• 유체기계공업학회:학술대회논문집
• /
• 유체기계공업학회 2003년도 유체기계 연구개발 발표회 논문집
• /
• pp.514-519
• /
• 2003

The objective of this study is to document the secondary flow and the total pressure loss distribution in the contoured endwall installed linear turbine nozzle guide vane cascade passage and to propose an appropriate contraction ratio of the contoured endwall which shows the best loss reduction among the simulated cases. In this study, three different contraction ratio of contoured endwalls have been tested. This study was performed by experimental method and when the contoured endwall has the contraction ratio of 0.17 on exit height the results showed the best loss reduction.

• 대한기계학회논문집
• /
• 제9권6호
• /
• pp.750-756
• /
• 1985

본 연구에서는 종횡비 0.1이고 상.하 수평경계면이 단열된 직각밀폐용기내에 서 Pr수가 1보다 큰 물(Pr=6.97, 20.deg. C) 및 실리콘 오일(Pr=1086.42, 20.deg. C)의 양단의 온도차에 의한 자연대류에서 아직 충분히 연구되지 않은 코어형상에 주안점을 두고 실 험적으로 관찰, 조사하였으며 그 결과를 Lee의 이론적인 예측과도 비교, 검토해 보았 다.

• 한국자동차공학회논문집
• /
• 제8권5호
• /
• pp.121-128
• /
• 2000

Simple design methods were developed to control the coolant flow rates through cylinder head gasket holes. Applying the concept of flow through an obstruction the ratio of intake to exhaust side flow rates could be easily controlled while maintaining the flow rates per cylinder of the original model. Flow distribution in the coolant passage of the original model was calculated by CFD and the flow rates at the gasket holes were modified based on the calculation results. The calculated flow rated of the modified gasket holes were reasonably close to target values. For more accurate control of the flow rate distribution, a design method with iterative CFD calculations was also suggested. The final size of gasket holes for the target flow rates were obtained just after a few optimization iterations. These methods can be very useful for the optimization of heat transfer characteristics in engine cylinder head and block.

• 대한기계학회논문집B
• /
• 제24권5호
• /
• pp.640-651
• /
• 2000

For the heat and fluid flow analyses of a parallel flow heat exchanger, an improved model considering the effect of flat tube with micro-channels is proposed. The effect of flow distribution on the thermal performance of a heat exchanger is numerically investigated. The flow distribution is examined by varying geometrical parameters, i.e., the position of the separators and the inlet/outlet, and the aspect ratio of micro-channels of the heat exchanger. The flow nonuniformities along the paths of the heat exchanger are proposed and observed to evaluate the thermal performance of the heat exchanger. The optimization using ALM method has been accomplished by minimizing the flow nonuniformity. It is found that the heat transfer rate of the optimized model is increased by 6.0% of that of the reference heat exchanger model, and the pressure drop by 0.4%

• 한국입자에어로졸학회지
• /
• 제13권4호
• /
• pp.173-182
• /
• 2017

An Eulerian-Lagrangin approach is used to compute particle dispersion from a power plant chimney. For air flow, three-dimensional incompressible filtered Navier-Stokes equations are solved with a subgrid-scale model by integrating the Newton's equation, while the dispersed phase is solved in a Lagrangian framework. The velocity ratios between crossflow and a jet of 0.455 and 0.727 are considered. Flow fields and particle distribution of both cases are evaluated and compared. When the velocity ratio is 0.455, it demonstrates a Kelvin-Helmholtz vortex structure above the chimney caused by the interaction between crossflow and a jet, whereas the other case shows flow structures at the top of the chimney collapsed by fast crossflow. Also, complex wake structures cause different particle distributions behind the chimney. The case with the velocity ratio of 0.727 demonstrates strong particle concentration at the vortical region, whereas the case with the velocity ratio of 0.455 shows more dispersive particle distribution. The simulation result shows similar tendency to the experimental result.

• 대한기계학회논문집
• /
• 제17권12호
• /
• pp.3208-3216
• /
• 1993

Heat transfer characteristics of the laminar oscillating flow in a circular pipe have been studied under the condition that the wall temperature of the pipe is distributed sinusoidally with the axial direction. The axial velocity was assumed to be uniform in radial direction and the temperature field was analyzed by means of the perturbation method. The results show that the difference between wall and section-time-averaged fluid temperature increases as the oscillating frequency increases and eventually converges to a constant value which is determined by the ratio of swept distance to the characteristic length of wall temperature distribution. Also it is shown that the dominant variable in the heat transfer process when swept distance ratio is greater than 1 is not thermal Womersley number(F) but thermal Womersley number multiplied by the square root of swept distance ratio. The variation of the time-averaged Nusselt number is obtained as a function of F. The results indicate that Nusselt number is proportional to $F_{\epsilon}^{1/2}$ when both of F and .epsilon. are much greater than 1.

