• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.11 no.1
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• pp.18-30
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• 1999

A heat transfer analysis for the two-dimensional (2-D) steady state using finite difference method (FDM) is performed to predict the thermal behavior of the primary first-wall (FW) system of fusion reactor under various geometric and thermo-hydraulic conditions, such as the beryllium (Be) armor thickness, pitch of cooling tube, and coolant velocity. The FW consists of authentic steel (type 316 stainless steel solution annealed) for cooling tubes, Cu for cooling tubes embedding material, and Be for a protective armor, based on the International Thermonuclear Experiment Reactor (ITER) report. The present 2-D analysis, the control volume discretized with hybrid grid (rectangular grid and polar grid) and Gauss-Seidel iteration method are adapted to solve the governing equations. In the present study, geometric and thermo-hydraulic parameters are optimized with consideration of several limitations. Consequently, it is suggested that the adequate pitch of cooling tube is 22-32mm, the beryllium armor thickness is 10-12mm, and that the coolant velocity is 4.5m/s-6m/s for $100^{\circ}C$ of inlet coolant temperature. The cooling tube should locate near beryllium armor. But, it would be better for locating the center of Cu wall, considering problems of material and manufacturing. Also, 2-D analysis neglecting the axial temperature distribution of cooling tube is appropriate, regarding the discretization error in axial direction.

• The KSFM Journal of Fluid Machinery
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• v.17 no.1
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• pp.12-21
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• 2014

An organic Rankine cycle was analyzed to work at the optimal operating point when the heat source is fluctuated. R245fa was adopted as a working fluid, and an axial-type turbine as expander on the cycle was designed to convert the heat energy to the electricity since the turbo-type expander works at off-design points better than the positive displacement-type expander. A supersonic nozzle was designed to increase the spouting velocity because a higher spouting velocity can produce more output power. They were designed by the method of characteristics for the operating fluid of R245fa. Three different cases, such as various spouting velocities, various inlet total temperatures, and various nozzle numbers, were studied. From these results, an optimal operating cycle can be designed with the organic Rankine cycle when the available heat source as renewable energy is low-grade temperature and fluctuated.

• Journal of Mechanical Science and Technology
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• v.17 no.8
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• pp.1234-1245
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• 2003

An experimental study was carried out to investigate the reduced frequency effect on the near-wake of an elliptic airfoil oscillating in pitch. The airfoil was sinusoidally pitched around the center of the chord between -5$^{\circ}$and ＋25$^{\circ}$angles of attack at an airspeed of 3.4 m/s. The chord Reynolds number and reduced frequencies were 3.3 ${\times}$10$^4$, and 0.1, 0.7, respectively Phase-averaged axial velocity and turbulent intensity profiles are presented to show the reduced frequency effects on the near-wake behind the airfoil oscillating In pitch. Axial velocity defects in the near-wake region have a tendency to increase in response to a reduced frequency during pitch up motion, whereas it tends to decrease during pitch down motion at a positive angle of attack. Turbulent intensity at positive angles of attack during the pitch up motion decreased in response to a reduced frequency, whereas turbulent intensity during the pitch down motion varies considerably with downstream stations. Although the true instantaneous angle of attack compensated for a phase-lag is large, the wake thickness of an oscillating airfoil is not always large because of laminar or turbulent separation.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.12
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• pp.1042-1047
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• 2007

A micro cyclone combustor was developed to be used as a heat source of thermoelectric power generator (TPG). The cyclone combustor was designed so that fuel and air were supplied to the combustion chamber separately. The mixing and flow characteristics in the combustor were investigated numerically. The global equivalence ratio ($\Phi$), defined using the fuel and air flow rates, was introduced to examine the flow features of the combustor. The mixing of fuel and air inside the combustor could be well understood using the fuel concentration distribution. It was found that the weak recirculating zone was formed upper the fuel-supplying tube in case of ${\Phi}$<1.0. In addition, it was found that small regions that have a negative axial velocity exist near the fuel injection ports. It is assumed that these negative axial velocity regions can stabilize a flame inside the micro cyclone combustor.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.6
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• pp.1390-1398
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• 1988

The purpose of this study was experimentally to investigate the disintegration process and disintegration mechanism when co-axial air flows vertically for the longest smooth liquid jet. These were affected by liquid velocity, air velocity, air-to-liquid diameter ratio, nozzle shape, and air-liquid contacting position. That is, this process of disintegration of the liquid jet was similar to that occurred when liquid pressure was increased. At Reynolds number of 10, 000 and below, the changes in the breakup length represent different tendency according to liquid flow rate. The influence of air flow on the disintegration of liquid jet was different according to air-to-liquid diameter ratio, air orifice diameter, nozzle shape and contacting position of liquid and air. In particular, when the tip of liquid nozzle was inside the air orifice, the effect of air flow was the larger than outside the air orifice. The effect of liquid mass flow rate on the change rate of the breakup length was also different.

