• Journal of the Korean Institute of Gas
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• v.23 no.1
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• pp.12-18
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• 2019

Exhaust gas recirculation method is widely used among various methods for reducing nitrogen oxides in automobile engines and incinerators. In the present study, the computational fluid dynamic analysis was accomplished to derive the optimal location of air nozzle exit position by changing its position in a venturi tube for the maximum flue gas recirculation effect. In addition, the flue gas recirculation characteristics with a cone at the exit of air nozzle was elucidated with flue gas recirculation flow rate ratio and mixed gas exit temperature. When the air nozzle exit position was changed from the start position (z = 0) to the end position (z = 0.6m) of the exhaust gas recirculation exit pipe, the change of streamline and temperature distribution in the venturi tube was observed. The exhaust gas recirculation flow rate and the average temperature at the mixed gas exit position was quantitatively compared. From the present study, the optimal location of air nozzle exit position for the maximum flue gas recirculation flow rate ratio and maximum mixed gas exit temperature is z = 0.15m (1/4L). In addition, when the cone is installed at the outlet of the air nozzle, the velocity of the air nozzle outlet is increased, the flue gas recirculation flow rate was increased by about 2 times of the flow rate without cone, and the mixed gas exit temperature is increased by $116^{\circ}C$.

• Journal of the Korean Society of Propulsion Engineers
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• v.21 no.4
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• pp.89-95
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• 2017

The improvement of a flow coefficient for the recirculation chill-down flow in a main oxidizer shut-off valve has been presented. The flow coefficient, which is mainly affected by the recirculation outlet port size and the configuration inside the valve, has been predicted with measured flow coefficient values. The comparison of experimentally measured flow coefficient with the predicted value shows the effect of valve inside configuration on the flow coefficient. Consequently, the flow coefficient is twice the previous value and about 75% of the pressure loss assigned to the main oxidizer shut-off valve can be used for additional pressure losses for other components in the recirculation chill-down system of a launch vehicle.

• Journal of the Korean Society of Visualization
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• v.6 no.1
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• pp.41-46
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• 2008

In this paper, the recirculation flow motion and mixing characteristics driven by air bubble stream in a rectangular water tank is studied. The time-resolved PIV technique is adopted for the quantitative visualization and analysis. 488 nm Ar-ion CW laser is used for illumination and orange fluorescent ($\lambda_{ex}=540nm,\;\lambda_{em}=560nm$) particle images are acquired by a PCO 10bit high-speed CCD camera (1280$\times$1024). To obtain clean particle images, 545 nm long pass optical filter and an image intensifier are employed and the flow rates of compressed air is 3 l/min at 0.5 MPa. The recirculation and mixing flow field is further investigated by time-resolved POD analysis technique. It is observed that the large scale recirculation resulting from the interaction between rising bubble stream and side wall is the most dominant flow structure and there are small scale vortex structures moving along with large scale recirculation flow. It is also verified that the sum of 20 modes of velocity field has about 67.4% of total turbulent energy.

• Nuclear Engineering and Technology
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• v.49 no.5
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• pp.979-988
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• 2017

The feasibility of cooling in a pressurized heavy water reactor after a large break loss-of-coolant accident has been analyzed using Multidimensional Analysis of Reactor Safety-KINS Standard code during the recirculation phase. Through evaluation of sensitivity of the fuel channel temperature to various effective recirculation flow areas, it is determined that proper cooling of the fuel channels in the broken loop is feasible if the effective flow area remains above approximately 70% of the nominal flow area. When the flow area is reduced by more than approximately 25% of the nominal value, however, incipience of boiling is expected, after which the thermal integrity of the fuel channel can be threatened. In addition, if a dramatic reduction of the recirculation flow occurs, excursions and frequent fluctuations of temperature in the fuel channels are likely to be unavoidable, and thus damage to the fuel channels would be anticipated. To resolve this, emergency coolant supply through the newly installed external injection path can be used as one alternative means of cooling, enabling fuel channel integrity to be maintained and permanently preventing severe accident conditions. Thus, the external injection flow required to guarantee fuel channel coolability has been estimated.

• Journal of ILASS-Korea
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• v.16 no.2
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• pp.90-96
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• 2011

Atomized liquid jets from the washing nozzle which configured with recirculation chamber for cleaning hot-zone area are accelerated and impinged on the head lamp surface. Cleaning efficiency of head lamp can be increased with injecting washing fluids into the hot-zone area. Experimental and numerical studies with various design parameters were executed to reveal the relations between internal geometry and internal flow in the washing nozzle. Spray structures were fitted with each of the head lamp surfaces and spray nozzles were optimized to the spray pattern. The recirculation chamber induces a recirculation flow and can be decreased the pressures perturbation inside the chamber. Orifice determines the mass flow rate. When the diameter of orifice is excessively large, it showed an unstable spray pattern. As a nozzle exit angle increases, density distributions are separated with two section. Also, as a protrusion length of nozzle exit increases, spray patterns are spread into a large area and density distributions showed unstable trend.

