• Korean Chemical Engineering Research
• /
• 제52권3호
• /
• pp.294-301
• /
• 2014

This study focuses on analysis and comparison of entropy generation in various cross-sectional ducts along with fully developed laminar flow and constant uniform wall heat flux. The obtained results were compared in ducts with circular, semicircular, and rectangular with semicircular ends, equilateral triangular, and square and symmetrical hexagonal cross-sectional areas. These results were separately studied for aspect ratio of different rectangular shapes. Characteristics of fluid were considered at average temperature between outlet and inlet ducts. Results showed that factors such as Reynolds number, cross section, hydraulic diameter, heat flux and aspect ratio were effective on entropy generation, and these effects are more evident than heat flux and occur more in high heat fluxes. Considering the performed comparisons, it seems that semicircular and circular cross section generates less entropy than other cross sections.

• International Journal of Fluid Machinery and Systems
• /
• 제1권1호
• /
• pp.24-32
• /
• 2008

Bleeding away a part of the boundary layer next to the wall is an effective method for controlling boundary-layer distortions from incident shock waves or curvature in geometry. When the boundary-layer flow is supersonic, the physics of bleeding with and without an incident shock wave is more complicated than just the removal of lower momentum fluid next to the wall. This paper reviews CFD studies of shock-wave/boundary-layer interactions on a flat plate with bleed into a plenum through a single hole, three holes in tandem, and four rows of staggered holes in which the simulation resolves not just the flow above the plate, but also the flow through each bleed hole and the plenum. The focus is on understanding the nature of the bleed process.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2001년도 춘계학술대회 논문집
• /
• pp.811-814
• /
• 2001

Warpage analysis of bobbin, molded by injection molding process was performed. Concerned with a mold design, cooling system was designed based on Taguchi method, the distance between cavity wall and cooling channel was most influent factor amongst four design variables like an inlet temperature of coolant, a coolant flow rate, a diameter of cooling channel, and the distance between cavity wall and cooling channel. Optimal packing processes to reduce the warpage of molded part was analyzed based on the response surface method by considering holding pressure. Their optimal processing conditions were 9.4 seconds, 5.3 seconds, 15.2 seconds, and 85MPa, respectively.

• 대한기계학회논문집
• /
• 제10권1호
• /
• pp.50-55
• /
• 1986

본 연구에서는 경계면에 맞춘 좌표계를 이용한 mapping을 통하여 37개봉으로 구성된 유로에서의 전달현상을 분석하였다.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2002년도 학술대회지
• /
• pp.729-732
• /
• 2002

This paper reports an experimental study around a module about forced air flow by blower($35{\times}35{\times}6mm^3$) in portable PC(10mm high, 200mm wide, and 235mm long). The channel inlet flow velocity has been varied between 0.26, 0.52 and 0.78m/s. The power input to the module is 4Wthis report, particular attention is directed to the fluid flow and adiabatic wall temperature($T_(ad)$) around a module which is under fluid mechanical and thermal influences of the module. The fluid flow around a module was visualized using PIV system. Liquid crystal thernography is used to determine the adiabatic wall temperature around a heated module on an acrylic board. Plots of $T_(ad)$ (or F) show marked effects of dispersion of thermal wake near the module.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2002년도 학술대회지
• /
• pp.643-646
• /
• 2002

Experimental study was conducted to reveal the flow mechanism under rotating stall in an axial flow fan. For this study unsteady pressure was measured using high frequency pressure transducers mounted on the casing wall of rotor passage and total pressure fields were measured at the rotor upstream and downstream. The measured pressure signal was analyzed by Wavelet Transform and Double Phase Locked Averaging Technique. From the result of unsteady pressure field of the casing wall, one period of rotating stall was divided into three zones and the flow characteristics on each zone were described in detail. The pressure field was also analyzed in terms of the pressure distribution along pressure side and suction side of blade tip. From the result of total pressure fields at inlet and outlet of the rotor, the useful information on the characteristics of the stall cell in radial direction was provided.

• Journal of Advanced Marine Engineering and Technology
• /
• 제27권3호
• /
• pp.437-446
• /
• 2003

A large eddy simulation (LES) is performed for turbulent pipe flow. The simulation code is constructed by using a general coordinate system based on the physical contravariant velocity components. The effects of grid fineness which can be well prediction of turbulent behavior in near wall region is investigated. The subgrid scale turbulent models are applied and validated emphasis is placed on the flow details of turbulent pipe flow The calculated Reynolds number is 360 based on the wall shear velocity and the inlet pipe diameter. The predicted turbulent statistics are evaluated by comparing with the DNS data of turbulent pipe flow Performed by Eggels et al. The agreement of LES with DNS data is shown to be satisfactory. The proper grid fineness of the well prediction of turbulent pipe flow is suggested and the turbulent behavior is analyzed by depict the contour plot of fluctuating velocity components.

• Journal of Advanced Marine Engineering and Technology
• /
• 제31권8호
• /
• pp.947-953
• /
• 2007

Occurrence of pressure pulsation in positive displacement hydraulic turbine is one of the principal problems which should be cleared to improve the turbine performance and to put the turbine to practical use. Therefore, present study is tried to examine the occurrence mechanism and characteristics of the pressure pulsation CFD analysis and experimental measurement are implemented in this study to clarify the phenomena of unsteady pressure pulsation. The results show that occurrence reason of the pressure pulsation is not only due to a series of opening and closing of the chamber formed between rotor and casing wall but also due to the variation of rotational speed of following rotor. The pressure pulsation causes torque variation and the curve patterns of the torque variation conforms to that of the pressure pulsation. Pressure in the chamber is equal to the averaged value of inlet and outlet pressures. Sudden pressure decrease by accelerated through-flow between lobe and casing wall results in torque loss.

• Journal of Advanced Marine Engineering and Technology
• /
• 제23권5호
• /
• pp.662-670
• /
• 1999

A numerical prediction was performed to clarify the air motion in the cylinder of an axisymmet-ric four-stroke reciprocating engine at its intake and compression stage. A scheme of finite volume method is used for the calculation. Modified $k-{\varepsilon}$ turbulence model is adopted and wall function is applied to the grids near the wall. The predicted mean velocity and rms velocity profiles showed a reasonable agreement with an available experimental data at its intake and compression stage. The predicted in-cylinder flow fields show that a strong turbulent twin vortex structure is pro-duced during induction but it commences to decay rapidly around inlet valve closure. The mean velocity continues to fall to a low level during compression but the turbulence intensity attains an approximate constant level.

• 한국생물환경조절학회:학술대회논문집
• /
• 한국생물환경조절학회 1999년도 학술발표논문집
• /
• pp.122-125
• /
• 1999

Ventilation is the primary method of controlling greenhouse air temperature, relative humidity, and carbon dioxide concentration. Two types of ventilation systems that are normally used are natural and fan. While fan ventilation is typically achieved with one wall as an inlet and the opposite wall as a fan outlet, natural ventilation is generally achieved by air exchanges that occur through multiple controlled openings due to natural pressure variations inside and outside the greenhouse. (omitted)