• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.15 no.9
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• pp.727-732
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• 2003

In the present study, a PIV measurement and image processing technique were applied in order to investigate the flow characteristics in the gas injected liquid bath. The circulation of liquid was induced by upward bubble flow. Due to the centrifugal force, the flow was well developed near both wall sides than in the center of a bath. The vortex flow irregularly repeated generation and disappearance which helped to accelerate the mixing process. The bubble rise velocity in the bottom region was relatively lower than in the upper region because the energy generated by bubbles' behavior in the region near the nozzle was almost converted into kinetic energy But bubble rise velocity increases with the increase of the axial distance since kinetic energy of rising bubbles is added to buoyancy force. In conclusion, the flow increased bubble rise velocity and the flow of the bottom region became more active.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.10
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• pp.685-691
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• 2017

In this study, the influence of mass flow rate on the isentropic efficiency of the steam turbine nozzle stage is investigated. A realistic three-dimensional numerical model, which is based on the compressible Navier-Stokes equations, is developed for the steam phase. The comprehensive conservation laws and a kinetic model for steam are investigated. With two different models for the three-dimensional geometry of the nozzle stage, the pressure and temperature distributions, velocity, Mach number. and Markov energy loss coefficient are calculated. A maximum efficiency of 96.66％ is found at a mass flow rate of 0.9 kg/s in model A. In model B, a maximum efficiency of 97.32％ is found at a rate of 1.6 kg/s. It is determined that the isentropic nozzle efficiency increases as the Markov energy loss coefficient decreases through a nearly linear relationship.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.2
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• pp.306-315
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• 2000

An experimental study was conducted to examine the internal flow patterns inside the mixing chamber of effervescent atomizers. The mixing chamber has the rectangular cross section ($8mm{\times}2mm$) and made of transparent acrylic plate for flow visualization. The parameters tested were the air/liquid ratio (ALR), injection. pressure, and the nozzle orifice diameter. Three different flow regimes were observed; bubbly, annular, and intermittent flows. In the bubbly flow regime, the discharged mixture was disintegrated into drops through the bubble expansion and the ligament breakup. On the other hand, in the annular flow regime, the liquid annulus was disintegrated into small drops by the aerodynamic interaction between the phases due to the high relative velocities between the gas and the liquid. In the intermittent flow regime, the bubble-expansion/ligament-disintegration mode and the annulus-disintegration mode appeared alternatively. The correlations representing the transition criteria between the two-phase flow patterns within the mixing chamber were proposed based on the drift-flux models.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.385-390
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• 2004

An unique ceramic material produced through unidirectional solidification with eutectic composition of two-phase oxides was introduced recently. This composite material has the microstructure of coupled networks of two single crystals interpenetrate each other without grain boundaries. Depending on this microstructure this material, called Melt Growth Composite (MGC), can sustain its room temperature strength up to 1$700^{\circ}C$ (near its melting point) and offer strong oxidization-resistant ability, making its characteristics quite ideal for the gas turbine application. The research project on MGC started in 2001 with the objective of establishing component technologies for MGC application to the high temperature components of the gas turbine engine. MGC turbine nozzles are expected to improve efficiency of gas turbine. However, reduction of the thermal stress is required since high thermal stress is easily generated in MGC turbine nozzles due to temperature distribution. Firstly, the hollow nozzle shape was optimized to reduce thermal stress using numerical analysis. From the results of the first hot gas flow tests, the thermal stress due to span-wise temperature distribution was required to be reduced, and separated nozzle to three pieces was designed. This was tested in hot gas flow at 140$0^{\circ}C$ level, and temperature distributions on the nozzle surface were obtained and stress field was evaluated.

• International Journal of Automotive Technology
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• v.1 no.2
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• pp.95-100
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• 2000

The droplet and the turbulent characteristics of a counterflowing internal mixing pneumatic nozzle mainly focused. The measurements were made using a Phase Doppler Particle Analyzer under the different air pressures. The nozzle with tangential-drilled holes at an angle of 30 to the central axis has been designed. The spatial distributions of velocities, fluctuating velocities, droplet diameters and SMD were quantitatively and qualitatively fluctuating velocities were substantially higher than the radial and the tangential ones. This implies that the disintegration process is enhanced with the higher air pressure. The larger droplets were detected near the spray centerline at the upstream while the smaller ones were generated at the downstream. This was attributed to the lower rates of spherical particles which were not subject to instantaneous breakup. However, substantial increases in SMD from the central part tower spray periphery were predictable in downstream regions.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.706-711
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• 2003

A numerical method is presented for computing unsteady incompressible two-phase flows with immersed solids. The method is based on a level set technique for capturing the phase interface, which is modified to satisfy a contact angle condition at the solid-fluid interface as well as to achieve mass conservation during the whole calculation procedure. The modified level set method is applied for numerical simulation of bubble deformation in a micro channel with a cylindrical solid block and liquid jet from a micro nozzle.

