• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.11
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• pp.915-924
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• 2014

In an aero gas-turbine engine, a surface air-oil heat exchanger (SAOHE) is used to cool the oil system for the gearboxes and electric generators. The SAOHE is installed inside the fan casing of the engine in order to dissipate the heat from the oil system into the bypass duct stream. The purpose of this study was to develop an effective numerical method for designing an SAOHE for an aero gas-turbine engine. A two-dimensional model using a porous medium was developed to evaluate the aero-thermal performance of the fins of the heat exchanger, and a one-dimensional flow and thermal network program was developed to save time and cost in the evaluation of the heat exchanger performance. Using this network program, the pressure drop and heat transfer performance of the heat exchanger were predicted, and the results were compared with two-dimensional computational fluid dynamics results and experiment data for validation.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.10
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• pp.229-235
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• 2019

A floating photovoltaic generation system is a new concept that combines existing photovoltaic generation technology with floating technology. This is installed in the water not on conventional land and a building. The system is designed as a unit module type that can be connected to other modules according to the power generation capacity, thereby forming a large-scale power generation facility. As a renewable energy source, it is composed of a floating structure, mooring device, photovoltaic power generation facility, and underwater cable. Because this system is installed outdoors, the effect of the wind load on the structure is very large. In this study, the wind loads most affected on the floating photovoltaic generation structure were obtained by computational fluid dynamic analysis. The flow characteristics and wind loads were analyzed for a range of wind orientations and angles of inclination. The analysis showed the position and magnitude of the maximum wind load to the wind direction and the flow characteristics around the solar panel and floating system. The wind load increased with increasing angle of inclination of the panel to the ground.

• Journal of Advanced Marine Engineering and Technology
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• v.34 no.1
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• pp.53-61
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• 2010

In the present study, a laminar natural convection flow of $H_2O$-Cu nanofluid in a two dimensional enclosure has been investigated using a thermal lattice Boltzmann approach with the Bhatnagar-Gross-Krook (BGK) model. The effect of suspended nanoparticles on the fluid flow and heat transfer process have been studied for different controlling parameters such as particle volume fraction ($\Phi$), Rayleigh number (Ra). For this investigation the Rayleigh number changes from 104 to 106 and volume fraction varied from 0 to 10% with three different particle diameters (dp), say 10 nm, 20 nm and 40 nm. It is shown that increasing the Rayleigh number (Ra) and the volume fraction of nanofluid causes an increase of the effective heat transfer rate in terms of average Nusselt number (Nu) as well as the thermal conductivity of nanofluid. On the other hand, increasing the particle diameter causes the decrease of the heat transfer rate and thermal conductivity. The result of the analysis are compared with experimental and numerical data both for pure and nanofluids and it is seen a relatively good agreement.

• Journal of Power System Engineering
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• v.9 no.2
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• pp.33-39
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• 2005

Experiments are performed to study the mixed convection flow and heat transfer in an inclined parallel plates with the upper part cooled and the lower part heated uniformly. The Reynolds number ranges from $4.0{\times}10^{-3}\;to\;6.2{\times}10^{-2}$, the angle of inclination, ${\theta}$, from 0 to 45 degree from the horizontal line, and Pr of the high viscosity fluid is 909. In this paper, the PIV(Particle image velocimetry) with TLC(Thermo-sensitive liquid crystal) tracers is used for visualizing and analysis. This method allows simultaneous measurement of velocity and temperature field at a given instant of time. Quantitative data of the temperature and velocity are obtained by applying the color-image processing to a visualized image, and neural network is applied to the color-to-temperature calibration. This paper describes the methods, and presents the quantitative visualization of mixed convection. From this study, it is found that the flow pattern can be classified into three patterns which are affected by Reynolds number and the angle of inclination.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.3 s.168
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• pp.46-51
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• 2005

The vacuum cleaner motor runs at very high speed for suction power. Specially, motor power is provided by the impeller being rotated at very high speed. The centrifugal fan consists of the impeller, the diffuser, and the circular casing. Due to the high rotating speed of the impeller and small gap distance between the impeller and the diffuser, the level of noise in the centrifugal fan is at BPF(Blade Passage Frequency) and its harmonic frequencies. In order to calculate the sound pressure of centrifugal fan, unsteady flow data are needed. The cause of noise is obtained by dividing the fluid noise by exhaust flow of fan and vibration noise by rotational vibration of vacuum cleaner fan motor. Until now, an accelerometer has been used to measure vibration. However, it can not measure vibration in some parts of brush and commutator because of motor construction and 3-D vibrating mode. This study was conducted to perform accurate analysis of vibration and aerodynamic sound for fan motor in a vacuum cleaner using a laser vibration analyzer. A silent fan motor can be designed using the data measured in this study.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.23 no.1
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• pp.1-7
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• 2011

