• 대한기계학회논문집B
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• 제33권6호
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• pp.427-434
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• 2009

A new surface shape of an internal cooling passage which largely reduces the pressure drop and enhances the surface heat transfer is proposed in the present study. The surface shape of the cooling passage is consisted of the concave dimple and the riblet inside the dimple which is protruded along the stream-wise direction. Direct Numerical Simulation (DNS) for the fully developed turbulent flow and thermal fields in the cooling passage is conducted. The numerical simulations for five different surface shapes are conducted at the Reynolds number of 2800 based on the mean bulk velocity and channel height and Prandtl number of 0.71. The driving pressure gradient is adjusted to keep a constant mass flow rate in the x direction. The thermoaerodynamic performance for five different cases used in the present study was assessed in terms of the drag, Nusselt number, Fanning friction factor, volume and area goodness factor in the cooling passage. The value of maximum ratio of drag reduction is -22.86 %, and the value of maximum ratio of Nusselt number augmentation is 7.05% when the riblet angle is $60^{\circ}$. The remarkable point is that the ratio of Nusselt number augmentation has the positive value for the surface shapes which have over $45^{\circ}$ of the riblet angle. The maximum volume and area goodness factors are obtained when the riblet angle is $60^{\circ}$.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.2465-2470
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• 2008

A new surface shape of an internal cooling passage which largely reduces the pressure drop and enhances the surface heat transfer is proposed in the present study. The surface shape of the cooling passage is consisted of the concave dimple and the riblet inside the dimple which is protruded along the stream-wise direction. Direct Numerical Simulation (DNS) for the fully developed turbulent flow and thermal fields in the cooling passage is conducted. The Numerical simulations for the 5 different surface shapes are conducted at the Reynolds number of 2800 based on the mean bulk velocity and channel height and Prandtl number of 0.71. The driving pressure gradient is adjusted to keep a constant mass flow rate in the x direction. The thermo-aerodynamic performance for the 5 different cases used in the present study was assessed in terms of the drag, Nusselt number, Fanning friction factor, Volume and Area goodness factor in the cooling passage. The value of maximum ratio of drag reduction is -22.86 [%], and the value of maximum ratio of Nusselt number augmentation is 7.05 [%] when the riblet angle is $60^{\circ}$ (Case5). The remarkable point is that the ratio of Nusselt number augmentation has the positive value for the surface shapes which have over $45^{\circ}$ of the riblet angle. The maximum Volume and Area goodness factor are obtained when the riblet angle is $60^{\circ}$ (Case5).

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2004년도 학술대회지
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• pp.99-107
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• 2004

Lubrication characteristics between a cylinder block and a valve plate for high speed bent-axis type hydraulic pump play an important role in volumetric efficiency and durability of pump. In this paper, a finite element method is presented for the computation of the pressure distribution between a cylinder block and a valve plate for high speed bent-axis type hydraulic pump. Also, a Runge-Kutta method is applied to simulate the cylinder block dynamics of three-degrees of freedom motion. From the results of computation, we can draw two major conclusions. One is related to the fluid film characteristics between a cylinder block and a valve plate and the other is related to the average leakage that is determined by the pressure gradient and the clearance near the discharge port. The numerical results of cylinder block dynamics were compared with the experimental results using eddy-current type gap sensors those are fixed at a pump housing.

• 에너지공학
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• 제18권2호
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• pp.108-113
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• 2009

균일한 열유속을 갖는 가열된 평판에 부착된 발포 알루미늄에 대한 충돌제트의 열유동 특성에 대한 실험적 연구가 수행되었다. 열전달 특성에 대한 기공도, 다공성 물질의 두께, Reynolds 수의 영향이 고찰되었다. 실험결과 가열평판에 부착된 발포 알루미늄에 의해 열전달의 증가를 얻을 수 있었고 다공성 물질의 삽입에 의한 열전달 증가는 열전달 표면적의 증가와 압력 손실에 의한 운동량 감소에 의해 영향을 받는 것을 확인하였다.