• 대한기계학회논문집
• /
• 제19권10호
• /
• pp.2586-2594
• /
• 1995

Two phase flow phenomena are observed in many industrial facilities and make much importance of optimum design for nuclear power plant and various heat exchangers. This experimental study has been investigated the classification of the flow pattern, the local void distribution and convective heat transfer in swirl and non-swirl two phase flow under the isothermal and nonisothermal conditions. The convective heat transfer coefficients in the single phase water flow were measured and compared with the calculated results from the Sieder-Tate correlation. These coefficients were used for comparisons with the two-phase heat transfer coefficients in the flow orientations. The experimental results indicate, that the void probe signal and probability density function of void distribution can used into classify the flow patterns, no significant difference in voidage distribution was observed between isothermal and non-isothermal condition in non-swirl flow, the values of two phase heat transfer coefficients increase when superficial air velocities increase, and the enhancement of the values is observed to be most pronounced at the highest superficial water velocity in non-swirl flow. Also two phase heat transfer coefficients in swirl flow are increased when the twist ratios are decreased.

• 대한기계학회논문집B
• /
• 제23권11호
• /
• pp.1390-1398
• /
• 1999

A numerical analysis for ROT sparger of PWR(Pressurized Water Reactor) is carried out. Computation is performed to investigate the flow characteristics as the change of design factor. As the result of this study, RDT sparger's flow resistance coefficient is K=3.53 at the present design condition if engineering mar&in is considered with 20%, and flow ratio into branch pipe is $Q_s/Q_i=0.41$. Velocity distribution at exit is not uniform because of separation in branch pipe. In the change of inlet flow rate and section area ratio of branch pipe for main pipe, flow resistance coefficient is increased as $Q_s/Q_i$ decreasing, but in the change of branch angle and outlet nozzle diameter of main pipe, flow resistance coefficient is decreased as $Q_s/Q_i$ decreasing. As the change rate of $Q_s/Q_i$ is the larger, the change rate of flow resistance coefficient is the larger. The change rate of pressure loss is the largest change as section area ratio changing. The optimal design condition of sparger is estimated as the outlet nozzle diameter ratio of main pipe is $D_s/D_i=0.333$, the section area ratio is $A_s/A_i=0.2$ and the branch angle is ${\alpha}=55^{\circ}$.

• 대한기계학회논문집B
• /
• 제20권12호
• /
• pp.4053-4061
• /
• 1996

Internal flow characteristics within Y-jet atomizers and the local drop size distribution and cross-sectional averaged drop size at the outside were investigated with the liquid and air injection pressures, mixing port length of atomizers, and the liquid properties taken as parameters. To examine the effect of the liquid viscosity, glycerin-water mixtures were used in this study. The liquid viscosity plays only a minor role in determining the internal flow pattern and the spatial distribution shape of drops, but the drop sizes themselves generally increase with increasing of the liquid viscosity. An empirical correlation for the liquid discharge coefficient at the liquid port was deduced from the experimental results; the liquid discharge coefficient strongly depends on the liquid flow area at the mixing point which is proportional to the local volumetric quality(.betha.$_{Y}$), and the volumetric quality was included in the correlation. Regardless of the value of the liquid viscosity, the compressible flow through the gas port was well represented by the polytropic expansion process(k=1.2), and the mixing point pressure could be simply correlated to the aspect ratio( $l_{m}$/ $d_{m}$) of the mixing port and the air/liquid mass flow rate ratio( $W_{g}$/ $W_{f}$) as reported in the previous study.udy.udy.y.

• 한국연소학회:학술대회논문집
• /
• 한국연소학회 2004년도 제28회 KOSCO SYMPOSIUM 논문집
• /
• pp.192-198
• /
• 2004

A numerical study was conducted to determine the effects of high temperature air, including equivalent ratio on flow field, temperature, evaporation, and overall temperature distribution in gas turbine combustor. A sector model of a typical wall jet can combustor, featuring introduction of primary air and dilution air via wall jet, was used in calculations. Flow field and temperature distribution were analyzed. Operating conditions such as inlet temperature and overall equivalent ratio were varied from 373 to 1300 K, and from 0.3 to 0.6, respectively, while any other operating conditions were fixed. The RNG ${\kappa}-{\varepsilon}$ model and eddy breakup model were used for turbulence and combustion model respectively. It was found that the increase with the inlet air temperature, velocity in the combustor is accelerated and evaporation of liquid fuel is not affected in primary zone, high temperature inlet air enhances the evaporation and improves overall temperature distribution factor.