• 한국소음진동공학회논문집
• /
• 제11권6호
• /
• pp.208-215
• /
• 2001

The paper presents both theoretical and experimental study fur dynamic instabilities of a vortical cantilevered pipe with two attached lumped masses conveying fluid. The two attached lumped masses can be considered as valves or some mechanical paras in real pipe systems. Eigenvalue behaviors depending on the flow velocity are investigated for the change of Positions and magnitudes of an attached lumped mass and a tip mass. In order to verify appropriate of numerical solutions, experiments were accomplished. Theoretical predictions have a good agreement with experimental ones.

• 한국안전학회지
• /
• 제8권4호
• /
• pp.120-126
• /
• 1993

This work was carried out to investigate the effects of solid mass flow rate, mean particle diameter and mesh number of screen packing material on minimum carrying velocity, which defined as the superficial gas velocity of the upper limit of chocking phenomenon. Vertical pneumatic conveying was studied on a 4.6cm 1. D. pipe, 180cm in length. Experiments were performed in both the empty and the screen-packed pipe. It was also examined the effect of superficial gas velocity, solid mass flow, mean particle diameter, and mesh number of packing material on pressure drop. Minimum carrying velocity in screen packed-pipe was lower than that in an empty pipe. besides minimum carrying velocity was decreased with increase in mesh number of screen packing material. The pressure drop In vortical packed-pipe was Increased with superficial gas velocity, mean particle diameter, and mesh number of screen packing material.

• 설비공학논문집
• /
• 제10권4호
• /
• pp.398-410
• /
• 1998

Two-phase flow phenomena are observed in many industrial facilities and make much importance of optimum design for nuclear power plant and the liquid transportation system. The particular flow pattern depends on the conditions of pressure, flow velocity, and channel geometry. However, the research on drag reduction in two-phase flow is not intensively investigated. Therefore, experimental investigations have been carried out to analyze the drag reduction and void fraction by polymer addition in the two-phase flow system. We find that the polymer solution changes the characteristic of two-phase flow. The peak position of local void friction moves from tile wall of the pipe to the center of the pipe when polymer concentration increase. And then we predict that it is closely related with the frau reduction.

• International Journal of Air-Conditioning and Refrigeration
• /
• 제9권4호
• /
• pp.27-36
• /
• 2001

A new two-phase non-boiling convective heat transfer correlation for turbulent flow $(Re_{SL}>4000)$ in vertical tubes with different fluid flow patterns and fluid combinations was developed using experimental data available from the literature. The correlation presented herein originates from a careful analysis of the major non-dimensional parameters affecting two-phase heat transfer. This model takes into account the appropriate contributions of both the liquid and gas phases using the respective cross-sectional areas occupied by the two phases. A total of 255 data points from three available studies (which included the four sets of data) were used to determine the curve-fitted constants in the improved correlation. The performance of the new correlation was compared with two-phase correlations from the literature, which were developed for specific fluid combinations.

• 한국원자력학회:학술대회논문집
• /
• 한국원자력학회 1999년도 춘계학술발표회요약집
• /
• pp.115-115
• /
• 1999

To demonstrate the applicability of RELAP5 to the prediction of the onset offlooding in the hot leg at the reflux condensation phase during mid-loop operation, numerical analysis is performed for the counter-current flow in a horizontal pipe with the inclined riser using the RELAP5/MOD3.2.2b code. It is found that the RELAP5, simulating the CCFL phenomena using interfacial friction along with the flow regime map in the horizontal pipe, produces unsatisfactory results. Under the CCFL condition, it is observed that large oscillation exists in the flow rate, void fraction, and etc. and the liquid flow rate is much lower than that predicted by the CCFL model measured in the experiment. The CCFL model of RELAP5 for the vertical volume is extended to the model for the horizontal and inclined volumes. The horizontal volume flow regime map and interfacial friction model coupled to the CCFL model are modified. And a new correlation developed from Kang's experiment is implemented to the CCFL model of RELAP5. With this modified RELAP5, the analysis of CCFL phenomena in the horizontal pipe and hot leg geometry is performed, and produces reasonable results in comparison with experimental data.

