28 results on '"Ji Soo Ha"'
Search Results
2. The Power Spectral Density Characteristics of Lift and Drag Fluctuation of Fin Tube in a Heat Recovery Steam Generator
- Author
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Boo Youn Lee and Ji Soo Ha
- Subjects
Lift-to-drag ratio ,Materials science ,Heat recovery steam generator ,Parasitic drag ,Vortex-induced vibration ,Drag ,Heat exchanger ,Thermodynamics ,Tube (fluid conveyance) ,Mechanics ,Fin (extended surface) - Published
- 2016
3. A Study on the Characteristics of Lift and Drag Fluctuation Power Spectral Density in a Heat Exchanger Tube Array
- Author
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Ji-Soo Ha
- Subjects
Lift-to-drag ratio ,Materials science ,business.industry ,Laminar flow ,Structural engineering ,Mechanics ,Concentric tube heat exchanger ,Physics::Fluid Dynamics ,symbols.namesake ,Vortex-induced vibration ,Heat recovery steam generator ,Heat exchanger ,symbols ,Strouhal number ,Tube (fluid conveyance) ,business - Abstract
A heat exchanger tube array in a heat recovery steam generator is exposed to hot exhaust gas flow that can cause flow induced vibrations, which could damage the heat exchanger tube array. The characteristics of flow induced vibration in the tube array need to be established for the structural safe operation of a heat exchanger. Several studies of the flow induced vibrations of typical heat exchangers have been conducted and the nondimensional PSD (Power Spectral Density) function with the Strouhal number, fD/U, had been derived using an experimental method. The present study examined the results of the previous experimental research on the nondimensional PSD characteristics by CFD analysis and the basis for the application of flow induced vibration to the heat recovery steam generator tube array was determined from the present CFD analysis. The present CFD analysis introduced circular cylinder tube array and calculated using unsteady laminar flow for the tube array. The characteristics of lift and drag fluctuations over the cylinder tube array was investigated. The derived nondimensional lift and drag PSD was compared with the results of the previous experimental research and the characteristics of lift and drag PSD for a circular cylinder tube array was established from the present CFD study.
- Published
- 2016
4. A Study on the Characteristics of Lift Fluctuation Power Spectral Density on a Fin Tube in the Heat Recovery Steam Generator
- Author
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Ji Soo Ha, Sung Hun Shim, and Boo Youn Lee
- Subjects
Materials science ,business.industry ,Laminar flow ,Structural engineering ,Mechanics ,Annular fin ,Concentric tube heat exchanger ,Lift (force) ,symbols.namesake ,Vortex-induced vibration ,Heat recovery steam generator ,Heat exchanger ,symbols ,Strouhal number ,business - Abstract
Heat exchanger tube array in a heat recovery steam generator is exposed to the hot exhaust gas flow and it could cause the flow induced vibration, which could damage the heat exchanger tube array. It is needed for the structural safe operation of the heat exchanger to establish the characteristics of flow induced vibration in the tube array. The researches for the flow induced vibration of typical heat exchangers have been conducted by using single cicular tube or circular tube array and the nondimensional PSD(Power Spectral Density) function with the Strouhal number, fD/U, had been derived by experimental method. From the present study, the basis for the application of flow induced vibration to the heat recovery steam generator tube array would be prepared. For the previous mentioned purpose, the present CFD analysis introduced a single fin tube and calculated with the unsteady laminar flow over the single fin tube. The characteristics of vortex shedding and lift fluctuation over the fin tube was investigated. The derived nondimensional PSD was compared with the results of the previous experimental researches and the characteristics of lift PSD over a single fin tube was established from the present CFD study.
- Published
- 2015
5. A study on the flow induced vibration on a heat exchanger circular cylinder
- Author
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Boo Youn Lee, Sung Hun Shim, and Ji Soo Ha
- Subjects
Materials science ,business.industry ,Laminar flow ,Mechanics ,Structural engineering ,Computational fluid dynamics ,Vortex shedding ,Physics::Fluid Dynamics ,Lift (force) ,symbols.namesake ,Heat recovery steam generator ,Vortex-induced vibration ,Heat exchanger ,symbols ,Strouhal number ,business - Abstract
Heat exchanger tube array in a heat recovery steam generator is exposed to the hot exhaust gas flow and it could cause the flow induced vibration, which could damage the heat exchanger tube array. It is needed for the structural safe operation of the heat exchanger to establish the characteristics of flow induced vibration in the tube array. The researches for the flow induced vibration of typical heat exchangers have been conducted and the nondimensional PSD(Power Spectral Density) function with the Strouhal number, fD/U, had been derived by experimental method. The present study examined the results of the previous experimental researches for the nondimensional PSD characteristics by CFD analysis and the basis for the application of flow induced vibration to the heat recovery steam generator tube array would be prepared from the present CFD analysis. For the previous mentioned purpose, the present CFD analysis introduced a single circular cylinder and calculated with the unsteady laminar flow over the cylinder. The characteristics of vortex shedding and lift fluctuation over the cylinder was investigated. The derived nondimensional PSD was compared with the results of the previous experimental researches and the characteristics of lift PSD over a single circular cylinder was established from the present CFD study.
