• Proceedings of the KSME Conference
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• 2001.06e
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• pp.131-135
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• 2001

The atomization characteristics of an annular liquid (water) sheet of small radius with a core gas (air) flow were studied. Different sizes of annular gaps (0.2, 0.4 and 0.8 mm) were tested to find the effect of liquid sheet thickness on SMD. The inner diameter of the gas port for the core gas flow was 4 mm. Cross-section averaged SMD was measured for various liquid and gas velocities. Regions of the SMD decrease with the increase of the liquid velocity always existed regardless of the liquid sheet thickness. This attributes to the transition of the flow patterns of spray and also to the aerodynamic interaction between the atomizing gas and the ripples on the liquid sheet surface.

• Journal of ILASS-Korea
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• v.10 no.4
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• pp.32-46
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• 2005

The breakup characteristics of liquid sheets formed by the impinging and swirl type injectors were studied as increasing the Weber number (or injection condition) and the ambient gas pressure to 4.0.MPa. In the case of impinging type injector. we compared the changes of breakup lengths between laminar and turbulent sheets. which are formed by the impingement of laminar and turbulent jets. respectively. The results showed that both sheets expand as increasing the injection velocity irrespective of the ambient gas density when the gas based Weber number is low. When the Weber number is high, however, the breakup of turbulent sheet depends on the hydraulic force of jets as well as the aerodynamic force of ambient gas which determines the breakup of laminar sheet. Using the experimental results. we could suggest empirical models on the breakup lengths of laminar and turbulent sheets. In the case of swirl type injector. as $We_l$, and ambient gas density increased, the disturbances on the annular liquid sheet surface were amplified by the increase of the aerodynamic forces. and thus the liquid sheet disintegrated near from the injector exit. Finally, the measured breakup length of swirl type injector according to the ambient gas density and $We_l$, was compared with the result by the linear instability theory. We found that the corrected breakup length relation derived from linear instability theory considering the attenuation of sheet thickness agrees well with our experimental results.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.7
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• pp.97-104
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• 2006

The spray and breakup characteristics of swirling liquid sheet were investigated by measuring the spray angle and breakup length as the axial Weber number Wel was increased up to 1554 and the ambient gas pressure up to 4.0MPa. As Wel and ambient gas density increased, the disturbances on the annular liquid sheet surface were amplified by the increase of the aerodynamic forces, and thus the liquid sheet disintegrated near from the injector exit. The measured spray angles according to the ambient gas density were different before and after the sheet breaks. Before the liquid sheet breaks, the spray angle was almost constant, but once the liquid sheet started to breakup, the spray angle decreased. And the breakup length decreased because of the increase of the aerodynamic force as the ambient gas density and Wel increased. Lastly, the measured breakup length according to the ambient gas density and Wel was compared with the result by the linear instability theory. We found that the corrected linear instability theory considering the attenuation of sheet thickness agrees well with our experimental results.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.05b
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• pp.233-240
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• 1996

Analyses of the viscous and end effects on electromagnetic (EM) pumps of annular linear induction type for the sodium coolant circulation in Liquid Metal Fast Breeder Reactors have been carried out based on the MHD laminar flow analysis and the electromagnetic field theory. A one-dimensional MHD analysis for the liquid metal flowing through an annular channel has been performed on the basis of a simplified model of equivalent current sheets instead of three-phase currents in the discrete primary windings. The calculations show that the developed pressure difference resulted from electromagnetic and viscous forces in the liquid metal is expressed in terms of the slip, and that the viscous loss effects are negligible compared with electromagnetic driving forces except in the low-slip region where the pumps operate with very high flow velocities comparable with the synchronous velocity of the electromagnetic fields, which is not applicable to the practical EM pumps. A two-dimensional electromagnetic field analysis based on an equivalent current sheet model has found the vector potentials in closed form by means of the Fourier transform method. The resultant magnetic fields and driving forces exerted on the liquid metal reveal that the end effects due to finiteness of the pump length are formidable. In addition, a two-dimensional numerical analysis for vector potentials has been performed by the SOR iterative method on a realistic EM pump model with discretely-distributed currents in the primary windings. The numerical computations for the distributions of magnetic fields and developed pressure differences along the pump axial length also show considerable end effects at both inlet and outlet ends, especially at high flow velocities. Calculations of each magnetic force contribution indicate that the end effects are originated from the magnetic force caused by the induced current ( u x B ) generated by the liquid metal movement across the magnetic field rather than the one (E) produced by externally applied magnetic fields by three-phase winding currents. It is concluded that since the influences of the end effects in addition to viscous losses are extensive particularly in high-velocity operations of the EM pumps, it is necessary to find ways to suppress them, such as proper selection of the pump parameters and compensation of the end effects.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.22 no.1
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• pp.227-237
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• 1998

In case the systems have radioactivity, toxic liquid or expensive fluid, and have to be performed repair work at one point of the system pipe, the formation of an internal ice plug by the removal of heat from the pipe is often consideredas a useful method. In this procedure, an annular jacket is placed around the pipe, and the jacket is then filled with liquid Nitrogen(-196.deg. C). Thermal analysis by the finite element method based on the laboratory experiments has been constructed. The result of the finite element analysis on the experimental model shows to be reasonable, and thus the finite element analysis for different pipe size, material and thickness has been performed to see if the ice plugging procedure in various applications can be safely performed without possibility of damage to the pipe. It has been confirmed that in carbon steel pipes the maximum stress is found around the boundary of the freezing jacket, and the stress increases as pipe thickness increases, but the maximum stress shows no consistency along the increment of the pipe diameter. The maximum stresses appear lower than yield stress in carbon steel. It has been also shown that in stainless steel pipes the maximum stresses are also found around the boundary of the freezing jacket, but almost the same value in spite of different pipe size an thickness, and the maximum stresses show slightly higher than the yield stress of the stainless steel.