• 한국압력기기공학회 논문집
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• 제19권2호
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• pp.109-116
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• 2023

This study presents a CRUD modelling to simulate the thermal resistance behavior of CRUD, deposited on the surface of a cladding tube of a fuel assembly. When heat produced from fuels transfers to a coolant through a cladding tube, the CRUD acting as an additional thermal resistance is expressed as two layers, i.e., a solid oxide layer and an imaginary fluid layer, which are added to the experimental tube's heat structure of the MARS-KS input data. The validation calculation for the experiments performed in UNIST-DISNY facility showed that the center and surface temperatures of the cladding tube increased as the porosity and the steam amount inside pores of the CRUD got higher. In addition, the temperature gradient in the imaginary fluid layer was calculated to be larger than that in the solid oxide part, indicating that the steam amount inside the layer acted more largely as thermal resistance. It was also evaluated through sensitivity calculations that the cladding tube temperature was more sensitive to the CRUD porosity and the steam amount in pores than to the inlet flow rate of the coolant.

• 한국분무공학회지
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• 제26권1호
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• pp.1-8
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• 2021

Droplet evaporation has been known as a common phenomenon in daily life, and it has been widely used for many applications. In particular, the influence of the different heated substrates on evaporation flux and flow characteristics is essential in understanding heat and mass transfer of evaporating droplets. This study aims to simulate the droplet evaporation process by considering variation of thermal property depending on the substrates and the surface temperature. The commercial program of ANSYS Fluent (V.17.2) is used for simulating the conjugated heat transfer in the solid-liquid-vapor domains. Moreover, we adopt the diffusion-limited model to predict the evaporation flux on the different heated substrates. It is found that the evaporation rate significantly changes with the increase in substrate temperature. The evaporation rate substantially varies with different substrates because of variation of thermal property. Also, the droplet evaporates more rapidly as the surface temperature increases owing to an increase in saturation vapor pressure as well as the free convection effect caused by the density gradient.

• 한국항공우주학회지
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• 제37권1호
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• pp.69-75
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• 2009

본 논문은 새로운 개념의 초음속 혼합기인 벤트 혼합기의 형상적 특성에 따른 공력 특성을 연구하였다. 홀의 크기는 2 mm이며 혼합기 벽면에서 2 mm 떨어진 곳에 위치한 모델(case 1)과 혼합기 벽면 뒤쪽에 위치한 모델(case 2)의 경우 같은 전압력 회복율을 보였으며, 홀의 크기를 반으로 줄인 1 mm(case 3) 모델은 cases 1, 2에 비해 낮은 전압력 회복율을 보였다. 재순환 영역의 크기는 cases 1-3은 같지만 전단층 두께는 cases 1, 2가 case 3 보다 두꺼웠다. 재순환 영역 내 압력 손실의 경우 cases 1, 2은 case 3에 비해 낮은 압력 손실과 높은 속도 구배를 보였으며, 이는 재순환 영역 내 공기와 연료의 혼합을 증대시키는 요인이다. 재순환 영역 내로 유입 되는 유동에 의해 형성되는 박리 버블은 연소기의 전압력 회복율과 재순환 영역 내 압력 분포와 순환 유동에 영향을 미친다. 따라서 박리 버블 형성에 영향을 주는 유입 공기 유량이 벤트 혼합기 성능에 주요한 영향을 미치는 것을 알 수 있다.

