• 설비공학논문집
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• 제26권11호
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• pp.522-528
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• 2014

This experimental study measured and analyzed the heat transfer and pressure drop performance of brazed plate heat exchangers. Heat exchangers with different plate numbers of 10, 20, 30, and 40 were used for measurement, and their plate pattern was identical. The experiment was performed with distilled water, by changing the hot-side flow rate, with the cold-side flow rate fixed. The experimental results were compared with the calculated values by correlations based on gasketed plate heat exchangers, and showed that the heat transfer performance and pressure drop of brazed plated heat exchangers were higher than those of gasketed plate heat exchangers. From the variation of the friction factor, it could be inferred that in the flow channels of brazed plate heat exchangers, turbulent flow occurred at Reynolds numbers higher than 500. A new correlation to predict the Nusselt number was developed, and its absolute average deviation was 2.62%, compared with the values from the experimental data.

• 에너지공학
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• 제24권2호
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• pp.103-109
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• 2015

배열회수 보일러는 입구 확관 덕트와 전열관군으로 이루어져 있는데 전열관군에서 열전달 효율을 향상하기 위해서는 전열관군 전에서 배기가스 유동이 균일하게 되어야 한다. 본 연구에서는 전열관군 전의 배열회수 보일러 입구 덕트에서 유동 특성을 살펴보았고 전열관군의 열전달 메커니즘을 지금까지 다른 연구들에서 적용하였던 일정한 열전달 량으로 한 경우와 전열관군 배관의 내부와 외부의 대류열전달을 고려한 열전달 메커니즘을 적용한 경우의 해석에서 온도 분포를 비교하여 배열회수 보일러의 전열관군에서 실제 현상에 보다 적합한 열전달 메커니즘을 정립하는 것을 목적으로 하였다. 본 연구를 통하여 전열관군 배관의 내부와 외부의 대류열전달을 고려한 열전달 메커니즘을 적용한 해석이 일정한 열전달 량을 적용한 경우보다 온도 분포가 타당한 결과를 도출하였고 이렇게 적용한 경우는 배열회수 보일러 탈질설비 전단에서 온도 분포가 설계 기준 ${\pm}10^{\circ}C$에 만족함을 알 수 있었다.

• 한국자동차공학회논문집
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• 제4권1호
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• pp.187-197
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• 1996

Many investigations have been made to determine the pressure drop and heat transfer characteristics for single phase flow in tape generated swirl flow. But few studies have been carried out to investigate the heat transfer in two component, two phase swirl flow with non-boiling. An experimental study has been conducted to determine the effects of tape twist ratios on two phase convective heat transfer coefficients, pressure drop, and void fraction distribution in a non-boiling, air-water, two phase flow. The flow conditions were both swirl and non swirl flows. The internal diameter of the test section is 42.5mm. The tape twist ratios of pitch to diameter ratio varied from 4.0 to 10.6. The heating conditions were isothermal and nonisothermal. The flow patterns identified with experiments were bubbly, bubbly-slug, slug, and slug-annular flow in up-flow. This study has concluded that no significant difference in void fraction distribution were observed both isothermal and nonisothermal conditions, the pressure drop for two phase flow with twisted tape swirler increase as the tape twist ratio decrease, and that values of two phase heat transfer coefficient increase when the tape twist ratio decreases.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2890-2895
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• 2007

Heat transfer on two identical nearby circular cylinders immersed in the uniform cross flow at Re = 100 and Pr = 7.0 was numerically studied. We consider all possible arrangements of the two circular cylinders in terms of the distance between the two cylinders and the inclination angle with respect to the direction of the main flow. It turns out that significant changes in the characteristics of heat transfer are noticed depending on how the two circular cylinders are positioned, resulting in quantitative changes of heat transfer coefficients on both cylinders. Collecting all the numerical results obtained, we propose a contour diagram for averaged Nusselt number for each of the two cylinders. The perfect geometrical symmetry implied in the flow configuration allows one to use those diagrams to estimate heat transfer rates on two identical circular cylinders arbitrarily positioned in physical space with respect to the main flow direction.

• 한국전산유체공학회지
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• 제13권2호
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• pp.42-47
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• 2008

Heat transfer on two identical nearby circular cylinders immersed in the uniform cross flow at Re=120 and Pr=0.7 was numerically studied. We consider all possible types of arrangements of the two circular cylinders in terms of the distance between the two cylinders and the inclination angle with respect to the direction of the main flow. It turns out that significant changes in the characteristics of heat transfer are noticed depending on how the two circular cylinders are positioned, resulting in quantitative changes of heat transfer coefficients on both cylinders. Collecting all the numerical results obtained, we propose a contour diagram for averaged Nusselt number for each of the two cylinders. The perfect geometrical symmetry implied in the flow configuration allows one to use those diagrams to estimate heat transfer rates on two identical circular cylinders arbitrarily positioned in physical space with respect to the main flow direction.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2009년도 하계학술발표대회 논문집
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• pp.1159-1165
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• 2009

