• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.8
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• pp.1005-1012
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• 2001

When vortex tubes are applied to enhance the coefficient of performance of refrigeration system, the smaller one is preferable. However, the existing vortex generator with a nozzle hole diameter of 0.5mm was not suitable due to chocking of the nozzle hole. Therefore, experimental investigation was made to find an appropriate geometry of vortex generator, which could give a comparable effect of energy separation to commercial ones without chocking problem. The tested vortex generators were tangential and spiral types, which had single inducing channel with larger cross-sectional area than that of conventional multi-hole ones. The experimental result showed that the performance of the spiral type was better than that of the tangential one. As a small size of spiral one, the diameter of cold-end orifice is proposed to an half of tube diameter for the application to refrigeration system, while cold mass fraction ratio is 0.5∼0.6 for a desirable operation.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.11
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• pp.900-908
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• 2009

Numerical simulation has been carried out to investigate the influence of radial temperature gradient on the Taylor Vortex flow. Varying the Grashof number, we study the detailed flow and temperature fields. The current numerical results show good agreement with the experimental results currently available. It turns out that wavy spiral vortices are generated by increasing temperature gradient. We classify flow patterns for various Grashof numbers based on the characteristics of flow fields and spiral vortices. The correlation between Grashof number with wave number shows that the spiral angle and size of Taylor vortices increase with increasing temperature gradient. Temperature gradient does not have a great influence on the heat transfer rate of the cylinder surfaces.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.23 no.6
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• pp.555-560
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• 2014

This paper presents a microparticle separator using a spiral microchannel. A particle separator based on the dean vortex was designed, fabricated, and characterized. Two different spiral microchannels were fabricated. Width and initial radius of rotation in the spiral microchannel were fixed to $300{\mu}m$ and 1.75 mm, respectively. Two different depths of the microchannels were designed at $50{\mu}m$ and $80{\mu}m$. In this experimental study, the equilibrium position of microparticles was monitored by using fluorescent microbeads. In the case of a low dean number (<1.0), lift force and dean drag force were similar, indicating that microbeads were distributed to almost all areas across microchannels. However, in the case of a high dean number (>1.0), dean drag force rather than lift force was dominant, indicating that microbeads moved toward the inner wall of the spiral microchannel.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.2029-2034
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• 2004

Spiral jet is characterized by a wide region of the free vortex flow with a steep axial velocity gradient, while swirl jet is largely governed by the forced vortex flow and has a very low axial velocity at the jet axis. However, detailed generation mechanism of spiral flow components is not well understood, although the spiral jet is extensively applied in a variety of industrial field. In general, it is known that spiral jet is generated by the radial flow injection through an annular slit which is installed at the inlet of a conical convergent nozzle. The present study describes a computational work to investigate the effects of annular slit on the spiral jet. In the present computation, a finite volume scheme is used to solve three dimensional Naver-Stokes equations with RNG ${\kappa}-{\varepsilon}$ turbulent model. The annular slit width and the pressure ratio of the spiral jet are varied to obtain different spiral flows inside the conical convergent nozzle. The present computational results are compared with the previous experimental data. The results obtained obviously show that the annular slit width and the pressure ratio of the spiral jet strongly influence the characteristics of the spiral jets, such as tangential and axial velocities.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.6 s.249
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• pp.578-586
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• 2006

Numerical simulations are carried out to investigate the thermal effects of the gravitational potential on the centrifugal instability of a Taylor-Couette flow, and to further study the detailed flow fields and flow bifurcations to spiral vortices. The effects of centrifugal potential on the centrifugal instability are also investigated in the current study. Spiral vortices have various types of mode depending on Grashof number and Reynolds number. The correlation of Richardson number with the spiral angle of the spiral vortices shows that the structure of the spiral vortices strongly depends on the Richardson number. The heat transfer rate of the inner cylinder increases with increasing Grashof number. It is also confirmed that the torque required to rotate the inner cylinder increases as Grashof number increases.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.502-507
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• 2003

Spiral jet is characterized by a wide region of the free vortex flow with a steep axial velocity gradient, while swirl jet is largely governed by the forced vortex flow and has a very low axial velocity at the jet axis. However, detailed generation mechanism of spiral flow components is not well understood, although the spiral jet is extensively applied in a variety of industrial field. In general, it is known that spiral jet is generated by the radial flow injection through an annular slit which is installed at the inlet of convergent nozzle. The objective of the present study is to understand the flow characteristics of the spiral jet, using a computational method. A finite volume scheme is used to solve 3-dimensional Navier-Stokes equations with RNG ${\kappa}-{\varepsilon}$ turbulent model. The computational results are validated by the previous experimental data. It is found that the spiral jet is generated by coanda effect at the inlet of the convergent nozzle and its fundamental features are dependent the pressure ratio of the radial flow through the annular slit and the coanda wall curvature.

• The KSFM Journal of Fluid Machinery
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• v.12 no.5
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• pp.13-18
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• 2009

In this paper, it is intended to figure out the features and causes of the processes of creation, growth and disappearance of spiral-vortex-flow generated in Francis turbines generally. The spiral-vortex-flow generated in draft tubes of the Francis turbines is estimated to have negative effects on power plant structure and to the people inside the building as well as to lead to a low-frequency-vibration driven by sub-synchronous whirl vibration. Therefore, we intend to investigate how much the low-frequency-vibration has an influence upon the powerhouse structure and practice analyzing the effectiveness on the previously-introduced methods to reduce side-effects of sub-synchronous whirl vibration and finally we intend to show the optimal solutions through this paper.

• Proceedings of the Korea Water Resources Association Conference
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• 2005.09a
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• pp.271-272
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• 2005

• Journal of computational fluids engineering
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• v.14 no.3
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• pp.16-24
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• 2009

Numerical simulation has been carried out to investigate the influence of radial temperature gradient on the Circular-Couette flow. Varying the Grashof number, we study the detailed flow and temperature fields. The current numerical results show good agreement with the analytical and experimental results currently available. It turns out that spiral vortices are generated by increasing temperature gradient. We classify the flow patterns for various Grashof number based on the characteristics of flow fields and spiral vortices. The correlation between Richardson number with wave number shows that the spiral angle and size of spiral vortices increase with increasing Richardson number.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.7
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• pp.1381-1390
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• 1992

This paper presents a dynamic characteristics of flow induced vibration of circular cylinder set with inclined angle against flow direction. The effect of the cylinder bounded by spiral fin and wire on the damping of flow induced vibration is investigated, i.e., inclined angle, spiral pitch angle and number of spiral thread are studied. As the results, the cylinder with spiral fin is most effective for the damping. Also the cylinder bounded by pitch angle 50.deg. and 2 spiral thread is most effective.