• 설비공학논문집
• /
• 제14권5호
• /
• pp.385-390
• /
• 2002

To clarify the hydraulic characteristics of ice slurry which made from 6.5% ethylene glycol-water solution flowing through circular pipes of small diameter, experimental studies were performed. The flow pattern was observed and the pressure drop was measured in acrylic pipes with inner diameter of 24 mm. The results of flow visualization revealed that ice particles flowed along the top of pipes in the ranges of small ice fraction and low flow rate, while Ice particles diffused into the whole region of pipes flowed like a homogeneous flow for high flow rate and high ice fraction. An increase in frictional pressure drop was measured as the ice fraction increased in all pipes and unstable flow was observed for up-ward vertical pipe.

• 대한기계학회논문집B
• /
• 제23권1호
• /
• pp.25-32
• /
• 1999

In the present paper, we theoretically analyze the flow of magnetic fluids in a circular pipe with a vertical magnetic field and investigate the magnetic response by the external magnetic field. Theoretical study through the governing equation derived by Siliomis is carried out with numerical analysis by the Gauss Elimination Method. Using polar and magnetic effect parameters, theoretical equations and distributions for the velocity, vorticity, internal angular momentum and induced magnetization as the magnetic response are shown. Especially, in the region of strong magnetic field the specific property is appeared by finding a critical magnetic effect parameter for a polar effect parameter.

• 대한기계학회논문집
• /
• 제6권4호
• /
• pp.308-314
• /
• 1982

An experimental study has been made for the dispersion phenomena by a stochastic model in a turbulent pipe flow. Local instantaneous passage of suspended solid particles were recorded in two dimensions, employing a periscopic system coupled vidicon camera. Probability density of passage was calculated. Second moment shows qualitatively that dispersive action is dependent on particle's geometric characteristics in vertical pipe flow. In case that density of the solid particles is larger than that of liquid, particles have a tendency to approach from the center of pipe to the wall, and in the contrary case the approach the center of pipe. It seems that there exists a field of radial accelerations, centrifugal or centripetal according to the sign of density difference between two phases.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2004년도 추계학술대회 논문집
• /
• pp.174-179
• /
• 2004

The paper deals with gravitational effect on dynamic stability of a cantilevered pipe conveying fluid. The eigenvalue branches and modes associated with flutter of cantilevered pipes conveying fluid are fully investigated. Governing equations of motion are derived by extended Hamilton's principle, and the solutions are sought by Galerkin's method. Root locus diagrams are plotted for different values of mass ratio of the pipe, and the order of branch in root locus diagrams is defined. The flutter modes of the pipe at the critical flow velocities are drawn at every one of the twelfth period. The transference of flutter-type instability from one eigenvalue branches to another is investigated thoroughly.

• Nuclear Engineering and Technology
• /
• 제56권1호
• /
• pp.19-33
• /
• 2024

In nuclear thermal-hydraulic system codes, most correlations used for vertical pipes, under downward two-phase flow, have been developed considering small pipes or pool systems. This suggests that there could be uncertainties in applying the correlations to accident scenarios involving large vertical pipes owing to the difference in the characteristics of two-phase flows, or flow conditions, between large and small pipes. In this study, we modified the Multi-dimensional Analysis of Reactor Safety KINS Standard (MARS-KS) code using correlations, such as the drift-flux model and two-phase multiplier, developed in a plant-scale air-inflow experiment conducted for a pipe of diameter 600 mm under downward two-phase flow. The results were then analyzed and compared with those based on previous correlations developed for small pipes and pool conditions. The modified code indicated a good estimation performance in two plant-scale experiments with large pipes. For the siphon-breaking experiment, the maximum errors in water flow for modified and original codes were 2.2% and 30.3%, respectively. For the air-inflow accident experiment, the original code could not predict the trend of frictional pressure gradient in two-phase flow as / increased, while the modified MARS-KS code showed a good estimation performance of the gradient with maximum error of 3.5%.