- Published
- 2015
6. The Power Spectral Density Characteristics of Lift and Drag Fluctuation on a Heat Exchanger Circular Tube
- Author
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Ji Soo Ha
- Subjects
Lift-to-drag ratio ,Materials science ,business.industry ,Laminar flow ,Structural engineering ,Mechanics ,Vortex shedding ,Cylinder (engine) ,law.invention ,Physics::Fluid Dynamics ,symbols.namesake ,law ,Vortex-induced vibration ,Heat recovery steam generator ,Heat exchanger ,symbols ,Strouhal number ,business - Abstract
Heat exchanger tube array in a heat recovery steam generator is exposed to the hot exhaust gas flow and it could cause the flow induced vibration, which could damage the heat exchanger tube array. It is needed for the structural safe operation of the heat exchanger to establish the characteristics of flow induced vibration in the tube array. The researches for the flow induced vibration of typical heat exchangers have been conducted and the nondimensional PSD(Power Spectral Density) function with the Strouhal number, fD/U, had been derived by experimental method. The present study examined the results of the previous experimental researches for the nondimensional PSD characteristics by CFD analysis and the basis for the application of flow induced vibration to the heat recovery steam generator tube array would be prepared from the present CFD analysis. For the previous mentioned purpose, the present CFD analysis introduced a single circular cylinder and calculated with the unsteady laminar flow over the cylinder. The characteristics of vortex shedding and lift and drag fluctuation over the cylinder was investigated. The derived nondimensional PSD was compared with the results of the previous experimental researches and the characteristics of lift and drag PSD over a single circular cylinder was established from the present CFD study.
- Published
- 2015
7. A study on the temperature distribution characteristics in the tube modules of a heat recovery steam generator ith the change of heat transfer modeling
- Author
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Ji Soo Ha
- Subjects
Physics::Fluid Dynamics ,NTU method ,Critical heat flux ,Chemistry ,Heat transfer ,Plate heat exchanger ,Mechanical engineering ,Plate fin heat exchanger ,Mechanics ,Heat transfer coefficient ,Heat sink ,Shell and tube heat exchanger - Abstract
A heat recovery steam generator consists of inlet expansion duct and heat transfer tube bank modules. For the enhancement of heat transfer in the tube bank modules, the flow should be uniform before the 1st heat transfer tube bank module. The present study has been carried out to analyze the flow characteristics in the inlet expansion duct of a heat recovery steam generator by using numerical flow analysis. The aim of the present study is to establish the proper heat transfer mechanism in the heat transfer tube bank modules by the comparison of the heat transfer models, the case with the constant heat loss per unit volume and the case with heat loss by using inner and outer convective heat transfer coefficient of heat transfer tube. From the present research, it could be seen that the heat transfer mechanism with using inner and outer convective heat transfer coefficient derives more proper temperature distribution results and the acceptance criteria of the temperature distribution within before SCR is satisfied with using this heat transfer mechanism.
- Published
- 2015
8. Characteristics of Entrainment Flow Rate in a Coanda Nozzle with or without Coaxial Contractor
- Author
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Ji Soo Ha and Sung Hoon Shim
- Subjects
Entrainment (hydrodynamics) ,symbols.namesake ,Materials science ,Nozzle ,symbols ,Mechanics ,Coaxial ,Coandă effect ,Marine engineering ,Volumetric flow rate - Published
- 2014
9. A study on the exhaust gas recirculation in a MILD combustion furnace by using a Venturi nozzle
- Author
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Sung Hoon Shim and Ji Soo Ha
- Subjects
Entrainment (hydrodynamics) ,business.industry ,Chemistry ,Venturi effect ,Nozzle ,Combustor ,Exhaust gas ,Exhaust gas recirculation ,Mechanics ,business ,Discharge coefficient ,Plug nozzle ,Marine engineering - Abstract
The present study used the MILD combustor, which has coaxial cylindrical tube. The outside tube of the MILD combustor corresponds to the exhaust gas passage and the inner side tube is the furnace passage. A numerical analysis was accomplished to elucidate the characteristics of exhaust gas entrainment toward the inner furnace with the changes of venturi nozzle geometrical parameters, nozzle position, nozzle gap between high pressure air nozzle and venturi nozzle, and with the change of high pressure nozzle inlet velocity. The entrainment flow rate for the case with the high pressure air nozzle attached at the exhaust gas wall has relatively small change with the change of nozzle gap. That for the case with the high pressure air nozzle exposed to the exhaust gas has monotonically increase with the change of nozzle gap. The flow rate ratio of entrainment flow rate has considerably increase tendency with relatively lower air inlet velocity, on the other hand, that with relatively higher air inlet velocity could be seen relatively small increase.
