• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2008년도 동계학술발표대회 논문집
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• pp.262-268
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• 2008

The present paper dealt with flow heat transfer characteristics of R-410A vaporization in horizontal smooth microchannel. The test sections were made of stainless steel tube with inner diameters of 300 mm and length of 300 mm. The refrigerant was supplied with mass flux range of 260-600 kg/$m^2s$ and applied under operating heat flux range of 5-20 kW/$m^2$ using a direct electric current heating method. The in let saturation temperature was set at $10^{\circ}C$ and vapor quality up to 1.0. The influences of mass flux, heat flux and inner tube diameter on local heat transfer coefficients were presented. Comparison with existing heat transfer coefficient correlations was performed. An improved heat transfer coefficient correlation for refrigerant vaporization in microchannel based on superposition model was developed with a mean deviation of 14.01%.

• 설비공학논문집
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• 제7권2호
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• pp.196-206
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• 1995

Experimental investigations on heat and mass transfer characteristics in a vertical tube absorber have been carried out. Three different copper tubes with a length of 1.5m have been tested using LiBr solution and LiBr-$CaCl_2$ solution. The effects of solution flow rate, cooling water temperature, solution inlet temperature and evaporation temperature have been investigated in detail. It is found that heat transfer coefficient increases gradually with the increase of solution flow rate, but decreases rapidly for the flow rates less than 0.02kg/ms. The grooved tube generally shows better heat transfer performances than the smooth tube. LiBr solution shows almost no absorption capability for the cooling water temperatures over $40^{\circ}C$. LiBr-$CaCl_2$ gives less decreasing rate in absorption capability at these temperatures and the heat transfer coefficient becomes less dependent on the types of tubes in use. Considering heat and mass transfer rates, LiBr-$CaCl_2$ solution is found to be more suitable than LiBr solution for air cooled absorber, which operates at higher temperature than water cooled absorber.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 제35회 춘계학술대회
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• pp.63-70
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• 2002

Wear on the tube-to-spring contact is investigated experimentally. The wear is caused by the vibration of the tube while the springs support it. As for the supporting conditions, applied are the contacting normal force (P) of 5 N, just-contact (P = 0 N) and the gap of 0.1 mm. The gap condition is tried far considering the influence of simultaneous impacting and sliding on wear. Results show that the wear volume increases in the order of the gap, the just-contact and the 5 N conditions. This is explained from the contact geometry of the spring, which is convex of smooth contour. The contact shear force is regarded smaller in the case of the gap existence compared with the other conditions. Wear mechanism is considered from SEM observation of the worn surface. The variation of the normal contact traction is analysed using the finite element analysis to estimate the slip displacement range on the contact with consulting the fretting map previously obtained.

• 동력기계공학회지
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• 제16권4호
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• pp.24-29
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• 2012

The numerical analysis by using CFX 11.0 commercial code was done for prediction of fluid flow and thermal field in the vertical heat exchanger. The present experimental studies were also conducted to investigate the effects of circulating solid particles on the fluid flow and temperatures in the fluidized bed vertical shell and tube type heat exchanger with counterflow, at which the solid particles of glasses (3 $mm{\Phi}$) were used in the fluidized bed with a smooth tube. The effect of circulation on the distance(L) of tube inlet and baffle plate was also examined. The present experimental and numerical results showed that the particles in the distance (Ds) of 15 mm showed a more efficient circulation without stacked the space and the LMTD(Log Mean Temperature Difference) in the fluidized bed type was much lower than that in the typical type shell and tube heat exchanger.

• 설비공학논문집
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• 제13권8호
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• pp.710-719
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• 2001

Pool boiling heat transfer coefficients (HTCs) of HCFC123, HFC134a, HCFC22, HFC407C, HFC410A and HFC32 wre measured on a horizontal smooth tube, 26 fpi low fin tube, Turbo-B and Thermoexcel-E enhanced tubes. AN experimental apparatus was designed such that all tubes heated by cartridge heaters could be installed at the same time to save the refrigerant. Data were taken in the pool of $7^{\circ}C$ with the heat flux decreasing from 80 kW/$m^2\;to\;5kW/m^2$. Test results showed that HTCs of pure refrigerants and those of a azeotrope were greatly influenced by reduced pressure. HTCs of HFC407C were 21~25% lower than those of HCFC22 due to mass transfer resistance. For all refrigerants, enhanced tubes with sub-surface and sub-tunnels showed the largest heat transfer enhancement. Especially the largest heat enhancement was obtained for HCFC123 whose reduced pressure is the lowest among al the refrigerants tested. This indicates that either Turbo-B or Thermoexcel-E enhanced tube would be the best choice when used with a low vapor pressure refrigerant.

