• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2005년도 학술발표회(1)
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• pp.588-589
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• 2005

Current expertise in air-water turbulent flows on stepped chutes is limited to laboratory experiments at low to moderate Reynolds numbers on flat horizontal steps. In this study, highly turbulent air-water flows skimming down a large-size stepped chute were systematically investigated with a $22^{\circ}$ slope (Fig. 1). Turbulence manipulation was conducted using vanes or longitudinal ribs to enhance interactions between skimming flows and cavity recirculating regions (Fig. 2). Systematic experiments were performed with seven configurations. The results demonstrated the strong influence of vanes on the air-water flow. An increase in flow resistance was observed consistently with maximum flow resistance achieved with vanes placed in a zigzag pattern.

• 설비공학논문집
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• 제13권10호
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• pp.1034-1041
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• 2001

A numerical model which simulates the flow boiling process of the ammonia/water solution within a plate type generator for ammonia/water absorption refrigerators was developed. The ammonia/water solution flows downward under gravity and the ammonia/water vapor generated by flow boiling flows upward. The heating medium flows counter to the ammonia/water solution. The flow pattern within the generator was assumed to be a bubbly flow, and the liquid and vapor phases were assumed to be saturated. It was shown that the boiling of ammonia occurred mainly in the upper part of the generator. The effects of the heating medium inlet temperature, the mass flow rate of the heating medium and the mass flow rate of ammonia/water solution into the generator on the generation of ammonia/water vapor were investigated.

• 한국안전학회지
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• 제32권1호
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• pp.75-81
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• 2017

A series of laboratory experiments has been performed in order to investigate the behavior of water-air two-phase flow in a horizontal pipe. A conductivity meter has been applied to detect the irregular alternation of air at the specific points in flows. The experimental condition has been established according to the water and air flowrates. Passing time, which is the time length for a measuring probe to pass through the entire length of a specific bubble, has been defined to evaluate the size of bubbles in the flow. Passing length, which can be considered as the equivalent value to bubble size and determined from the product of passing time and cross-sectional averaged velocity, and its corresponding occurrence frequency have been analyzed to classify the air flow patterns according to the condition of air and water fluxes. From the result, the dependancy of flow patterns on the variation of air-water flux ratio has been investigated and the existence of thresholds also checked for classifying the behavior of air in the flow.

• 한국전산유체공학회지
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• 제21권3호
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• pp.31-38
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• 2016

The FDS-HCIB method is expanded to simulate water-oil-air flows around oil booms under relative motion, which is intended to increase the thickness of contained oil. The FDS scheme captures discontinuity in the density field and abrupt change of the tangential velocity across an interface without smearing. The HCIB method handles relative motions of thin oil booms with ease. To validate the developed FDS-HCIB code for water-oil-air flow around a moving body, the computed results are compared with the reported experimental results on the shape, length, and thickness of the oil slicks under towing. It is observed that the increase in pressure field between two barriers lifts the oil slick and the interfacial wave propagates and reflects as one barrier gets closer to the other barrier.

• 설비공학논문집
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• 제18권9호
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• pp.687-697
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• 2006

The air and water flow distribution are experimentally studied for a heat exchanger composed of round headers and 10 flat tubes. The effects of tube protrusion depth as well as mass flux, and quality are investigated, and the results are compared with the previous 30 channel results. The flow at the header inlet is annular. For the downward flow configuration, the water flow distribution is significantly affected by the tube protrusion depth. For flush-mounted geometry, significant portion of the water flows through frontal part of the header. As the protrusion depth increases, more water is forced to the rear part of the header. The effect of mass flux or quality is qualitatively the same as that of the protrusion depth. Increase of the mass flux or quality forces the water to rear part of the header. For the upward flow configuration, different from the downward configuration, significant portion of the water flows through the rear part of the header. The effect of the protrusion depth is the same as that of the downward flow. As the protrusion depth increases, more water is forced to the rear part of the header. However, the effect of mass flux or quality is opposite to the downward flow case. As the mass flux or quality increases, more water flows through the frontal part of the header. Compared with the previous thirty channel configuration, the present ten channel configuration yields better flow distribution. Possible explanation is provided from the flow visualization results.