- Published
- 2013
10. A Study on the Exhaust Gas Recirculation in a MILD Combustion Furnace by Using the Coanda Nozzle Effect
- Author
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Sung Hoon Shim and Ji Soo Ha
- Subjects
Materials science ,business.industry ,Nozzle ,Combustor ,Exhaust gas ,Exhaust gas recirculation ,Mechanics ,Aerospace engineering ,Propelling nozzle ,business ,Combustion ,Discharge coefficient ,Plug nozzle - Abstract
A MILD (Moderate and Intense Low oxygen Dilution) combustion, which is effective in the reduction of NOx, is considerably affected by the recirculation flow rate of hot exhaust gas to the combustion furnace. The present study used the MILD combustor, which has coaxial cylindrical tube. The outside tube of the MILD combustor corresponds to the exhaust gas passage and the inner side tube is the furnace passage. A numerical analysis was accomplished to elucidate the characteristics of exhaust gas entrainment toward the inner furnace with the changes of coanda nozzle geometrical parameters, nozzle passage gap length, nozzle passage length, nozzle angle and expansion length. The optimal configuration of coanda nozzle for the best entrainment flow rate was gap length, 0.5 mm, expansion angle, 4o and expansion length, 146 mm. The nozzle passage length was irrelevant to the exhaust gas entrainement.
- Published
- 2013
11. A Study on the Heat Flux Meter Location for the Performance Test of a Refrigerator Vacuum Insulation Panel
- Author
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Ji Soo Ha
- Subjects
Vacuum insulated panel ,Materials science ,Heat flux ,Heat flux sensor ,Heat transfer ,Refrigerator car ,Thermodynamics ,Metre ,Test method ,Mechanics - Abstract
The present study has been carried out to elucidate the optimal method for the performance test of a refrigeratorvacuum insulation panel (VIP), by using numerical heat transfer analysis. Three locations of heat flux meter have been tested,for deriving the best test method to clarify the normal or the abnormal condition of the vacuum insulation panel in a refrigerator.The first location of the heat flux sensor is at the same place as the heater, the second one is at the nearby side locationof the heater and the third one is at the opposite side location of heater in the refrigerator. The heat flux and 1/q” 2 orq” 4 were calculated for the cases with the normal VIP, and with the abnormal VIP, and their differences analyzed. From the present study, the first and the second method had a mere difference characteristics of heat flux and 1/q” 2 or q” 4 , betweenthe cases with the normal or the abnormal VIP. The magnitude of the heat flux after 300sec had a great difference between the cases with the normal or abnormal VIP for the third method, and it could be considered the most optimal method totest the performance of a refrigerator vacuum insulation panel.
- Published
- 2013
12. A Study on the Heat Loss Improvement in a Refrigerator Ice Dispenser by Using Reverse Heat Loss Method
- Author
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Ji Soo Ha
- Subjects
Materials science ,business.industry ,Refrigerator car ,Heat losses ,Mechanics ,Radius ,Curvature ,Thermographic camera ,law.invention ,Optics ,law ,Heat transfer ,Astrophysics::Earth and Planetary Astrophysics ,business - Abstract
The present study has been carried out to reduce the heat loss from a built in refrigerator by using reverse heat loss method to discern the region with larger heat loss. To perform this purpose, an infrared thermographic camera has been used to measure the surface temperature of the refrigerator and tried to improve the heat loss near the ice dispenser. The numerical heat transfer analysis also has been accomplished to clarify the heat transfer mechanism near the ice dispenser. The possible applicable method to reduce heat loss was increasing the curvature radius at the ice dispenser corner. The curvature radius has been changed from 0mm to 40mm to see the effect of the curvature at the corner. From the present research, the optimal curvature radius for the reduction of heat loss at the ice dispenser could be 30mm.