The performance of louver-finned flat-tube and fin and tube radiators for computer CPU liquid cooling was experimentally investigated. In this study, 7 samples of radiators with different shape and pass number (1, 2, 10) were tested in a wind tunnel. The experiments were conducted under the different air velocity ranged from 1 to 4 m/s. The water flow rate through a pass was 1.2 LPM. Inlet temperatures of air and water were $20^{\circ}C$ and $30^{\circ}C$ respectively. It was found that the best performance was observed in the louver-finned flat-tube sample considering pressure drop and heat transfer coefficient.

• 한국전산유체공학회:학술대회논문집
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• 2008.03a
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• pp.131-136
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• 2008

Three-dimensional characteristics of fluid flow and heat transfer around a wavy circular cylinder having sinusoidal variation in cross sectional area along the spanwise direction are numerically investigated using the immersed boundary method. The three different wavelengths of ${\pi}/4$, ${\pi}/3$ and ${\pi}/2$ and at the fixed wavy amplitude of 0.1 have been considered to investigate the effects of waviness on especially the forced convection heat transfer around a wavy cylinder when the Reynolds and Prandtl numbers are 300 and 0.71, respectively. The present computational results for a wavy cylinder are compared with those for a smooth cylinder. The time- and total surface-averaged Nusselt number for a wavy cylinder with is larger than that for a smooth cylinder, whereas that with ${\lambda}={\pi}/4$ and ${\pi}/3$ is smaller than that for a smooth cylinder. However, because the surface area exposed to heat transfer for a wavy cylinder is larger than that for a smooth cylinder, the total heat transfer rate for a wavy cylinder with different wavelengths of ${\lambda}={\pi}/4$, ${\pi}/3$ and ${\pi}/2$ is larger than that for a smooth cylinder.

• Journal of Power System Engineering
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• v.18 no.5
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• pp.88-93
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• 2014

In this paper, the performance analysis of condensation and evaporation capacity, turbine work and efficiency of the OTEC power system using vapor-liquid Ejector is presented to offer the basic design data for the operating parameters of the system. The working fluid used in this system is $CO_2$. The operating parameters considered in this study include the vapor quality at heat exchanger outlet, pressure ratio of ejector and inlet pressure of low turbine, mass flow ratio of separator at condenser outlet. The main results were summarized as follows. The efficiency of the OTEC power cycle has an enormous effect on the mass flow ratio of separator at condenser outlet. With a thorough grasp of these effects, it is possible to design the OTEC power cycle proposed in this study.

• 한국전산유체공학회:학술대회논문집
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• 2011.05a
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• pp.488-493
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• 2011

The object of this study is to develope the program for analyzing the fluid flow and heat transfer of PMSM electric motor. The program will be mainly used for inexperienced users of CFD analysis. So it has to be performed using the geometry data and the heat source of each part only. Interface program for converting the given data to the instruction of pre-processor is developed. The conjugate heat transfer between a flow passage of the motor and inner parts consisting of rotor and stator is regarded. In order to reduce the computational time and memory storage, cyclic boundary condition is applied. For the numerical simulation, MRF(Multi-Reference Frame) method is used to consider rotating operation of the rotor and heat source is applied to the copper, wire, and magnetic parts in the motor. On the screen of computer, the users can show the velocity distributions and the contours such as pressure, turbulent kinetic energy, turbulent dissipation rate and temperature.

• Wind and Structures
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• v.29 no.6
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• pp.405-416
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• 2019

Aerodynamic characteristic of a small scale wind turbine under the influence of an incoming uniform wind field is studied using k-ω Shear Stress Transport turbulence model. Firstly, the lift and drag characteristics of the blade section consisting of S826 airfoil is studied using 2D simulations at a Reynolds number of 1×10⁵. After that, the full turbine including the rotational effects of the blade is simulated using Multiple Reference Frames (MRF) and Sliding Mesh Interface (SMI) numerical techniques. The differences between the two techniques are quantified. It is then followed by a detailed comparison of the turbine's power/thrust output and the associated wake development at three tip speeds ratios (λ = 3, 6, 10). The phenomenon of blockage effect and spatial features of the flow are explained and linked to the turbines power output. Validation of wake profiles patterns at multiple locations downstream is also performed at each λ. The present work aims to evaluate the potential of the numerical methods in reproducing wind tunnel experimental results such that the method can be applied to full-scale turbines operating under realistic conditions in which observation data is scarce or lacking.