In the present study, the flow and heat transfer characteristics of a large plate heat exchanger are investigated numerically. The flow passages are very complicated due to the grooved corrugation patterns of the plate surface so that the detailed mesh and the large amount of the computation time have to be required in the numerical simulation for the conjugate heat transfer analysis. In order to accomplish the efficient and fast analysis of the heat transfer characteristics in the plate heat exchanger, a semimicroscopic method using the porous media model has been investigated numerically. The results showed that the characteristics of the heat transfer and pressure drop, which are respectively presented with Colburn j-factor and Fanning f-factor, are in a good agreement between the detailed mesh and the porous media model. The results of the present study could be applicable to the numerical analysis of entire flow passages in the large plate heat exchanger using porous media treatment.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집D
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• pp.459-464
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• 2001

A mathematical model has been developed to describe the turbulent and reversed flow with convective heat transfer in a cylindrical combustion chamber. By using the mathematical model for high temperature flow enables the trends in overall heat transfer rates to be predicted. The model was applied to the design of the combustion chamber. The influences of the size of air inlet and inlet velocity were investigated for process optimization. Through modelling work it is found that the heat transfer rate to the chamber wall may be enhanced by adjusting the air flow and heat transfer pattern through selecting the air inlet condition. Internal plate has less influence to the heat transfer characteristics.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2006년도 하계학술발표대회 논문집
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• pp.150-155
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• 2006

Falling liquid plays a role in a wide variety of naturally occurring phenomena as well as in the operation of industrial process equipment where heat and mass transfer take place. In such cases, it is required that the falling film should spread widely on the surface forming thin liquid film to enlarge contact surface. An addition of surface active agent to a falling liquid film affects the flow characteristics of the falling film. In this study the heat transfer characteristics for a falling liquid film has been investigated by an addition of the surface active agents. The falling liquid film was formed on a vertical flat plate. As the mass flow rate of liquid falling film is increased, the wetted area is a little increased while the heat transfer rate as well as heat transfer coefficient is significantly increased. It is also found that both wetted area and heat transfer rate is substantially increased while heat transfer coefficient is a little increased with an increase in the surfactant concentration at a given mass flow rate.

• 대한기계학회논문집B
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• 제29권4호
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• pp.485-494
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• 2005

For the extensive investigation of local heat/mass transfer on the near-tip surface of turbine blade, experiments were conducted in a low speed stationary annular cascade. The turbine test section has a single stage composed of sixteen guide vanes and blades. The chord length and the height of the tested blade are 150 mm and about 125 mm, respectively. The blade has flat tip geometry and the mean tip clearance is about $2.5{\%}$ of the blade chord. Detailed mass transfer coefficient on the blade near-tip surface was obtained using a naphthalene sublimation technique. The inlet flow Reynolds number based on chord length and incoming flow velocity is changed from $1.0{\times}10^{5}\;to\;2.3{\times}10^{5}.$ Extremely complex heat transfer characteristics are observed on the blade surface due, to complicated flow patterns, such as flow acceleration, laminarization, transition, separation bubble and tip leakage flow. Especially, the suction side surface of the blade has higher heat/mass transfer coefficients and more complex distribution than the pressure side surface, which is related to the leakage flow. For all the tested Reynolds numbers, the heat/mass transfer characteristics on the turbine blade are the similar. The overall averaged $Sh_{c}$ values are proportional to $Re_{c}^{0.5}$ on the stagnation region and the laminar flow region such as the pressure side surface. However, since the flow is fully turbulent in the near-tip region, the heat/mass transfer coefficients are proportional to $Re_{c}^{0.8}.$

• 한국태양에너지학회 논문집
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• 제26권4호
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• pp.93-100
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• 2006

An experimental study of a counterflow heat exchanger was performed. The heat exchanger had an effective heat transfer length of 1000mm and was operated in a counterflow arrangement with hot water($30{\pm}0.5^{\circ}C$, $Re_i=3500{\sim}20000$) in the inner tube(copper tube, $d_0=9.52mm$) and cold water($15{\pm}0.5^{\circ}C$, $Re_{DH}=10700{\sim}39000$) in the annulus(copper tube, $D_0=19.05mm$). Overall heat transfer coefficients were calculated and heat transfer coefficients in the inner tube and the annulus were determined using Wilson plots. The inner Nusselt number was compared with that of Gnielinski's correlation and they agreed within ${\pm}10%$ error. The trends were typical for a fluid-to-fluid heat exchanger with the overall heat transfer coefficient increasing with both inner and annulus flow rates. In the range of this experiment, Nusselt numbers for the inner tube flow were almost identical with those of the annulus flow at the same Reynolds number.