- Published
- 2013
13. An Analysis on the Temperature Safety of a Boiler Desuperheater
- Author
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Hyuksang Chang, Ji-Soo Ha, and Tae-Kwon Kim
- Subjects
Convection ,Chemistry ,Boiling ,Superheated steam ,Heat transfer ,Fluid dynamics ,Boiler (power generation) ,Water cooling ,Thermodynamics ,Internal pressure ,Mechanics - Abstract
The present study has been carried out to diagnose the temperature safety of a boiler desuperheater which decreases abnormally higher temperature of superheated steam in a reheater of a power plant. The liquid water in the desuperheater stays in a closed space. It becomes heated by the high temperature superheated steam and boiling could occur. Boiling might increase internal pressure and it could destroy the desuperheater if the internal pressure exceeds the allowable pressure of the desuperheater. The present study modeled reasonably the desuperheater and four cases of heat transfer analysis are executed with the consideration of insulator and natural convective fluid flow of the inside cooling water. For the case excluded the natural convective fluid flow, the temperature exceeds the allowable temperature and pressure. On the other hand, for the real case included natural convective fluid flow and insulator, the active heat transfer from higher temperature region to lower temperature region occurs and it makes the temperature in the cooling water below the allowable temperature and pressure. From this fact, it could be thought that the desuperheater in the reheater is safe from destroy or back flow.
- Published
- 2012
14. Characteristics of Flow Uniformity at the Section before Tube Bank with the Change of Expansion Inlet Duct Shape in a Heat Recovery Steam Generator
- Author
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Ji-Soo Ha
- Subjects
Gas turbines ,Hydrology ,congenital, hereditary, and neonatal diseases and abnormalities ,geography ,Engineering ,geography.geographical_feature_category ,business.industry ,Turbulence ,Optimal flow ,technology, industry, and agriculture ,Inlet flow ,Mechanics ,Inlet ,Heat recovery steam generator ,cardiovascular system ,Duct (flow) ,cardiovascular diseases ,business ,circulatory and respiratory physiology - Abstract
The present study has been carried out to analyze the flow characteristics in the inlet expasion duct of a heat recovery steam generator by using numerical flow analysis. The inlet of HRSG corresponds the outlet of gas turbine exit and the flow after gas turbine has strong swirl flow and turbulence. The inlet flow condition of HRSG should be included the exit flow characteristics of gas turbine. The present numerical analysis adopted the flow analysis result of gas turbine exit flow as a inlet flow condition of HRSG analysis. Because the flow characteristics in the inlet duct of the tube bank is strongly related to the performance of a HRSG, it is most important for the optimal design of HGSG to understanding the flow phenomena in the inlet duct of HRSG. From the present study, the position of breakpoint in the inlet expansion duct should be lower than the reference breakpoint position for the optimal flow uniformity before the tube bank.
- Published
- 2012
15. A Numerical Analysis of the Reverse Heat Loss Method for a Refrigerator
- Author
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Ji Soo Ha and Jae Sung Shim
- Subjects
Materials science ,Thermal conductivity ,Heat flux ,Thermal resistance ,Heat spreader ,Heat transfer ,Thermodynamics ,Heat transfer coefficient ,Mechanics ,Thermal conduction ,Thermal diffusivity - Abstract
The present study has been carried out to predict the heat transfer characteristics of reverse heat loss method for a residential refrigerator by using numerical analysis and corresponding experiment. From the measured values of temperature and heat input, one can conclude that, the temperature inside the refrigerator has a nearly linear relationship with heat input. The effect of gasket heat loss was examined with the change of thermal conductivity of gasket region. The appropriate thermal conductivity of gasket region was acquired from the comparison of heat losses with the experimental result and numerical analysis. The result of calculated heat losses had accuracy within 1.8% error with the experimental result. With the selected thermal conductivity of gasket region, the effectiveness of reverse heat loss method was examined with the change of thermal conductivity of vacuum insulation panel.
- Published
- 2011
16. A study on the heat transfer characteristics near the magnetic door gasket of a refrigerator
- Author
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Ji Soo Ha, Hyungseok Kim, and Jae Seong Sim
- Subjects
Materials science ,Convective heat transfer ,General Chemical Engineering ,Gasket ,Refrigerator car ,Thermodynamics ,Film temperature ,Heat transfer coefficient ,Mechanics ,Condensed Matter Physics ,Temperature measurement ,Atomic and Molecular Physics, and Optics ,Heat transfer ,Fluid dynamics - Abstract
The present study has been carried out to predict the heat transfer characteristics near the door gasket of a residential refrigerator. Temperature measurement and numerical heat transfer analysis were conducted and compared to each other to achieve a more proper numerical analysis method. Three cases of numerical analysis were tried while changing the boundary conditions. The calculated result of temperature using a uniform free stream temperature showed a great difference from the measured temperature. The numerical result including two dimensional fluid flow was also shown to be far from the measured result. The measured temperature had periodic characteristics which were divided into two parts, an increasing part and a decreasing part during an 18 minute period because of the operation of compressor in a refrigerator. The heat transfer might contain three dimensional forced and natural convective heat transfer phenomena near the door gasket. Instead of adopting the complicated three dimensional numerical analysis the two dimensional heat transfer analysis with the measured free stream temperature derived more accurate temperature prediction than the other numerical analyses.