• 설비공학논문집
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• 제18권1호
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• pp.55-65
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• 2006

The air and water flow distribution are experimentally studied for a round header - flat tube geometry simulating a parallel flow heat exchanger. The number of branch flat tube is thirty. The effects of tube outlet direction, tube protrusion depth as well as mass flux, and quality are investigated. The flow at the header inlet is identified as annular. For the downward flow configuration, the water flow distribution is significantly affected by the tube protrusion depth. For flush-mounted configuration, most of the water flows through frontal part of the header. As the protrusion depth increases, more water is forced to the rear part of the header. The effect of mass flux or quality is qualitatively the same as that of the protrusion depth. Increase of the mass flux or quality forces the water to rear part of the header. For the upward flow configuration, however, most of the water flows through rear part of the header. The protrusion depth, mass flux, or quality does not significantly alter the flow pattern. Possible explanations are provided based on the flow visualization results. Negligible difference on the water flow distribution was observed between the parallel and the reverse flow configuration.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2005년도 학술발표회(1)
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• pp.252-252
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• 2005

• 동력기계공학회지
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• 제4권3호
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• pp.34-39
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• 2000

Performance data in the literature on air lift pumps have been based primarily on pumps of long length and large diameter (high lift pumps). Since mariculture operations involve pumps of relatively short length and small diameter, performance data are required for efficient operation. To provide such data, an experimental apparatus was designed and fabricated to test all lift pumps from 2.1 to 3.4 cm inside diameter and from 40 to 300 cm in length. Instrumentation was provided to measure water flow rate and air flow rate as well as water temperature, air temperature, and pressure throughout the system. Results from this study correlate well with high lift pump data in that, for a given pump geometry, maximum water flow occurs for a specific air flow rate. Driving the pump with air flows larger or smaller than this optimum flow rate will decrease the pumping rate. The optimum flows are significantly different for low lift pumps compared to high lift pumps. However, the pumping rate for low lift pumps approaches that for high lift pumps with increasing length.

• 한국해양공학회지
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• 제26권3호
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• pp.61-65
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• 2012

Air-water flow measurements are of importance for the coastal and ocean engineering fields. Although kinematic investigations of the multi-phase flows have been conducted for long time, velocity measurements still are concerned with many researchers and engineers in coastal and ocean areas. In the present study, an imaging technique using shadowgraphy and fiber optic probe for velocity measurements of air bubbles is introduced. The shadow graphy image technique is modified from the typical image velocimetry methods, and optical fibers are used for the well-known intrusive coupled phase-detection probe system. Since the imaging technique is a non-intrusive optical method from the air, it is usually applied for 2D flows. On the other hand, the double fiber optic probes touch flows regardless of flow patterns. The results of the flow measurements by both methods are compared and discussed. The methods are also applied to the measurements of overtopping flows by a breaking wave over the structure fixed on the free surface.

• Journal of Mechanical Science and Technology
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• 제14권7호
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• pp.789-795
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• 2000

Free-surface flows with an arbitrary deformation, induced by a submerged hydrofoil, are simulated numerically, considering two-fluid flows of both water and air. The computation is performed by a finite volume method using unstructured meshes and an interface capturing scheme to determine the shape of the free surface. The method uses control volumes with an arbitrary number of faces and allows cell wise local mesh refinement. The integration in space is of second order, based on midpoint rule integration and linear interpolation. The method is fully implicit and uses quadratic interpolation in time through three time levels. The linear equations are solved by conjugate gradient type solvers, and the non-linearity of equations is accounted for through Picard iterations. The solution method is of pressure-correction type and solves sequentially the linearized momentum equations, the continuity equation, the conservation equation of one species, and the equations for two turbulence quantities. Finally, a comparison is quantitatively made at the same speed between the computation and experiment in which the grid sensitivity is numerically checked.