• 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.

• Journal of Advanced Marine Engineering and Technology
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• 제28권1호
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• pp.65-74
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• 2004

The heat transfer coefficient and pressure drop of $CO_2$(R-744) during gas cooling Process of carbon dioxide in a horizontal tube were investigated experimentally and theoretically. The experiments were conducted without oil in the refrigerant loop. The main components of the refrigerant loop consist of 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 constant temperature bath. 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 9.53 mm outer diameter and 7.75 mm inner diameter. The length of test section is 6 m. The refrigerant mass fluxes were 200 ~ 300 kg/($m^2{\cdot}s$) and the inlet pressure of the gas cooler varied from 7.5 MPa to 8.5 MPa. The main results were summarized as follows : The predicted correlation can evaluated the R-744 exit temperature from the gas cooler within ${\pm}10%$ for most of the experimental data, given only the inlet conditions. The predicted gas cooley capacity using log mean temperature difference showed relatively food agreement with gas cooler capacity within ${\pm}5%$. The pressure drop predicted by Blasius estimated the pressure drop on the $CO_2$ side within ${\pm}4.3%$. The predicted heat transfer coefficients using Gnielinski's correlation evaluated the heat transfer coefficients on the $CO_2$ side well within the range of experimental error. The predicted heat transfer coefficients using Gao and Honda's correlation estimated the heat transfer coefficients on the coolant side well within ${\pm}10\;%$. Therefore. The predicted equation's usefulness is demonstrated by analyzing data obtained in experiments.

• 소성∙가공
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• 제20권7호
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• pp.473-478
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• 2011

In this study, the performance of a thermo siphon type radiator made of copper for LED lighting system was evaluated by using an inverse heat transfer method. Heating experiments and finite element heat transfer analysis were conducted for three different cases. The data obtained from experiments were compared with the analysis results. Based on the data obtained from experiments, the inverse heat transfer method was used in order to evaluate the heat transfer coefficient. First, the heat transfer analysis was conducted for non-vacuum state, without the refrigerant. The evaluated heat transfer coefficient on the radiator surface was 40W/$m^2^{\circ}C$. Second, the heat transfer analysis was conducted for non-vacuum state, with the refrigerant, resulting in the heat transfer coefficient of 95W/$m^2^{\circ}C$. Third, the heat transfer analysis was conducted for vacuum state, with refrigerant. For the third case, the evaluated heat transfer coefficients were 140W/$m^2^{\circ}C$. Third, the heat transfer analysis was conducted for vacuum state, with refrigerant. For the third case, the evaluated heat transfer coefficients were 140W/$m^2^{\circ}C$ for the radiator body, 5W/$m^2^{\circ}C$. Third, the heat transfer analysis was conducted for vacuum state, with refrigerant for the rising position of radiator pipe, 35W/$m^2^{\circ}C$. Third, the heat transfer analysis was conducted for vacuum state, with refrigerant. For the highest position of radiator pipe, and 120W/$m^2^{\circ}C$ for the downturn position of radiator pipe. As a result of inverse heat transfer analysis, it was confirmed that the thermal performance of the current radiator was best in the case of the vacuum state using the refrigerant.

• 한국유체기계학회 논문집
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• 제3권2호
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• pp.24-30
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• 2000

The structural analysis of a reactor coolant pump(RCP) of a nuclear power plant is very important for the safety assessment of the plant. Accurate boundary conditions for the heat transfer coefficient are required for reliable thermal stress analysis of the pump casing, especially in transient operations of the pump since the coolant properties are largely dependent on operational conditions. In the present study, a 3D mixed flow type coolant pump was modeled from the RCP drawings and analyzed in the steady state and number of transient flow conditions by using a commercial code STAR-CD. From the result of the computation, it is seen that the average heat transfer coefficients for the cases considered are found to be the suggested values of the manufacturer, Westinghouse Energy System. The unevenness in local heat transfer coefficients, however, is found to be considerable so that the use of average heat transfer coefficients in all boundaries might not give reliable thermal stress predictions.

• 대한기계학회논문집B
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• 제25권2호
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• pp.164-170
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• 2001

The influence of unsteady wake on the flow and heat transfer characteristics in a four-vane linear cascade was experimentally investigated. The unsteady wake was generated with four rotating rectangular plates located upstream of the cascade. Tested inlet Reynolds number based on chord length was set to 66,000 by controlling free-stream velocity. A hot-wire anemometer system was employed to measure turbulent velocity components. For the convective heat transfer coefficients measurement on turbine blade surface, thermochromic liquid crystal and gold film Intrex were used. It was found that the unsteady wake enhances the turbulent motion in the cascade passage and accordingly promotes the development and transition of boundary layer. It was found that the heat transfer coefficients on the blade surface increase as the plate rotating speed increases. However, the increasing of heat transfer coefficients is not significant in the case that Strouhal number is higher than 0.503.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2005년도 연구개발 발표회 논문집
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• pp.459-466
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• 2005