- Published
- 2011
17. A Numerical Analysis of Flow Characteristics in a Heat Recovery Steam Generator with the Change of Inlet Flow Conditions
- Author
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Boo-Yoon Lee, Tae-Kwon Kim, and Ji-Soo Ha
- Subjects
Engineering ,geography ,geography.geographical_feature_category ,Chézy formula ,business.industry ,Turbulence ,Isothermal flow ,Thermodynamics ,Mechanics ,Inlet ,Flow measurement ,Open-channel flow ,Physics::Fluid Dynamics ,Heat recovery steam generator ,Turbulence kinetic energy ,business - Abstract
The present study has been carried out to analyze the flow characteristics of a heat recovery steam generator with the change of inlet flow conditions by using numerical flow analysis. The inlet of HRSG corresponds the outlet of gas turbine exit and the flow after gas turbine has strong swirl flow and turbulence. The inlet flow condition of HRSG should be included the exit flow characteristics of gas turbine. The present numerical analysis adopted the flow analysis result of gas turbine exit flow as a inlet flow condition of HRSG analysis. The computational flow analysis result of gas turbine exit shows that the maximum axial velocity appears near circular duct wall and the maximum turbulent kinetic energy and dissipation rate exist relatively higher gradient region of axial velocity. The comparison of flow analysis will be executed with change of inlet turbulent flow condition. The first case is using the inlet turbulent properties from the result of computational analysis of gas turbine exit flow, and the second case is using the assumed turbulent intensity with the magnitude proportional to the velocity magnitude and length scale. The computational results of flow characteristics for two cases show great difference especially in the velocity field and turbulent properties. The main conclusion of the present study is that the flow inlet condition of HRSG should be included the turbulent properties for the accurate computational result of flow analysis.
- Published
- 2011
18. A Numerical Study of the Combustion Characteristics in a MILD Combustor with the Change of the Fuel and Air Nozzle Position and Air Mass Flow Rate
- Author
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Huyk-Sang Chang, Tae-Kwon Kim, Ji-Soo Ha, and Sung-Hoon Shim
- Subjects
Waste management ,Chemistry ,Nozzle ,Thermal ,Flow (psychology) ,Combustor ,Mechanics ,Combustion ,Discharge coefficient ,Air mass ,Volumetric flow rate - Abstract
A numerical analysis of reactive flow in a MILD(Moderate and Intense Low oxygen Dilution) combustor is accomplished to elucidate the characteristics of combustion phenomena in the furnace with the change of fuel and air nozzle position and air mass flow rate. For the case with the fuel nozzle located near center position of combustor, the reaction zone started at the fuel nozzle and had inclined shape toward combustor wall when the air mass flow rate was relatively smaller. On the other hand, the end of reaction zone moved toward center of combustor from combustor wall when the air flow rate was relatively larger. For the case with the air nozzle located near center position of combustor, the reaction zone started at the fuel nozzle and had inclined shape toward combustor wall when the air mass flow rate was relatively small, which was similar as the previous case with smaller air mass flow rate. On the other hand, the end of reaction zone moved toward combustor wall when the air flow rate was relatively larger. The maximum temperature increased as the air mass flow rate increasing for both cases, and the concentration of thermal NOx increased also from the previous reason of temperature characteristics. The concentration of NOx for the case with the air nozzle located near center position of combustor was considerably smaller than that for the case with the fuel nozzle located near center position of combustor. From the present study, the case with the air nozzle located near center position of combustor and theoretical air flow rate was the most effective condition for the NOx reduction and perfect combustion.
- Published
- 2011
19. A Study on The Flame Propagation Velocity of Laminar Lifted Flame with Flame Curvatur e and Scalar Dissipation Rate
- Author
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Jeong Park, Tae-Kwon Kim, Kyung-Ho Kim, and Ji-Soo Ha
- Subjects
Physics::Fluid Dynamics ,Premixed flame ,Classical mechanics ,Computer simulation ,Laminar flame speed ,Chemistry ,Numerical analysis ,Laminar flow ,Mechanics ,Radius ,Physics::Chemical Physics ,Flame speed ,Curvature - Abstract
Flame propagation velocity is the one ofmainmechanismof the stabilization of triple flame. To quantify the triple flame propagation velocity, Bilger presents the triple flame propagation velocity depending on the mixture fraction gradient, based on the laminar jet flow theory. However, in spite of these many analyses, there was not presented any relation of these variables, triple flame propagation velocity, radius of flame curvature and scalar dissipation rate indirectly. In the present research, we have checked the results of numerical simulation with experiment and numerical analysis and verified the flame propagation velocity with a scalar dissipation rate proposed by Bilger through the numerical simulation. Also we have clarified that flame propagation velocity was depended on the radius of flame curvature and scalar dissipation rate.
