• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.5
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• pp.691-699
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• 1997

The effects of concave hemispherical surface curvature on the local heat transfer from a turbulent round impinging jet were experimentally investigated. The liquid crystal transient method was used for these measurements. This method, which is a variation on the transient method, suddenly exposes a preheated wall to an impinging jet while video recording the response of liquid crystals for the measurement of the surface temperature. The Reynolds number ranges from Re=11,000 to 50,000, the nozzle-to- surface distance from L/d=2 to 10, and the surface curvature from D/d=6 to 12.The present results are also compared to those for the flat plate case. In the experiment, the local Nusselt numbers tend to increase in all regions with an increasing surface curvature. The maximum Nusselt number for all Reynolds numbers occurred at L/d .ident. 6 and a second maximum in the Nusselt number occurred at R/d .ident. 2 for both Re=23,000 and Re=50,000 in the case of L/d=2 and for Re=50,000 only in the case of L/d=4. Meanwhile, as the surface curvature increases, the value of the secondary maximum Nusselt number decreases. All the other cases exhibit monotonically decreasing values of the Nusselt number along the curved surface. The stagnation point Nusselt numbers are well correlated with Re, L/d, and D/d.

• Journal of Biomedical Engineering Research
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• v.26 no.3
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• pp.157-161
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• 2005

Direct injection of a fibrinolytic agent to the intraarterial thrombosis may increase the effectiveness of thrombolysis by enhancing the permeation of thrombolytic agents into the blood clot. Permeation of fibrinolytic agents into a clot is influenced by the surface pressure, which is determined by the injection velocity of fibrinolytic agents. In order to calculate the pressure distribution on the clot surface for different jet velocities (1, 3, 5 m/sec) and nozzle arrangements (1, 9, 17 nozzles), computational fluid dynamic methods were used. Thrombolysis of a clot was mathematically modeled based on the pressure and lysis front velocity relationship. Direct injection of a thrombolytic agent increased the speed of thrombolysis significantly and the effectiveness was increased as the ejecting velocity increased. The nine nozzles model showed about $20\%$ increase of the lysed volume, and the one and seventeen nozzles models did not show significant differences. The wall shear stress decreased as the number of nozzles increased, and the wall shear stress in most vessel wall was lower than 25 Pa. The results implied that thrombolysis could be accelerated by direct injection of a drug with the moderate velocity without damaging the blood vessel wall.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.21 no.9
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• pp.483-495
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• 2009

Feedwater heaters of many nuclear power plants have recently experienced severe wall thinning damange, which will increase as operating time progresses. Several nuclear power plants in Korea have experienced wall thinning damage in the area around the impingement baffle-installed downstream of the high pressure turbine extraction stream line-inside number 5A and 5B feedwater heaters. At that point, the extracted steam from the high pressure turbine is two phase fluid at high temperature, high pressure, and high speed. Since it flows in reverse direction after impinging the impingement baffle, the shell wall of the number 5 high pressure feedwater heater may be affected by flow-accelerated corrosion. This paper describes operation of experience and numerical analysis composed similar condition with real high pressure feedwater heater. This study applied squared, curved and new type impingement baffle plates to feedwater heater same as previous study. In addition, it shows difference of pressure distribution and value between single phase and two phase based on experience and numerical analysis.

• 한국전산유체공학회:학술대회논문집
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• 2005.10a
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• pp.93-97
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• 2005

Air interlacing serves to protect the yarn against damage, strengthens inter-filament compactness or cohesion, and ensures fabric consistency. The air interlacing nozzle is used to introduce intermittent nips to a filament yarn so as to improve its performance in textile processing. This study investigates the effect of interlacing nozzle geometry on the interlacing process. The geometries of interlacing nozzles with multiple air inlets located across the width of a yarn channels are investigated. The basic interlacing nozzle is the yarn channel, with a perpendicular single air inlet in the middle. The yarn channel shapes are cross sections with semicircular or rectangular shapes. This paper presents three doubled sub air inlets with main air inlet and one of them is slightly inclined doubled sub air inlets with main air inlet. The compressed air coming out from the inlet hits the opposing wall of the yarn channel, divides into two branches, flows trough the top side of yarn channel, joins with the compressed air coming out from the sub air inlet and then creates two free jets at both ends of the yarn channel. The compressed air moves in the shape of two opposing directional vortices. The CFD-FASTRAN was used to perform steady simulations of impinging jet flow inside of the interlace nozzles. The vortical structure and the flow pattern such as pressure contour, particle traces, velocity vector plots inside of interlace nozzle geometry are discussed in this paper.

• Journal of the Korean Society of Propulsion Engineers
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• v.20 no.4
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• pp.59-67
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• 2016

Numerical simulations have been performed to investigate thrust characteristics of a through-type pintle nozzle with or without flow separation at various operating altitudes. The low Reynolds number $k-{\varepsilon}$ with compressibility correction proposed by Sarkar are applied. The detail flow structures are observed and static pressures along nozzle wall are compared with experimental results. The flow separation in the pintle nozzle disappears and jet plume strongly expands as its operating altitude increases. To evaluate the thrust characteristics, the momentum term and pressure term of thrust are analyzed. Thrust and thrust coefficient at altitude 20 km are about 10% more than them at the ground 0km.