The present study investigates the heat transfer characteristics of a triangular channel. Three different rib configurations are tested. The ribs are installed on two sides of the channel. The rib height (e) to channel hydraulic diameter is 0.079 and the rib-to-rib pitch (p) is 8 times of the rib height. The rotation number ranges from 0.0 to 0.1 while the Reynolds number is fixed at 10,000. The copper blocks with heaters are installed on the channel walls to measure the regionally averaged heat transfer coefficients. For the stationary $45^{\circ}$ and $135^{\circ}$ ribbed channels, a pair of counter rotating vortices is induced by the angled rib arrangements, and high heat transfer coefficients are obtained on the regions near the inner wall for the $45^{\circ}$ ribbed channel and near the leading edge for the $90^{\circ}$ ribbed channel. The heat transfer coefficients of angled ribbed channels are changed little with rotation, whereas those of the transverse ribbed channel are changed significantly with rotation.

• Journal of Advanced Marine Engineering and Technology
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• 제28권1호
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• pp.29-38
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• 2004

The Condensation heat transfer coefficients of R-22 and R-l34a were measured in smooth horizontal copper tubes with inner diameters of 1.77. 3.36 and 5.35 mm. respectively. The experiments were conducted in a closed loop. which was driven by a magnetic gear pump. They were Performed for the following ranges of variables: mass flux (200 to $500\;kg/\textrm{m}^2{\cdot}s$) saturation temperature $30^{\circ}C$ and quality (0 to 1.0). The main results obtained are as follows Condensation heat transfer coefficients in the small diameter tubes (ID < 7 mm) were observed to be strongly affected by inner diameter change and to differ from those in the large diameter tubes. The heat transfer coefficients in the small diameter tubes were 20 ~ 40 % higher than those in the large diameter tubes as the inner diameter of the tube was reduced. Also. it was very difficult to apply some well-known previous predictions (Cavallini-Zecchin's. Haraguchi's and Dobson's correlation) to small diameter tubes. Based on an analogy between heat and mass transfer the new correlation is Proposed to predict the experimental data more accurately.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집D
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• pp.765-770
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• 2001

The objective of the present study is to investigate the effects of the various inlet boundary layer thickness on convective heat transfer distribution in a turbine cascade endwall and blade suction surface. In addition, the proper height of the boundary layer fences for various inlet boundary layer thickness were applied to turbine cascade endwall in order to reduce the secondary flow, and to verify its influence on the heat transfer process within the turbine cascade. Convective heat transfer distributions on the experimental regions were measured by the image processing system. The results show that heat transfer coefficients on the blade suction surface were increased with an augmentation of inlet boundary layer thickness. However, in a turbine cascade endwall, magnitude of heat transfer coefficients did not change with variation of inlet boundary layer thickness. The results also present that the boundary layer fence is effective in reducing heat transfer on the suction surface. On the other hand, in the endwall region, boundary layer fence brought about the subsidiary heat transfer increment.

• 한국유체기계학회 논문집
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• 제10권3호
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• pp.25-32
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• 2007

The present paper deals with the heat/mass transfer characteristics for the rotating impingement/effusion cooling system. By changing the size and number of injection hole, its effects on heat/mass transfer are investigated and three different injection hole cases are considered such as LH, DH and SH, respectively. Reynolds number based on the effusion hole diameter is fixed to 3,330 and two jet orientations are considered. A naphthalene sublimation method is used to obtain the heat/mass transfer coefficients on the effusion plate. The LH case shows that the local heat/mass transfer is significantly varied by the rotation. Moreover, the low and non-uniform Sh distributions occur because the impinging jet is deflected by Coriolis force. Meanwhile, for DH and SH cases, the local heat/mass transfer coefficients are enhanced significantly compared to LH case and the rotation effect decreases with increasing the jet velocity. The averaged Sh value of DH and SH case rises up to 45%, 85% than that of LH case. However, the uniformity of heat/mass transfer deteriorates due to the steep variation of heat/mass transfer.

• Journal of Advanced Marine Engineering and Technology
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• 제28권4호
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• pp.593-602
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• 2004

This paper is a study on the model of simultaneous heat and mass transfer process in the absorption of refrigerant vapor into a lithium bromide solution of water-cooled vertical plate absorber. The model can predict temperature and concentration profiles as well as the effect of Reynolds number on them. Also. the variations of the absorption heat and mass fluxes. and the heat and mass transfer coefficients have been investigated. The numerical result shows that the interface temperature and concentration decrease as film Reynolds number does. The absorption heat and mass fluxes, and the heat and mass transfer coefficients get their maximum values adjacent to the inlet solution. Analyses on a constant wall temperature condition have been also carried out to exam the reliability of the present numerical method by comparing to previous investigations.