• International Journal of Fluid Machinery and Systems
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• v.7 no.2
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• pp.60-67
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• 2014

In order to clarify the effect of inlet bellmouth size of semi-opened type axial fan on its performance and flow fields around rotor, fan test and flow field measurements using hotwire anemometer were carried out for 6 kinds of bellmouth size. As results of fan test, the shaft power curve hardly changed, even if the bellmouth size changed. On the other hand, the pressure-rise near best efficiency point became small with the bellmouth size decreasing. Therefore, the value of maximum efficiency became small as the bellmouth size decreased. As results of flow field measurements at fan inlet, the main flow region with large meridional velocity existed near blade tip when the bellmouth size was large. As bellmouth size became smaller, the meridional velocity at fan inlet became smaller and the one at outside of blade tip became larger. As results of flow field measurements at fan outlet, the main flow region existed near rotor hub side.

• Journal of the Korean Society of Safety
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• v.19 no.1
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• pp.124-130
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• 2004

The structure of the nonpremixed methane-air counterflow flames in microgravity was investigated by axisymmetric simulation with Fire Dynamics Simulator (FDS) to evaluate the numerical method and to see the effects of strain rate and fuel concentration on the diffusion flame structure in microgravity. Results of FDS for the methane mole fractions, $X_m$=20, 50, and 80% in the fuel stream, and the global strain rates $a_g$=20, 50, and $90s^{-1}$ for each methane mole fraction were compared with those of OPPDIF, an one-dimensional flamelet code. There was good agreement in the temperature and axial velocity profiles between the axisymmetric and one-dimensional computations. It was shown that FDS is applicable to the counterflow flames in a wide range of strain rate and fuel concentration by predicting accurately the flame thickness, flame positions and stagnation points.

• Journal of Power System Engineering
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• v.6 no.4
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• pp.23-29
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• 2002

This paper is studied to investigate the effect of slits and swirl vanes on the main flow fields of a gun-type gas burner through X-Y plane and Y-Z plane respectively by using X-probe from hot-wire anemometer system. This experiment was carried out with flow rate $450{\ell}/min$ in respective burner models installed in the test section of a subsonic wind tunnel. The burner models with only slits and only swirl vanes respectively were made by modifying original gun-type gas burner. The fast jet flow spurted from slits played a role such as an air-curtain because it encircled rotational flow by swirl vanes and drives mixed main flow to axial direction. As a result, the gun-type gas burner had a wider flow range up to about Y/R=1.5 deviated from slits and maintains a comparatively large velocity in the central part of burner within the range of about X/R=2.5. Therefore, it was very desirable that swirl vanes were installed within slits in gun-type gas burner in order to control the main flow fields effectively.

• Journal of the Korean Institute of Gas
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• v.8 no.2 s.23
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• pp.42-47
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• 2004

The axisymmetric methane-air counterflow flame in microgravity was simulated to investigate effects of the global strain rate on the flame structure. The flame shapes and profiles of temperature and the axial velocity for the mole fraction of methane in the methane-nitrogen fuel stream, Xm= 20, 50, $80\%$, and the global strain rate, ag= 20, 60, 90 $s^{-1}$ each mole fraction were compared. The profiles of the temperature and axial velocity of the axisymmetric simulations were in good agreement with those of OPPDIF, an one-dimensional flamelet code. It was confirmed that the flame is stretched more and the flame radius increases and the flame thickness decreases as the global strain rate increases.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.803-808
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• 2006

This paper was a study about noise reduction through flow stabilization in duel using experimental method and numerical analysis at the same time. To determine the fan's type three kinds of fans(axial fan, centrifugal fan, and axial fan with centrifugal type) was examined to investigate the suitability for duct. As a result, under the equal number of rotation 2000 RPM, performance of an axial fan with centrifugal type was the most superior by 55dBA at 4.3CMM among other fans. After this, analyzed the results of the numerical analysis to find out the optimum design of pitch angle such as $0^{\circ},\;10^{\circ},\;15^{\circ}\;and\;20^{\circ}$. The intensity of turbulence was low when pitch angle was $15^{\circ}$ and air volume became peak by 5.08 CMM. It was observed that axis component of velocity increased gradually when pitch angle increased from $0^{\circ}\;to\;20^{\circ}$. Finally, designed the shapes of D/S(Down Stream) in duct that agreed inlet angle($\delta$) of stationary blades with pitch angle($\beta$) of axial fan with centrifugal type and derived flow to duct medial, and changed the shape of motor-mount to reduce occurance of unstable vortex in tip of impeller, and embodied noise reduction and improvement of air flow rate through flow stabilization.