• 설비공학논문집
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• 제6권2호
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• pp.166-174
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• 1994

An experimental study has been performed to identify the evaporation characteristics of HCFC-22 for transport refrigeration system. Heat transfer coefficients were measured in a horizontal, smooth evaporating tube with an inner diameter of 10.7mm and a length of 2.8m. The refrigerant was heated electrically by surface-wrapped heaters and uniform power is applied along the tube. The entire tube was divided into 7 sections. Surface temperatures of tube and refrigerant temperature in each test section were measured. Pressure drops in each section and the inlet pressure were also measured. The mass flowrate of the refrigerant was controlled and measured. A single tube evaporation test was conducted for different ranges of mass flux of refrigerant, heat flux of evaporator and condensing temperature of transport refrigeration system. The evaporation heat transfer coefficients of HCFC-22 were compared with predictions from the well known Chen's correlations. Averaged heat transfer coefficients in this experiment range from $2kW/m^2/^{\circ}C$ to $3kW/m^2/^{\circ}C$. Most of the experimental results differ from the predicted ones by less than ${\pm}30%$.

• 한국안전학회지
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• 제16권3호
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• pp.35-40
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• 2001

An internal finishing process applying Magnetic Abrasive Finishing (MAF) was proposed to produce smooth inner surfaces of tubes at a high rate. Since this process uses the tube rotation system, it has been considered applicable only to tubes which are rotatable at high speeds. Here development of the stainless tube(STS 304) rotation system to extend the scope of the application of the internal finishing process applying MAF was made. By the stainless tube(STS 304) rotation system, the abrasive magnetically attracted by the poles is rotated along the inner surface of the tube by magnetic force together with fixed poles, finishing the inner surface of the tube. The main results obtained are as follows : 1) The magnet abrasive finishing minimized influence due to external force because non-contact finishing, 2) The profile of surface roughness decreased very good in 11.4m/min range because abrasive size and speed, 3) The profile of surface roughness by flux density decreased in finishing speed 28m/min, 4) The profile of surface roughness by fled rate decreased in 0.16mm/rev and 0.18mm/rev.

• International Journal of Air-Conditioning and Refrigeration
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• 제17권4호
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• pp.129-134
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• 2009

The objectives of this paper are to study the effects of thermal and geometric conditions on the performance of indoor heat exchangers with R-410A for Gas Engine Driven Heat Pump (GHP) application and to find the optimum design conditions of indoor heat exchangers by parametric analysis for the key parameters. The key parameters are number of tube row, number of tube pipe, fin pitch and transverse tube pitch. In the air side, moisture out of the humid air condenses on the fin surface while the refrigerant (R-410A) boils inside the smooth tube. Therefore this study uses Log Mean Enthalpy Difference (LMHD) method to analyze the heat transfer from the humid air to the refrigerant. This study determines the heat exchanger size, air side/refrigerant side pressure drop and overall heat transfer coefficient. Optimum design conditions for the key parameters are also determined by the parametric analysis. The results show that number of rows and pipes, fin pitch have significant effect on the heat exchanger size. It is also found that the tube length of the louver fin is $17{\sim}30%$ shorter than that of the plate fin.

• 한국산학기술학회논문지
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• 제17권3호
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• pp.716-723
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• 2016

전열 촉진관은 흡수식 냉동기에 널리 사용되고 있다. 본 연구에서는 흡수식 냉동기의 재생기에 주로 사용되는 평활관, 리브 튜브, 코류게이트 튜브, 플로랄 튜브에 대하여 관 내측 열전달계수 및 마찰계수를 측정하였다. 실험 결과 열전달계수 및 마찰계수는 코류게이트 튜브에서 가장 크게 나타나고 다음으로 리브 튜브에서 크게 나타났다. 한편 플로랄 튜브의 열전달계수 및 마찰계수는 평활관 값과 4% 내에서 일치하였다. 이로부터 플로랄 튜브의 열전달 및 압력손실 특성이 수력직경으로 적절히 표현될 수 있음을 알 수 있다. 실험 데이터로부터 코류게이트 튜브와 리브 튜브의 B(e+)와 g(e+) 상관식을 구하였는데 코류게이트 튜브의 B(e+)와 g(e+)는 기존 상관식의 예측치와 20% 내에서 일치하였다. 본 연구 결과는 고온 영역에서 재생기용 전열촉진관의 관 내측 열전달 계수 및 마찰계수 산정에 활용될 수 있을 것이다.

• 한국초전도저온공학회:학술대회논문집
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• 한국초전도저온공학회 2001년도 학술대회 논문집
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• pp.25-28
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• 2001

Bi-2212 HTS tube was fabricated by centrifugal forming process(CFP). As a variation of melt casting process(MCP) or centrifugal casting technique, the centrifugal forming process is a flexible method for manufacturing Bi-2212 bulk tubes and has been optimized to achieve smooth surface and uniform thickness. At this process, the slurry was prepared in the mixing ratio of 10:1 between Bi-2212 powder and binder and initially charged into the rotating mold under the speed of 300~450 rpm Heat-treatment was performed at the temperature ranges of 860 ~ $890^{\circ}C$ in air for partial melting. The HTS tube fabricated by centrifugal forming process at $890^{\circ}C$ under the rotating speed of 450 rpm was highly densified and the plate-like grains with more than 20$\mu$m were well oriented along the rotating axis. The measured Tc and Jc at 10K were around 85K and 3,000A/cm2 respectively.