- Published
- 2011
20. A study on methane–air premixed flames interacting with syngas–air premixed flames
- Author
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Ji-Soo Ha, Dae Seok Bae, Tran Manh Vu, Jeong Park, Jeong Soo Kim, and Tae Kwon Kim
- Subjects
Premixed flame ,Hydrogen ,Laminar flame speed ,Renewable Energy, Sustainability and the Environment ,Flame structure ,Diffusion flame ,Energy Engineering and Power Technology ,chemistry.chemical_element ,Mechanics ,Condensed Matter Physics ,Methane ,chemistry.chemical_compound ,Fuel Technology ,chemistry ,Syngas ,Flammability limit - Abstract
Numerical study on the interaction between methane–air and syngas–air premixed flames is conducted according to equivalence ratio and global strain rate in detailed chemistry. This study targets at understanding of an interacting combustion system as an alternative retrofit concept where one can modify the existing facilities minimally in industrial and power plant burners in order to reduce the emission of carbon dioxide. It is seen that methane premixed flame interacting with syngas premixed flame can be sustained even over the rich flammable limit of single methane premixed flame. The inspection of detailed flame structure such as the distributions of major species and chain carrier radicals, flame separation distance, spatial flow velocity, and spatial distribution of the rate of production and consumption of CH4, H2, and CO is also conducted to depict the flame interactions. The importance of global strain rate and thus the flame separation distance in the enhanced burning of methane premixed flame is also stressed through the inspection of the consumption rates of H2, CO, and CH4. Anomalous phenomena such as the migration of premixed flame cross the stagnation plane and the nearly constant flame separation distance are also discussed.
- Published
- 2010
21. The Characteristics of the Flame Propagation Velocity and Volume Integral of Reaction Rate with the Variation of Fuel Injection Velocity for a Liftoff Flame
- Author
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Jeung Park, Tae-Kwon Kim, and Ji-Soo Ha
- Subjects
Reaction rate ,Premixed flame ,Laminar flame speed ,Chemistry ,Flame propagation ,Analytical chemistry ,Mechanics ,Fuel injection ,Flame speed ,Volume integral - Abstract
: A numerical analysis of reactive flow in a liftoff flame is acc omplished to elucidate the characteristics of flame propagation velocity and volume integral of reaction rate with the variation of fuel injection velocity at the fuel rich region, fuel lean region and diffusion flame region. The increase of fuel in jection velocity enhances flame propagation velocity, but its effect on the flame propaga tion velocity is not much greater under 4%. The increase of fuel injection velocity affec ts directly and linearly on the flame surface area in the fuel rich region and so enhances volume integral of reaction rate to accommodate the increment of fuel. Key words :liftoff flame(부상높이), flame propagation velocity( 화염전파속도), volume integral of reaction rate( 체적연소반응속도), flame surface area(화염표면적) †교신저자(계명대학교 에너지환경과학과, E-mail:jisooha@kmu.ac.kr, Tel: 053-580-5919) * 계명대학교 기계자동차공학부** 부경대학교 기계공학부 1. 서 론 일반적으로 연료노즐에서 분출된 연료는 공기와 만나서 제트확산화염을 형성한다. 연료분출속도가 증가되어 연료노즐에 부착된 화염이 노즐에서 분리되어 부상화염이 형성되면 연료노즐 분출 중심선 부근은 연료가 과농한 연소가 일어나고 중심선에서 떨어진 영역인 공기측은 연료가 희박한 연소가 일어난다. 연료가 과농한 영역에서 연소가 일어나고 난 뒤 남은 연료는 다시 공기와 확산 화염을 형성하게 된다. 이렇게 하여 부상화염은 과농연소영역, 희박연소 영역, 확산화염 영역의 세 부분으로 이루어지고 이 세 부분이 만나는 곳을 삼지점(triple point)이라고 하고 이러한 화염을 삼지화염(triple flame)이라고 한다. 삼지화염은 화염의 점화 및 소화에 관계한 화염안정화를 위해 많은 연구자들에 의해 연구되어져 왔다. Mungal
- Published
- 2009
22. The Evaluation of Performance and Flow Characteristics on the Diffuser Geometries Variations of the Centrifugal Compressor in a Marine Engine Turbocharger
- Author
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Ji-Soo Ha, Bong-Hwan Kim, and Hong-Won Kim
- Subjects
Airfoil ,Impeller ,Engineering ,business.industry ,Centrifugal compressor ,Mechanics ,Computational fluid dynamics ,business ,Gas compressor ,Turbocharger ,NACA airfoil ,Marine engineering ,Diffuser (thermodynamics) - Abstract
An examination of the condition of the flow leaving the impeller exit kinetic energy often accounts for 30-50% of the shaft work input to the compressor stage, and for energy efficiency it is important to recover as much of this as possible. This is the function of the diffuser which follows the impeller. The purpose of this study is to investigate the sensitivity of how compressor performances changes as vaned diffuser geometry is varied. Three kinds of vaned diffusers were studied and its results were compared. First vaned diffuser type is based on NACA airfoil and second is channel diffuser and third is conformal transformation of NACA65(4A10)06 airfoil. Mean-line prediction method was applied to investigate the performance and stability for three kinds of diffusers. And CFD analyses have been done for comparison and detailed interior flow pattern study. NACA65(4A10)06 airfoil showed the widest operating range and higher pressure characteristics than the others.