• 한국결정성장학회지
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• 제19권1호
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• pp.39-47
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• 2009

The effects of thermo-solutal convection on mercurous chloride system of ${Hg_2}{Cl_2}$, and Ne during physical vapor transport are numerically investigated for further understanding and insight into essence of transport phenomena, For $10\;K{\le}{\Delta}T{\le}30\;K$, the growth rate slowly increases and, then is decreased gradually until ${\Delta}T$=50 K, The occurrence of this critical point near at ${\Delta}T$=30 K is likely to be due to the effects of thermo-physical properties stronger than the temperature gradient corresponding to driving force for thermal convection. For the range of $10\;Torr{\le}P_B{\le}300\;Torr$, the rate is second order-exponentially decayed with partial pressures of component B, $P_B$. For the range of $5{\le}M_B{\le}200$, the rate is second order-exponentially decayed with a function of molecular weight of component B, $M_B$. Like the case of a partial pressure of component B, the effects of a molecular weight arc: reflected through the binary diffusivity coefficients, which are intimately related with suppressing the convection flow inside the growth enclosure, i,e., transition from convection to diffusion-dominant flow mode as the molecular weight of B increases. The convective mode is near at a ground level, i,e., on earth (1 $g_0$), and the convection is switched to the diffusion mode for $0.1\;g_0{\le}g{\le}10^{-2}g_0$, whereas the diffusion region ranges from $10^{-2}g_0$ up to $10^{-5}g_0$.

• 한국수자원학회논문집
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• 제53권8호
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• pp.617-626
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• 2020

본 연구에서는 TELEMAC-2D를 이용하여 개수로 분류부에서 분류각과 분류유량비 변화에 따른 유속분포, 흐름분리구역의 크기, 분류각과 유량비 변화의 상관관계를 파악하였다. 상·하류단 경계조건의 변화 없이 분류각만 90°에서 45°로 감소하면 주흐름에서 분리되어 분류수로로 유입되는 흐름의 곡률반경이 증가하고 급격한 흐름방향의 전환에 의한 에너지손실은 감소하며, 주수로와 분류수로 하류방향으로 흐르는 흐름의 관성력과 하류단 경계조건에 의한 압력경사의 영향으로 분류수로에 유입되는 분류유량비가 0.523에서 0.785로 약 1.5배 증가하였다. 분류부 상류 유입흐름의 프루우드 수가 F₁ = 0.45~0.74인 흐름에서 분류각을 90°에서 45°로 15° 간격으로 감소할 때마다 분류유량비는 각각 6~10%, 17~30%, 32~54%로 비선형적으로 증가하며, F₁가 최대 0.74인 흐름에서 분류유량비 증가율이 31.1%로 최소값을 나타내고 F₁ = 0.58 일 때 분류유량비가 0.7 이하이면서 최대 분류유량비 증가율 53.5%을 나타내며, F₁이 0.58보다 감소할수록 분류유량비가 0.7을 초과하면서 그 증가율도 함께 감소하게 된다. F₁ > 0.4인 흐름은 F₁ < 0.4의 흐름보다 무차원 흐름분리구역의 폭(S_W/B) 변화율은 약 2.56배 높으며 무차원 흐름분리구역 길이(S_L/B) 변화율은 약 5.5배 높게 나타난다.

• 한국유체기계학회 논문집
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• 제10권6호
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• pp.7-16
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• 2007

An axial-type fan which operates at the relative total pressure of 671Pa and static pressure of 560Pa with the flow rate of $416.6m^3/min$ is developed with an optimization technique based on the gradient method. Prior to the optimization of fan blade, a three-dimensional axial-type fan blade is designed based on the free-vortex method along the radial direction. Twelve design variables are applied to the optimization of the rotor blade, and one design variable is selected for optimizing a stator which is located behind of the rotor and is used to support a fan driving motor. The total and static pressure are applied to the restriction condition with the operating flowrate on the design point, and the efficiency is chosen as the response variable to be maximized. Through these procedures, an initial axial-fan blade designed by the free vortex method is modified to increase the efficiency with the satisfaction of the operating condition. The optimized fan is tested to compare the aerodynamic performance with an imported same class fan. The test result shows that the optimized fan operates with the satisfaction of restriction conditions, but the imported fan cannot. From the experimental and numerical test, they show that this optimization method improves the fan efficiency and operating pressures of a fan designed by the classical fan design method.