• 설비공학논문집
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• 제22권5호
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• pp.322-327
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• 2010

It is a critical task to keep the ventilation system working in a proper and efficient manner in large multi-storey buildings, and the enthalpy exchanger is becoming an increasingly important part of the ventilation system by playing the function of channeling heat and moisture. We present a computational study on the heat transfer performance of the cross-flow enthalpy exchanger, which is in large use for residential buildings. The ducts are considered whose cross-sectional shapes resemble triangle and longitudinal centerline a cosine wave. It is shown that, as the cross-sectional shape departs from triangle, the heat transfer performance of the duct tends to deteriorate. Also, applying the wave-like shape to the longitudinal centerline of the duct increases the rate of heat transfer and the applied pressure-gradient at the same time. The origin of the performance variations in the cases considered are quantitatively analyzed and discussed.

• 동력기계공학회지
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• 제12권5호
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• pp.48-53
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• 2008

Heat exchangers are commonly used in practice in a wide range of application, from heating and air-conditioning system in a household, to chemical processing and power production in a large plant. Heat transfer in a heat exchanger usually involves convection in each fluid and conduction through the wall separating the two fluids. The heat transfer characteristics of tube banks of in-line arrangements of four circular cylinders in a cross flow are compared for a range of tube locations and Reynolds numbers. The in-line pitch ratio was set up in the range of $1.5\leq L/d\leq4.0$, where L is the center to center distance and d the circular cylinder diameter, and in the Reynolds number of $13,000\leq Re\leq50,000$. The local and mean Nusselt numbers were estimated, and then. Subsequently, the heat transfer characteristics of four circular cylinders were found to exhibit a strong dependency upon the cylinder spacing and separation point of their upstream cylinders.

• 대한기계학회논문집
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• 제16권5호
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• pp.983-991
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• 1992

본 연구에서는 정사각형 밀폐공간에서 밑면과 윗면이 각각 고온과 저온부이고 좌측, 우측면일부가 단열이며 우측면 일부는 저온부인 온돌공간으로 가정하였다. 일 사에너지가 우측면 저온부(창)으로 통과된 경우와 통과되지 않는 경우의 표면복사와 자연대류에 관하여 연구하였다.그리고 창에서 일사 에너지가 존재하는 표면복사의 경우는 표면복사와 구별하기 위하여 일사복사로 취급하였다. 표면복사 열전달을 해 석하기 위해서는 Hottel에 의해 고안된후 보안 발전된 정미복사방법(net radiation method)을 이용하여 벽면에서의 정미 복사량을 구하였으며 형상계수(shape factor)를 구하기 위하여 교차선방법(crossed string method)을 이용하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.154-161
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• 2000

As a mass flow controller is widely used in many manufacturing processes for controlling a mass flow rate of gas with accuracy of 1%, several investigators have tried to describe the heat transfer phenomena in a sensor tube of an MFC. They suggested a few analytic solutions and numerical models based on simple assumptions, which are physically unrealistic. In the present work, the heat transfer phenomena in the sensor tube of the MFC are studied by using both experimental and numerical methods. The numerical model is introduced to estimate the temperature profile in the sensor tube as well as in the gas stream. In the numerical model, the conjugate heat transfer problem comprising the tube wall and the gas stream is analyzed to fully understand the heat transfer interaction between the sensor tube and the fluid stream using a single domain approach. This numerical model is further verified by experimental investigation. In order to describe the transport of heat energy in both the flow region and the sensor tube, the Nusselt number at the interface between the tube wall and the gas stream as well as heatlines is presented from the numerical solution.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.311-315
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• 2000