- Published
- 2008
23. An Experimental Study Improving Ventilation of Container Ship Hold Using Horizontal Upward Jet Duct
- Author
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Ji Soo Ha, Sang-Min Park, and Il-Seouk Park
- Subjects
Ventilation duct ,Engineering ,business.industry ,Thermal ,Refrigerator car ,Duct (flow) ,Mechanics ,business ,Simulation - Abstract
The ventilation performance for the various venting duct arrays has been experimentally compared in the scaled model of the container hold. Most container ships have the ventilation duct system to remove effectively the condensing heat released from container refrigerator. The existing duct system is vertically installed and basically has the number of duct as many as the columns of reefer container stack. In this study, to make up for the weak points having stagnantly hot legions in the centered area of container hold for the present system, the horizontal upward jotting duct system was proposed and proved by temperature rising tests on the scaled model. In this paper, the expected flow regimes and the thermal and hydrodynamic analogies as well as the measured temperature distributions in a hold for various duct types and heat released rates are deeply discussed.
- Published
- 2006
24. Design of Thermal Vapor Compressor by Numerical Analysis and Experimental Verification
- Author
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Sang-Min Park, Il-Seouk Park, and Ji Soo Ha
- Subjects
Chemistry ,business.industry ,Thermal ,Nozzle ,Thermodynamics ,Duct (flow) ,Mechanics ,Boundary value problem ,Computational fluid dynamics ,business ,Choked flow ,Discharge pressure ,Gas compressor - Abstract
A thermal vapor compressor in which the subsonic/supersonic flow appears simultaneously, has been accurately designed through the CFD analysis for the various shape parameters such as the primary nozzle shape, converging duct shape, mixing tube diameter, and so on. The performance of the developed thermal vapor compressor has been experimentally verified to be installed in a Multi Effect Desalination(MED) plant as an important element. In this paper, the effects of each parameter are discussed on the basis of CFD results and the experimental results for various boundary conditions(motive pressure, suction pressure, and discharge pressure) are presented in compared with CFD results. The two results show a good agreement with each other within 2 % accuracy with regard to the entrainment ratio.
- Published
- 2005
25. Design and application of thermal vapor compressor for multi-effect desalination plant
- Author
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S.M. Park, Ji-Soo Ha, and I.S. Park
- Subjects
Engineering ,business.industry ,Mechanical Engineering ,General Chemical Engineering ,Nozzle ,Mechanical engineering ,General Chemistry ,Mechanics ,Computational fluid dynamics ,Desalination ,Discharge pressure ,Pilot plant ,General Materials Science ,Duct (flow) ,business ,Choked flow ,Gas compressor ,Water Science and Technology - Abstract
A thermal vapor compressor (TVC) in which the subsonic/supersonic flow appears simultaneously, has been accurately designed through the CFD analysis for the various shape parameters such as the primary nozzle shape, converging duct shape, mixing tube diameter, and so on. The performance of the developed TVD has been experimentally verified to be installed in a multi-effect desalination (MED) pilot plant. In this paper, the experimental results for various boundary conditions (motive pressure, suction pressure, and discharge pressure) are presented in comparing with CFD results. The two results show a good agreement with each other within 3.5% accuracy with regard to the entrainment ratio.
