• Fire Science and Engineering
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• v.15 no.1
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• pp.1-6
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• 2001

In this study, reduced-scale experiments were conducted to understand smoke movements in tunnel fires with the natural ventilation. The 1/20 scale experiments were conducted under the Froude scaling since the smoke movement in tunnels is governed by buoyancy force. Three cases of experiments, in which a natural vent location varied from 1 m, 2 m and 3 m from the fire source symmetrically, were conducted in order to evaluate the effect of the position of ventilation systems on smoke movement. In case of a poo1 whose diameter is 4.36 cm, the temperature of smoke layer passed through the vent was maintained 7~$8^{\circ}c$ less than that of smoke layer without a vent. In case of a pool whose diameter is 5.23 cm, the average velocity passed through the vent was decreased when it was close to the fire source. And the maximum delay time was 3.86s. In CASE 1, the ceiling temperature was decreased by approximately 8$^{\circ}C$ and the vertical temperature was decreased by approximately $7^{\circ}c$. In CASE 2, both ceiling and vertical temperature wert decreased by $3^{\circ}c$ and in CASE 3, they were decreased by $2^{\circ}c$ each. It was confirmed that the thickness of smoke layer was maintained uniformly under the 25% height of tunnel through the visualized smoke flow by a laser sheet and the digital camcoder.

• Journal of the Korean Society of Combustion
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• v.19 no.2
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• pp.8-14
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• 2014

Experiments were conducted to clarify role of the outermost edge flame on low-strain-rate flame extinction in buoyancy-suppressed non-premixed methane flames diluted with He and $N_2$. The use of He curtain flow produced a microgravity level of $10^{-2}-10^{-3}g$ in $N_2$- and He-diluted non-premixed counterflow flame experiments. The critical He and $N_2$ mole fractions at extinction with a global strain rate were examined at various burner diameters (10, 20, and 25 mm). The results showed that the extinction curves differed appreciably with burner diameter. Before the turning point along the extinction curve, low-strain-rate flames were extinguished via shrinkage of the outermost edge flame with and without self-excitation. High-strain-rate flames were extinguished via a flame hole while the outermost edge flame was stationary. These characteristics could be identified by the behavior of the outermost edge flame. The results also showed that the outermost edge flame was not influenced by radiative heat loss but by convective heat addition and conductive heat losses to the ambient He curtain flow. The numerical results were discussed in detail. The self-excitation before the extinction of a low-strain-rate flame was well described by a dependency of the Strouhal number on global strain rate and normalized nozzle exit velocity.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.3
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• pp.211-217
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• 2014

This study analyzes the nonlinear interaction between two different vortex shedding frequencies from a cylinder with two diameters. In particular, two different vortex shedding frequencies are generated by preparing a cylinder having two diameters artificially. Flow velocity fluctuations behind the cylinder are measured three-dimensionally. Additionally, we fabricated a hole and placed a pressure transducer for measuring the pressure on the cylinder surface. The pressure signal from the pressure transducer is used as basic signal. A TSC(Trans Spectrum Coherence) is used for checking the strength of the nonlinear interaction between two different vortex shedding frequencies. As a result, the following are clarified: i) frequency distribution behind the cylinder, ii) three-dimensional flow state behind the cylinder through calculation of ensemble average, and iii) close relationship between the vertical vortex and change of low frequency by nonlinear interaction between two different vortex shedding frequencies from the cylinder with two diameters.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.11a
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• pp.399-402
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• 2006

The purpose of this study is to propose a method for protecting injector face for prolonged combustion time and heat flux measurement technique at the injector face. To obtain basic design data and verify the performance of the proposed method, a regenerative cooling injector face was designed and manufactured for the hot firing test. Due to the safety reason, hot fire test were performed 3, 10, 30, 60 and 120 seconds time step. The discrepancy between analytical results adapting to combustion and nozzle and experimental results is believed due to the over estimation of the convection heat transfer calculation. for the injector face, flow velocity is almost negligible, therefore radiation is more important than convection. Consecutive hot firing test during 10, 30, 60 and 120 seconds combustion time shows good repeatability.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.3
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• pp.275-283
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• 2013

An injector that uses methane gas ($CH_4$) and liquid oxygen ($LO_x$) as propellants was designed to verify the combustion characteristics of an engine that uses methane, which is one of the next-generation propellants. A swirl/shear coaxial-type injector was used, and flow analysis was performed using Fluent to determine the main design parameters of the injector. A hydraulic test was performed to understand the atomization and spray pattern characteristics of the injector. Next, a combustion test was performed at the design point to understand the ignition and combustion stability. Additional combustion tests were performed according to the O/F ratio to investigate the combustion characteristics and stabilities using the characteristic exhaust velocity ($C^*$) and fluctuation of the chamber pressure. The experimental results showed that the combustion efficiency was greater than 90%, and the pressure fluctuation was lower than 2% under all conditions.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.12
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• pp.7443-7450
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• 2014

To resolve shortcomings of high-rate anaerobic processes, such as high upward flow velocity, this study sought to improve the structure of the high-rate anaerobic reactor and evaluate its performance. The improved reactor was manufactured by adjusting the diameter and dividing the reactor into three parts. The evaluation of the structurally improved reactor revealed that the reactor could stabilize a single circuit, and prevent the accumulation of solid matter and leakage of microbes, thereby stabilize the microbes. In the process of anaerobic digestion, an increase in pH and alkalinity within the reactor was presumably attributed to bicarbonate created in the process of organic matter decomposition and due to the re-dissolution of some biogas. To maintain a high rate of organic matter removal, the reactor should be operated with more than 9 hrs of HRT and an organic matter load of under $10.kgTCODcr/m^3{\cdot}d$. The methane gas generated in the anaerobic digestion process showed a high content of 65~83 % at the organic matter load of over $7.7kgTCODcr/m^3{\cdot}d$. per removal of CODcr. The methane quantity was generated at $0.10{\sim}0.23m^3CH_4/kgCOD_{rem}$, showing that it was smaller than the theoretical methane generation amount (0.35) in the STP state. In the latter part of high-rate anaerobic process, an advanced treatment process was required to remove nitrogen.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.1
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• pp.53-62
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• 2017

The forced convection heat transfer performance of a twist-vane spacer grid for a dual-cooled annular fuel assembly was examined experimentally. The twist-vane spacer grid was uniquely designed to enhance mixing inside subchannels and mixing between adjacent subchannels. For testing, a $4{\times}4$ square-arrayed rod bundle with narrow gaps between rods was prepared as the dual-cooled annular fuel assembly to be simulated. The pitch-to-rod diameter ratio of simulated dual-cooled annular fuel assembly was 1.08. The experiments were performed under the following conditions: axial bulk velocity, 1.5 m/s and heat flux, $26kW/m^2$. With regard to the circumferential temperature distribution, the lowest rod-wall temperatures upstream and downstream were measured at the subchannel center and the position toward the tip of twist-vane, respectively. With regard to the axial temperature distribution, behind the twist-vane spacer grid, the rod-wall temperature decreased drastically, and the Nusselt number was enhanced by up to 56 %. The present measured data indicate that the twist-vane spacer grid can effectively improve the forced convection heat transfer in the dual-cooled annular fuel assembly with narrow gaps.