• Journal of Mechanical Science and Technology
• /
• 제18권2호
• /
• pp.286-293
• /
• 2004

The air fuel ratios of current gasoline engines are almost controlled by several air flow meters. When CVVT (Continuous Variable Valve Timing) is applied to a gasoline engine for higher engine performance, the MAP (Manifold Absolute Pressure) sensor is difficult to follow the instantaneous air fuel ratio due to the valve timing effect. Therefore, a HFM (Hot Film Flow Meter) is widely used for measuring intake air flow in this case. However, the HFMs are incapable of indicating to reverse flow, the oscillation of intake air flow has an negative effect on the precision of the HFM. Consequently, the various duct configurations in front of the air flow sensor affect the precision of HFM sensitivity. This paper mainly focused on the analysis of the reverse flow, flow fluctuation in throttle upstream and the geometry of intake system which influence the HFM measurement.

• 한국신재생에너지학회:학술대회논문집
• /
• 한국신재생에너지학회 2008년도 춘계학술대회 논문집
• /
• pp.554-557
• /
• 2008

In this study, two types of central flow distributor designs are presented and compared to obtain the optimal compact design which has the least flow resistance and the uniform flow distribution in a vehicular fuel cell stack. For effective and reliable prediction on the thermo-flow characteristics of the reactants flow over the entire fuel cell stack domain, open channel flow in the bipolar plates of the power generating cells were simulated by applying a simplified flow resistance model with an empirical porous concept. A number of case studies were performed to figure out an optimal configuration of a central flow distributor device in terms of the time-dependent thermo-flow behavior and load-dependent flow distribution. The results showed that the stable and load-independent thermo-flow uniformity is very design specific, which is closely associated with the design of central manifolding devices in order to achieve the enhanced volumetric power density and the reliable long-lasting operating of fuel cells.

• 한국원자력학회:학술대회논문집
• /
• 한국원자력학회 1995년도 추계학술발표회논문집(1)
• /
• pp.475-479
• /
• 1995

During the hypothetical loss of coolant accident in the nuclear power plant the emergency core cooling water could not penetrate to the reactor core when the steam flow rate from the reactor core exceeds CCFL (Countercurrent flow limitation). The CCFL generated by earlier investigators are developed under the steady gas flow. However the flow instability in the reactor loop could generate oscillatory steam flow, hence their applicability under oscillating flow should be investigated. In this work, an experimental investigation of countercurrent flow in the vertical flow channel has been conducted under oscillatory gas flow. Pulsation of gas under oscillatory flow disturbs the flow pattern significantly and prevents flooding (CCFL) when its minimum value is less than the threshold gas flow rate value.

• 한국물환경학회지
• /
• 제21권4호
• /
• pp.393-397
• /
• 2005

In this study, flow in a porous medium is analyzed using a computer-extended perturbation series solution. The flow is modelled as a creeping flow in a periodically constricted channel. The channel walls have a sinusoidally varying width and the flow is analyzed in terms of its vorticity and stream functions in the Stokes flow regime. The perturbation series in terms of a small parameter, average width to length ratio, is extended with a computer resulting in purely asymptotic series and Pade summation is used to obtain final results. Resulting flow shows flow separations in the widening section and immobile zones in the widest section of the flow regime with reattachment in the narrowing section. Analysis of the flow separation phenomena resulted in a correlation between the two geometric parameters of the channel walls to predict the onset of flow separation in the Stokes flow regime.

• 유체기계공업학회:학술대회논문집
• /
• 유체기계공업학회 2004년도 유체기계 연구개발 발표회 논문집
• /
• pp.65-69
• /
• 2004

In the present work, characteristics of an axial flow fan haying distorted inlet flow produced by hub cap are investigated. The distorted inlet flow is generated by the shape of hub cap installed in front of the axial flow fan. Two different cases of hub cap geometry are analyzed to verify the influence of flow distortion. The flow fields are analyzed numerically by solving steady form of three-dimensional Reynolds-averaged Wavier-Stokes equation and standard k-$\epsilon$ model is used for a turbulence closure. The results obtained from the numerical simulation are compared to those from experimental measurements. It is found that the overall performance of the axial flow fan is increased by reducing the flow distortion at the hub. Detailed characteristics of the flow fields of two different geometric conditions are also discussed.

