heat pump which consisted of a refrigerant loop and a coolant loop. The test sections(condenser and evaporator) were made of tube-in-tube heat exchanger with the horizontal copper tube of 12.7[mm] outer diameter and 9.5[mm] inner diameter. The evaporating temperatures ranged from $-5[^{\circ}C]$ to $0[^{\circ}C]$ and the subcooling degrees of the refrigerant varied from $15[^{\circ}C]$ to $25[^{\circ}C]$. The test of the ice storage was carried out at evaporating temperature of $-10[^{\circ}C]$ and the ice storage mode is an ice-on-coil type. The main results were summarized as follows ; The refrigerant mass flow rate and compressor shaft power of the heat pump system were independent of the subcooling degrees. The cooling capacity o the heat pump system increases as the evaporating temperature and subcooling degree increases. The cooling capacity of the heat pump system is about 25 to 30% higher than that of normal heat pump system. The COP of the heat pump system which subcooled the refrigerant liquid at the outlet of the condenser is about 28% higher than that of the normal heat pump system.

• 한국산업융합학회 논문집
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• 제25권5호
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• pp.899-908
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• 2022

In this study, a study was conducted to localize a large aluminum turbo fan used for tank powerpack. The turbo fan was scanned with a 3D scanner and then 3D modeling was performed. Computational fluid dynamics (CFD) were performed from the performance conditions of the fan, and structural analysis was performed using the pressure data obtained from CFD. The fan was reduced to 1/5 size by applying the geometric similarity. A 1/5 size fan has a honeycomb structure inserted into the front shroud and back shroud to reduce the weight by 5.3%. A 1/5 size fan was printed using a PBF 3D printer, and a 1/5 size fan with honeycombs was also printed. The pressure drop of 8.67 kPa and the required power of 138.19 kW, which satisfies the performance conditions of the fan, were confirmed from the results of CFD. The values of the maximum deformation amount of 0.000788 mm and the maximum effective stress of 0.241 MPa were confirmed from the structural analysis results. The fan printed by the PBF 3D printer had the same shape as the modeling, and the shape was perfect. There are no defects anywhere in appearance. However, the condition of the outer surface of the fan's back shroud is rough compared to other locations. The fan in which the honeycomb was inserted was also perfectly output, and the shape of the honeycomb was the same as the modeling.