• Journal of ILASS-Korea
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• v.10 no.1
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• pp.17-23
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• 2005

Even though a relatively complete knowledge base has been established for diesel sprays, much of the knowledge cannot be directly translated to correlate the characteristics of gasoline spray. The macroscopic characteristics of gasoline impingement spray was investigated with photographic and image processing technique by Particle Motion Analysis System. The injector with single hole nozzle diameter of 0.28 mm was used in this experiment and the injection duration was selected as 10 msec. The injection pressure with 0.3, 0.35, and 0.4 MPa, impingement distance or 70, 100 and 130m, impingement angle or 0.15, 30 and $45^{\circ}$ were employed for the variables to affect the spray characteristics of impinging spray. It is clear that there is the analogy on the spray tip penetration between the gasoline impinging jet and diesel free jet. The spray tip penetration of impinging gasoline spray is proportional to the quarter power of the time after start of injection. The maximum height of impinging gasoline spray is also proportional to the quarter power of the time regardless of impingement distance, impingement angle and injection pressure. In addition, the effect of impingement angle on the spray tip penetration is significant according to the time after start of injection, even though there is minor effect in the initial stage of time after start of injection. Moreover, there is no remarkable effect of injection pressure on the spray tip Penetration under the experimental condition used in this study.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.6
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• pp.734-743
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• 1999

The local Nusselt numbers have been measured for a round turbulent jet impinging on the concave surface with and without rib. Liquid crystal/transient method was used to determine the Nusselt number distributions along the surface. The temperature on the surface was measured using liquid crystal and a digital color image processing system. The experiments were made for the jet Reynolds number (Re) 23,000, the dimensionless nozzle-to-surface distance (L/d) from 4 to 10, the dimensionless surface curvature (d/D) 0.056, and the rib type (height ($d_1$) 0.2 cm, pitch (p) from 1.2 to 3.2 cm). It was founded that only when $L/d{\geq}6$, the average Nusselt numbers on the concave surface with rib are higher than those without rib, mainly due to an increase in the turbulent intensity caused by the effect of rib attached to the wall surface. It was realized that the rib attached to the concave surface may no longer enhance the heat transfer rate or even lowers it depending on the rib type and flow conditions. In addition, the results by the steady-state method using the gold-film Intrex were in good agreement with those by the transient shroud method.

• Nuclear Engineering and Technology
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• v.44 no.7
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• pp.727-734
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• 2012

A new advanced safety feature of DVI+ (Direct Vessel Injection Plus) for the APR+ (Advanced Power Reactor Plus), to mitigate the ECC (Emergency Core Cooling) bypass fraction and to prevent switching an ECC outlet to a break flow inlet during a DVI line break, is presented for an advanced DVI system. In the current DVI system, the ECC water injected into the downcomer is easily shifted to the broken cold leg by a high steam cross flow which comes from the intact cold legs during the late reflood phase of a LBLOCA (Large Break Loss Of Coolant Accident)For the new DVI+ system, an ECBD (Emergency Core Barrel Duct) is installed on the outside of a core barrel cylinder. The ECBD has a gap (From the core barrel wall to the ECBD inner wall to the radial direction) of 3/25~7/25 of the downcomer annulus gap. The DVI nozzle and the ECBD are only connected by the ECC water jet, which is called a hydrodynamic water bridge, during the ECC injection period. Otherwise these two components are disconnected from each other without any pipes inside the downcomer. The ECBD is an ECC downward isolation flow sub-channel which protects the ECC water from the high speed steam crossflow in the downcomer annulus during a LOCA event. The injected ECC water flows downward into the lower downcomer through the ECBD without a strong entrainment to a steam cross flow. The outer downcomer annulus of the ECBD is the major steam flow zone coming from the intact cold leg during a LBLOCA. During a DVI line break, the separated DVI nozzle and ECBD have the effect of preventing the level of the cooling water from being lowered in the downcomer due to an inlet-outlet reverse phenomenon at the lowest position of the outlet of the ECBD.

• Journal of Korean Tunnelling and Underground Space Association
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• v.23 no.6
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• pp.535-547
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• 2021

A policy to expand the hydrogen economy has been established in Korea and the supply of FCEV is being expanded to realize a hydrogen society. Therefore, the supply of FCEV is expected to increase rapidly, and a solution to respond to accidents of FCEV is required. In this study, an experimental study was conducted to analyze the effect of the hydrogen jet flame generated by a FCEV on the inner wall of the tunnel and the characteristics of the internal radiant heat. For the experiment, the initial pressure of hydrogen tank was set to 700 bar, and the injection nozzle diameter was set to 1.8 mm in order to make the same as the conditions generated in the FCEV. In addition, a tunnel fire resistance test specimen having the same strength as the compressive strength of concrete applied to general tunnels of 40 MPa was manufactured and used in the experiment. The results were analyzed for the separation distance (2 m and 4 m) between the hydrogen release nozzle and the tunnel fire resistance test concrete. As the result, the maximum internal temperature of the test concrete was measured to 1,349.9℃ (2 m separation distance), and the radiant heat around the jet flame was up to 39.16 kW/m².

• 한국가시화정보학회:학술대회논문집
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• 2005.12a
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• pp.69-73
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• 2005

Three-dimensional density distributions of an impinging and eccentric flame have been analyzed numerically and experimentally by a combined optical system with a digital speckle tomography. The flame has been ignited by premixed butane/air from air holes and impinged vertically against a plate located at the upper side of tile burner nozzle. In order to compare with experimental data, computer synthesized phantoms of impinging and eccentric flames have been made and reconstructed by a developed three-dimensional multiplicative algebraic reconstruction technique (MART). A new scanning technique has been developed for the analysis of speckle displacements to investigate wall jet regions of the impinging flame including sharp variation of the flow direction and pressure gradient. The reconstructed temperatures have been compared with a temperature photography by an infrared camera and results of numerical analysis using a finite-element method.