• 설비공학논문집
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• 제18권12호
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• pp.977-983
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• 2006

Experimental results for heat transfer characteristic and pressure gradient of hydrocarbon refrigerants (R-290, R-600a, R-1270) and HCFC refrigerant (R-22) during condensation inside horizontal double pipe heat exchangers are presented. The test sections which have one tube diameter of 12.70 mm with 0.89 mm, 9.52 mm with 0.76 mm, 6.35 mm with 0.13 mm wall thickness are used for this investigation, respectively. The local condensing heat transfer coefficients of hydrocarbon refrigerants were higher than those of R-22. The average condensing heat transfer coefficient increased with the increase of the mass flux. It showed the higher values in hydrocarbon refrigerants than R-22. Hydrocarbon refrigerants have higher pressure drop than R-22 in 10.92 mm, 8 mm and 6.1 mm inner diameters. These results from the investigation can be used in the design of heat transfer exchangers using hydrocarbons as the refrigerant for the air-conditioning systems.

• 대한기계학회논문집
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• 제17권10호
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• pp.2582-2589
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• 1993

Transient heat transfer characteristics of cooling of a spherical body were investigated in the radiatively active spherical medium. Initially the spherical body and the medium were maintained at their constant temperatures. Then heat transfer begins from spherical body t medium. The heat transfer mode inside the spherical body is just conduction. But heat is transferred by both conduction and radiation inside the medium. All thermodynamic properties were held constant in time. Spherical symmetry is assumed. DOM was adopted to solve RTE. The effect of characteries-tic optical thickness, conduction to radiation parameters, and solid surface emissivity has been studied.

• 한국산학기술학회논문지
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• 제13권4호
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• pp.1466-1473
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• 2012

소프트 아이스크림은 환형 증발부의 외측에서 증발하는 R-404A에 의해 형성된 얼음을 스크레이퍼로 깍아내어 제조된다. 본 연구에서는 소프트 아이스크림 증발기의 냉매 측 및 아이스크림 측 열전달계수를 도출하였다. 실험 결과 환형부 내 냉매 유동은 격막에 의해 매우 복잡한 양상을 보이고 열전달계수도 위치에 따라 현저히 달랐다. 즉, 유입위치의 열전달 계수가 다른 부분에 비하여 낮게 나타났다. 냉매측 평균 열전달계수는 열유속의 증가에 따라 또한 포화온도의 감소에 따라 증가하였다. 열유속과 포화온도를 변수로 하여 평균 열전달계수를 예측하는 상관식을 도출하였다. 아이스크림 측 열전달계수는 연속적으로 진동하였다. 이는 스크레이퍼에 의해 관벽의 얼음이 주기적으로 탈착되기 때문으로 판단된다. 아이스크림 원액의 단상 열전달계수는 냉각 기간 중 150 W/$m^2K$에서 250 W/$m^2K$로 증가하였다. 아이스크림 제조 시 열전달계수는 대략 280 W/$m^2K$로 나타났다.

• 대한기계학회논문집B
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• 제24권3호
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• pp.435-442
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• 2000

The present study is conducted to investigate the local heat/mass transfer characteristics for flow through perforated plates. A naphthalene sublimation method is employed to determine the local heat/mass transfer coefficients on the effusion plate. Two parallel perforated plates are arranged for the two different ways: staggered and shifted in one direction. The experiments are conducted for hole pitch-to-diameter ratios of 6.0, for gap distance between the perforated plates of 0.33 to 10 hole diameters, and for Reynolds numbers of 5,000 to 12,000. The result shows that the high transfer region is formed at stagnation region and at the mid-line of the adjacent impinging jets due to secondary vortices and flow acceleration to the effusion hole. For flows through the perforated plates, the mass transfer rates on the surface of the effusion plate are about six to ten times higher than for effusion cooling alone (single perforated plate). More uniform and higher heat/mass transfer characteristic is obtained in overall region with small gap between two perforated plates.