• 대한기계학회논문집B
• /
• 제26권11호
• /
• pp.1559-1569
• /
• 2002

In order to investigate the characteristics of electromagnetic flowmeter in two -phase flow, an AC electromagnetic flowmeter was designed and manufactured. In various flow conditions, the signals and noises from the flowmeter were obtained and analyzed by comparison with the observed flow patterns with a high speed CCD camera. The experiment with the void simulators in which rod shaped non-conducting material was used was carried out to investigate the effect of the bubble position and the void fraction on the flowmeter. Based on the results from the void simulator, two -phase flow experiments encompassed from bubbly to slug flow regime were conducted. The simple relation $\Delta$ $U_{TP}$ = $\Delta$ $U_{SP}$ (l-$\alpha$) was verified with measurements of the potential difference and the void fraction. Due to the lack of homogeneity in a rent two -phase flow, the discrepancy between the relation and the present measurement was slightly increased with void fraction and also liquid volumetric flux jf. Whereas there is no difference in the shape of the raw signal between single-phase flow and bubbly flow, the signal amplitude for bubbly flow is higher than that for single -phase flow at the same water flow rate, since the passage area of the water flow is reduced. In the case of slug flow, the phase and the amplitude of the flowmeter output show dramatically the flow characteristics around each slug bubble and the position of a slug bubble itself. Therefore, the electromagnetic flowmeter shows a good possibility of being useful for identifying the flow regimes.ul for identifying the flow regimes.

• 한국조사연구학회지:조사연구
• /
• 제3권2호
• /
• pp.17-45
• /
• 2002

본 연구는 Flow 경험이 인터넷 사용자의 상황이나, 목적에 따라서 인터넷을 항해하는데 어떠한 영향을 미치는지, 그리고 기존의 구매의도 관련 변인들과 어떠한 차이를 보이는가를 고찰하기 위해 이루어 졌다. 연구결과 첫째, 인터넷 사용자의 (On-line)구매의도는 인터넷 사용자의 경험의 정도에 따라 증가하는 것으로 나타났다. 둘째, 인터넷 쇼핑몰을 항해하는 동안 경험하게 되는 Flow는 인터넷 쇼핑몰을 탐색하는 동기에 따라 다른 것으로 나타났다. 셋째, Flow경험을 높게 인지한 사용자일수록 온라인을 통한 구매의도(또는 구매의도 관련변인)는 증가한 것으로 나타나 온라인을 통한 구매과정을 설명하는데 Flow가 영향을 미치는 것으로 나타났다. 넷째, 목적적 Flow를 경험하는 인터넷 사용자의 경우 Flow 변인이 다른 구매의도 관련 변인들(태도, 효용, 위험)보다 온라인을 통한 구매의도에 가장 높은 영향을 미치는 것으로 나타났으며 경험적 Flow를 경험하는 인터넷 사용자는 인터넷 쇼핑몰을 구매장소로 인지하기 보다는 즐거움(fun)의 장소로 인지하는 것으로 나타났다.

• 대한기계학회논문집B
• /
• 제27권8호
• /
• pp.1033-1041
• /
• 2003

Two-phase flow pattern data during horizontal in-tube flow boiling are presented for pure and mixed refrigerants of R134a and Rl23, The flow pattern is observed through tubular sight glasses located at inlet and outlet of the test section, which is made of a stainless steel tube, 2m long with 10mm I.D., 1.5mm wall thickness. The obtained results are compared with the available various correlations for flow pattern. The flow pattern map of Hashizume was in good agreement with the present data except the region of low mass velocity. Weisman flow pattern map was also known to satisfactorily predict data for refrigerants in the region of annular flow. In this study, the flow pattern are simply classified into two groups; stratified(including intermittent, stratified and stratified-wavy) flow and annular flow. The transition quality from stratified to annular flow was obtained by modifying the liquid Froude number.

• 한국산업융합학회 논문집
• /
• 제23권2_2호
• /
• pp.199-207
• /
• 2020

These days, many different types of valves are developed in the industrial area according to their use purpose. Multiple kinds of valves are installed to control a flow and pressure of the pipe conveying fluid. Valves serve as critical roles in land plants such as power plants. The performance of equipment varies depending on valve characteristics. In this study, the internal flow analysis on Cone-type valve is conducted to analyze flow field and secure a value of the flow coefficient Cv. According to the internal flow analysis, when the flow distribution of the middle cross-section of valve was open 100%, flow field was relatively and smoothly taken out. If it was open 50%, flow recirculation region increased and a little complex flow field occurred. Unlike ball valve or butterfly valve, this valve had flow recirculation in its outlet depending on a valve opening amount. Therefore, it was found that there was no flow recirculation in the outlet of Cone-type valve.

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 2010년 춘계학술대회논문집
• /
• pp.352-357
• /
• 2010

A parametric study has been carried out to elucidate the characteristics of channel flow with a streamwise-periodic array of cylinders. This flow configuration is relevant to heat exchanger applications. The presence of cylinders in channel flow causes the attached wall boundary layer to separate, leading to significant change in flow instabilities. There exist two kinds of instabilities; flow undergoes a primary instability (Hopf bifurcaiton) at a lower Reynolds number, and the unsteady two-dimensional flow becomes unstable to three-dimensional disturbances at a higher Reynolds number. We report here the dependencies of the primary instability as well as the flow characteristics of the subsequent unsteady flow including flow-induced forces and Strouhal number of vortex shedding, on the distance between the cylinder and the channel wall.