• Journal of Mechanical Science and Technology
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• v.16 no.12
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• pp.1693-1701
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• 2002

The intermittent spray characteristics of a multi-hole and a single-hole diesel nozzle were experimentally investigated. The hole number of the multi-hole nozzle was 5, and the hole diameter of the 5-hole and the single-hole nozzle was the same as d$\_$n/=0.32 ㎜ with the constant hole length to diameter ratio(l$\_$n//d$\_$n/=2.81). The droplet diameters of the spray, including the time-resolved droplet diameter, SMD (Sauter mean diameter) and AMD (arithmetic mean diameter) , injected intermittently from the two nozzles into the still ambient were measured by using a 2-D PDPA (phase Doppler particle analyzer). Through the time-resolved evolutions of the droplet diameter, it was found that the structure of the multi-hole and the single-hole nozzle spray consisted of the three main parts : (a) the leading edge affected by surrounding air. and composed of small droplets; (b) the central part surrounded by the leading edge and mixing flow region and scarcely affected by the resistance of air, (c) the trailing edge formed by the passage of the central part. The SMD decreases gradually with the increase in the radial distance, and the constant value is obtained at the outer region of the radial distance (normalized by hole diameter) of 7-8 and 6 for the 5-hole and single-hole nozzle, respectively. The SMD along the centerline of the spray decrease shapely with the increase in the axial distance after showing the maximum value near the nozzle tip. The SMD remains the constant value near the axial distance(normalized by hole diameter) of 150 and 180 for the 5-hole and the single-hole nozzle, respectively.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.11 s.254
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• pp.1131-1138
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• 2006

Aerodynamic shape design of a partial admission turbine using CFD has been performed. Two step approaches are adopted in this study. Firstly, two-dimensional blade shape is optimized using CFD and genetic algorithm. Initially, the turbine cascade shape is represented by four design parameters. By controlling the design parameters as variables, the non-gradient search is analyzed for obtaining the maximum efficiency. The final two-dimensional blade proved to have a more blade power than the initial blade. Secondly, the three-dimensional CFD analysis including the nozzle, rotor and stator has been conducted. To avoid a heavy computational load due to an unsteady calculation, the frozen rotor method is implemented in steady calculation. The frozen rotor method can detect a variation of the flow-field dependent upon the blade's circumferential position relative to the nozzle. It gives a better idea of wake loss mechanism starting from the lip of the nozzle than the mixing plane concept. Finally, the combination of two and three dimensional design method of the partial admission turbine in this study has proven to be a robust tool in development phase.

• The KSFM Journal of Fluid Machinery
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• v.8 no.5 s.32
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• pp.7-12
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• 2005

Experimental study was conducted to increase the oxygen transfer efficiency of air diffusers in clean water. By measuring the bubble size from the bubbly two-phase flow visualization with several air diffusers, the size of air bubbles near the top surface of aeration tank seems to be independent on the diffuser types. Considering design parameters for the better break-up of larger bubbles around the air diffusers, advanced conceptual air diffusers using nozzle-type throat showing the higher oxygen transfer efficiencies were made.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.6
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• pp.1613-1620
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• 1990

For the purpose of the study on the spray characteristics of a coaxial nozzle, the measurement of the velocity and size of droplets, concentration, and the statistical correlation coefficient between the fluctuation of the velocity and that of the corresponding drop diameter have been carried out. Various method of simultaneous measurement of velocity and drop size have been developed from LDV techniques. The technique used here belongs to the method that supposed by Yule, Holve and Self. It has the advantages of making use of a standard LDV apparatus to which minor modifications have been brought, photomultiplier is equipped with a slit instead of a pinhole and observed the measuring volume at an angle of 90.deg.. The voltage supplied by the photomultiplier has undergone an appropriate analog and digital processing. The experimental results give a good idea of the two phase flow organization and can be helpful to find a drop diffusion model when suitable data are imput.