• 한국지열·수열에너지학회논문집
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• 제7권2호
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• pp.23-29
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• 2011

The objectives of this paper are to study the characteristics of heat transfer and pressure drop of the plate heat exchanger with corrugation height by numerical analysis. Plate heat exchanger of three types was designed, which was corrugation height 3.1mm, 2.8mm and 2.5mm. The plate heat exchanger was numerically investigated for Reynolds number in a range of 950~3,380. The temperatures of the hot side were performed at $14.5^{\circ}C$ while that of the cold side was conducted at $4.5^{\circ}C$. The results show that the performance of heat transfer coefficient for corrugation height 2.5mm increases about 9.5~17.1% compared to that of corrugation height 3.1mm. On the other hand, the performance of pressure drop for corrugation height 2.5mm is remarkably higher than that of corrugation height 3.1mm, about 65.7~86.0%.

• 설비공학논문집
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• 제20권2호
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• pp.87-96
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• 2008

Flow condensation heat transfer coefficients(HTCs) of R123 and R245fa are measured in a horizontal plain tube. The main test section in the experimental flow loop is made of a plain copper tube of 9.52 mm outside diameter and 530 mm length. The refrigerant is cooled by passing cold water through an annulus surrounding the test section. Tests are performed at a fixed saturation temperature of $50\;{\pm}\;0.2\;^{\circ}C$ with mass fluxes of 50, 100, $150\;kg/m^2s$ and heat flux of $7.3{\sim}7.7\;kW/m^2$. Heat transfer data are obtained in the vapor quality range of $10{\sim}90%$. Test results show that the flow condensation HTCs of R245fa are overall 7.9% higher than those of R123 at all mass fluxes. The pressure drop of R245fa is smaller than that of R123 at the same heat flux. In conclusion, R245fa is a good candidate to replace ozone depleting R123 currently used in chillers from the view point heat transfer and environmental properties.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2006년도 하계학술발표대회 논문집
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• pp.111-115
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• 2006

To clarify the hydraulic and thermal characteristics of ice slurry which made from 6.5% ethylene glycol-water solution flow in the double tube and plate type heat exchanger, experimental studies were performed. The mass flux and Ice fraction of ice slurry were varied from 800 to $3,500 kg/m^2s$(or 7 to 17 kg/min) and from 0 to 25%, respectively. During the experiment, it was found that the measured pressure drop and heat transfer rate increase with the mass flux and ice fraction; however the effect of ice fraction appears not to be significant at high mass flux region. At the region of low mass flux, a sharp increase in the pressure drop and heat transfer rate were observed depends on mass flux.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2010년도 춘계학술대회 논문집
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• pp.1355-1356
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• 2010

• 소성∙가공
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• 제13권4호
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• pp.319-325
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• 2004

Continuous casting machine has been experienced a rapid development to increase productivity with high casting speed and to meet consumer's strict demands for high quality. However, because most of defects and cracks are initially formed in mold and grown into surface cracks during the post process, more specific and clear investigations upon heat transfer mechanism between mold and solidified shell are necessarily needed. In this study heat transfer coefficients which shows the characteristic of heat transfer mechanism are calculated with temperatures measured in bloom mold using optimal algorithm, and thermal analysis are investigated using the calculated heat transfer coefficients. Finally uniformity of solidified shell is investigated for high carbon steel, 0.187%C from thermal analysis.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2006년도 제27회 추계학술대회논문집
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• pp.371-374
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• 2006

초음속 유동장 내에서 돌출된 sharp fin형상에 의해 발생하는 충격파로 인한 열전달 특성변화 연구를 수행하였다. IR camera를 이용하여 마하 3의 유동 내에 attack angle이 $10^{\circ}$ 부터 $20^{\circ}$ 의 fin을 돌출시켜 생기는 충격파에 의한 바닥면 열전달 계수 변화를 측정하였으며, 유동장의 변화를 알아보기 보기 위해 oil flow method를 사용하였다.