• Journal of Advanced Marine Engineering and Technology
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• v.25 no.6
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• pp.1308-1316
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• 2001

This paper described a numerical investigation performed to understand better the effects of flow parameters in an entrained flow combustor on the flow characteristics. The computational model was based on the gas phase Eulerian equations of mass, momentum and energy. The code was formulated with RNG $k-\varepsilon$ model for turbulent flow. The calculation parameters were the ratio of primary and secondary jet velocity and the height difference between primary and secondary jet As the secondary jet velocity increased, the upper recirculation 3one of the primary jet was strengthened. It was found that as the primary jet velocity increased, there was a critical jet Velocity at which the size of upper and lower recirculation zone was reversed.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.6
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• pp.446-454
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• 2008

The purpose of this paper is to analyze two-phase flows of the hydrogen recirculation system. Two-phase flow modeling is one of the great challenges in the classical sciences. As with most problems in engineering, the interest in two-phase flow is due to its extreme importance in various industrial applications. In hydrogen recirculation systems of fuel cell, the changes in pressure and temperature affect the phase change of mixture. Therefore, two-phase flow analysis of the hydrogen recirculation system is very important. Two-phase computation fluid dynamics (CFD) calculations, using a commercial CFD package FLUENT 6.2, were employed to calculate the gas-liquid flow. A two-phase flow calculation was conducted to solve continuity, momentum, energy equation for each phase. Then, the mass transfer between water vapor and liquid water was calculated. Through an experiment to measure production of liquid water with change of pressure, the analysis model was verified. The predictions of rate of condensed liquid water with change of pressure were within an average error of about 5%. A comparison of experimental and computed data was found to be in good agreement. The variations of performance, properties, mass fraction and two-phase flow characteristic of mixture with resepct to the fuel cell power were investigated.

• Journal of Industrial Technology
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• v.19
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• pp.59-65
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• 1999

This study is to analyze turbulent flow over a backward-facing step in a rectangular duct. The side wall effects on the internal flow were determined by varying the aspect ratio(defined as the step span-to-height ratio) from 1 to 20. In the flow behind a backward-facing step, separation, recirculation and redeveloping is occurred frequently. These phenomena appear in a particular variation by varying the aspect ratio. The results show that the aspect ratio has an influence on the velocity and reattachment length. When the AR is increased, the reattachment length is increased. For 6 over aspect ration, the rate of increase is decreased. The length of recirculation in the upper corner is increased, as the increase of aspect ration. It's width is not changed in the variation of aspect ration. The transverse, streamwise and spanwise velocities were decreased along the flow down stream of the step.

• Journal of the Korean Society of Visualization
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• v.19 no.1
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• pp.88-93
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• 2021

For a flow normal to a circular disk, the flow separation occurs from the edge of the disk and the flow recirculation zone exists behind the disk. Many existing studies conducted simulations of flow normal to a circular disk under low Reynolds numbers. Some studies performed LES or DES simulations under high Reynolds numbers. However, comparative study for different RANS models for high Reynolds numbers is very limited. This study presents numerical simulations of a flow normal to a circular disk using Realizable k-ε model and SST k-ω model. The recirculation bubble length and drag coefficient were compared with the experimental data. The SST k-ω model showed the excellent predictions for the recirculation bubble length and drag coefficient.

• 유체기계공업학회:학술대회논문집
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• 2006.08a
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• pp.551-554
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• 2006

Inhibition of propellant temperature rising in liquid propulsion rocket using cryogenic fluid as a propellant is very important. Especially propellant temperature rising during stand-by after filling and pre-pressurization can bring into cavitation in turbo-pump. One of the method preventing propellant temperature rising in cryogenic feeding system is recirculating propellant through the loop composed of propellant tank, feed pipe, and recirculation pipe. The circulation of propellant is promoted through gas-lift effect by gas injection to lower position of recirculation pipe. In this experiment liquid oxygen and gas helium is used as propellant and injection gas. Under atmospheric and pressurized tank ullage condition, helium injection flow-rate is varied to observe the variation of recirculating flow-rate and propellant temperature in the feed pipe. There is appropriate helium injection flow-rate for gas-lift recirculation system.