A numerical investigation is made of time-dependent buoyant convection in a square of a non-Boussinesq fluid. The density-temperature$({\rho}-T)$ relation is modeled by a quadratic function, with the maximum density ${\rho}_M$ at temperature $T_M$. The horizontal walls of the square are insulated, and a pulsating temperature $T_H=T_M+{\Delta}T'\;sin({\omega}{\tau})$ is imposed on the hot vertical sidewall. The temperature at the cold wall $T_c$ is constant. Extensive numerical solutions to the governing Navier-Stokes equations are portrayed. Resonance is identified by monitoring the amplitude of the mid-plane Nusselt number, $A(Nu^*)$. The primary resonance frequency is found by matching ${\omega}$ to the nondimensional basic mode $N_1$ of internal gravity oscillations. Due to the quadratic$({\rho}-T)$ relationship, the effective pulsation frequency for density, $2{\omega}$, is meaningful, which brings forth the secondary resonance frequency, i.e., $2{\omega}=N_1$

• 한국정밀공학회지
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• 제32권2호
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• pp.219-227
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• 2015

A dehumidifier using a thermoelement has many advantages compare to a dehumidifier using compressor systems. However, it is crucial to optimize the performance of heat sink for improving heat dissipation problem on the heat generation part. In this study, we utilized computational fluid dynamics software to compare Nusselt number, temperature and system efficiency based on fin thickness, flow gap between fin and fin length. Moreover, slip flow on the boundary layer was applied for the further analysis. Our objective in this study is to suggest an optimal fin shape to improve heat transfer with the tendency of performance factor depending on change of the shapes. Our results on the optimization of fin shape and analysis of slip flow will be utilized to enhance the heat transfer in the heat sink which is important in the design of dehumidifier using a thermoelement.

• 한국가시화정보학회지
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• 제8권1호
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• pp.53-60
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• 2010

Experimental investigations were conducted to study the characteristics of turbulent swirling flow in an axisymmetric annuli. Swirl angle measurements were performed using a flow visualization technique using smoke and dye liquid for Re=60,00080,000. Using the two-dimensional particle image velocimetry method, we found the time-mean velocity distribution and turbulent intensities in water with swirl for Re=20,000, 30,000, and 40,000 along longitudinal sections. Neutral points occurred for equal axial velocity at y/(R-r)=0.70.75, and the highest axial velocity was recorded near y/(R-r)=0.9. Negative axial velocity was observed near the convex tube along X/(D-d)=3~23. Another experimental study was performed to investigate heat transfer characteristics of turbulent swirling flow in an axisymmetric annuli. Static pressure, and local flow temperature were measured using tangential inlet condition and the friction factors and Nusselt number were calculated for several Reynolds numbers.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2001년도 춘계학술대회 논문집 전기기기 및 에너지변환시스템부문
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• pp.113-115
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• 2001

In order to design the power appratus such ac bus bar, the current carrying ampacity should be determined, Since it is limited by maxium operating temperature, it is very important to predict temperature-rise on it. The main causes to raise temperature are joule's loss in the current carrying conductor and induced circulating and eddy current in the tank. The heat transfer is divided into convection and radiation on boundary, determining convection heat transfer coefficient is not easy. This paper propose a new technique that can be used to estimate the temperature rise in the extra high voltage bus bar. The heat transfer coefficient is analytically calculated by applying Nusselt Number depending on temperature as well as model geometry. The analytic method which use heat transfer coefficient is coupled with finite element method. The temperature distribution in the bus bar by the proposed method shows good agreement with experimental data.

• 설비공학논문집
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• 제17권4호
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• pp.318-324
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• 2005

The objectives of this paper are to study the heat transfer characteristics on enhanced surfaces, to develop experimental correlations of friction factor and Nusselt number, and to provide a guideline for optimum operation conditions at low temperature boiling for practical refrigeration applications. The working fluid (water, EG $30\%$) flows inside the enhanced tube and R134a boils on the outer surface. Two different types of Turbo-B tubes (Tube I and Tube II) are tested in the present study. The results show that Tube I gives a higher heat transfer coefficient with higher friction factor than Tube II. The present study provided experimental correlations for friction factor and heat transfer coefficient with error bands of ${\pm}5\%\;and\;{\pm}\;15\%$, respectively.

• 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.