- Published
- 2005
26. A Study on the Calculation of Heat Release Rate to Compensate the Error Due to Single Zone Assumption in Diesel Engine
- Author
-
Ji-Soo Ha, Ki Doo Kim, Wook Hyeon Yoon, and Seung Hyup Ryu
- Subjects
Diesel fuel ,Materials science ,law ,Homogeneity (statistics) ,Release model ,Mechanical engineering ,Single zone ,Mechanics ,Combustion ,Diesel engine ,Equivalence ratio ,Cylinder (engine) ,law.invention - Abstract
Accurate heat release analysis based on the cylinder pressure trace is important for evaluating combustion process of diesel engines. However, traditional single-zone heat release models (SZM) have significant limitations due mainly to their simplified assumptions of uniform charge and homogeneity while neglecting local temperature distribution inside cylinder during combustion process. In this study, a heat release analysis based on single-zone model has been evaluated by comparison with computational analysis result using Fire-code, which is based on multi-dimensional model (MDM). The limitations of the single-zone assumption have been estimated. To overcome these limitations, an improved model that includes the effects of spatial non-uniformity has been applied. From this improved single-zone heat release model (Improved-SZM), two effective values of specific heats ratios, denoted by γV and γH in this study, have been introduced. These values are formulated as the function of charge temperature changing rate and overall equivalence ratio by matching the results of the single-zone analysis to those of computational analysis using Fire-code about medium speed marine diesel engine. Also, it is applied that each equation of γV and γH has respectively different slopes according to several meaningful regions such as the start of injection, the end of injection, the maximum cylinder temperature, and the exhaust valve open. This calculation method based on improved single-zone model gives a good agreement with Fire-code results over the whole range of operating conditions.Copyright © 2005 by ASME
- Published
- 2005
27. Numerical Prediction on the Characteristics of Spray-Induced Mixing and Thermal Decomposition of Urea Solution in SCR System
- Author
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Ji-Soo Ha, Joo Youn Kim, and Seung Hyup Ryu
- Subjects
Spray characteristics ,Chemistry ,Thermal decomposition ,Nozzle ,Mixing (process engineering) ,Fluent ,Exhaust gas ,Selective catalytic reduction ,Mechanics ,Simulation ,Volumetric flow rate - Abstract
The spray-induced mixing characteristics and thermal decomposition of aqueous urea solution into ammonia have been studied to design optimum sizes and geometries of the mixing chamber in SCR (Selective Catalytic Reduction) system. The cold flow tests about the urea-injection nozzle were performed to clarify the parameters of spray mixing characteristics such as mean diameter and velocity of drops and spray width determined from the interactions between incoming air and injected drops. Discrete particle model in Fluent code was adopted to simulate spray-induced mixing process and the experimental results on the spray characteristics were used as input data of numerical calculations. The simulation results on the spray-induced mixing were verified by comparing the spray width extracted from the digital images with the simulated particle tracks of injected drops. The single kinetic model was adopted to predict thermal decomposition of urea solution into ammonia and solved simultaneously along with the verified spray model. The hot air generator was designed to match the flow rate and temperature of the exhaust gas of the real engines. The measured ammonia productions in the hot air generator were compared with the numerical predictions and the comparison results showed good agreements. Finally, we concluded that the design capabilities for sizing optimum mixing chamber were established.
- Published
- 2004
28. Velocity field of pulsatile flow in a porous tube
- Author
-
Joong Kon Park, In Ho Kim, Ji Soo Ha, Ho Nam Chang, and Hyun Dong Shin
- Subjects
Materials science ,Rehabilitation ,Models, Cardiovascular ,Biomedical Engineering ,Biophysics ,Pulsatile flow ,Thermodynamics ,Laminar flow ,Mechanics ,Law of the wall ,Physics::Fluid Dynamics ,Thermal velocity ,Womersley number ,Pulsatile Flow ,Orthopedics and Sports Medicine ,Tube (fluid conveyance) ,Shear velocity ,Rheology ,Blood Flow Velocity ,Mathematics ,Concentration polarization - Abstract
This paper describes velocity fields for fully developed periodic laminar flow in a rigid tube with a porous wall. We obtained an analytical solution of the flow by the linear approximation of the Navier-Stokes equation. Unlike the previous works with a constant seepage rate along the axis, we used a wall velocity which contained hydraulic permeation constant Lp. The axial velocity profile shows a local maximum velocity near the wall at a large Womersley number α. This suggests that concentration polarization in porous tubular membrane may be reduced at high frequencies if a membrane device is operated under pulsatile flow conditions. The magnitude of wall permeation velocity deceases linearly along the tube axis because the damping of the pressure difference between the inside and the outside of the tube is very small.
- Published
- 1989
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